SURFACE EFFECT SHIP (SES)DEVELOPMENTS WORLDWIDE

BY

David R. Lavis’ and Kenneth B. Spaulding, Jr?

’ Band, Lavis & Associates, inc., President2 M. Rosenblatt & Son, Inc., Project Manager

SURFACE EFFECT SHlP (SES) DEVELOPMENTS WORLDWiDE

David R. Lavis’ and Kenneth 6. Spaulding, Jr.’

ABSTRACT

It has been more than 30 years since the introduction of the SES. There are several hundred operating SES in theworld today. Most are relatively small (less than 200 tons) and have operating speeds of 25 to 40 knots. T h epotential for larger, faster, S&S has long been recognized. Today, with the emergence of six independent Europeaninitiatives for the development of 40 to 50-knot, 500 to 2000-ton, SES car ferries, we are on the threshold of a newgeneration of SES (Figure 1) - which will be introduced solely because they are perceived, by hard-headed investors,as competitive commercial ventures.

In this paper the history of SES development is summarized and a world-wide census of SES craft presented.Current fast-ferry and military initiatives are discussed. The SES concept is defined and characterized including adiscussion of SES technologies. Predict ions are made regarding future SES developments, followed by conclusionsand recommendations.

Figure 1. Italian 2000-Ton SEC-774 Car Ferry - The Largest SES (Under Construction)

’ Band, Lavis & Associates, Inc., President

’ M. Rosenblatt & Son, Inc., Project ManagerPaperpresented at the Chesapeake Section of SNAME on 12 March 1991, in Arlington, Virginia.Currently revised and proposed forpublication in the ASNE Journal.

INTRODUCTION

Commercial shipbuilding in the United States hasnearly disappeared. Many yards have closed and theNaval bui lding programs sustaining the survivors areexpected to diminish as the defense budget contracts.The good news may be that the labor rates of U.S.yards are now below those of yards in Japan andNorthern Europe. In any case, U.S. yards must seekinnovative entries into the domestic and foreignmarketplace. The SES is an example of an innova-tion for which the U.S. should be exploiting its earlytechnology lead. The U.S. Navy invested over $400million in the 3KSES program alone. The technologylead is now transferring back to Europe where, as thispaper will show, the concept is being aggressivelypursued for commercial and mil i tary appl icat ions. TheItalian SEC Car Ferry (Figure l), now in construction,and the French AGNES 200 (Figure 2) now undergo-ing Navy evaluation, are examples. The design andconstruction capability for SES is in place in the U.S.The European experience has surely proven theeconomic feasibility of SES ferries. Perhaps the timehas come for our community to realize the potential ofSES in the marketplace.

4

SES HISTORY - CURRENT DEVELOPMENTS

Development of the SES through the 1950’s, 1960’sand 1970’s has been amply documented, notably inReferences 1 through 7. In this section these earlyyears are summarized, leading to discussions of thecurrent generation of 40 to 50 knot craft and, mostimportantly, the introduction of several new large fastcar-ferry and military initiatives.

Estimates of total SES constructed to date vary withthe sources, the highest being “over 450”. Table Ilists the leading particulars of 297 of the mostprominent. This table is based on References 5, 6and 7 and the authors’ personal files, maintainedsince 1959.

Historv

The concept of supporting craft on pressurized airdates to the 18th century (Reference 1). Air CushionVehicles (ACVs) and Surface-Effect Ships (SES),however, as we know them today, clearly evolvedfrom the pioneering work of Sir Christopher Cockerell,in the UK, starting in 1953. Cockerell’s initial focus

Figure 2. The Latest Military SES, The French N a v y ’ s AGNES 200 (Commissioned in February 1991)

2

Table 1

Leading Particulars of Prominent SES

-zFowrdl

0

Cengmowrall

(W

66 12 17.681.5 19 27to34

49 13.5 4072.3 12.9 2049 19 3524 12 2551 20 3573 13.2 19

77.7 35 949.1 .Q 41.9 7673 13.3 33

46.75 a25 2s50 19 43

64.6 21.3 3207 23.3 3660 20 35110 39 3060 20 3527 Unknown Unknown48 24 33

65.6 21.3 2770 20 30

63.3 13 2139.7 11.3 1669.3 335 40160 39 3273 22.6 30

39.4 15.1 3075 12.6 2470 20 %.+70 16.2 24

116 25 30106 36 4659.4 30 4084 33.5 351% 36 47116 37.7 so110 34 4.9

211.6 55.8 IJnknown55 17.7 35

131 27 28ss 23.6 5257 16.5 30

109 34 30131 41 52118 42.7 52

167.3 42.6 4480 2% 37160 42.6 4333 8.5 2%100 37.4 so

N u m b e rBuitCcunby Hull Mat&lBuilda

01

02X%1

D e n n yDennyNAEFMoscow ShpUSNUSNHovermarineKSSGSdlAWojasomlwoUSNRohr

sosmvaka

Sell Haker

knllSellC O 8HOVM-llal?neCbohuFmmh NayHovermannew HdtsrD A G UKTMIA&akhanHalierDFSwsBmdrene AAKTMIUMIBrdrane AABmdrene AAKIWKSSBarant+Jarodrene AAKmlAVQnddtlWBSImZlllllSlohm 6 VossCMNFloyd SchddeBellLUBSMWV

UKUKUS

USSRususUK

USSRusus

USSRusus

USSRUSSR

UKusUK

KmUS

USSRUK

ChinaFrance

UKus

China

USSRus

ChinaChina

N‘XW#Korea

1961196219631963I%51967196819691972197219721973,97419741974197619761976197619791980(98119811981IQ@2198219821982198319841984198419841985198819%1987I%7198719%19%19%19%196919891989IQW19%loo01990I%1

1

41

s4verd11

30+111

loo+11

We

2+65111641S11121

Unknawrn11531

1121111112111111

WoodG R P

Wood. Al Al@Al Alby

Wood. Al Alloy. GRPAlAlby

G R PAl AbyAl AlbyAl AlbyAl AtbvAl Allo;

Wood. Al Alicy. GRPAl AlbyAl Alby

G R PAl Alkw

G R P ’UnknownAl AlbAl Alby

G R PG R P

Wood. Al Al!qGAP

Al AlloyUnkrmvmAlAlloyAl AlbyAl Alby

Al Alloy. GRPSteel. GRP

G R PAl AlbyAl AlbV

G R PG R PGRP

MknObWlAl AlbysteelG R P

Al AlIcyAl AlbyAl Ai6

G R PAl Alby

G R PAl Alby

GRP. WoodG R P

ZARYA (WYTNYE-1)XR-1 BXRJHM-216GORKOVCHANIN10%1WAZARNITSAXR-5XR-1DORICNMRAssvErHM.216BH-110HM-2 MC4TURT-IIROOOLFPLAMYAHM 221WR-901MOLENESHM-527SES-2QoTYPE 7203KrMI-aMLUCHHALTER YACHTWRIC-7172 and -3WRIC-7iQCIRR-IOSPKIWI-18MK-w 26MCIRR-i1SPCIRR-IZOPJET RIDERDERGACH’BES 16MARIC-7192H A R P O O NKTMI-17MAIR-RIDE 109WESTAMARIN 4GG3C O R S A I RAGNES 2CrlSEASWIFT 23SESZCOAM T G _ MOSESTESTRIGG (SMYGD

‘Largest SES buiH to date (1991) at 650 tons. see Figure 26.

E+imntdE~timentd

ASW ’FSnY

E&imentd

on 13 May 1961. This craft (Figure 3) was developed,under license to, and with partial funding from,Cockerell’s government-sponsored* HovercraftDevelopment Ltd (HDL), and achieved a maximumspeed of 17.6 knots. This was followed, in 1962, bythe first GRP SES, the Denny D-2 (Figure 4). four ofwhich were built as commercial ferries capable ofcarrying 70 passengers and of achieving a maximumspeed of 27 knots. Subsequently, they were modifiedto allow speeds of 34 knots.

was on amphibious applications while others, in thelate 1950’s, including Denny Hovercraft Ltd (with helpfrom Cockerell) and Allen Ford at the Naval AirExperimental Facility (NAEF) in the U.S., pioneeredthe development of non-amphibious applications andwhat has now come to be known as the SurfaceEffect Ship.

United Kingdom

The first practical SES was the experimental highlength-to-beam ratio Denny D-l which was launched

*UK National Research Development Corp. (NRDC).

3

Figure 3. Denny D-l Test Craft (UK)

Figure 4. Denny D-2 Passenger Ferry (UK)

In late 1963, HDL (formed in 1958) launched theHD.l, a research SES which was later converted to afully amphibious ACV. In 1965 SES development waspicked up by Hovermarine, Ltd who launched, in1968, the first of a very successful series of diesel-GRP SES including the HM-216, 218, 221 and 527(Figures 6 to 9). These craft primarily operated aspassenger ferries but included a number of utility craftsuch as fireboats (Reference 8). By 1991, a total of113 HM craft had been delivered. Many of thesecraft, operating at speeds of 35 to 40 knots, are still inservice, with the majority in East Asia.

United States

At NAEF in the U.S., the objective was to achievehigher speeds for military applications. In 1963 theU.S. Navy’s low length-to-beam ratio experimentalXR-1 (Figure 5) was launched (Reference 9). Thiscraft saw four major configuration changes in its20-year life, including waterjets in 1970, to achievespeeds of over 40 knots before it was retired as theXR-1 E in 1983 (Figure 11 shows the XR-1 D).

Continuing the pursuit of high speed, in 1965 the U.S.Navy and the Maritime Administration created theJoint Surface Effect Ship Project Office (JSESPO) todevelop large SES for both military and commercialappl icat ions. MARAD’s support was subsequently

Figure 5. NAEF XR-1 Test Craft (U.S.)

Figure 6. HM-216 Passenger Ferry (UK)

Figure 7. HM 218 Passenger Ferry (UK)

Figure 8. HM 2;!1 Multi-Role Craft (UK)

4

__-

_. - --

Figure 9.

withdrawn andmiss ions on ly .

HM 527 Passenger Ferry (UK)

development proceeded on militaryJSESPO became SESPO and later

In 1972, two loo-ton test craft, the Aerojet SES-1OOA(Figure 12) and Bell SES-1008 (Figure 13) werelaunched. These craft achieved 76 knots (1OOA) and94 knots (100B). From the experience with thesecraft, and extensive testing, analysis and componentdevelopment, the design of a 2000-ton ASW frigatewas developed. As the ship reached the contractdesign stage the requirements had changed and theship had grown to 3000 tons (Figure 14). The 3KSESprogram was discontinued in 1979. U.S. Navyinvestment in this program, from its inception in 1967,totaled over $400 million.

NAVSEA PMS 304.

To provide further understanding of SES seakeepingand stability, another experimental craft, the XR-3(Figure lo), was built and launched in 1967 asplanning evolved for a 500-ton, and subsequently a2000-ton, SES capable of ASW operations at 80knots .

Figure 12. U.S. Navy’s .SES-1 OOA Test Craft

Figure 10. U.S. Navy’s XR-3 Test Craft

Figure 11. U.S. Navy’s XR-1 D Test Craft

Figure 13. U.S. Navy’s SES-1008 Test Craft

Figure 14. U.S. Navy’s BKSES (Artist’s Drawing)

5

There is still controversy surrounding the demise ofthe BKSES program. Clearly cost, risk and acontinuing inability to credibly assess the utility ofspeed were factors (Reference 10). In any case, themilitary potential of SES was still recognized. Asillustrated later in this, paper, the higher length-to-beam ratio SES offered significant speed benefits withreduced development risks and operating costs.Accordingly, sights we(e lowered from 80 - 100 knotsto 40 - 50 knots. The U.S. Navy’s high length-to-beam XR-5 test craft (Figure 15) had been launchedin 1973 to explore this approach.

.

The U.S. Coast Guard Surface Effect Ship Division inKey West, Florida was established in November 1982with delivery of the threle BH-110 SES which weredesignated WSES 2, 3 and 4. initially a series ofengineering and maintenance problems compromisedthe effectiveness of the squadron but by 1986 thesecraft had emerged as the most efficient workhorses inthe cutter inventory (Reference 13). Since 1987 theWSESs have averaged well over 3100 undetwayhours per year with the lowest ratio of maintenance tounderway hours of any USCG cutter class. The mosteconomic operating speed is the maximum-contin-uous speed of 30+ knots. In their drug interdictionrole the WSESs operate in a sprint-and-drift mode.These craft are noted for their platform stability,maneuverability, seakeeping and usable deck spaceas well as their speed. The large deck area hasproven particularly effective for migrant interdictions.

- ,

Figure 15. U.S. Navy’s XR-5 Test Craft (Two Views)

In 1978 Bell-Halter (currently Textron MarineSystems) designed and built, on speculation, the firstcommercial SES in the U.S. (Figure 16, References11 and 12) Six of these craft were built. Three wereacquired by the U.S. Coast Guard (Figure 17), onewas purchased by the U.S. Navy (modified to becomethe SES 200) and two are operating as crew boats.Both were shipped to Egypt in 1984 - 1985. Onereturned to New Orleans and the other was shipped toBrazil in 1988. A scaled down version of the Belldesign, the 48-ft Rodolf (Figure 18), was delivered tothe U.S. Army Corps of Engineers in 1979. Thishydrographic-survey craft is operating out of Portland,OR. At this point the Bell 11 OS, the Rodolf and theSES 200 are completely successful applications of theSES concept, both military and commercial, by a U.S.company .

Figure 16. Bell (U.S.) BH-110 Crew Boat

Figure 17. Bel l-Halter. USCG Cutters

Figure 18. Bell Rodolf, U.S. Army, HydrographicVessel

6

The DTRC SES-200 was launched in 1978 as a BellHalter 110. The craft was purchased by the Navy andlengthened by 50 ft (Figure 19). A ride-control systemwas also added. A six nation NATO test deploymentwas completed in 1986, followed by various SEStechnology a n d weapon-systems evaluations(including the Vulcan Gun and Hellfire missilesystems). The SES 200 has just completed a majorupgrade under a Foreign Comparative Test Program(FCT) which included hull modifications and installa-tion of MTU diesels, KaMeWa waterjets and ZEgearboxes (Figure 20). The new propulsion system issimilar to that in the AGNES 200 prototype and theGerman SES-700 design. As the modified SES-200enters its test and evaluation period it has alreadydemonstrated speeds of over 40 knots.

In the early 1980’s a contract was awarded to TextronMarine Systems for the construction of a number ofUS. Navy GRP SES Mine Countermeasures craft(MSH). The contract was terminated before construc-tion of the first craft.

At this time, the Navy also developed the concept ofan SES Special Warfare Craft, Medium (SWCM). Acontract was awarded to RMI which was alsoterminated before completion of the first craft.

An SES motor yacht was constructed by HalterMarine in 1983. It is currently being upgraded by theTrinity Marine Group (Figure 21).

Two 109~ft aluminum hybrid SES (wet-deck formsstern seal) were constructed by Avondale ShipyardYacht Division to a design by Air Ride Craft, Inc. Thefirst of these air-ride ferries (Figure 22) initiatedoperations from lower Manhattan to Kennedy airportin the Spring of 1990.

A twin-cushion (SECAT) SES manned model wasbuilt and tested by the U.S. Navy in 1985. An artistdrawing of the full-scale concept is shown in Figure 23(Reference 37).

Figure 19. U.S. Navy’s SES-200

Figure 20. U.S. Navy 250-Ton SES 200 After Waterjet Retrofit

7

Figure 21. Halter 70-ft SES Sport Fisherman(U.S. )

Figure 22. Avondale (U.S.), Metro Marine Express

Figure 23. U.S. Navy’s Surface Effect Catamaran,SECAT (Artists Drawing)

During the 1970’s and 1980’s a large number offeasibility level SES design studies were conducted

by the Navy. These ranged from a 300-ton NATOPatrol Craft to large Air Capable Cruisers and Sealiftships to over 20,000 tons (References 14 and 15).

San Diego Shipbuilding has, for several years, beenlicensed by the Norwegian firm of Cirrus for theconstruction of several 120P passenger ferries foroperation in Hawaii. At this time, the future of thisventure is uncertain.

U S S R

Commercial SES development in the USSR hasconcentrated on relatively low-speed, shallow-draftpassenger ferries for operation in the vast Sovietnetwork of shallow rivers and tributaries.

Craft built and operated to date have been relativelysmall (50 to 80 seats) and have operatedpredominantly on short routes in protected waters.

The Zarnitsa (Figure 24) was the first Soviet SES ferryput into production and evolved from the Gorkov-chanin prototype which was first tested in 1968. TheZarnitsa is a 72-ft long, 50-seat, waterjet-propelledcraft capable of operation in water depths of less than2-ft and at speeds of over 30 knots. More than 100 ofthese craft are employed on rivers throughout theUSSR.

Figure 24. Soviet Zarnitsa (“Lightning”)

This was followed by the series production of severalhundred SES, principally river ferries, of severalclasses, including Orion-01 (1975), Chayka (1976),Rassvet (1976, Figure 25), Plamya (1980, Figure 26)and Luch (1983).

The Orion is an 80-passenger ferry capable of slightlyhigher speeds than the Zarnitsa. Like the Zarnitsa,the Orion is intended for service along shallow rivers,tributaries and reservoirs and is waterjet propelled. At

8

a displacement of 35 tons and a length of 85 ft, theOrion can operate in choppier water conditions thancan the Zarnitsa.

Figure 25. Soviet Rassvet

Figure 26. Soviet Plamya

The Rassvet (Figure 25) is the largest Sovietcommercial SES built to date. The 47-ton Rassvet isdesigned to operate on offshore routes in the Baltic,Caspian and Black Seas, as well as on large lakesand reservoirs in conditions up to sea-state 3.

The Plamya (Figure 26) is a variant of the Orion and itis designed to transport and land vehicles. Versionsare also used as river fire boats.

The Luch-I is the newest Soviet SES ferry and wasdesigned to replace the then 12-year old Zarnitsaclass. Although approximately the same size as theZarnitsa, the Luch-1 has an increased speedcapability and greater payload capacity (up to 66passengers). Like all of the Soviet SES ferries, it isdesigned to run bow-on to any flat sloping bank and toembark and disembark passengers via an art iculatedgangway.

One Soviet ferry, the Zarya (Figure 27) is oftendiscussed along with SES. However, the Zarya is not

an SES, merely a very shallow draft planing trimaran-type craft. Claims of a significant. ram-& cushionbeing generated at the 24-knot service speed of thecraft must be viewed with extreme skepticism. Over150 of these 60-passenger shallow-draft planing craftare in operation.

Figure 27. Soviet Zarya Catamaran (Two Views)

The Soviets are reportedly developing faster, largerSES passenger/car ferries (having speeds of 36 knotsand displacements up to 100 tons) for use alongshallow waterways unsuitable for hydrofoils. Recentreports also suggest that the Soviets are developinglarge (2000- to 4000-ton) SES freighters. However,construction of these larger craft has not beenconfirmed.

For military applications, the Soviets have concen-trated on amphibious ACVs. However, during the1980’s, the Kamysh-Burun Shipyard (KBS) in Kerch,developed what is currently the world’s largest SES,the 650-ton Dergach Patrol Craft, which was commis-sioned in early 1990 (Reference 16). This SES,shown in Figure 26, is discussed in more depth laterin the paper.

