SNAME SHIP DESIGN AND CONSTRUCTION REVISION
Chapter 44
Philippe Goubault and John Allison
Advanced Marine Surface Craft
44.1
DESCRIPTIONS44.1.1Mission
Advanced Marine Surface Craft are obviously not destined to only
one type of mission, but their profile will typically include a
need for higher speed and greater seakeeping than can be achieved
by conventional means.
For military applications, missions of fast patrol boats are
most commonly found to use advanced hullforms, while commercial
applications encompass high speed ferries.
44.1.1.1Military Missions
Patrol boats are often required to operate swiftly and present a
significant and unpredictable threat to larger vessels by carrying
missiles or torpedoes at high speed in coastal zones where
detection is more difficult than in open oceans. To further these
capabilities, patrol craft are increasingly required to make use of
stealth technologies.
In order to remain operational in rough weather, these small
craft are also required to offer good seakeeping while maintaining
speed. These capabilities require the use of advanced hullform
concepts such as hydrofoil or Surface Effect Ships.
Larger vessels such as corvettes, also capable of high speeds,
have been considered for more significant military missions such as
anti-submarine warfare, but have not been built yet for these
missions.
44.1.1.2Commercial VesselsThe common purpose of developing
advanced hullforms for commercial use has consistently been to
provide faster and/or more comfortable vessels to carry passengers
and cars. It is notable, however, that with the growth in use of
the generally more stable multi-hulls, combined with todays more
capable collision avoidance systems, there has been a significant
improvement in the safety of operation of these vessels.
Most advanced hullforms are designed to have low resistance at
high-speed compared to conventional (e.g., displacement) monohulls.
This is usually achieved by reducing wetted surface by lifting the
hull entirely or partially out of the water. To achieve this,
hydrodynamic lift is used by hydrofoils and planing hulls, while
powered aerostatic lift is used by air cushion vehicles and surface
effect ships.
Aerodynamic lift is used by Wing-In-Ground effect vehicles.
In some instances, the speed is high only relatively speaking
if, for example, the goal is to maintain speed in a heavy sea.
Small waterplane area vessels are designed to provide a high
comfort and small added resistance in waves, but may not
necessarily be intended for speeds higher than that of conventional
vessels in calm water. Thus, their speed can be relatively high
when compared to conventional craft in high sea states.
Passenger comfort on high-speed ferries is a critical issue and
is addressed by most hullforms through the choice of vessel size
and, in some instances, through active means of controlling the
motions. Hydrofoils are the most extreme in this regard since the
craft is supported entirely by the foils, which are actively
controlled. Platforms such as Surface Effect Ships have been fitted
successfully with active vent valves to regulate the cushion
pressure and, therefore, the motions. Trim tabs, T-foils and other
active ride control systems are now utilized on many types of
platforms to improve their seakeeping and ride comfort.
The growth of high-speed ferries has also been made possible by
advances in propulsion plant technology, as lightweight diesel
engines and waterjet propulsors have become more readily available
in larger sizes. Meanwhile, the use of gas turbine propulsion for
larger vessels has become acceptable to operators who realize the
benefit of a lightweight propulsion plant in improving the
deadweight capacity and, therefore, revenue on such vessels.
One benefit of advanced hullforms is their stability
characteristics which are usually far superior to that of
conventional monohull ferries. This is achieved with planing
monohulls due their wide beam. For multi-hulls and air cushion
vehicles it is because of their wide beam and high amount of
reserve buoyancy provided by the box structure.
Another characteristic found in most multi-hull car-ferries is
that their car deck usually sits much higher above the water than
in conventional monohull ferries, making flooding of this deck much
less likely.
The few accidents in which advanced ferries were involved only
reinforced the point that they are safer than conventional ferries.
This, in the end, may be the most important aspect which convinces
ferry operators to turn towards the advanced concepts addressed in
this Bulletin.
44.1.2Unique Features44.1.2.1Vessel Lift
There are essentially four practical ways of providing the
fundamental lifting force for marine vessels. These are hydrostatic
lift or buoyancy, hydrodynamic lift, aerodynamic lift and powered
aerostatic lift. These means of lift can be simply represented
through the use of the lift pyramid, Figure 44.1, which is usually
shown as a simple triangle when the aerodynamically supported craft
(which are still very few in the marine world) are excluded. Every
marine vehicle hullform investigated can be located in the lift
pyramid according to the type of lift by which it is supported.
At the four corners of the pyramid are the vessels which rely on
a single mode of support. They are as shown in Table 44.I. Any
combination of the four modes of support result in a hybrid
vehicle. It is to be noted that most high performance craft are
hybrids of some sort. Most high-speed vessels are designed to
benefit from some hydrodynamic lift even if the vessel is not
entirely supported by this means alone.
Figure 44.1 - Lift Pyramid
Table 44.1 - The Four Pure Types of HullformsStaticDynamic
WaterHydrostaticHydrodynamic
AirAerostaticAerodynamic
44.1.2.2Hull Shape
The shape of the hull itself is often what characterizes a
high-performance ferry. In the past decade, the emergence of
multi-hulls, especially catamarans, has been significant. Such
hullforms are still most often conventional in that they are
supported by conventional displacement means and do not rely on
advanced means of lifting themselves out of the water. In such
case, the resistance may be reduced instead by the use of fine
sidehulls which cut effortlessly through the water. Such fine hulls
are not suitable for monohulls as they would not provide adequate
stability in roll. This problem is alleviated when used in a
multi-hull configuration.
The following list delineates the hullforms discussed in this
chapter:
Monohull: Semi-planing and Planing
Multi-Hulls:
Catamarans: Displacement, Planing, Low Wash,
Wave-Piercer
Trimarans
SWATH: And other small waterplane area
vessels (including Semi-SWATH)
Hydrofoil: Fully submerged or surface piercing foils (Monohulls
and Catamarans) and HYSWAS (hybrid of hydrofoil and small
waterplane area singe hull)
Air Cushion Vehicle and SES
Wing-in-Ground-Effect Vehicles (WIGs)
SPECIFIC ATTRIBUTES AND ISSUES
The following sections present a qualitative discussion of the
principal strengths and weaknesses of each concept. The text
provides an examination of each type of platform and identifies the
most suitable types prior to examining vessels available on the
market. Only those aspects which are particularly important to a
given concept are discussed. Attributes or issues that are not
mentioned can be assumed to be minor for the platform or comparable
to others.
44.2.