Figure 28. Soviet 650-Ton Dergach Combatant SES (Canadian Forces Photo courtesyGuide to the Soviet Navy)

People’s Republic 0.f China (PRC)

The Marine Design and Research Institute of China(MARK) began investigation of the SES concept inthe early 1960’s. By 1967 MARK was testing a 2-tonSES test craft, designated 71 l-3. In 1975 the ChaohuShipyard in Au-Hui Province was testing an ex-perimental 5-ton MARK design. This yard produced,in 1980, the 70-seat Jing-Sah SES ferry, followed in1981 by the waterjetpropelled SES ferry, WR-901, ofwhich four were built, and, in 1983, the 42-seat TaiHU.

The Dagu Shipyard in Tianjin was next with their Type713 and 717 (built in the 1970’s), the 7203 passengerferries the prototype of which was launched in 1982and the JINXIANG 80-seat passenger ferry launchedin 1983.

In 1984 the WUhlJ Shipyard (WS) produced theMARIC-719, the first SES with a hull constructed ofsteel (and superstructure of GRP, (Figure 29)). AMark-II version of this craft, also built of steel, enteredpassenger service in 1988.

Figure 29. China’s MARIC 719-11 Steel SES

The Dong Feng Shipyard (DFS) has also builtpassenger-carrying SES, two of which are waterjetpropelled, designated Type 717 (Figure 30). Theirlatest version, Type 717 III, carries up to 171passengers. Two of these craft entered service in1984 and 1988, respectively.

1 0

Figure 31. French Navy’s Molenes Test Craft

Figure 30. China’s MARL 717-11 Waterjet SES

The Huangpu Shipyard in Guangzhou is scheduled todeliver another MARL design in 1991. This craft isdesignated Type 7211 and will carry up to 171passengers at 30 knots. According to JANE’S (1985)the Chinese have also built (starting in 1977) anumber of waterjet-propelled military river-patrol craft.

South Korea

In 1978 Korea Tacoma Marine Industries (KTMI)launched the 27-ft experimental Turt-II SES. By 1988KTMI had launched five 60-ft SE& one 36-ft SES,one 56-ft SES, two 85-ft SES and one 92-ft SES ferry,the latter developed as a derivative of the 85ftversion. Further details, including photographs, ofthese craft can be found in References 5 and 6.

France

During the late 1970’s serious interest in SES frommainland Europe was beginning to appear and by1981 the French Navy’s Direction Des ConstructionsNavales (DCN) were testing a small experimentalcraft called Molenes (Figure 31).

DCN recognized the potential of SES as a helicopterplatform and embarked upon an extensive researchand development program aimed at a 1250-ton ASWcorvette, the Eoles (Reference 21) Their next stepbeyond the Molenes was the AGNES 200 (Figure 2)which was launched at CMN in Cherbourg during1990, and is currently undergoing trials with U.S.Navy support,

The hull structure and deckhouse of the AGNES 200are welded aluminum (described in more depth later).Propulsion is MTU diesels with KaMeWa waterjets.The deck aft will accommodate a Dauphin helicopter.The prototype has a go-seat passenger salon but, in aferry configuration, the AGNES 200 could accommo-date 450 passengers. AGNE.S 200 is classified byBureau Veritas as an AUT-CC passenger ship.

The design of a 152 passenger fast ferry SES hasbeen developed by the firm of lngenierie Maritime etCommercialisation (IMC)/Efair. The hull is cored GRPand propulsion options include MAN or Deutz dieselsand waterjets or propellers. Details can be found inReference 5.

Norway

The geography of Norway has supported a prolifera-tion of passenger ferries of many types. Competitionis intense and new concepts are aggressively pursuedwhenever economic advantages are perceived. Thebuilding firm of Brodrene Aa, with yards at Eikefjordand Hyen, pioneered the application of cored GRP tohull construction and, subsemquently, in partnershipwith the design firm of Cirrus, evolved theircatamarans into the first Norwegian “Air CushionCatamaran,” or SES, the Norcat (Figure 32). Thiscraft was launched with marine-screw propulsion andwas subsequently converted to waterjet propulsion.The Cirrus/Brodrene Aa team subsequently produceda second “Norcat” (CIRR 115P, Figure 34), theEkwata and the experimental, hybrid propeller driven,Harpoon (CIRR 60P) (Figure, 33) followed by seriesproduction of eleven CIRR 12OP class ferries (Figure35). The 12OPs, operating in many parts of the world,represent the state-of-the-art in SES passenger

1 1

ferries. Of GRP cored construction, they are poweredby MWM diesels with KaMeWa waterjets providing aservice speed in the mid 40s. All of the 12OPs areequipped with ridecontrol systems developed by theU.S. firm of Maritime Dynamics. The most recentdelivery, the Nissho for a Japanese customer, waspowered by MTU diesels for a service speed of 51knots .

Figure 32. Norway’s CIRR 105P Norcat

Figure 33. Norway’s Harpoon - CIRR 6OP

Figure 34. Norway’s CIRR 115P

Figure 35. Norway’s CIRR 12OP

Early in 1990 Cirrus acquired 50% interest in ashipyard in Rosendal and, on 1 June, the partnershipwith Brodrene Aa was dissolved. Cirrus has devel-oped designs for two large SES car ferries and a220-ton SES attack craft. They have also participatedin the design of the Nclrwegian SES MCMVs (Figure36). These activities arts described later.

Figure 36. Norwegian Navy’s MCMV SES(Artisl.‘s Drawing)

Brodrene Aa has now joined the Ulstein Group and isbuilding two luxury 37-meter SES passenger ferriesdesignated UT904. Th,e first is scheduled for deliveryto a customer in Greece in July of this year. TheUT904 is also being offered in an offshore supplyvariant which will carry 100 passengers and 20 tons ofdeck cargo.

Westamarin, in partnership with Karlskronavarvet(KKrV) in Sweden, has produced two aluminum

1 2

SES-4000 class ferries (Figure 38). The two SESJet-Rider 3400 ferries (Fig&e 37), designed by KKrVin conjunction with Textron Marine Systems andconstructed by KKrV in cored GRP, were fitted out atthe Westamarin yard.

1987, FMV initiated a comprehensive SES R&Dprogram involving a number of Swedish firms andgovernment agencies. These activities led to a 1989building contract with KKrV for the stealth test craft“Testrigg SMYGE,” Figure 39, (Reference 18), whichis discussed in more depth later.

Figure 39. Sweden’s KKrV Testrigg “SMYGE”(Artist’s Drawingi)

Figure 37. Sweden’s, KKrV Jet Rider 3400 Ferry

Germany

Figure 38. SES-4000 Class Ferry (Norway/Sweden)

Sweden

Karlskronavarvet (KKrV) entered into an agreementwith Textron Marine Systems in the U.S., and in 1987completed construction of the two cored-GRP JetRiders (Figure 37, Reference 17). In 1989, KKrVsupported construction of the two SES-4000 craft byWestamarin Norway (Figure 38).

The Swedish Defence Materiel Administration (FMV)and KKrV have engaged in the development of SESconcepts and technology since 1983. Studies andtests were conducted by KKrV in 1985 to 1986 and, in

The firm of Blohm und Voss in Hamburg, Germany,began their studies of SES in 1982. These studiesculminated in the launching, in 1989, of the 36-meterCorsair (Figure 40). This (50+-knot) demonstrator forboth mil i tary and commercial appl icat ions, embodiesseveral significant technology advances. The hull iscored GRP utilizing a high-strength core material.MTU diesels, suspended in modules from anoverhead foundation for shock and vibration isolation,dr ive Escher-Wyss seven bladed semi-submerged CPpropellers with flow control flaps mounted forward ofthe propellers. The design is based on the Blohm undVoss modular MEKO princ:iples allowing use ofvarious demonstrator modules. The construct ion andevaluation of the Corsair has been supportedfinancially by equipment, or manpower, from 21 firms.Corsair trials continued through 1990 and into 1991,in cooperation with the German MOD. Trial displace-ments have ranged from 165 to 195 tons and speedsof 20 knots have been maintained in 3-meter seas.During February of this year, a 57-mm Bofors gunmodule was installed for firing tests, with the SignalGemini Fire-Control System.

Based on the Corsair experiment, Blohm und Voss isdeveloping a number of larger military and civilianSES concepts.

1 3

Figure 40. Germany’s B+V Corsair

For eight years, the German MOD, supported by MTGin Hamburg, has been developing, in cooperation withthe U.S., the design of a 700-ton SES (Reference 19).A lo-meter 1 to 6.3-scale test craft, the Moses,designed by MTG and built by Lurssen Werft inBremen, is currently being evaluated at the MOD NavyShip Test Center at Eckernforde, near Kiel (Reference20).

Figure 42. Spanish Navy BES 16

Italy

In 1987, an 8-meter test craft, the TSES8, wasevaluated in a collaboration of the Italian firms of Stainand Turmomecoania Italiana. Subsequently, a26-meter, 200-passenger, SES ferry design, theTSES26, was developed and a 26-meter, 400-passenger, SES was proposed as a challenger for theTrans-Atlantic Blue Riband.

The Italian MOD has been active with the NATOSWG/G Group and has contracted SES studies withCetena and Fincantieri. The current SEC andFincantieri initiatives are discussed later.

The NetherlandsSpain

The Spanish Ministry of Defense initiated an ACVdevelopment program in 1976 which has resulted inthe construction, by the firm of Chaconsa, of the45ton amphibious assault VCA-36 which hassuccessful ly completed an evaluat ion program and isa candidate for series production. Spain subse-quently entered the SES field with the NATO SWG/6design of an SES Corvette and has now embarked ona patrol-craft program targeted on the 350-ton BES 50(Figure 41). A 14-ton, 1 B-meter, proof-of-conceptcraft, the BES 16 (Figure 42) is currently completingsea trials.

Royal Schelde’s 24-mel:er, 132-passenger, aluminumSES ferry, Seaswift 23’ (Figure 43) began builder’strials in August of 1990. Construction of this craft wassupported by a $1 million development loan from theMinistry of Economic Affairs. Thirty-four meter and60-meter designs have also been developed.

Figure 43. Royal Schelde’s Seaswift 23(Netherlands)

The firm of LeComte has, in construction, an innova-tive 89-ft SES which utilizes cored GRP hulls withFigure 41. Spanish Navy BES 50 (Artist’s Drawing)

1 4

modular aluminum deck and superstructure. Ofparticular interest are the bow and stern seals whichare formed from hinged individual GRP “fingers”.

NATO Special Working Group Six (SWGIG)(Advanced Vehicles) (Reference 21)

This NATO working group, which currently includes11 nations, is chartered to assess the potential ofadvanced vehicles for the various NATO Navalmissions. In 1987 the group completed a four yearASW study. Seven designs, including four SES ASWCorvettes were developed and assessed. Currentlythe group is evaluating Advanced Naval Vehicles(ANVs) for the NATO Patrol and MCM missions. SESdesigns have been developed for three patrolmissions and an SES option is being explored for theMCM mission. One option for the Patrol-CraftMission, designed for NAVSEA by Band, Lavis &Associates, Inc., is shown in Figure 44. Of the 11NATO SWG/G nations, eight have actively pursuedSES studies and/or development programs.

II-

The New Wave - Ferries and Military Craft

It appears that we are on the threshold of a newgeneration of large, high-speed, passenger-car andmilitary SES. The initiatives de,scribed in this sectionrepresent a major technological step in scale, if not inbasic technologies. The potential benefits, bothcommercial and military, are significant. Table 2,summarizes the leading particulars of the car-ferrydesigns.

Germany

Studies for the SES-700 began in 1984 (Reference19). The principal design analysis was accomplishedby MTG Marinetechnik GmbH in Hamburg underdirection of the Ministry of Defense. Under FMSagreements, model testing was conducted at DTRCand NAVSEA design support was provided. By theSpring of 1987 a Contract Design was complete.Model testing continued inb 1989, focused onreducing motions in 3-meter seas. Acquisition fundingfor the SES-700 would not be available before 1995.

The SES-700 would enter the FRG test fleet as ahigh-speed test craft for evaluation of combat systemsand SES technology. It could ialso be considered as aproof-of-concept for an SEE; Corvette or Frigate.Requirements specified a minimum speed of 50 knotsand unrestricted Baltic operation up to a significantwave height of 3 meters.

The result ing Contract Design (Figure 45) representeda steel hull SES with two Allison 571KF turbinesdriving KaMeWa waterjets.

Figure 44. SES Design for NATO Patrol-CraftMissions (U.S.)

Table 2

Leading Particulars of Passenger-Car Ferry Designs

I IBuilder/Designer

SEC Italy Steel 3 0 2 7 5Cirrus Norway G R P 198 5 5Fincantieri Italy Al Alloy 2 1 7 6 0Hovermarine U K Al Alloy 2 6 2 8 2Royal Schelde Netherlands Al Alloy 1 9 4 5 4Textron (Bell) U.S. Al Alloy 1 6 2 4 8MTG Germany Al Alloy 2 2 6 5 3

CountryHull

Material

LengthOverall

(ft)

7 5 0 180 5 03 6 4 5 6 4 74 5 0 8 0 4 67 5 0 9 5 55+4 3 6 6 2 4 62 8 9 2 7 4 33 8 0 5 6 5 0

1 5

Figure 45. German, SES-700 (Display Model)

A lo-meter manned model of the SES-700 (Figure46), was designed by MTG and completed by Fr.Lurssen Werft in Bremen in August of 1990(Reference 20). This craft will be tested extensively in1991 and 1992 by the German MOD Navy Ship TestCenter at Eckernforde.

Figure 46. German 6.3-Scale Manned Model(Moses) of SES-700

MTG (Reference 57) has also designed a 600-toncar-ferry variant of the SES-700, designated SES 600(Figure 47). The SES 600, of aluminum construction,will cary 380 passengers and 56 cars. The propulsionsystem consists of four LM500s and two KaMeWawaterjets.

Based on experience with the Corsair (Figure 40),Blohm und Voss has developed the design of a coredGRP, 300-passenger, SES ferry. A 500-passengerferry has also been considered. A 43-meter militaryversion with a full-load displacement of 185-tons anda speed over 40 knots has been proposed. Applica-tion of the Blohm und Voss modular MEKO system

--will facilitate application of one basic platform to MCM,police, surveillance, fast attack and ASW missions, allof which could include helicopter capability.

Figure 47. SES 600 MTG Design Study of aPassenger/Car Ferry

France

The French Navy has a firmly established SESdevelopment program leading from the AGNES 200(Figure 2) to a 1250-ton ASW Corvette (EOLES). Avariant of the EOLES was developed by France forthe NATO SWGI6 ASW studies reported in Reference21.

Italy

Societa Escercizio Cantieri SpA (SEC), the largestprivate shipbuilder in Ita.ly, initiated studies in 1986 toidentify the best concept for transporting 300passengers and 70 cars at speeds over 40 knots.These studies considered SWATH, hydrofoils, SES,catamarans and wave-pliercing catamarans. SES wasselected and consultants from Sweden, the U.S. andthe UK were engaged.. Studies included extensivemodel testing. Navy International of September 1990reported that two vessels (with an option for a third)were contracted with Sea Searchers Sud for theItaly-to-Sardinia and Corsica routes. Construction ofthe first ferry, designated SEC-774 is underway.

The hull of the 2000-ton SEC-774 (Figures 1 and 48)is constructed of high tensile steel. Trade-off studieswith cored GRP and aluminum were conducted. Thesuperstructure is aluminum. Payload is 750 passen-gers and 180 cars. With a length of 302 ft she is 36.ftlonger than the U.S. Navy’s 3KSES design. Maxi-mum speed, full-loacl, is 50 knots (32 knots insea-state 6). Model tests at 35 knots in sea-state 6

1 6

reported accelerations of less than 0.15 g, rms.Propulsion is two LM-2500 gas turbines with water-jets. A ride-control system is provided. Full com-pliance with SOLAS rules is specified as IMO 373 islimited to 450 passengers (Reference 22).

Figure 48. Italian SEC-774 Car Ferry (DisplayModel)

A “Fast Frigate” variant of the SEC-774 with speedsto 50 knots (Figure 49) has been proposed. Inaddition 450-passengers/208-tars/59-knots and750-passengersJ208-tars/45-knot variants have beendeveloped.

Figure 49. ltalian Fast Frigate Variant of SEC-774Car Ferry (Display Model)

Fincantieri has completed the detail design phase oftheir two standard platforms; the SES 250 and SES500. These designs were developed in the NavalShipbuilding Division in Genoa where the Sparvierohydrofoils were designed and constructed. Bothdesigns were extensively model tested and structuralf in i te e lement analysis was performed. Cost analysis

for various Mediterranean ferry routes has also beencompleted. Both ferries would be built in accordancewith Registro Italiano, Navale’s highest light craftrequirements; 100 - A(UL) - 1.1 - NAV.S. Both craftwill also meet applicable Det Norske Veritas require-ments (Reference 23). Both SES 250 and SES 500are welded aluminum and have ride-control systemsand Riva Calzoni waterjets.

The SES 250, with a full-load displacement of 220tons, carries 450 passengers with a maximumfull-load speed of 42 knots. Propulsion units are twoMTU diesels. Military versions of the SES 250 includea Strike (Figure 52) and an ASW version withmaximum continuous speeds c’f 50 knots.The SES 500 (Figures 50 and 51) with a full-loaddisplacement of 520 tons, carries 450 passengers and80 cars with a full-load speed of 46 knots. Propulsionunits are two Allison 571 KF gas turbines.

Figure 50. Italian Fincantieri SES-500 Car Ferry(Display Model)

Figure 51. ftalian Fincantieri SES-500 (Cut-AwayDisplay Model)

The Italian MOD has developed requirements and adesign for an SES patrol cr,aft as part of the currentNATO SWG/G studies.

1 7

Figure 52. Italian Fincantieri - Strike Version ofSES 250 (Display Model)

J a p a n

A five year project, “Techno-Superliner ‘93,” wasinitiated in Japan at the beginning of 1989. Fundingof the study is understood to be $11 million, one thirdprovided by the Ministry of Transport and theremainder by seven shipyards and heavy industries.The objective of the study is the definition of a feasibleconcept, by the end of 1993, for a vessel carrying1000 tonnes at 50 knots for 500 miles, with accept-able seakeeping capability. The first three years areto be devoted to research and design with the finaltwo years for the development of a demonstrationmodel. Such a high speed carrier would allow transitfrom Japan to China, Taiwan or Korea in one day. Atthis point it is understood that SES is very much in therunning.

The Netherlands

As noted previously, Royal Schelde is currentlyevaluating the Seaswift 23 (Figure 43), They havedeveloped designs for the 34.meter Seaswift 34(Figure 53) and the GO-meter Seaswift 60.

The Seaswift 60 (Figure 54) has undergone someredesign based on results of trials on the Seaswift 23.The current version is understood to carry 436passengers and 62 cars. Diesel and gas turbineoptions are offered, both with waterjet propulsors.

Figure 53. Dutch, Royal Schelde, Seaswift-Passenger-Ferry (Art ist ’s Drawing)

Figure 54. Dutch, Royal Schelde Seaswift- CarFerry (Artist’s Drawing)

Norway

Norway embarked, in 1989, on a five year, $15million, research and technology developmentprogram funded jointly by Norway’s State Scientificand Industrial Research Council (NTNF) and industry.The program addresses four areas; foilcats, SES,machinery/propulsion and operational safety/economics. The SES section includes ride control,speed loss in a seaway, seal technology, cored GRPconstruction and noise & vibration. Model tests of ago-meter cargo carrying SES (1000 tons) and aside-by-side run of a catamaran and an SES ferryfrom Kirkeness to Murmansk in heavy seas areexamples of funded efforts related to SES. The aimof the safety studies is to modify the IMO require-ments for advanced craft. This is being addressed byDnV and Norway’s Maritime Directorate. The overallobjectives of this program are more economic thantechnological, as all efforts are focused on improvingthe competitive position of the Norwegian fast craftbui lders.

1 8

Ulstein International, in cooperation with Brodrene Aa,has been studying the feasibility of a 55 to 60 meterpassengers-only ferry that would provide betterseakeeping by simply being larger. Initially, they arelooking at 450 passengers which is the current IMOlimit.

The Royal Norwegian Navy (RNN), in November of1989, signed a contract with Kvaerner Batsewice A/Sto build nine 350-ton SES, cored-GRP, Mine Counter-measures Vessels (MCMVs) (Figure 36); four huntersand five sweepers - with a sixth optional sweeper. Anew production facility for cored GRP construction, to100 meters in length, has been erected in Mandal.

Selection of the cored GRP SES configuration, overthe more conventional monohull and catamaranoptions, was based on extensive analysis and shocktesting. The fol lowing advantages were cited:

. Major shock attenuation on cushion

. Ability to place shock sensitive equipmenthigher in the craft

. Reduced acoustic signature

. Reduced magnetic signature

. Improved EMI/EMC associated with the largedeck area

. Personnel safety improvements associated wi thincreased space and volume

. A speed advantage of 6 to 7 knots. Maneuverability. Stability.

The propulsion system is MTU diesels with waterjets.

The Royal Norwegian Navy is projecting a replace-ment requirement for more than 20 high-speedpatrol/attack craft in the mid 1990s. Their experiencewith several charter evaluations of the Cirrus 12OPshas established a favorable climate for SES. Since1989, Cirrus has been developing designs for33-meter and 42-meter fast-patrol craft. The 42-metercraft, the ClRR 42 (Figure 56) has been selected asthe most suitable candidate for the Royal Navyprogram and has been carried to the detail design andmodel testing stage. To finance and market the CIRR42, Cirrus has combined with Det Norske Veritas andIMX, whose specialty is defense marketing, toestablish what they have called the Nortest Group. Aconsortium of equipment and weapons companieshas also been proposed to support the prototype,which may begin construction in 1991. The U.S. Navyand U.S. Coast Guard have both received presenta-tions on this craft.

The CIRR 42 is of cored GRP construction withturbine/diesel waterjet propulsion providing a servicespeed between 50 and 60 knots. Full-load displace-ment is just over 200 tons. The craft is sized toaccommodate an impressive and versatile weaponssuit.

Cirrus has developed SES ca’r ferry designs in both60-meter and go-meter lengths. T h e go-meterdesign, the CIRR 200P (Figure 55) has beendeveloped to the detail-design stage and has beensupported, in 1990, by tests of a manned model. It isunderstood that a construction contract for the firstship is imminent which would allow construction tobegin this year.

J

Figure 55. Norwegian CIRR 200P Design

Figure 56. Norwegian CfRR 42 (Nortest)(Art ist ’s Drawing)

The 2OOP, with a full-load displacement of close to500 tons, will carry 364 passengers and 56 cars(typical deadweight of 123 LT). Hull material is coredGRP. The propulsion system consists of twin 6000 hpturbines with waterjets. The lift engines are diesels.

1 9

The 200P will meet classification standards of theNorwegian Maritime Directorate, the IMO resolutionA 373 (X) and DnV + lAlR40, Light Vessel SF-F-EOILC. The car deck is equipped with sprinklers andis isolated from the passenger companments by acofferdam ceiling.

Spain

Testing of the BES16 proof-of-concept for the 370-tonBESSO is nearing completion. The BES50 design iswell advanced at this time (Figure 41). Constructionis welded aluminum with propulsion by two Allison571KF turbines with KaMeWa waterjets. Sustainedspeeds in the mid 40 knot range are predicted. Thisprogram is being executed by an MoDJBazanJChaconsa team.

Sweden

In June of 1989 a contract was awarded to Karls-kronavarvet by the Swedish Defence MaterialAdministration to construct an SES test craft desig-nated Testrigg (Figure 39). This craft (called theSMYGE, which means to sneak or smuggle) isintended to evaluate stealth optimization, newweapons systems, cored GRP construction, the SESconcept and waterjet propulsion. SMYGE is consid-ered a test platform for future MCMs as well ascombatant craft. Construction should be completed in1991.

Cored GRP construction was selected for reduction ofweight, cost and magnetic and infrared signatures.Waterjets provided significant improvements inacoustic signature. The SES concept was consideredto provide the best platform for a multi-mission craft.SES “pros” were; seakeeping, resistance, area/volume, pressure signature, hydroacoust ic signature,shock resistance and draft. SES “cons” were;increased cost, sensitivity to trim and overload andvulnerability to ice.

The 145-ton Testrigg SMYGE is 100 ft overall with abeam of 37 ft. Speeds to 50 knots are attainable withtwo MTU diesels and KaMeWa waterjets (Reference18).

United Kingdom

Initial designs of the Hovermarine ‘700” series weredeveloped in the early 1980s. The concept, describedas the “Deep Cushion” craft, provides a cushion depth

of 20-ft or more on a 60-meter SES, an approach - ,demonstrated by a manned model (Figure 57) toprovide reduced motions’ in high sea states.

Figure 57. Manned Model of Hovermarine Deep-Cushion Craft (UK)

The 262-ft HM780 carries a payload of 750 passen-gers and a typical vehicle mix of 77 cars, 5 coachesand 8 light vans (239 tonnes). The entire craft iswelded aluminum for a full-load of 850 tons. Propul-sion is two Rolls Royce Spey SM2 turbines withKaMeWa waterjets. The HM780 is capable ofoperating at 48 knots in, 1 0-ft seas.

Hovermarine International are also marketing the 82-ftHM 424, a 165 to 200 seat passenger-ferry design inGRP capable of speeds up to 50 knots depending onengines selected (Reference 6).

United States

In the United States, Textron (Bell), Lockheed, Trinity,Newport News and Ing~alls have all recently developeddesigns of large SES. Textron has a design for anSES car ferry reported in Reference 5. The leadingparticulars of this SES are listed in Table 2. TheTrinity Marine Group has a design for a passengerferry developed as a derivative of the Bell-HalterBH-110 (Figure 58). Trinity is also marketing a largerhigh-speed passenger ferry for operation on theEastern Seaboard and a 115-ft SES motor yacht(Figure 59). Lockheed, Newport News and Ingallshave each developeld SES conceptual designs ascandidates for the US. Navy’s Fast Sealift require-ment. Band, Lavis & Associates, Inc. (BLA) has alsodeveloped an SES car-ferry design (Figure 62,Reference 26) a 70”knot Mega-Yacht SES design,(Figure 60, Reference 27) and an SES design (Figure61) as a possible future candidate for consideration asa 70+-knot Trans-Atlantic, Blue-Riband, Challenger.

2 0

Figure 58. Artist’s Drawing of Trinity SES Ferry(U.S. )

Figure 59. Artist’s Drawing of Trinity SES MotorYacht (U.S.)

Figure 60. BLA SES Mega-Yacht Design (U.S.)

1 -.

/ iea b ‘-, -- - -

Figure 61. BLA SES Blue-Riband ChallengerDesign (U.S.)’

m ‘-.--- //- - -- - - ---y

Figure 62. Outboard Profile of BLA SES Passenger-Car Ferry

U S S R

In the Spring of 1990, the world’s largest SES wascommissioned by the Soviet Navy after a year of seatrials (Reference 16). The Dergach was built at theKamysh-Burun Shipyard in Kerch on the Black Sea.A second SES of the class is under construction.

Propulsion and lift power for the 650-ton Dergach isprovided by three gas turbines. Armament consists oftwo SS-N-22 quad launchs!rs, twin SA-N-4 Geckomissile launchers, a 76.2 mm gun and two 30 mmGatling guns (see Figure 26).

Summary

Since 1961 there have basin over 50 SES designswhich have been built as test craft, or as prototypeswhich have lead to quantity production. Figure 63shows the number of the most prominent SES of anew design launched each year. The numbers

include only the first in any series production and crafthaving major modifications.

Figure 63 shows, clearly, the significant increase inworld-wide activity in the last ten years.

The annual breakdown by regional group is shown inFigure 64. The three groups are (1) the UnitedStates, (2) China, Korea and USSR, and (3) Europe.This shows that the majority of the recent growth inactivity is in Europe followed by the group of China,Korea and USSR. In the US., only four new designshave been built since 1980.

2 1

Number of SES of a New DesignLaunched Each Year

I

Figure 63. SES Prototypes

Number of St!j, by Kegron, ot a NewDesign, Launched Each Year

”JIIIzxr- .___._.__...........................................-..... 1

Figure 64. SES Prototypes by Region

The growth in the world’s market for fast ferries isillustrated in Figure 65. This growth has been met byhydrofoil craft, catamarans, monohulls, SES andACVs with SES now taking an increasingly largershare.

Number of Fast Ferries Delivered1970-I 990

(Ref. Fast Ferries, RINA, Dec. 1990)Paramilitary Vessels Excluded

T - - - - - - - - - - - - l

The comoetition is fierce and SES can only bejustified on routes where high speeds, generally over40 knots, are of interest.

SES CHARACTERIZATION-

The Name

Air-cushion supported craft, generally referred to as“Hovercraft,” have been known by a variety of names:the amphibious type that is fully supported by the aircushion has been called the “Ground Effect Machine”(GEM, now obsolete), or “Air-Cushion Vehicle (ACV -now in general use in the USA); while the type inwhich the air cushion is partially contained bycatamaran-like hulls has been called the “CapturedAir Bubble” (CAB, now obsolete) the “Air-CushionCatamaran” (still in use in Scandinavia) or the“Surface Effect Ship” (SES, now in general use,particularly in the USA), and which is the subject ofthis paper.

Why SES?

Although the SES ha.s a number of unique ad-vantages, the principal motivation behind the SESconcept is that the air cushion, which supports themajority of the weight of the craft, significantly reducescraft resistance to forward motion at high speed andhelps to mitigate the effect on craft motions andaccelerations of operating in rough seas. Althoughpower is required to create and sustain the aircushion, the reduction iIn resistance is so large at highspeed that the sum of lift and propulsion power issignificantly less than the propulsion power of theequivalent conventional craft.

This feature (discussed in more detail later) isillustrated in Figure 66, in which total installedhorsepower per ton (of full-load displacement) isplotted against design-speed Froude Number

(v/m. The open symbols represent SES and theblack symbols represent monohulls. The data pointsare for craft which have successfully operated or (asin a few cases shown) have been the subject of detaildesign. Curves have been drawn in Figure 66 tobound the lower extremes of the data for each of thetwo types of craft. These curves on Figure 66 arelabeled “state-of-the-art” and show that, beyond anoverall-length Froude Number of about 0.75, the SEShas an increasingly distinct advantage in total powerdespite having to provide power for lift.

Figure 65. The Fast-Ferry Market

2 2

Figure 66. installed Power/Full-Load DisplacementVersus Froude Number

For the data shown in Figure 66 “speed” is themaximum continuous speed obtainable at ful l- load incalm water (and still air). The comparison changessomewhat for operation in rough water in favor of themonohull.

The SES has flexible seals at the bow and stern thatspan between the sidehulls to impede the loss ofcushion air fore and aft. These seals are designed tominimize air loss from the cushion by tracking thesurface of the waves. For high-speed operation inrough water the seals (in particular the stern seal)have more difficulty in containing the cushion. Theconsequence is that, as sea state increases, morecushion air flow is lost and cushion pressure isreduced. The side hulls are then required to carry alarger fraction of the weight, they operate with ahigher time-average draft and, hence, with morewetted area which results in an increase in drag. Atthe limit, the operation of an SES approaches that ofa catamaran. Fortunately, this is usually a gradualprocess with increasing sea state but can result in alarger, involuntary (constant power), speed loss invery rough seas as compared to conventional craft.This feature of the SES applies particularly tooperation in head seas and to a lesser extent in beamseas and following seas.

When the significant wave height reaches about twicethe height of the cushion (i.e., twice the height fromkeel to wet-deck) the SES ceases to have a poweringadvantage over conventional craft. However, in suchconditions, speed is usually voluntarily limited by craftmotions (particularly for a conventional craft) so thisloss in advantage has not been found to besignificant.

For some conditions, cushion flow rate can bedeliberately reduced to improve performance. Thisoccurs when high sea states cause operation to occurnear hump speed (see Figure 67) at which a reductionin cushion pressure can significantly reduce cushionwave drag, albeit with an increas#e in sidehull drag.

The corresponding reduction in lift power (due toreduced air flow and pressure) combined, in the caseof waterjet propulsion, with an improvement inpropulsive efficiency due to having the inlets operatewith a deeper draft can, within limits, result in anoverall reduction in total power. This can also cause,in some cases, a reduction in pitch motion due toincreased damping from the sidehulls (as explainedby Lewthwaite, Reference 19).

The performance of an SES, and other high-performance craft, is also more sensitive to weightthan that of conventional low-speed craft. Thus, thereis always a motivation to find acceptably-reliablesubsystems of minimum possible weight albeit at ahigher price. This has beer1 construed, in somecircles, as a major disadvantage for SES. However,we prefer to view the SES as a craft that can takecost-effective advantage of using light-weight systemsunlike most other marine craft (and particularly unlikeMonohulls). What seemingly little motivation therehas been in the marine industry to develop lightweightsystems (for power plants, transmission systems,structures outfitting, auxiliary systems, etc.) hasresulted, however, in very significant progress overthe years, and at a rate which is continuing. Withouthigh power-to-weight diesel elngines and the use ofaluminum alloy or foam-core (SRP for hull structure,all of the total power-to-weight advantage of SES,shown in Figure 66, would not have been possible.As further progress is made to develop even lightersystems the advantage for the SES will increase.

SES Geometry

The features of an SES which set it apart fromconventional craft are:

a. The air cushion, formed by the two hulls oneither side of the cushion and the flexible sealsat the bow and stern

b. The lift-air-supply syste’m consisting of engine,power train, fan(s), air-distribution ducting and aridecontrol system if ins’talled.

Other features required for propulsion, steering,stability and onboard systems are generally similar, tothose of conventional monohulls or catamarans.

2 3

The Cushion low drag in the so-called “drag bucket”. This is theusual choice for most military craft which also allowsfor lower drag, and more economical operation over awider range of speeds (Reference 24).

The choice of the length, L,, and breadth, B,, of the

cushion is influenced by many factors foremost ofwhich is their effect on the wave-making drag of thecushion which, at some speeds, can be a largefraction of the total drag of the craft.

Figure 67 shows how the predicted non-dimensionalcushion wave drag, for deep water, varies withchanges in Froude Number and the ratio of cushionlength-to-beam (L&B,). For L&B, ratios less than

about 5 a significant “bucket” exists between theso-called primary and secondary drag humps atFroude Numbers (based on cushion length) ofbetween 0.4 and 0.7.

3 . 5 Waler Depth 10 Cushion Lenglh Ratio - 100

0.0-l0 . 0 OS 1 . 0 1 . 5 2.0 2 . 5

FROUOE NUMBER. m - Y-hiq

i3.0

Figure 67. Cushion Wave-Drag Parameter VersusFroude Number

It would be natural., of course, to avoid cushiondimensions which would cause the craft to operateclose to either of the secondary or primary humps, sodimensions are usually chosen to have the craftoperate either in the drag bucket or at speeds abovethe primary hump. This is illustrated in Figure 67 bythe choice of LdB, ratios of approximately 6.0 and 3.5

for the low-speed Dl and the high-speed XR-1,respectively.

If the craft is relatively small and has a high designspeed, then a low LJB, is usually favored to obtain

low drag in the post-primary hump condition. This isthe usual choice for small high-speed passengerferries or for small very high-speed military craft thatspend most of their time underway at cruise speed.

If the craft is large and has a low to moderate designspeed then a high LJB, is usually favored to obtain

However, selection of cushion area and LJB, ratios is

not based entirely on wavemaking resistance.Factors such as overall craft size, dictated bypayload-deck area and lirnited by docking or construc-tion limits, can play an important role. The choice oflength and beam also affects seakeeping, dynamicstability, static stability, arrangements, structural loadsand costs. Generally, seakeeping in head seas isimproved with increasing craft length. increasing craftbeam increases maneuverability and lateral stabilityor allows for a deeper cushion to minimize wet-deckslamming and results in a higher freeboard tominimize deck wetness. This is illustrated by Figure68 which shows platform acquisition cost versuscushion length and beam. Similar plots can beproduced.for power and full-load weight. Figure 68 isa carpet plot produced using a whole-ship SESDesign Synthesis Model (References 25, 26 and 27)which integrates the effects of resistance andpowering, structural toads, material properties,stability, seakeeping, as well as sidehulf shaping andvolume for waterjet pump installations among manyother considerat ions. Estimates of the acquisitioncost depend upon factors such as design cost andlabor and material cost for construction.

Figure 68. Typical Plot of Cost Versus Length andBeam for an SES

The results of the seakeeping predictions for thisexample are overlaid on Figure 68 as lines of constantrms vertical acceleration at the bow and cg of thecraft. The design point selected represents theleast-cost craft with acceptable ride quality andperformance.

2 4

A further explanation of this figure is given later in thepaper under the subject of “Design for Seakeeping.

Sidehulls

Figure 69 illustrates a typical midship cross-section ofan SES. The terminology used to define the various

A E i C

dimensions are those in common use, at least in theUSA. A corresponding prospective view of an SEShull, without seals, is illustrated in Figure 70.

Figure 69. SES Midship Geometry

Figure 70. Perspective View of an SES Hullform .

Sidehull geometry is selected primarily to providesatisfactory on-cushion performance, stability andseakeeping based on prior experience. Figures 71and 72 illustrate the wide variety of sidehull shapes .

that have been used in the past. Some of thefeatures exhibited by current trends include:

-.----I ----.-..,---y-T_il. I .-.&.L;,.I ‘,\ j ,j -.

.alRsoliT UI BH- 110 HM s1974 ,970 twz

Figure 71. Early Trends in Sidehull Mid-ShipSections

D E F

Figure 72. Recent Trends in Sidehull MidshipSections

High cushion heights, with the ratio of cushionheight to beam amidships, in some cases,greater than 0.35 (with even a larger valueforward) to minimize slamming of the wet-deckboth on and off-cushion.

Sidehulls having a fine entry forward to reduceresistance and to reduce pounding and pitchingin moderate seas but incorporating flare toincrease lift during bow submergence in heavyseas with rails inboard and outboard (shown inFigure 69) to minimize spray.

A keel flat for docking and an outer deadrisesurface (of 30 to 45 degrees to the horizontal),for a significant length of each sidehull todevelop sufficient dynamic: lift during high-speedturning maneuvers to prevent roll out.

An internal haunch to the sidehull to increasesidehull d isplacement, to minimize draftoff-cushion, maximize wet-deck clearanceoff-cushion and to provide extra space formachinery installed in the sidehulls. A relativelyfine entry forward but a relatively abrupt changein section aft for the haunch will minimizeresistance.

A wider keel flat, wider deadrise surface, orreduced deadrise aft to accommodate a flush,or semiflush, waterjet inlet with gradual changesin sectional shape ahead ‘of the inlet sometimescombined with inboard and/or outboard fencesto impede the cross flow of air to the waterjetinlet.

2 5

Recent trends in sidehull geometry are also illustratedby the range of dimensional and non-dimensionalparameters shown in Table 3.

Table 3

Range of Hull Characteristics of SES Designs

High L a w

Overall Characteristics

Cushion Length to Seam, k; 7 . 0 2 .0

DFreeboardlBeam Overa l l . B- 0 . 5 0 . 2 5

Cushion Height to Beam Overall . %0 . 3 0 .1

VCG Height to Beam Overall . Y 0 . 4 0 . 2

Cushion Pressure to Length. PJ4, lbft3 3 .0 1 .0

Cushion Density, W/(A3”5, lb/f? 6 . 0 2 . 0

Sidehull Characteristics:

LVLLength to Beam Ratio, 9;- 26.0 17.0

Hullbome Beam to Draft Ratio, $ 1.45 0 . 7 0

Gap Ratio, e 0 . 2 4 0 . 1 0

(6, = Maximum Craft WL Beam Hullborne)

Prismatic Coefficient, C, 0 . 8 9 0 . 6 0

Block Coefficient, C, 0 . 7 4 0 . 5 4

DisplacementfLength Ratio. 49.0 27.0

Deadrise Angle Amidships, Q 45O 3o”

3.3.3 Cushion Seals

The current status of SES seal technology can beconsidered in terms of 30 years of operationalexperience with both military and commercial SESand ACVs up to 300 tons and a large body of testdata and analysis an seal systems for high-speed,high-cushion-pressure, ocean-going SES (e.g.,3KSES and related studies).

An analysis of the history of seals developmentreveals three basic design approaches that have beentaken towards meeting the cushion sealing require-ments for ACVs and SESs. They are as follows:

,. Flexible Membrane Seals

- Bag-and-finger (SRN-series, SES-1006,LCAC, LAW-SO)

- Loop-segment (Vosper VT1 and 2,HM-series

- Ful l -depth-f inger (BH-I IO, SES 200,Norcat, Jet Rider)

- Loop-Pericell (AALC JEFF(A))- Multi-lobe stern seals (most SES)

. Semi-Flexible Reinforced Membrane Seals

- Stay-sti f fened membrane (SES-1 OOA,XR-1 C)

- Transversely stiffened membrane (EarlySES 200)

. Semi-Rigid Planing Seals

- Bag and planing surface (XR-1 D)- Bag and segmented p lan ing sur face

(SES-1 OOAl, ,3KSES).

The most common types of SES cushion seals usedtoday are:

. Full-depth, or bag-and-finger, bow seals

. Double or triple-loloe stern seals.

All are, essentially, two-dimensional, flexible-membrane seals using varying types of elastomer-coated fabric (usually neoprene or natural rubber-coated nylon fabric) weighing between 40 and 100 ozper sq. yd. depending on craft size and duty.

All are highly compliant, responsive, low-drag cushionseals, while the bag of ,a bag-and-finger bow seal actsas an air-distribution duct and provides increasedrestoring moments and protection for the localstructure from slamming when encountering largewaves. Additionally, finger seals provide a high levelof redundancy in that the failure of individual fingers islargely compensated for by expansion of the adjacentunits.

The longitudinal location of the bow and stern sealson the craft defines the cushion length and center ofcushion area, which must be carefully selected to befairly close to the craft’s longitudinal center-of-gravityfor correct trim. At high speed, an out-of-trimcondition by as little as 25% of the cushion length canincrease drag signific:antly. Thrust contributions topitching moments mu,st also be taken into account.

2 6

4

Bow-down trim will reduce directional stability and cancause a higher likelihood of propulsor broaching.Bow-up trim will reduce maneuverability and mayincrease vertical accelerations in a seaway.

Bow-Seal Geometry

The fingers of a full-depth-finger bow seal or of abag-and-finger bow seal are inflated by cushionpressure.

The bag of a bag-and-finger bow seal is inflated to apressure 10% to 15% higher than cushion pressureusing fan-supplied air ducted within the hull structure(usually using space available in the double bottom ofthe cross-structure). An illustration of a bag-and-finger bow seal is shown in Figure 73.

.E

/c

Figure 73. I l lustration of Bag-and-Finger Bow Seal

The fingers shown in this figure are similar in conceptto those used for full-depth finger seals.

The exterior angle between the water surface and theexternal forward face of the finger, can greatly affectcraft heave and pitch stiffness. The smaller the angle,the greater the stiffness but the smaller the cushionarea.

Also, at small exterior angles, there is a tendency toincrease wetted length; therefore, there is an increasein drag plus a greater tendency for the fingers toscoop when the craft is moving astern. At largeangles, the resulting increase in cushion area is offsetby slower finger recovery after deflection andincreased difficulty in providing a practical configura-tion for long support webs. Angles from ap-proximately 45 to 50 degrees are considered to beopt imum.

The included angle formed by the outboard forwardside of the finger and a line from the inboard attach-ment to the tip of the finger, should preferably be 90degrees to generate a satisfacitory geometry whichwill inflate properly to the desired configuration.Normal cushion pressure acting on the finger’ssurfaces generates tension in the semi-cylindricalouter face. This tension is supported by the fingerwebs which are in turn attached to the hull or primaryloop. As the included angle is allowed to fall below 90degrees, the section of the finger that is between thetop and the go-degree intersection is no longersupported in direct tension. It, therefore, has to relyfor stability on shear resistance from the elastomericcoatings, plus a degree of interlocking from the loadedwarp and fill threads. A form of instability occurswhen the tension loads can no Ilonger be supported inthis fashion and the lower unsta.ble finger area is freeto extend outwards. Fingers with a tip angle in therange of 80 to 90 degrees will, however, performsatisfactorily if fabric stiffness and/or shear resistancein the lower finger area are adequate.

The ratio (expressed in terms of percent) of fingerdepth to cushion depth for a bag-and-finger seal cangreatly affect seakeeping. Increasing the depth of thefinger reduces the rough-water drag, but with apenalty of reduced stability and, generally, reducedcushion area. Originally, one of the objectives ofselecting a combination of bag and secondary skirtwas to provide replaceable sections in the areasubjected to the highest wear and abrasive action.Finger life on high-speed SES is typically 500 to 1000hours, or six months of comm’ercial service, beforerefurbishment is required.

Early bag-and-finger designs used a 30% finger-to-cushion depth ratio; however, the bag was often incontact with green water while t’he craft was operatingover waves. Since then, there has been a steadygrowth in finger depth percentage, and currentbag-and-finger bow seal desigrls for most ACVs andSES have finger depths from 50 to 70%.

A depth-to-width ratio of approximately four has beenestablished for open finger segments based on modeltest and full-scale development. There is evidencethat relatively wide fingers are1 more susceptible toscooping loads when backing up. This is attributed tothe larger hoop tensions and vertical resistance ofwider fingers. On the other hand, very narrow fingersor cells suffer from poor reoovety and temporaryhang-ups in conditions where large deflections occur.

27

A bow seal should respond to the waves, but notcollapse or tuck-under. The basic aim is to preventthe bag from distorting appreciably, as a result ofwater contact drag, and thereby moving aft and underthe craft with a consequent loss in cushion area andrestoring pitch moment. Increasing the bag’sresistance to deformation is achieved by choice ofinflated radius, pressure, and location of attachmentsto the hard structure. Several design approaches areavailable to meet these requirements. First, theshape of the bag in planform is curved or bowed outas much as possible (to create a three-dimensionaleffect) within the limits of any craft-length restrictions.This creates additional longitudinal stresses in thebag, which in turn leads to a stiffening effect underbag deformation. Next, the outer attachment of theloop can be raised as far as possible to increase theouter loop radius and the hoop tension and therebyreduce the tendency for collapse during wave contact.

Stern-Seal Geometry

An illustration of a three-lobe stern seal is shown inFigure 74 installed between the vertical and parallelsides of the inner surface of the sidehulls aft.

E\

Figure 74. Illustration of Triple-Lobe Stem Seal

It is generally recognized that stern seals should beintentionally more sensitive to lifting forces andpressure changes than bow seals since compliance isrequired to allow effective contouring of the waves forefficient cushion sealing and to reduce drag and wearloads.

Stern seals are either fed by the main air supply, aseparate air supply, or via a boost fan which takescushion air and increases the steady or time-averagepressure to a pressure of from just above thetime-average cushion pressure in rough water to ashigh as 30% above cushion pressure in calm water.

Stern seals can be prone to flutter due to the airpassing under the trailing edge causing an unsteadystate at the surface and causing the seal to oscillate.Typically this is more of a problem in calm water. Thiscan be corrected by adding devices to the wear stripto break up the air-flow patterns. Studies utilizing theLCAC and the LAW-30 with small reinforcedelastomer-coated fabric planing surfaces on the sternseals proved very effective in reducing drag andreducing stern-seal wear. UK (Hovermarine)experience is that conventional stern seals for SEShave wear lives of several thousands of hours.

The geometric layout of the stern seal requires asimilar approach to balancing the forces with cushionpressure, seal pressure and system weight as for thebow seal. Mathematical models can be used toanalyze the two dimensional geometry under variousloading conditions. A key design consideration for thestern seal is rapid response to waves to minimizecushion leakage at high forward speed. This requirescareful design of the air supply and exhaust system toensure that when the seal is compressed the bagpressure is dissipated and then rapidly replenished torestore its seal to the deployed position.

To allow adequate freedom of movement, but toprevent excessive air leakage, the total width of thestern seal must be carefully tailored to achieve a smallclearance between the outboard edge of the seal andthe vertical sides of the sidehull at the stern.

Cushion-Air-Supply Systems

The cushion-air-supply system of an SES is designedas an integral part of the design of the craft. Initially,emphasis is on the quantity and location of lift airrequired, the cushion pressure and hence, the liftpower required.

Cushion Air Flow

Flow is generally split between the cushion, bow sealand stern seal in the approximate proportions of 65 to75%, 15 to 20% and 10 to 15%, respectively. Even ifa full-depth finger bow seal is used, air is usually fedforward to a transverse manifold in the structure of the

28

L

hull to discharge air through the wet-deck above eachindividual finger. Air fed directly to the cushion is alsousually discharged through the wet-deck at a forwardlocation on the craft.

There are several formulations in current use for thecalculation of required total air flow. These methodsuse different approaches for the calculation and givesomewhat different results depending on the Craftsize, speed, sea state and length-to-beam ratio.Some judgment is required in selecting the design-point lift-air flow.

Usually a compromise is made which is neither thehighest or the lowest flow calculated. If a ride-controlsystem is to b8 used, the normal design flow for thecushion is increased in some cases by up to 30%.For a 200-ton SES the total air flow rat8 would beabout 3000 to 4000 cfs depending on design speedand the cushion pressure would be a little less than 1psi.

Cushion Pressure

At design speed in calm water the cushion would beexpected to support at least 85% Of the weight Of theSES (although existing craft have values ranging from75 to 90%). When operating in head s8as having asignificant wave height equal to the height of thecushion, th8 cushion would be expected to contributeonly about 50% of the time-average lift (depending,primarily, on the efficiency of the stern seal); the Other50% would be contributad by the sidehulls. Thus, thetime-average cushion pressure, in this cas8, wouldvary from 85% to 50% oi the weight of the SESdivided by the cushion area, which is the product ofcushion length and cushion beam.

Types of Fan for SES Use

The most common arrangement has centrifugal fansin rectangular-section spiral-volute casings driven bydiesel engines. In a few cas8s, axial fans have beenemployed, but generally centrifugal fans have provedto be superior beCaUSe of their relatively flat, Bssen-tially stall-free pressure-versus-flow characteristicsand simple, rugged mechanical design.

There are several types of Centrifugal fans which canbe considered. The most common and successful sofar is the backwardly-inclined, airfoil-bladed centrifugalfan specially adapted for SES use. This general typeof fan is widely used in large ventilating systems andother industrial applications, where it is Valued for its

high efficiency, relative quietniess and simplicity ofdesign. For SES use it has b8eln found advantageousto design the fan impeller with a narrower blade widthand a somewhat higher blade angle than is usual forits industrial counterpart. These features enable thefan to be designed for higher pressures withoutexceeding structural l imitations while retaining a highflow capacity.

Detail Design Features of Lift Fans

The detailed design of lift fans requires specialattention to features that haV8 significant effect on fanperformance. One of th8Se features is the interfacebetween the inlet bellmouth and the impeller shroud.The shaping of the inlet beilmouth, the shroud, andthe clearance between them, have a profoundinfluence on the pressure-flow characteristic, thedesign flow capacity and the efficiency of the fan.Another feature is the volute s’ize and shape and thecut-off lip configuration. Solutes of different spiralangles and forms have been tested includingarithmetic and logarithmic log spirals, circular arc andcomposite forms. The Shape of the cut-off lip and itsclearance affect the fan characteristics and the noiseproduced.

Fan Pressure-Flow CharaCt8riStiC Shape

It is desirable that the fan or fans produce a flatpressure-flow characteristic. The reason for this isthat the vessel’s heave stability and the comfort of th8rid8 are affected by the slope of the pressure-flowcurv8 at the fan operating point. It is desirable thatthe pressure-flow curve should have a low negativeslop8 at the fan design operating point which shouldbe coincident with the maximum fan efficiency.Off-the-shetf fans saldom satisfy th8S8 two conditionssimultaneously, i.e.. low slope and peak efficiency.Fan performance in a dynamic environment isdiscussed in Reference 28. Limitations for large SESapplications are discussed in IReference 29.

Lift-Fan Power Transmission

With regard to the fan power transmission, it isfrequently possible to use direct drive from a dieselengine to the fan coupling. Sometimes two fans maybe connected in series to the same lift engine. Somedies81 engines permit power to be taken from bothends of the crank shaft, thus, a fan may be drivenfrom each end of the same engine. Almost invariably,SESs us8 double-width, double-inlet fans rather thanlarger single-width, single-inlet fans, with a conse-

29

quent saving of space, weight and cost and generallywith a better speed match to the engine.

Due regard must be paid to the dynamics of all drivesystems including diesel engine and fan combina-tions. Improper shafting and coupling designs canlead to serious torsional oscillations.

Usually the diesel engine torque characteristics will befound to be well-suited to lift-fan operation but it isnecessary to plot on the H-engine map the fantorque-and-power demand curves for all forseeablemodes of operation of the ship to ensure that theengine is not over loaded under any normalcircumstances.

Failure Modes

Special cases which must be considered for lift-system operation include engine or fan-failure modes.Lit fans are often fitted with shut-off vanes which arenormally fully open and are of airfoil shape forminimum flow resistance. In the event of fan orengine failure the vanes may be closed to preventloss of cushion air and windmilling of the fan. Thedesign and location of these vanes for minimum lossand maximum sealing is a special part of thelift-system design.

Lift-System Performance

Lift system performance is handled best by amathematical model of the entire lift system. Such amath model is particularly desirable if an integrated liftand propulsion system is to be used.

The lift system math model represents the entire flowpath of the air from the atmosphere, taking intoaccount ship speed, wind speed and direction, inletgrill and other inlet losses, possible ram recovery,pressure rise through the impeller, exit vane losses,duct losses to bow and or stern seal, direct flowlosses to the cushion, flow losses from the seals tothe cushion, and from the cushion to atmosphere.The model takes into account changes of cushion andseal pressures due to variations of craft displacement,sidehull immersion, fan speed, ambient air condit ions(temperature, pressure, humidity and wind velocity).If cushion air is used for bow-thruster purposes (formaneuvering and control) then the bow thruster andits control vanes are also modeled. The enginecharacteristics are modeled so that changes of fanspeed reflect changes of fuel consumption and other

engine parameters as well as fan pressure, f low andhorsepower. Such a model can provide a completepicture of lift-system operation for all quasi-steadyoperating condit ions foreseeable.

In summary, it may be stated that lift-system design isa fairly mature art, but attaining optimum performanceand efficiency depends on extensive experience andskill on the part of the designer.

SES Resistance

An understanding of the performance of SES hasbeen slowly and painfully acquired within thecommunity over the last thirty years through in-numerable design studies, model tests, full-scale trialsand operational experience. This has now matured tothe point that reliable performance predictions can bemade for new designs which conform rationally to theestablished principles whlich have been formulated.

The resistance of an SES, like that of other marinecraft, is the sum of several elements which include thefollowing:

Cushion Wave-Making Drag

Several theoretical formulations have been made forthe resistance of a pressure distribution moving over afree surface, including those of Newman & Poole(Reference 30) and Doctors (Reference 31).

Sldehull Drag

Sidehull drag is composed primarily of sidehullwave-making and frictional components. Since, invery rough water, the average support from thesidehulls can increase to 50%, or more, they have theequivalent hydrodynamic resistance of similar-catamaran-like slender hulls. The main differencebeing that the average water level is lower on thecushion side of the sidehull due to the cushionpressure. For ACVs, rough-water drag can bepredicted as a function of sea-state modal period, andthis relationship has recently been perfected for SES(Reference 55).

Appendage Drag

SESs may have appendages in the form of rudders,stabilizing fins, or waterjet-inlet fences and, ifpropulsion is by means of marine screws, there maybe shaft and bracket appendage drag also.

3 0

.

Seal Drag

The seals of an SES are seldom fully out of contactwith the water, even in calm water and at highlift-system power settings. In waves and at all normaloperating conditions the fabric tips of the fingerswhich form the seal will make a brushing contact withthe water and create drag.

Spray Drag

Sidehulls will generate spray which can be controlled,to some extent, by external and internal spray rails.Also, the air escaping under the seals generatesconsiderable amounts of spray. Spray which impactsany part of the craft adds to the drag.

Momentum Drag

lf there is any relative motion between the craft andthe ambient air, as in normal forward motion, orotherwise, there wil l be a momentum drag associatedwith the lift-fan flow for the cushion, and other, lesssignificant, air flows to the engines and ventilatingsystems, etc.

Likewise, as with most marine craft, any cooling wateror water for other purposes, which enter intakes onthe sidehulls, contributes to momentum drag.However, if the SES is propelled by waterjets thewaterjet-inlet momentum drag is charged to thepropulsor and does not enter into the total ship-resistance calculation. Other types of waterjet-inletdrag are part of the appendage drag of an SES.

Aerodynamic Drag

Because of their potential for high speed theaerodynamic drag coefficients of SESs must bedetermined so that aerodynamic drag may becalculated. If the craft is experiencing a head wind,and has a high water speed., the effective air speedcan result in significant aerodynamic drag.

Drag Predlctlon

Predictions of resistance can be made analyticallyusing a combination of theory and empirical knowl-edge and experience. Such predictions are mostuseful in parametric design studies such as thosewhich use a design synthesis model (Reference 25).However once a point design has been identified it iscustomary to confirm the resistance predictions bymeans of tow-tank model tests.

Tow-Tank Tests

Tow-tank model tests are usually conducted for arange of Froude-scaled speeds in calm water andscaled sea states. Other parameters which should becorrectly scaled include model weight, pitch radius ofgyration, trim, lift flow and seal pressures. The modelis usually free in pitch and heave and may also befree in surge. Self-propulsion tests may also beconducted. Many variations on the basic resistancetests are possible.

The tow-tank resistance data must be corrected forReynolds number and tank effects when scaling tofull-size craft resistance. Underwater photos arehelpful in determining sidehull wetted area, since theskin frictional resistance of the sidehulls has to becorrected. Aerodynamic drag of the model may alsobe measured approximafely by towing the model fixedin heave and clear of the water or, more precisely, byusing a separate wind-tunnel test. Tow-tank modelsdo not operate at the appropriate Reynolds Numberand seldom represent the profile of the full-scale craftaccurately, so they can only give an approximateestimate of the aerodynamic clrag. For very. high-speed craft, the aerodynamic drag is best determinedfrom wind-tunnel tests.

Propulsor lnstallatlon Effects

Due to installation with respect to the free-streamflow, marine propulsors suffer a loss of apparentthrust which is reflected by the so-called thrustdeduction factor (Reference 32). When the marinepropulsor is a waterjet. under some conditions thethrust deduction factor, (I - t) may be greater thanunity, partly accounting for the surprisingly highpropulsive coefficients for waterliets.

Current Design Issues for SES Resistance

The prediction of resistance for SESs has reached afairly advanced stage of maturity and reliability.

Theoretical formulations for cushion wave-makingdrag are necessarily based on simplifications in orderto handle the highly complex mathematics. In anycase, the detailed information necessary for morerealistic math modeling of an actual air cushion issimply not available in numeric.al form. Newman andPoole’s method allows correction to be made fortow-tank width and depth effects but producesunrealistically high drag peaks; at low speed. Thisproblem is presently overcome by applying atheoretical wave steepness limitation.

3 1

lt is always assumed that cushion wave-making dragis independent of sea state, and that the largeincrease of total drag with increased wave height ismainly a function of increased wetting and skin-frictionresistance. lf so, seal resistance, for instance, shouldscale with Reynolds number as has been found withthe skirts of ACVs. This is an area of currentinvestigation. Typically seal resistance of an SES, isobtained from model data by subtracting the sum ofthe other drag elements from the total drag of themodel. Although seal drag is a small fraction of thetotal drag, much discussion and analysis has beendevoted to this subject over the years without a finalconsensus being reached.

SES Powering Requirements

The power required for the lift and propulsion of anSES depends not only on the performance require-ments but also on the choices made for subsystemsand how successfully the designer has optimized theirintegration balanced against the demands of otherrequirements, not the least of which is cost. This taskcan best be handled by a whole-ship design synthesismodel (Reference 25) which can quickly examine thecost impacts and merits of a very wide range of hullgeometry and subsystem choices.

The range of powering requirements exhibited byexisting SES including a few recent SES designs isillustrated in Figure 75 in terms of total-installedcontinuous power per unit full-load displacementversus Froude Number. The Froude Number here isbased on overall craft length and speed in calm water.The SES in Figure 75 are compared with a cor-responding set of data representing contemporarymonohulls including some designed for very highspeed. Data from the same craft are shown inFigures 76 through 78. Figure 76 is similar to Figure75 but uses speed as the abscissa. Figure 77 usesthe displacement Froude Number instead of FroudeNumber based on overall length. This was includedto avoid biasing the results since monohulls generallyhave higher length-to-beam ratios than SES. Thebasic trend, however, is much the same as in Figure75.

Figure 78 shows installed power per ton knot versusFroude Number. In this case, the continuous powerwas divided by the product of full-load displacementand the (continuous) calm-water speed. Again, thebasic trend is unchanged. The SES is demonstratedto have a very significant powering advantage overthe monohulls for operation at high speeds.

Figure 75. Instal led Power/Full-Load DisplacementVersus Froude Number

WEED - KNOTS

Figure 76. Instal led Power/Full-Load DisplacementVersus Speed

140

120 . __._ i ..-- ._.._.__ /..- _.__._....___ +-.~ . I..._..-_..: _....

g1 i

100 .._____...._______ ~_____._._._._.. I..__ .._...___._.__ f ._. ---q.. _._............ j .._._. -

z0 0

/ i I I..- . . . . . . . . . . . . . . . . ___._...__.___._. i ___..^..__..__.... :- ._.__... p .........m..... j .--- .._._.

Fg 80

0

FiJ

.._..__._...._ /..__.___.____. / ..___....___.__._ J ..-.?-, __............_ / .._ -._-.-

I 8

%40 _.__._ - _..___. [ ._._.___.__._._ j.___.._ ,Jq --pqf..-- ..̂ _. i .._- _..-...

r! _...: .._. ..-...- ..-

“Ic 20

1~..._.._......____ t..-- ____. y _._____j gP+i

y a” /.._.._. ~ ___.__......._ - ..---

10+

0 0.5 1 1.5 2 2.5 3

DISPLACEMENT FROUOE NUMBER

(oCONSTRUCTED~ DRIoSESKI

Figure 77. Instal led Power/Full-Load DisplacementVs Displacement Froude No.

0

3 2

.2.51

‘a

E

2 .._...___: , 5 ._._....._zw” , . ..-. --_52 0 5 ..__...-.zP

0I0 0 15 0.5 0.75 1 1.25 1 . 5 1.75 2

FROIJDE NUMBER, ‘.‘a

U.S. it is customary to use the lJ.S. Navy’s Ship WorkBreakdown Structure (SWBS). For SES, this systemconsists of:

SWBS 100: Hull structure including end sealsSWBS 200: Propulsion including lift systemSWBS 300: Electrical systemsSWBS 400: Command, Control and Communication

and Navigation Systems (C3N)SWBS 500: Auxiliary SystemsSWBS 600: Outfit and FurnishilngsSWBS 700: Armament.

[ 0 CONSTRUCTED 9 DESIGNI ClSES l MONOHULLj

The sum of these weight groups comprises thelightship weight.

Figure 78. Instal led Power/Full-Load Displacement/Speed Versus Froude Number

What is also clear from these data is that there is afairly wide scatter in the points plotted for SES,particularly at the higher speeds, indicating the rangeof success that the various designers have been ableto achieve for their particular set of requirements.

Subsystem Weights Structure (SWBS 100)

During the early stage of a design the weights of thevarious subsystems can be approximated usingtrends from prior experience. However, if a whole-ship design synthesis model is available for the earlydesign stage it is preferable that the weights becalculated from first principles for as many subsys-tems as possible. The weight of the structure of thehull, the seals, and fuel load are examples where thisis clearly possible and was used, for example, in themodel of Reference 25. In later stages of design,estimates can be more precise as a result of moredetailed analysis and from the known weights ofoff-the-shelf systems and equipment.

Trends exhibited by the comparison of the subsystemweights of existing craft are useful, however, as asanity check in early stage design. If used for design,they must be accompanied by fairly large margins toallow for uncertainties in design and construction.Weight margins can vary from subsystem to subsys-tem with the value depending upon how well theyhave been defined, or the margin can be applied as asingle value to the lightship weight. Weight marginsvarying from 8% to 20% are typically used.

R is essential to use a consistent definition of theweights included in each subsystem group. In the

These definitions are used for the weight trendsdiscussed below for which the known weights ofsubsystems for a range of existing SES are plotted,generally, as a function of full-load displacement.Parameters, other than full-load displacement, areoften more appropriate. These include hull volume forSWBS Group 100, installed power for SWBS Group200 and total electrical load for SWBS Group 300.

The weights of the structure for a number of SES areshown in Figure 79 as a function of hull cubic number.The cubic number used here is the product of overallcraft length and a cross-sectional area amidshipsformed by rectangles containing the two sidehulls andthe main hull (including superstructure). No attempthas been made to distinguish between the choices ofstructural concept or types of material used inconstruction of the various craft represented in Figure79. However, they are either constructed of welded orriveted marine-grade aluminum alloy or single-skinglass reinforced plastic (GRP). In comparison to thisdata, a weight savings of between 5 and 10% couldbe expected with the use of foam-core GRP. Figure80 is similar to Figure 79 but, this time, full-loaddisplacement is used as the aiocissa, instead of cubicnumber. A mean l ine through the data would suggestthat the average weight of the structure is ap-proximately 36% of the full-load displacement with lowand high extremes of 24% and 40%, respectively.

Lift and Propulsion (SWBS 200)

The weight of SWBS Group 200 for various SES isshown in Figure 81 versus full-load displacement.The SES represented have either diesels or gas

3 3

turbines, waterjets, or marine screws. With oneexception they are fitted with centrifugal fans. A meanline through the data suggests that SWBS Group 200is approximately 21% of the full-load displacement.

CUBIC NUMBER

a CONSTRUCTED a DESIGN

Figure 79. Weight of Structure Versus StructuralCubic Number

Figure 80.

FULL-LOAD DISPLACEMENT

q CONSTRUCTED ? DESIGN

Weight of Structure Versus Full-LoadDisplacement

FULL-LOAD DISPLACEMENT

DCONSI-RUCTED q DESIGN

Figure 81. Weight of Lift and Propulsion SystemVersus Full-Load Displacement

Electric System (SWBS 300)

The weight of SWBS Group 300 shown in Figure 82shows considerable scatter among the various SESrepresented, which include experimental craft,commercial ferries and paramilitary craft. Over thisspectrum of applications it would appear that theweight of SWBS Group 300 could vary from as littleas 0.6% to as high as 5.5% of the full-load displace-ment. Note that the weight of SWBS Group 300 (aswell as Groups 400 through 700) would generally beexpected to be more dependent upon operational rolethan would the weights of SWBS Groups 100 and200.

5 0

~!~ ~ ; ~ yiI

FULL-LOAD OISPLACEMENT

oCONSTRUCTE0 9 DESIGN

Figure 82. Weight of Electrical System VersusFull-Load Displacement

C3N (SWBS 400)

The weight of C3N systelms are shown in Figure 83.Values vary from, apprloximately, 0.5% to 4% offull-load displacement, with the higher percentageapplicable to military craft.

FULL-LOAD OISPLACEMENT

0 CONSTRUCTED 4 DESIGN

Figure 83. Weight of Command and Survei l lanceSystem Versus Ful l-Load Displacement

3 4

Auxiliary Systems (SWBS 500)

The weight of auxiliary systems are shown in Figure84. Although there is significant scatter, there is adistinct trend with a mean of approximately 8.5% offul l - load displacement.

g----y- j ----q---y

i~~~~

FULL-LOAO DISPLACEMENT

0 CONSTRUCTED 2 DESIGN

Figure 84. Weight of Auxiliary Systems VersusFull-Load Displacement

Outfit and Furnishings (SWBS 600)

The weight of this group is shown in Figure 85 andappears to be even more widely scattered than SWBSGroup 400. The average is approximately 5% offull-load displacement with commercial ferriesgenerally on the high side of the scatter.

cl” ai

FULL-LOAD DISPLACEMENT

oCONSTRUCTE0 a DESIGN

Figure 85. Weight of Outfit and FurnishingsVersus Full-Load Displacement

Armament (SWBS 700)

This weight group, applicable only to military craft,was found to be extremely mission dependent andgenerally in the range of 2 to 7% of full-loaddisplacement.

Disposable Load

The difference between the full-load displacement andthe sum of the weights of SWBS Groups 100 through700 and any margin is often referred to as thedisposable load and is the sum of fuel load andpayload. Typically, this weight can be from 15 to 30%of the ful l- load displacement depending upon the mixof requirements.

Seakeeping

Important aspects of SES seaklaeping include:

a.

b.

C.

d.

8.

f.

9.

Ride comfort as determined by the magnitudeand frequency of vertical, longitudinal andlateral accelerations at c:ritical locations on thecraft.

The amplitude and period of motions in pitch,heave and roll (and in solme cases yaw).

The frequency of propulsor broaching.

The frequency of shipping water on deck.

Course-keeping.

Structural loads including shock and vibration.

Speed reduction.

All of these will vary with sea state, (wave height,modal period, heading), craft speed, craft heading,craft geometry, lift system setting and masspropert ies.

The importance of these measures of seakeeping wil ldepend upon the intended role of the craft. High-speed passenger ferries operating in coastal watersare usually restricted by item.s a, c, e, f and g. Formilitary weapon platforms, all categories are usuallyimportant. Since the provisron for acceptable ridecomfort is often the most challenging, the followingfocuses on this aspect of SES design and operation.

Ride Comfort

Ride comfort is an ongoing concern for all high-performance marine craft.

Passengers and crew can be exposed to bodilyvibration which may cause motion sickness, fatigue,and reduced working eff icioncy. It is, therefore,

3 5

important that human tolerance to such vibrations beconsidered in the selection of design parameterswhich influence vehicle dynamic response.

Despite the fact that the relationship between man’scomfort, working efficiency and vibration environmentis very complex, a standard (or set of criteria) hasbeen established (Reference 33) by the InternationalOrganization for Standardization (ISO) as a guide forthe evaluation of human exposure to whole-bodyvibrat ion.

The International Standard defines numerical valuesfor limits and duration of exposure for vibrationstransmitted to the human body in the frequency range1 to 80 Hz. The standard states that it may beapplied, within the specified frequency range, toperiodic vibrations and to random or non-periodicvibrations with a distributed frequency spectrum. Thelimits are given for use according to three (3)generally recognizable criteria for preserving comfort,working efficiency, safety and health. The limits setaccording fo these criteria are named, respectively asthe “Reduced Comfort (RC) Boundary,” “Fatigue-Decreased Proficiency (FDP) Boundary” and the“Exposure Limit” (EL). For example, when theprimary concern is to maintain working efficiency ofthe crew in performing their various tasks the FDPBoundary would be used as the guiding limit, while inthe design of passenger accommodation the RCBoundary should be considered.

The IS0 standard provides guidelines to the limita-tions of vibrations that the operators or passengers, ina vehicle such as an SES, would experience in surge,sway and heave.

This IS0 standard, however, does not extend below afrequency of about 1.0 Hz. Unfortunately, this regionincludes the frequencies for which wave-inducedmotions can be dominant. It is also within this rangeof frequencies where man is most prone to motionsickness. The appearance of such symptomsdepends, however, on complicated individual factorsnot simply related to the intensity, frequency orduration of the motion. Although, so far, motionssickness has not been a particular problem with SESoperations in rough seas, it is clear that the range ofmotion frequencies encountered are not adequatelycovered by existing IS0 standards.

To remedy this situation it is customary to adopt amodification to the standard IS0 curves based on thework of O’Hanlon and McCauley (Reference 34).

Ride Control

Continuing efforts are bein,g made to improve the ridequality of SESs through better lift-fan characteristics(Reference 35) and the development of improvedride-control systems (RCSs), References 36, 37, 17and 19.

These ride-control systems seek to maintain aconstant cushion pressure thereby minimizing craftvertical accelerations ancl motions. This is accom-plished by venting cushion air when cushion pressurerises, and increasing l i f t f low when cushion pressurefalls. An RCS requires a control law, sensitiveinstrumentation and a responsive hydraulic system toadjust the vent vanes and/or fan inlet-guide vanes orother fan-flow-control devices.

The systems are most effective in dampening craftheave motion at high speed in low-to-moderate seastates, particularly when wave encounter frequency isclose to the heave natural frequency of the craft. Inhigh sea states, when the sidehulls support asubstantial portion of the vehicle weight, and contrib-ute more to inducing crafi motion, current systems arenot as effective, particularly when operating close topitch resonance.

Ride-control systems (R’CS) are available and havebeen used on many craft. The first RCS wasdeveloped by Aerojet General and used successfullyon the SES-1OOA in 1972. Subsequent craft withRCSs have included the Bell SES-1 OOB, 1974; XRl -D(1975) subsequently fitted with variable-flow fans; BH110; SES 200; and others including the CIRRUSfamily of 105P, 115P ancl 12OPs which, apart from theSES 1 OOA and 1008, used systems successfullydeveloped by Maritime Dynamics Inc (MDI) in theUnited States (Reference 37).

KKrV in conjunction with SSPA in Sweden have alsodeveloped a similar ride-control system that was usedsuccessfully on the JETRIDER (Reference 17).

Other efforts to improve SES ride comfort haveincluded the rudder-rol l stabi l ization systems used byHovermarine on their HM5 series of SES. Thissystem could half the roll of the craft in rough beamseas. The stern-seal pressure-control studies byClayton at the Universi ty Col lege, London,(References 59, 60 and 61) and the general seakeep-ing studies and tests by Knupffer et. al., (Reference19) are examples of recent efforts conducted tominimize SES pitch motions in heavy seas.

3 6

MDI has continued the development and demonstra-tion of more effective RCSs. An advanced digitalRCS involving “distributed” vent valves and amulti-input/multi-output controller has been installedon the SES 200 for evaluation in 1991.

Design for Seakeeping

It is extremely important that considerations ofseakeeping be included in the earliest stages ofdesign. Too often, designs have been developedwithout this consideration only to be faced withserious problems later that development in the towingtank or use of an RCS cannot necessarily solve.

It is important to start with a good knowledge of thearea in which the SES is expected to operate. Thisknowledge must include a description of the energy-frequency spectrum of the waves, and their frequencyof occurrence and direction relative to the intendedroute.

Foremost it is important to select a vehicle largeenough and of the appropriate length and length-to-beam ratio. The size and geometry of the craft maybe dictated by the size and geometry of the payloadbut can be dictated by seakeeping, particularly whenavoiding pitch, or roll, resonance in high sea states forthe operational area of interest.

Figure 68 (Reference 21) shown earlier, is anexample in which seakeeping requirements havedetermined the minimum acceptable size of an SES.

Figure 68 was produced with the use of a whole-shipdesign synthesis computer model (Reference 25)from which a plot has been produced showing relativecost versus platform dimensions. Plots like Figure 68can be used to determine the minimum cost solutionfor any set of requirements. Figure 68 presents abusy chart but shows how cost varies with changinglength and beam for craft all designed to meet justone set of speed, payload and range requirements.

Overlaid on Figure 68, as broken lines, are two sets ofcurves of varying RMS vertical acceleration. There isone set for CG acceleration and another set for bowacceleration, all for operation at 35 knots whileheading into a sea-state 3.

Craft which exceed the bow vertical acceleration limit(of 0.275 g rms) are below the lowest shaded area ofthe plot. None of the craft, however, exceed the CGvertical acceleration limit (of 0.15 g rms). A single

value, in each case, for an acceptable rms verticalacceleration at the bow and CG in head seas wasselected here for convenience in early-stage design.These limiting values of rms accelerations can changedepending upon operator’s requirements.

Also shown are the freeboard limits for acceptablede& wetness which restrict the choice of platforms tothose which are to the left of the shaded areas on theright-hand side of Figure 68. The freeboard limitsused are based on the curves derived from Reference21 developed by Savitsky and Koelbel for smallmonohulls and show the ratio of freeboard (at theforward perpendicular) to the length on the waterlineplotted as a function of waterliine length. The curvesuitable for open ocean was adopted for this exampleand was applied to govern the minimum acceptablefreeboard for SES operating hullborne.

The least-cost solution which satisfies these specificrequirements is a craft having cushion dimensions of98 ft by 39 ft, as shown on Figure 68.

Figure 86 shows all the least-cost solutions for therequirements stated on the figure. The solution takenfrom Figure 68 is shown at the bottom. Similar figurescan be developed to describe the relationshipbetween cost and any other set of requirements.

1 TRANSIT SPEED - 35 KTS IN SEA-STATE 3 WEAO SEASION-STATION ENOURANCE - 3 DAY?;

1 SOLUTION FROM FIGURE 6B-

Figure 86. Cost Versus Range and Payload forCraft Designed for Acceptable Sea-keeping in Sea-State 3

The results shown in Figures 68 and 86 were foroperation in sea-state 3. Thus, all craft weredesigned with power to achieve 35 knots whileheading into a sea-state 3 with acceptable ridequality.

However, for operators interested in a highersea-state capability the effect on seakeeping of

3 7

operating these same craft in sea-state 4, at a lowerspeed of 25 knots, is shown in Figure 87. This is aspeed that all the craft could achieve without increasein total power.

ganization’s (IMO ‘s) regulations for dynamicallysupported craft, the US. Coast Guard’s (USCG’s)requirements defined by the appropriate code ofFederal Regulations and/o’r U.S. Navy’s requi rementsfor Advanced Naval Vehicles.

Stability On-Cushion

k.8

Figure 87. SES Design Selected on the Basis ofSeakeeping

In this case, as shown in Figure 87, much larger craftare required to meet the requirements. Here thevertical acceleration at the bow is the controlling factorand we cannot select craft dimensions from within theshaded area of this figure.

The least-cost craft for sea-state 4 that meets thestated requirements listed at the top of this figure is,therefore, a craft with cushion dimensions of 164 ft by59 ft as compared to 98 ft by 39 ft for sea-state 3.The corresponding cast had, in fact. doubled as aresuft of designing for sea-state 4 as compared tosea-state 3.

Stability

Stability Hullborne

When an SES is hullborne its stability in the intact anddamaged condit ion is dominated by hydrostat ics andcan be determined and assessed using proceduresand criteria which are similar to those used forconventional vessels. Predictions are most easilymade using a modified version of the U.S. Navy’s“Ship Hull Characteristics Program (SHCP)” or theprogram called “Stability of Any Arbitrary Form(STAFF)“. The assessment of acceptable stability willdepend on the size, gross registered tonnage andintended role of the vessel and can be governed bythe classification societies such as the AmericanBureau of Shipping (ABS) and Det norske Veritas(DnV) and also by the International Maritime Or-

When an SES is underway at high speed thehydrodynamic forces acting on the sidehulls, thebow-and-stern seals, the appendages and the forcesdue to the waterjet inlet: and nozzle deflection, orrudder deflection, dominate the hydrostatic andaerodynamic forces. Estimates of these forces arefairly accurate if the hull parameters and verticalcenter-ofgravity/overall-beam ratio of the new SESdesign are within the range of known proven designs.Variation in hull parameters such as length/beamratio, sidehull width/beam ratio, cushion depth/beamratio, sidehull volume, etc.; seal geometry, fins,rudders, and fences; and propulsion parameters suchas fully-submerged propellers, semi-submergedpropellers and waterjets make each design unique.Towing tank stability tests of the final design arerecommended to accurately predict SES stabilityon-cushion (References 38 through 41).

Pitch stability can be readily obtained by propershaping of the sidehulls and bow seal as discussedearlier.

Roll stability at hover and at speed, at zero sideslip, isprovided by the sidehull geometry and the ratio ofvertical center-of-gravity to overall beam. Flexiblebow and stem seals do not contribute much to rollstability. However, the cushion pressure acting aboutthe roll center produces a destabilizing roll moment.

When an SES is in a turn, the centrifugal force acts atthe VCG in a direction away from the center of theturn. In a steady turn, this force must be counteractedby sidehull hydrodynamic forces. These forces are afunction of sidehull immersion determined by craftheave, pitch and roll and by local water sideslip angle.Proper shaping of the deadrise surface up to thechine will ensure that the planing force acts above theVCG and produces a restoring roll moment.However, hydrodynamic forces acting above the chineon the leading sidehull, and on the cushion side of thetrailing sidehull, act below the VCG and produce adestabil izing rol l moment.

Directional stability (yaw) is largely a function of craftattitude relative to the water surface and appendages

3 8

(fins, rudders, fences). The craft is usually designedto have a small, positive controls-fixed directionalstability for the range of normal operating pitchattitudes. Bowdown trims from these attitudes canlead to directional instability requiring constantsteering. However, at bow-up trims the craft can havetoo much directional stability and therefore poormaneuverability. Also, the craft is significantly moredirectionally stable when rolled out of the turn thenwhen rolled in. SES designs with fins or rudders canalso produce large changes in sideforce, roll and yawmoments at sideslip angles due to ventilation/cavitation effects that alter the lift coefficient. Thesecyclic variation in appendage forces can contribute toa “limit cycle oscillation” in pitch, roll and yaw(References 39 and 40). Therefore, by operating thecraft at the proper pitch, attitude, appendages may notbe required for a craft with waterjet propulsion.

Open sea radio-controlled SES model tests in theon-cushion mode have demonstrated (Reference 40)that, for the model tested, capsize in wind and wavesoccurred at a lower VCG than when maneuvering atmaximum speed in calm water. In fact, capsizes inthe latter condition only happened at very elevatedVCGs. However, all models exhibited highly undesir-able large amplitude roll/yaw oscillations in calm-water turns if the VCG was sufficiently high, such asto cause extreme difficulty in directional control. Theranges of VCG location for which capsizes occurredwere well outside the values used in contemporarySES.

Thus, the Reference 40 tests identified two quitedistinct areas for closer examination, synchronousrolling motion in beam seas and roil/yaw oscillations inhigh speed turns.

f t has been found that an SES is most vulnerable tocapsize if the rolling motion is excited near itsresonant frequency, and if the roll energy imparted tothe craft by the oncoming wave cannot be dissipatedas the craft travels from trough to the next crest.Reference 40 discusses the complete critical cycle ofan SES rolling in regular beam seas of resonantperiod, at a VCG just high enough to cause capsize.

The Reference-40 radio-controlled tests ascertainedthat forward speed did not affect beam-sea-capsizebehavior significantly. Therefore, towing-tank testswere conducted with these models at zero speed (butfree to sway) beam-on to artificially generated windand steepness-limited waves to obtain the criticalVCG. It was found that as the VCG of the model israised, capsize first occurs in waves of approximately

resonant encounter frequency., when wave heightexceeds about one third craft beam.

Also, certain models were tested with roll radius ofgyration (K) varied substantially and with thetransverse CG offset down-sea by 2% of beam. Thisoffset can be due to improper loading of fuel, stores,cars, passengers and luggage. Full-scale large craftbuilt to date have a roll gyradius/beam ratio (K/B) ofabout 0.3 while a majority of tlhe models had a K/Bratio greater than 0.35. Limited model-test dataindicate that if KfB is less than 0.35, then roll inertiahas little effect on critical VCG.

Heave Stability

Heave stability can be examilned by analyzing thecushion dynamics of the craft while hovering fullyon-cushion in a stationary condition. It is not possibleto predict full-scale cushion !cehavior based uponmodel test results. This is due to the problemspresented in trying to scale cushion dynamics(References 42, 43 and 58). Because the compres-sibility of the cushion is governed by the gas laws,which depend upon absolute pressure rather thangauge pressure, it has been shown (Reference 42)that heave motion of an SES is more lightly dampedthan its corresponding model. This explains thetendency for SES to “cobblestone” at full-scale inrelatively smooth seas where the predominant waveencounter frequency can excite the cushion naturalfrequency in heave. In rough seas the predominantencounter frequency is usually ,too low to excite heaveat its resonant frequency unless the SES is extremelylarge (Reference 43).

Structural Design Loads

Considerable emphasis has been placed on thedevelopment of rational design loads during thedesign and testing of the U.S. Navy’s SES-lOOA,SES-1008 and XR-ID and during the very extensivedesign work carried out on the :3KSES (References 44and 45). One important development in the structuralloads work for the 3KSES was the use of scalemodels to measure bending moments experimental ly.Both rigid and structural-dynamic grillage modelswere developed and tested (Reference 45). Aphotograph of the grillage model is shown in Figure88. It was by using these models that it was discov-ered that the loads experienced while operating SESat low speeds in the hullborne condition were usuallyhigher than the loads measured at high speed oncushion.

39

L

Figure 88. Structural Dynamic Model of 3KSES

Structural loads for a new SES design are developedfrom a number of sources:

. The growing data base of loads used for earlier,successfu l designs.

. Loads measured experimentally during modeltests and during full-scale trials. These loadsare extrapolated by probabilistic methods todefine maximum life-time loads.

. Loads specified by classification societies forhigh-speed craft such as those formulated byDet Norske Veritas (Reference 23) the BritishCivil Aeronauti,cs Authority (Reference 46) andthe American Bureau of Shipping (Reference47, for example).

. Procedures developed by U.S. Navy activitiessuch as NAVSEA Norfolk.

All of these sources provide information that can beused directly.

The loads of concern are the maximum expectedlifetime values of, and fatigue-stress cycles related tothe following quantities:

. Hog and sag longitudinal bending moments

. Transverse bending moments

. Vertical shear force

. Torsion about the longitudinal axis

. Hydrodynamic and hydrostat ic pressures on al lexternal surfaces

. inertia loads on all components, subsystemsand cargo due to wave-induced accelerations

. Machinery-induced vibration.

ABS Structural Design Loads

Design loads specified by the American Bureau ofShipping (ABS) for SES are generally obtained fromthe ABS Proposed Guide for Building and ClassingHigh-Speed Craft (Commercial, Patrol and UtilityCraft) which is currently in publication (Reference 47).Design parameters necessary for obtaining designloads are to be submitted by the designer and includethe following:

Vessel Dimensions (L, LwL, Beam, Draft,

Molded Depth)

Vessel Displacement

Maximum Calm-VVater Design Speed

Vessel Deadrise at LCG (in degrees)

Running Trim (in degrees)

Vertical Acceleration at Both Wet-Deck and atSidehulls

Expected Operating Environment.

Wherever possible, submitted data for running trimand vertical accelerations are to be obtained frommodel tests.

The guidance requirements are augmented for bottomand cross structure loading by using, for example,bottom and cross structure design pressures obtainedfrom Reference 48. These pressures are used inassociation with design allowable stresses for thematerials as indicated in the ABS Proposed Guide.Other methods of obtaining design pressures may beaccepted on a case by case basis.

Commercial Regulation and Classification

Fulfilling all regulatory, statutory and classificationrequirements for the safe design and operation of fastpassenger craft is a challenge and must be consid-ered early in the design process. The various statutesand regulations to be satisfied are numerous, subjectto interpretation, often not conducive to the use of

4 0

l ight-weight systems and dependent upon the countryin which (or to and from which) the craft will operate.In the United States the Coast Guard has jurisdictionover the certification of commercial craft via thegeneral rules established by the applicable Code ofFederal Regulations (CFR Title 46, for example). Thiscode applies rules which vary depending upon thesize (i.e., gross tonnage) and length of the craft andthe number of passengers to be carried. Often designstandards such as those defined by the AmericanBureau of Shipping (ABS) are referenced directly bythe CFR. Until recently, neither the CFR or the ABSrules recognized the unique features of and construc-tion methods for light-weight craft, but in 1989 ABSpublished, for review, their first set of applicable rules(Reference 47) which has now been issued in its finalform.

Classification societies in other countries have alsobeen very active in updating their rules for theclassi f icat ion of high-speed commercial craf t spurredon by the rapid worldwide expansion of the fast-craftmarket . Most notable are the revised rules(distributed in draft form last year) to be published byDet norske Veritas(DnV) in Norway (Reference 23)and by Lloyd’s Register (LR) in the UK, although UKcraft are governed (at least until recently) by the rulesset, in the 1960’s (and periodically updated since), bythe British Hovercraft Safety Requirements publishedby the British Civil Aviation Authority (CAA, Reference46). Both the ABS and DnV rules follow the basicphilosophy adopted initially by the Briiish CAA andsubsequently by the International Maritime Organiza-tion’s (IMO’s) “Code of Safety for DynamicallySupported Craft” (Resolution A 373 (X), Reference22). This philosophy recognizes that high-speedferries will be restricted to operate in well defined(coastal) areas where rescue services would bereadily available. This restricts craft to operate withinset limits such as speed and sea state.

Unlike the SOLAS 74 approach which calls for fullyself-contained escape systems and onboard firestations, the IMO Resolution A 373 (X) defines a setof more flexible requirements (and equivalences) . . .a move to ensure safety without stunting the fast-ferryindustry’s growth and ability to compete (Reference49).

This recent flourish of activity by the classificationsocieties is testimony to the recent and projectedrapid expansion of the fast-ferry market. Readersinterested in how these various rules are applied canrefer to the respective codes or the summaries givenin References 50,51 and 52.

3.11 Hull Structure

SES hulls are being built from a variety of materialsincluding welded marine-grade aluminum alloy, singleskin or foam-cored Fiber-Reinforced Plastic (FRP),and high-strength steel. Each has its advantages anddisadvantages and each yard tends to select thatwhich they know best. Major considerations includematerial and construction cost, weight, strength,maintainability and fire resistance.

Aluminum Alloy

This has usually been the preferred choice in the U.S.lt is readily available, its properties are well known, itcan be easily formed and joilned without expensivetooling, with careful design it can be reliably inspectedand, more importantly, design standards and criteriaare well established.

Welding is usually the preferred choice of construc-tion. AJthough earlier regarded as being more of anart than a science, modern automated weldingequipment has reached a very high level of develop-ment and is capable of economically welding muchlighter gauge material, with lower thermal distortionthan has hitherto been possible.

Because of the relatively low fatigue strength ofwelded aluminum, high-cycle fatigue of local structureis usually the greatest concern, avoidable preferablyin the design stage by the avoidance of, or appropri-ate location of, stress concentrations, and by ensuringthat the natural frequencies of structural componentsare not excited by predictable machinery vibrations.

The all-welded aluminum-alloy 250-ton AGNES 200(Figure 2) is shown under construction in Figure 89.Construction began in May 1988 at CMN in Cher-bourg and the ship was launched 26 months later, inJuly 1990. Construction proceeded initially bybuilding four separate modules: one for the super-structure and one each for the forward, midships andaft sections of the ship.

These modules were eventually joined prior to theinstallation of machinery and other ship systems.

Figure 90 shows a view from behind the ship at thesame stage of construction (May 1990) as in Figure89. This view shows the unique shape of thesidehulls aft and the KaMeWa 71862 waterjet pumpsin place.

4 1

Figure 89. AGNES-200 Under Construction

Figure 90. AGNES-200 From Astern (May 1990)

Figures 91 and 92 shaw the completed superstructureincluding the helicopter hangar and flight deck.

Fiber-Reinforced Plastic (FRP)

The first SES ferry (the Denny D-2) was constructedof single-skin glass-fiber-reinforced plastic (GRP) aswere the extensive production series of Hovermarine(HM) craft in the UK. Fiber-Reinforced Plastic (FRP)construction offers lightweight, durability, repairability,corrosion resistance, ease of construction (particularlyof complex shapes) and reasonably low cost. The

’HM craft used woven anld unidirectional glass rovingswith polyester resin. Figures 93 through 96 show thevarious stages of construction of the HM 527.According to Reference 37, the structure of this craftcould be built in less than four months while the costof the molds and tooling amounted to about 15% ofthe total cost of the prototype. The molds wereexpected to be sufficiently durable to produce over100 craft.

Figure 91. AGNES 200 Helicopter Fl ightdeck.

Figure 92. AGNES 200 Helicopter Hangar

Cored GRP was introduced by the U.S. Navy in 1955(Reference 53). Over ‘the seven years to 1962, 32Navy GRP boats from 33 to 50 ft in length wereconstructed by the “core mold” method, a techniquesimilar to that employed today in Norway andSweden. Since the early 1960’s the Royal Nether-lands Navy has had many PVC-cored GRP craftconstructed in lengths up to 77 ft. The 77-ft PilotBoats, in particular, have seen nearly 30 years ofextremely rough service. After many years operatingoff the Hook of Holland .they were sold to India wherethey are still in operation.

4 2

PVC. With the trend toward la,rger SES the introduc-tion of higher-modulus fibers (avamids or carbon) maybe attractive to improve laminate stiffness.

Figure 95. HM-527, FRP Hull Upside Down ViewedFrom Ahead (UK)

Figure 93. HM-527 FRP Interior Structure (UK)

Figure 96. HM-527, FRP Superstructure (UK)

Figure 94. HM-527, FRP Hull Upside DownViewed From Astern (UK)

Currently, the very successful series of craft designedby Cirrus and constructed by Brodrene Aa in Norway,the SES by Karlskronavarvet (KKrV) in Sweden(Figure 97, Reference 17) and the Blohm und VossCorsair from Germany are examples of successfulefforts to significantly reduce structural cost andweight using foam-cored structures.

Traditionally, glass-reinforced polyester is used for theskin, to sandwich a laid-up core of expanded cellular

Figure 97. Norway, KKrV, Jetrider (The CompleteHull and Superstructure Built in CoredGRP-Sandwich)

4 3

Cored GRP structure also offers advantages inthermal and acoustic insulation. The NorwegianMCMs and the Swedish stealth Testrigg haveemphasized the noise and vibration dampingadvantages along with IR reduction. In the case ofthe passenger ferries it is clear that cost savingsplayed as much a role in selection of cored GRP asdid weight savings.

Steel

China was the first to use steel for SES structures.The Italian shipyard, Societa Escercizio Cantieri SpA(SEC), now has fhe main hull of the world’s largestSES (at 2000 ton) under construction in steel(Figure 1). MTG’s SE!:-700 (Figure 45) is also to beconstructed of steel. High-tensile steel results in aheavier, more rugged structure, but is less expensivethan aluminum alloy or FRP. It is also more fireresistant and has a higher fatigue strength thanwelded aluminum al loy.

As SES become larger, steel becomes more attractivesince the need for minimum gauges for welding nolonger presents a serious weight penalty. Also, thetechnology required for the design and construction/producibility of large steel structures is less of atechnical risk.

Marine Promlsors

configuration studies which led to their presentdesigns.

KaMeWa is not alone in discovering anomalouswaterjet inlet effects. During the waterjet-inlet modeltest program for the 2W3KSES much attentionfocused on inlet drag. It was found that, over acertain range of flow parametric% the inlet dragcoefficient appeared to be negative. Originally, thiseffect was thought to be due to either an instrumenta-tion error or an accounting error. It is now believedthat it may have been due, in part at least, to the hulleffects postulated and investigated by KaMeWa.

Another aspect of the problem concerns the compari-son with marine propeller propulsion on similar hulls.A strict comparison of propulsar performance in thetwo cases is complicatecl due to the influence of theappendages (shaft, shaf? brackets, rudders) in thecase of propeller propulsion, which are no longerpresent when waterjets are installed. It may well bethat the propulsive coefficients claimed for propellersare too high due to the difficulties of properly account-ing for all the appendage and wake effects. Theresult would be that a waterjet giving the same shipperformance would be credited with a comparablepropulsive coefficient. To verify such propulsivecoefficients analytically necessitates invocation ofnegative inlet drag and/or hull lift effects which areotherwise difficult to quarltify.

The problem of properly defining marine propulsorperformance, particularly of waterjets, is relativelycomplicated. To reproduce waterjet propulsorperformance maps generated by a manufacturerusually requires the selection of high values forcomponent efficiencies such as inlet recovery, pumpefficiency and nozzle efficiency, etc., unless accountis taken of other factors such as hull influences.These inf luences include the nature and thickness ofthe boundary layer on the hull ahead of the inlet,changes to the hull pressure distribution due to thepresence of the flowing inlet (Reference 54), changesto the hull flow field far ahead of the inlet, and factorsassociated with outflow from the air cushion andfeatures of the sidehull shaping in way of the inlet.

KaMeWa, for example, has shown, by painstakinginlet model testing over many years that relativelysmall shaping changes to the inlet, particularly theinlet lip configuration, can exert a profound influenceon the inlet performance. KaMeWa provides the inletduct drawings to the shipyard for each application.They have not revealed the details of their inlet

Air Ingestion by Waterjots

An important aspect of waterjet propulsion for SESconcerns the phenomenon of air ingestion by thewaterjet inlets.

Inevitably, the water approaching a waterjet inletcontains air bubbles. The mixture of water and airbubbles may arise from air entrainment at theforefoot, which is swept back to the inlets in the wake(boundary layer). Normally, the pump is very tolerantof this type of air/water mixture and there is minimaleffect on thrust performance. However, entrainmentof air exiting from the ClJShiOn under the sidehulls ofan SES can affect pump performance. When thisoccurs, the usual symptoms are surging of the enginespeed due to sudden loss of resisting torque when airis gulped by the inlet. In severe cases, this over-speed can cause the engine governor to shut downthe engine. Obviously, ‘the effect is likely to be moresevere in waves than in Calm seas.

4 4

Steps which can be taken to minimize inlet broaching(gulping of air), and other forms of air ingestioninclude careful design of the sidehull ahead of theinlet (Figure 98), choice of inlet (sidehull) submer-gence and sometimes the provision of inboard fencesto exclude cushion air, and outboard fences tominimize air ingestion directly from the atmosphere.

Figure 98. SES-200 New Waterjet Instal lat ion

Cavitation Limits of Waterjets

Waterjet propulsors designed for high speed cannotnormally operate at full power at low ship speed dueto cavitation in the impeller. A measure of the limit ofcavitation-free operation of a pump is the suctionspecific speed:

Ns s = NQ’?NPSHY4

Nss = suct ion spec i f i c speed (a quasi-

dimensionless number)

N = pump speed, rpm

Q = pump flow rate, gpm (by convention)

NPSH = net positive suction head, ft.

With the above units, a mixed-flow pump without aninducer, such as the KaMeWa pump, would not beexpected to operate much above a suction specificspeed of 10,000. Inducer pumps such as the2KDKSES pumps can operate at full power withsuction specific speeds up to 30,000.

pump map (thrust versus ship speed for variouspower levels). These limit lines which divide the mapinto zones I. II and Ill. are similar to, but not coincidentwith, lines of constant suction specific speed, and arebased on experience. Operation in Zone I is unlimitedwith regard to ship speed anld pump power (rpm).Operation in Zone II is for rough-water operation.Sustained operation is permitted and will notnoticeably affect pump performance, or life, but willnot be cavitation-free. Operation in Zone III is foremergency use only and will be marked by reducedtorque, severe cavitation, cavitation damage reducingpump life, vibration.

Part of the pump selection prclcess is to superimposethe ship-resistance curves for various sea states onthe pump map to see under what conditions operationin Zones II and III may occur. A speed-sea stateenvelope can be generated for each ship displace-ment of interest, limiting operation to Zone I, and toZone I and II, for instance. Gf particular interest, ishump transition in rough seas. If the hump ispronounced (depending on the length-to-beam ratio ofthe ship) hump transit ion with adequate thrust marginmay necessitate intrusion into Zone II. Since thecondition is transitory this is of no consequence. Useof Zone Ill for this purpose might be questionable,however.

Pump Performance Optimization

Some variation of the pump thrust curves is possiblebefore or after pump installation, by choice of nozzlediameter within the normal range of nozzle ratioprovided by the pump manufacturer. A larger nozzlewill provide higher low-speed thrust with a steeperfall-off with speed and possibly a lower ship maximumcalm-water speed. The final choice of nozzle size is arefinement in the detailed-design phase.

Marine Propellers

Marine propellers have been used on many SESincluding the UK HM-Series of craft, the U.S. CoastGuard WSES-Patrol Craft, the SES200 and theworld’s fastest ship, the SESl OOB. Propellers may beof conventional high-speed subcavitat ing design, e.g.Gawn Burrill types, or of partially submerged, fullvent i lated supercavi tat ing design as on theSESlOO(B) (Figure 99) and Corsair (Figure 100). Adetailed account of propeller theory and matching toSES requirements can be found in Reference 32.

KaMeWa, for example, provides guidance on theoperation of its pumps in the form of limit lines on the

4 5

Figure 99. SES-1006 Surface Piercing Propeller

Prime Mover Characteristics

The characteristics of prime movers must be consid-ered along with the performance of the propulsor. It isnecessary to ensure that the engine has adequatetorque for the propulsor and engine speeds con-sidered. Matching of a diesel engine to a waterjetpump and choice of gear ratio for the transmission, ismuch simpler than for a propeller case. This isbecause the speed of the pump is almost constant fora given power over a wide range of ship speed.Never-the-less, engine-pump matching is just asimportant an aspect of the design of the propulsionsystem as is engine-propeller matching.

Propulslon System Installation

Other aspects of the propulsion system design whichmust be considered include propulsor installation,gearbox and engine founldations in the sidehulls andthe necessity to ensure that there is adequate spacearound the machinery for operation and maintenance.To minimize noise and %vibration the diesel enginesshould be shod-mounted. This will require theprovision of suitable flexible couplings, and shafts.

Figure 100. Blohm und Voss Corsair - SurfacePiercing Props

For moderate speeds, waterjets have been preferredto propellers for recent SES because they allowoperation in shallower water, have minimum ap-pendage drag and are more easily matched to dieselengines. However, for very high speeds partiallysubmerged propellers continue to be attractive.Generally a propeller installation will be lighter and theeffective disc area allows for a high potential propul-sive coefficient. Careful detail design of the propellerinstallation may allow a high overall propulsiveefficiency to be released.

Propulsion-System Performance

The prediction of the performance of the propulsionsystem is handled best by a mathematical model ofthe entire propulsion system. Such a model isparticularly desirable if a.n integrated lift and propul-sion system is to be used.

The propulsion system model combines the charac-teristics of the propufsor, transmission system, primemover and any auxiliaries driven by the propulsionsystem engines.

THE FUTURE: SES POTENTIAL

In considering the future of SES it is useful todistinguish between those applications which areessentially profit driven (transport of people, vehiclesand freight) and those which are essentially military,or non-transport, with missions where differentmeasures of cost effectiveness are applied. For thepurposes of this discussion the categories oftransport, military and “other” have been chosen.

The beginning of the paper narrated the history ofSES, its current applicai.ions and on-going develop-ment initiatives. With the exception of the SovietDergach, the Norwegian MCMs and the three U.S.

4 6

Coast Guard Sea Bird class SES, the militaryapplications are still on paper.

TRANSPORT

SES have proven to be commercially competitive inthe business of moving people from place to place(ferry service). Several hundred Hovermarine andSoviet SES operate at speeds below 35 knots,generally in sheltered waters where higher sea statesare not routinely encountered. The new generation ofSES people ferries, typified by the Cirrus 12OP,operate at speeds of 45 knot,s with hull configurationsand/or ride-control systems that allow operation onmore open-water routes.

Competition

SES are compet ing wi th planing craf t , fastcatamarans, wave piercers, hydrofoils (with fully-submerged or surface-piercing foil systems) andACVs as well as the slower conventional ferries.More recently the FBM Fast Displacement Catamaran(SWATH), with a 30-knot-plus capability, has enteredservice from the island of Madeira. There appears tobe considerable semantic confusion, in the minds ofpotential operators and builders, regarding distinctionsbetween the various catamarans, SWATH and SESdesigns.

The essential parameters of a successful operationare cost, comfort and speed. “Convenience” mayalso be considered as a factor in the sense thatamphibious ACVs may more effectively access shoreconnections and the increased draft of hydrofoils andSWATH may restrict operation in shallow waters.Generally, increased speed and/or comfort willincrease the cost per passenger mile. In mostapplications, comfort tends to be more important thanspeed. The majority of current ferry routes are twohours or less in duration and are associated withtraffic and queuing delays on either end whichdiminish the importance of small time savings. Givena choice, few passengers will return, however, after about of seasickness or the discomfort of a noisycramped passage with an inability to move about thecabin. There are a number of quantitative measures(rms acceleration, roll period, etc.) which are appliedto define acceptable motions but true measures ofpassenger satisfaction are elusive and, in the finalanalysis, only ridership and profit balance willdetermine the success of an operation.

The economic success of the new generation of45-knot ferries is best evidenced by the number of

Cirrus 12OPs delivered by Brodrene Aa. T h eeleventh, the Nissho, for Jaoan’s Yasuda OceanCruise Line, has just completed builder’s trials.Brodrene Aa is currently building the larger UT904luxury SES in partnership with the Ulstein Group.Designs for similar craft have been developed byRoyal Schelde, Hovermarin,e International andFincantieri. The 12OPs are operating on many routesworldwide, predominant ly in Norway & theMediterranean.

Car Ferries

The success of the people-carrying SES has led,logically, to the current wave of SES car-ferryinitiatives described earlier. Potential routes aroundthe world include the English Channel, the Mediter-ranean, the North Sea, Scandinavia and NewZealand. Competition alreacly includes the opera-t ional 300-ton SRN-4 ACVs and the 74-meterwave-piercer, Hoverspeed Great Britain (Sea Cat).SWATH car-ferry designs with speeds over 30 knotshave been developed.

At this writing it appears that ,the Italian SEC-774 willbe the first operational SES car ferry (1992) - with theothers to follow.

Studies, including model tests, of a perishable-freight-carrying SES, of over 1000 tons, have beencompleted in Norway. This project is believed to bedormant at this time.

A consortium of seven Japanese shipyards isdeveloping the design of a 50-knot “Techno-Superl iner,” with an SES version as a principalcandidate.

MILITAAY

Coastal patrol (Coast Guard) missions are consideredhere to be military.

A significant military potential for SES has long beenenvisioned, as witnessed by U.S. expenditures of over$400 million on the BKSES program which was closedout in 1979. The U.S. Navy’s SES 200 has conductedat-sea trials with the Sea Vulcan and Hellfire weaponsystems. The SES-IOOB successfully launched asurface-to-air missile. The NATO SWG/G studies,addressing ASW, MCM and Patrol missions, arediscussed in Reference 21. Many U.S. Navy designstudies have been conducted under the NAVSEACONFORM and other programs addressing missionsranging from MCM and Escorts to Air-Capable

4 7

Cruisers and Sealift. The French AGNES 200,currently undergoing Navy trials, is intended to provethe concept of an air-capable ASW Corvette. TheGerman SES 700, although by mission a testplatform, would assess the suitability of SES for aCorvette or Frigate. The Spanish BES-50 programprojects a 350-ton patrol craft. The Blohm und VossCorsair is being fitted with a gun module for militarydemonstrations and the company has developed aseries of 43-meter military derivatives of this craft.Military derivatives of at least two of the SES carferries have also been proposed. The NorwegianNortest, 220-ton, Fast-Attack Craft initiative appearsto be close to implementation.

Hardware

Today there are four operational “military” SES; theSoviet Navy’s 650-ton Dergach, designated “guided-missile patrol combatant, air-cushioned,” and thethree U.S. Coast Guard Sea Bird class SES (140tons). Construction is underway on the NorwegianNavy’s nine-ship SES MCM class (350 tons). TheFrench AGNES 200 and the U.S. re-engined SES 200(both about 250 tons) are currently undergoing furthertest and evaluation focused on military missions.

Advantages of SES

Speed, which could exceed 60 knots but morepractically would be in the 40 to 55 knot range, is themost obvious military advantage of the SES. Withcareful design and installation of state-of-the-artride-control systems, SES offers significant seakeep-ing improvements over equivalent monohulls. Thereare other advantages, depending on the mission. Forthe MCM, shock attenuation is most important. In thecase of the U.S. Coast Guard SES, which haveoperational speeds only a little over 30 knots, platformstability during long hours of loiter on drug-interdictionpatrols have made these craft the most popularcutters in the fleet from a habitability standpoint(Reference 13). The twin-hull configuration andshallow draft introduce survivability/vulnerabilitybenefits. SES deck area is particularly generous, asis enclosed volume, since SES designs are generallyvolume and not weight-driven. Excess volume isdesirable where modular concepts are considered.

M C M

The SES concept was selected for the NorwegianMCM program as the result of a comprehensiveanalysis of SES, conventional and catamaran

alternatives. A key parameter in their analysis washull material. The MCM,V is built of cored GRP, asare all the Cirrus designs and three Karlskronavarvet(KKrV) designed SES. Norwegian analysis and shocktests of the Harpoon SES, and of a full-scale midshipsection of the Norwegian MCMV, have shown verysignificant shock attenuation for the SES on cushion.Shock tests conducted by Germany on the SES 200showed similar results. The current NATO SWG/6studies are considering SES in competition withACVs, SWATH, catamarans and conventionalmonohulls for the MCM mission. Several of theNATO nations are most attentive to the NorwegianSES MCMV development. U.S. interest in SES as anMCM platform was derailed by the demise of the MSHprogram in the mid eighties. The U.S. is, however,developing the SES MCMV design as part of thecurrent NATO SWGI6 stLidies.

ASW

The U.S. 3KSES program produced a contract designfor a frigate with ASW capability and a projectedmaximum speed of over 80 knots. The NATO ASWstudies produced conceptual designs of four air-capable SES ASW Corvettes (by the U.S., UK,France and Spain) which were designed to usespr int-search tact ics. These designs had full-loaddisplacements between 1200 and 2000 tons. TheFrench AGNES 200 is iintended as proof of conceptfor a 1250-ton SES Corvette (EOLES). The GermanSES 700 design would have applicability to largerASW escorts. In addition, several SES ASW variantdesigns were developed under the NAVSEA CON-FORM program. The 650-ton Soviet Dergach isapparently outfitted principally for air and surfacedefense.

Clearly, SES offer speed and survivability advantagesfor the ASW mission. The principal obstacle todeveloping an ASW SES at this time is simply size(displacement). To achieve acceptable ASWcapability a major increment in displacement over theexisting SES (260-ton in the U.S. and France,650-tons in the USSR) is required. The NATOSWG/G studies by the U.S. indicated that, forminimum acceptable ASW capability, an SES of atleast 2000 tons (constructed of steel) would berequired. The French E.OLES, to be constructed ofaluminum alloy, is close to 1250 tons.

A realistic expectation lor an ASW SES would beeither the French EOLES or a military derivative ofone of the Italian car ferries. The Italian SEC-774

4 8

now under construction in steel, for example, has alength of 302 ft, and a full-load displacement of over2000 tons. This ship is scheduled to be launched in1992.

Patrol

Following a period of non-SES-related technicaldifficulties, the U.S. Coast Guard SES have emergedas three of the most effedive cutters in the fleet(Reference 13). At this time, however, all near-termcutter replacements are expected to be conventionaldesigns. The AGNES 200 and the Blohm und VossCorsair are both being marketed in military variants.The Spanish BES-50 program is directed to a 350-tonpatrol craft with a l&meter manned model currently inevaluation. The Nortest initiative is particularlynoteworthy. This Fast-Attack Craft promises speedsof 60 knots with an impressive armament suit. Thecurrent NATO SWGI6 studies include SES designs forHarbor/Coastal Patrol (Figure 44) Enforcement ofLaws and Treaties (ELT), Fast Surface-Combatantand MCM missions.

As the U.S. reevaluates the Navy’s mission in thechanging world arenas it is likely that the threat of athird-world conflict in areas like the Caribbean and thePersian Gulf will dictate new requirements for moreexpendable resources.

The risks associated with development of an effectiveSES patrol/attack capability, particularly as feedbackon the car ferries materializes, should be mostacceptable.

Sealift

The seaiift issue has been very much in the news withDesert Shield and Desert Storm. The U. S. Navy’sfast sealift ships have shuttled to and from the Gulf at30-plus knots. High-speed is surely a desirablefeature. Several studies have been conducted of SESsealift ships of over 20,000 tons, or more, with speedsexceeding 40 knots in calm water. Definition of theseships is still very soft and the associated technicalrisks are considerable. The step from 260 tons is twoorders of magnitude. At some point in the 21stcentury such ships could provide a feasible and costeffective option. The Japanese studies discussedearlier suggest that, as with SWATH, the Japanesemay show us the way in large SES.

OTHER

The Bell-Halter 110s have been effectively used asoffshore support craft for the oil industry. They offergood speed and seakeeping, a stable platform andlarge deck areas.

The City of Takoma in Washington state has, forsome years, operated two Hovermarine SESfi reboats. The City of New York is acquiring twosimilar craft.

The SES attributes of high-speed, good seakeeping,good platform stability, large <deck area and shallowdraft are attractive for numerous survey, supply andworkboat applications.

CONCLUSIONS

The following conclusions are supported by thispaper:

1.

2.

3.

4.

5.

6.

After 30 years of development and application,SES technology, as applied to small craft, ismature (state-of-the-art).

Associated design analysis, performanceprediction and model--testing techniques arecredible and reasonably well documented.

Hardware feasibility to 250 tons is established(650 tons in the case of the Soviet Dergach).

Potential advantages of SES are improved:

. Speed. Seakeeping. Platform Stability. Deck Area. Enclosed Volume. Shock Attenuation. Helo Support.

Although variants and hybrids have beensuccessfully demonstrated, a least-risk hullformhas been established. A very consistent patternfor the selection of seals, lift systems, ridecontrol and propulsors inas emerged.

The designs of the several proposed car ferriesreflect a consistency logically deriving fromconclusion no. 5. Hull material is the principalvariant.

4 9

7.

8.

9.

10.

11.

12.

The feasibility of steel, aluminum and singleskin or cored GRP SES construction has beendemonstrated.

National practices, economics, componentmanufacture and the rules of local regulatoryagencies strongly influence the selection of craftmaterials and components.

The commercial viability of passenger ferries to150 tons full-load, operating at block speedsover 40 knots, has been demonstrated.

The current emergence of SES car-ferryinitiatives in six nations reflects a considerableconfidence in the technical and economicviability of the SES concept to over 2000 tons.

Similarly, the appearance of the Dergach, theoperation of the USCG Sea Bird class, and thedevelopment of the Norwegian Nortest FAC andNavy MCMs establish SES as a concept thatmust at least be considered for Patrol and MCMmissions.

Many studies and designs notwithstanding, thefeasibility of large (over 2000 tons) SES has notyet been credibly established. This is, realisti-cally, dependent upon the evaluation ofhardware at intermediate displacements. SESof intermediate displacements are, however,being built, or are under development in othercountries by commercial concerns and bygovernment programs.

RECOMMENDATIONS

Where do we in the U.S. maritime community go fromhere with SES? The design and constructioncapability for SES is in place in the U.S. Much of thetechnology was developed here. Other nations havedeveloped the applications. The European experi-ence is establishing the competitive viability of SESferries, at least in their market. The military potentialhas been recognized and is being implemented inNorway, France, Germany, Italy, Spain and theUSSR. Perhaps it is not too late for us in the U.S. torealize the economic and military potential of thistechnology we helped to introduce.

The following suggestions are categorized as: SESGeneric, Transport, Military and Other.

SES Generic

lt may be argued that., after committing majorresources to the 3KSES program, the SES communityproceeded to oversell the concept for Naval missionsranging from ASW Frigates to Air Capable Cruisersand, most recently, 20,000-ton sealift ships. The SESconcepts’ credibility has suffered accordingly. Theproblem has been that all the SES R&D investmentswere directed to Navy blue-water missions which didnot include anything smaller than a Frigate. T h eCoast Guard, however, has most effectively utilizedthe military version of the state-of-the-art Bell-Halter140-ton SES.

The lesson suggested here is simply; “walk beforeyou run”. Risk must be commensurate with potentialgain. Historically, advanced vehicles have only beendeveloped, or been successful, under these terms.

In proposing applications, military or commer-cial, risks must be realistically assessed.State-of-the-art today, in the U.S., is 250 tons.

Based on world experience today, proposingcurrent development of an SES, military orcommercial, of 2000 tons full-load or less wouldbe reasonable - if the design and all compo-nents are essentially state-of-the-art and thepotential benefits, economic or military, justifythe risk associated with simply increasing scale(and cost).

SES experiences must be credibly documentedand translated into design and regulatorystandards and methodology. The SNAME SD-5Panel (Advanced Vehicles) is current lydeveloping a T&R Bulletin for SES design. ABSand U.S. Coast Guard rules have been modifiedfor commercial SES. Navy standards forbuilding a 2000-ton SES do not exist.

Foreign experience, particularly with the currentand developing high-speed ferries and militarycraft, must be careful ly observed anddocumented.

Transport

U.S. ferry operations, as long as they include two U.S.ports, are currently subject to the Jones Act whichrequires U.S. construction of the ferries. Given aroute, an operator and financial backing, there aremany U.S. yards well qualified to construct an SES

5 0

ferry. A design is required. Licensing of a U.S. yardfor an “off-the-shelf” foreign SES ferry is one alterna-tive. The other is to utilize the existing U.S. designcapability to develop a state-of-the-art ferry specifi-cally for U.S. shipyards, regulatory agencies andoperating condit ions.

The UMTA study (Reference 50), completed in 1984,was an in-depth assessment of the potential ofhigh-speed waterborne passenger service for U.S.routes. Economics and technology have evolved inseven years but this seven-volume study offersvaluable guidance for any, and all, of the participantsin a present day high-speed ferry venture. Twenty-four foreign hydrofoil, SES, ACV and fast catamaranoperations in Scandinavia, the Mediterranean, the FarEast and South America were examined. It wasconcluded that these services were successful underthe fol lowing condit ions:

a . Adequate numbers of passengers had a historyof using public transportation and had limitedaccess to automobi les.

b. Competitive, reliable, high-speed ferries werereadily available.

C . Experienced operators existed with financialbacking and management experience.

d. Water transport had significant advantages overcompeting modes of transportation (road, railand air).

In 1984, the most consistent detriment to successfuloperations was the prevalence of adverse sea states.

Ten potential U.S. routes were studied with theconclusion that several were feasible. A potential for24 ferries was identified, which, in 1984, translated toa $130 million market for U.S. shipyards.

Twenty examples of U.S. operations of high-speedferr ies, largely unsuccessful, between 1962 and 1984were examined. Several “facts” emerged from thisphase of the study:

a. A one-vehicle operation without back-up cannotsucceed.

b. Developmental vehicles are not suitable for alink in a transportation system.

C .

d.

8.

1.

h.

i.

T h e

The f inancial manager must not be subordinateto the technical manager (developer).

Repair and maintenance support must beadequate.

Financial planning and support of the operationis vital.

Competent market analysis is a prerequisite toany operation.

Political considerations, particularly with respectto competing systems, are criiical.

The fast ferry must be an effective link in atransportation system, i..e., effective connec-tions on both ends are necessary.

The operation must be effectively promoted(advert ised).

issue of public (possibly subsidized) versusprivate ventures is also a consideration.

The bottom line of all this “gloom and doom” is simplythat there must be a genuine need for the service andit must be economically competitive, reliable andattractive to the rider. This requires careful planningand adequate financial backing. The opportunitiesclearly exist.

Military

Patrol/Attack

The U.S. Coast Guard has already implemented aneffective cutter role for SES in the 140-ton size. SEScould be a competitor for other cutter replacementsbut this is not highly probable in the near term. Withrespect to Navy requirements; aside from ForeignMilitary Sales (FMS), the only recent requirement forNavy craft in the 100 to 300-ton range has been thePBC where requirements cal led for a Non-Developmental Item (NDI) resulting in procurement ofconventional craft. Reassessment of Navy require-ments in the light of changinlg world conditions couldresult in requirements for larger, faster and morecapable patrol craft for which SES could be con-sidered. Air capability could be a key selection factorfor such a craft.

5 1

Foreign Military Sales, to Latin America in particular,may be an attractive arena for marketing of SESpatrol craft. Note should be taken of the Nor-testconsortium approach in Norway for a 220-tonfast-attack craft.

ASW

As previously discussed, a “small” U.S. ASW platformwould likely be in the 1500 to 2500-ton range whichwould represent a large step in scale for near-termconsideration.

MCM

It is anticipated that performance of the NorwegianSES MCMs will be closely observed by the U.S. TheNATO SWG/G SES MCM study is continuing. Currentacquisition planning, however, is expected to precludeconsideration of SES in the near term.

Other

Workboats, fireboats, survey boats and offshoresupply craft are among the logical candidates forSES. These craft are generally within currentstate-of-the-art with respect to speed and displace-ment, so it is simply an issue of cost effectiveness.

ACKNOWLEDGEMENTS

The authors acknowledge the contributions of thefollowing companies and government agencies.Without their contributions including photographs,preparation of this paper would not have beenpossible.

Companies and Government Agencies

Blohm und VossBrodrene AaCirrusFincantier iHovermarine InternationalKarlskronavarvetMarinetechnik GmbHRoyal ScheldeSocieta Escercizio Cantieri, SpAService Technique Des Constructions et Armes

NavalesTrinity Marine GroupUlstein International

The authors also acknowledge the contributions madeby:

Bill Band (BLA), John Allison (BLA), John Adams *(MDI), Charles Atchison (NAVSEA 501), Tom Cannon(NAVSEA 50141) Alan Ford (DTRC 12), Chr isMcKesson (NAVSEA 50 141) Jack Offutt (DTRC 12),Pat Smith (MDI), Steve Wynn (NAVSEA 50141)Norman Polmar (U.S. Naval Institute) and thetechnical publications effort by Linda Peters (BLA).

Mr. John Lewthwaite is also acknowledged for hisreview of, and valuable contributions to, the paper.

The publications: “Janes High-Speed Marine Craft”(Reference 5), “Fast Ferry International” (Reference6), and “Work Boat World” (Reference 49) are alsoacknowledged as very valuable sources of informationused in the preparation of this paper.

REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

Hayward, L, “Thle History of Air CushionVehic les,” Kalerghi McCleary Publications,London, 1963.

Trillo, R.L., “Marine Hovercraft Technology,”book published by Leonard Hil l Books, London,1971.

Mantle, P.J., “Air Cushion Craft Development,”book published Iby DTNSRDC, No. 80/012(4727 Revised), 1980.

Tattersall, E.G., “The History and Future of theSurface Effect Ship in the United Kingdom, APersonal Account,” Naval Engineers Journal,Volume 94, Number 2, ASNE. April 1982.

“Janes High-Speed Marine Craft,” ( Issues 1971to 1990) Jane’s Information Group Ltd, Editor,Robert Trillo; Sentinel House, 163 BrightonRoad, Coulsdon, Surrey, CR5 2NH, UK.

“Fast Ferry International,” formally “High-SpeedSurface Craft,” and “Hovering Craft andHydrofoil,” (Issues 1961 to 1990) High-SpeedSurface Craft Ltd, Editor Alan Blunden, 24 LeafClose Northwood, Middlesex, HA6 2YY, UK.

“Air-Cushion Vehicles,” (Issues 1963 to 1971)Horizon Publications Ltd, Somerset, UK(formally a Flight International supplement).

Tattersall, E.G., “The HM 500 Series of SidewallHovercraft,” Royal Institution of Naval Ar-chitects, April 1984.

5 2

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

Ford, A.G., “Captured Air Bubble (CAB) VehicleProgress Report , ” Al AA Journal ofHydronautics, Apri l 1968.

Mantle, P.S. and Lavis, D.R.. “Domain of the AirCushion Craft,” SAE Paper 680273, April 1968.

Chaplin, J.B., “A Rational Approach to an SESDesign,” AlAA/SNAME Advanced MarineVehicle Conference, Paper No. 79-2032,October 1979.

Chaplin, J.B., “Development of the Bell Halter110 SES,” Journal of Hydronautics, Volume 15,No. l-4, January - December 1981.

Sara, A. CDR, USCG, Presentation given to theU.S. Hovercraft Society on experience with U.S.Coast Guard WSES Cutters, April 1990.

21.

22.

23.

24.

25.Spaulding, K.B., Jr., “The CONFORM Program- An Update,” Naval Engineers Journal, May1984.

Spaulding, K.B., Jr., “SES and ACV for NavalMlssions - The CONFORM Studies,” presentedat the 1985 Joint International Conference onAir Cushion Technology, Rockville, Maryland,September 1985.

“Soviet SES Combatant Joins GrowingAir-Effect Fleet,” Navy News and UnderseaTechnology, Volume 7, No. 28, 23 July 1990.

Gullberg, O., “Jetrider SES 300 PassengerFerry Development,” Canadian Aeronautics andSpace Journal, Volume 35, No. 2, June 1989.

Salomonsson, L., Bergman, M. and Nilsson, J.,“The ‘TESTRIGG’ Vessel - A Consequence ofFuturistic Ideas,” Karlskronavarvet (KKrV),Sweden.

Knupffer, K., Frambaurg, J., Lewthwake, J. andAdams, J., “SES 700: The Federal Republic ofGermany’s Fast Test Craft,” IntersocietyAdvanced Marine Vehicle Conference,Arlington, Virginia, June 1989.

Lewthwaite, J . , Presentation to the (UK)Hovercraft Society, Hovercraft Bulletin,February 1991, The Hovercraft Society, 24Jellicoe Avenue, Alverstoke, Gosport, Hants,PO1 22PE.

26.

27.

28.

29.

30.

31.

Lavis, D.R., Rogalski, W.W. and Spaulding,K.B., “The Promise of Advanced Naval Vehiclesfor NATO,” Marine Technology, March 1990.

Code of Safety for “Dynamically SupportedCraft,” (Resolution A 373 (X) not yet ratified byall countries), International Maritime Organiza-tion (IMO).

“Rules for Classification of High-Speed Craft,”Det norske Veritas, 1985 (Draft Revision Issuedfor Review, January 1990).

White, W.N., “Advanced Marine Vehicles - AReview,” Section Ill Surface Effect Ship (SES),23rd Annual Technical Symposium, NAVSEA,Association of Scientists and Engineers, April1986.

Lavis, D.R. and Forstell,, B.G., “Computer-AidedConceptual Design of Surface-Effect Ships,”Canadian Aeronautics and Space Journal,Volume 35, No. 2, June 1989.

Band, E.G.U. and Lavis, D.R., “Computer-AidedDesign of Air-Cushion Vehicles and Surface-Effect Ships,” International High-PerformanceVehicle Conference, Shanghai, Nov. 1988.

Lavis, D.R. and Bagnell, D.G., “Computer-AidedEarly-Stage Design of High-Speed Craft,”Intersociety Conference, Arlington, Virginia,June 1989.

Durkin, J.M., “An Experimental Investigation ofthe Performance of the Aerojet l/4-Scale,Variable-Geometry Centrifugal Lift Fan UnderDynamic Flow Conditions,” DTNSRDC Report76-0073, June 1976.

Moore, R.G. and Omega, G.T.. Bell AerospaceTextron, “Large SES Design Limits,” ATAA,Spring 1979.

Newman, J.N. and Poole, F.A., “The WaveResistance of a Moving Pressure Distribution ina Canal,” DTNSRDC Report No. 1619, March1962.

Doctors, L.J., “The Wave Resistance of an AirCushion Vehicle,” University of Michigan,December 1970.

5 3

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

Allison, J., “Propellers for High-Performance 43. Band, E.G.U. and Lavis D.R., “Heave StabilityCraft,” SNAME Marine Technology, Volume 15, of Air-Cushion Supported Ships,” PRADS’ 89No. 4, October 1978. Conference, Varna, Bulgaria, October 1989.

IS0 2631, “Guide for Evaluation of Human 44. Band, E.G.U., Lavis, D.R., Giannotti, “PredictionExposure to Whole-Body vibration,” Interna- of Hydrodynamic Impact Loads Acting on SEStional Standard Organization (ISO) Document and ACV Structures,” AIAA Paper 76-868,ISOiDIS 2631, 1972. September 1976.

O’Hanlon, J.F. amd McCauley, “Motion 45. Band, E.G.U. and Baca, A.F., “Predicting theSickness Incidence as a Function of the Unpredictable - Development of RationalFrequency and Acceleration of Vert ical Design Loads for High-Performance Vessels,”Sinusoidal Motion,” Human Factors Research Hovering Craft and Hydrofoil Exhibition,Inc., Technical Report 1733-1, September 1973. Brighton, England, June 1980.

Allison, J., “Air Cushion Vehicles and SurfaceEffect Ships for Great Lakes and Great RiverTransportation,” SNAME Marine Technology,November 1990.

Adams, J.D. and Beverly, W.F., “TechnicalEvaluation of the SES-200 High Length-to-Beam Surface Effect Ship,” Naval EngineersJournal, Volume !36, Number 3, May 1984.

Butler, E.A., “The Surface Effect Ship,” ChapterVI of “Modern Ships and Craft,” published byThe American Society of Naval Engineers as aspecial edition of the Naval Engineers Journal,February 1985.

Wilson, R.A., “Captured Air Bubble VehicleStability Tests,” AIAA/SNAME Advanced MarineVehicle Meeting, Norfolk, Virginia, Report No.67-349, Macy 1967.

Lavis, D.R., Band, E.G.U. and Hoyt, E.D.,“Development of Intact Stability Standards forRigid Sidehull Surface-Effect Ships,” USCGReport No. CG-D-53-81, December 1981.

Blyth, A., “Recent Research into the UltimateStability of Surface-Effect Ships,” RINAConference on Ship Stability and Safety, June1986.

“Report of the ARB Special Committee onHovercraft Stability and Control,” Civil AviationAuthority, CAA Report 75017, June 1975.

Lavis, D.R., Bartholomew, R.J. and Jones, J.C.,“On the Prediction of Acceleration Response ofAir Cushion Vehicles to Random Seaways andthe Distortion Effects of the Cushion Inherent inScale Models,” AIAA Paper 72-598, July 1972.

46. “British Hovercraft Safety Requirements,” CivilAviation Authority, Surrey, England.

47. “ABS Proposed Rules for High-Speed Craft,”American Bureau of Shipping, Draft Issued forReview, March 9, 1!389.

48. Allen, R.G. and Jones, R.R., “Considerations onthe Structural Design of High PerformanceMarine Vehicles,” New York Section, SNAME,January 1977.

49. Work Boat World, IPage 10, by George Marsh.Published by Baird Publications, EastgateHouse, Town Quay, Southampton, SO1 LX, UK.

50. “A Guide for Implementing High-SpeedWaterborne Passenger Transportation Ser-vices,” Urban Mass Transportation Administra-tion (UMTA), Office of Technical Assistance,September 1984.

51. “Overview of Coast Guard Plan Review forHigh-Tech Ship Design,” James A. Watson andWilliam M. Hayden, paper presented to theChesapeake Section of SNAME, 22 February1989.

52. “Leisure Industries Promote Increased Activity,”The Motor Ship, January 1991.

53. Spaulding, K.B., Jr., “Cored FiberglassReinforced Hull Construction,” Conference onFishing Vessel Construct ion Materials,Montreal, October 11968.

54. Svensen, R., “Experience with the KaMeWaWaterjet Propulsion System,” IntersocietyAdvanced Marine-Vehicle Conference,Arlington, Virginia, ,June 1989.

5 4

, -

55.

56.

57.

58.

59.

60.

61.

Oehlmann, H. and Lewthwaite, J.C., “ThePrediction of Resistance of Surface EffectShips,” FAST 91, Trondheim, Norway.

Goubault, P., Oehlmann, H., Lavis, D.R. andGoetsch, W., “Comparative Parametric Studiesof Monohull and Surface Effect Ships,”presented at FAST 91, Trondheim, Norway.

Knupffer, K., Reischauer, J. and Witschel, H.,“SES Technology,” SMM-1990 Conference,HANSA Sonderdruck, Germany.

Kaplan, P. et al, “Dynamics and Hydrodynamicsof Surface Effect Ships,” SNAME Transactions,Volume 89, pages 211 - 247, 1981.

Clayton, B.R. and Tuckey, P.R., “A SpeedControl System for High-Speed and HighPower-to-Weight Ratio Motors With SpecificApplication to Model Hovercraft Lit Fans,”High-Speed Surface Craft, June 1982.

Clayton, B.R. and Tuckey, P.R., “DynamicResponse of Hovercraft to Regular WaveExcitation,” High-Speed Surface Craft Con-ference, May 1983.

Clayton, B.R. and Webb, R., “The DynamicResponse of Surface Effect Ships in RegularHead Seas Using Model Simultations,” FifthInternational High-Speed Sur face Craft

Conference, May 1986.

LIST OF SYMBOLS AND ABBREVIATIONS

AALC

AC

ASW

B

4

54

B L A

B,

Amphibious Assault Landing Craft

Cushion Area (ft*)

Anti-Submarine Warfare

Beam Overall (ft)

Cushion Beam (ft)

Maximum Craft WL Beam Hullborne (ft)

Band, Lavis & Associates, Inc.

Sidehull Width Amidships at Hullborne

Waterline (ft)

Sidehull Block Coefficient

%

CG

D

d

D T R C

Sidehull Prismatic Coefficient

Center-of-Gravity

Freeboard (ft)

Draft (ft)

David Taylor Resea.rch Center

Acceleration Due to’ Gravity (32.2 ft/sec’)

Cushion Height Amidships, Keel to Wet-Deck

WI

K

K B S

K G

Roll Radius of Gyration

Kamysh-Burun Shipyard, USSR

Vertical Center-of-Gravity (VCG) Height AboveKeel

KKrV Karlskronavarvet

L Length Overall (ft)

LACV-30 Lighter Air Cushion Vehicle (30-TonPayload)

Lc Cushion Length (ft)

L C A C Landing Craft Air Cushion

4-w Sidehull Waterline Length on Cushion (ft)

MDI Maritime Dynamics Inc.

MTG Marinetechnik GmbH

N Pump Speed, rpm

NAVSEA Naval Sea Systems Command

N P S H Net Positive Suction Head, ft

N s s Suction Specif ic Speed (a Quasi-Dimensionless

Number)

PC

0

RNN

Cushion Pressure (lbIft2)

Pump Flow Rate, gpm (by convention)

Royal Norwegian Navy

55

S E C Societa Escercizio Cantieri, SpA

SSPA Marit ime Consult ing AB

T C G Transverse Center-of-Gravity

VCG Vertical Center-of-Gravity

W Full-Load Displacement (L. Tons, lb)

W (l/2) Half the Full-Load Displacement (lb)

a Sidehull Outer Deadrise Angle Amidships(degrees)

5 6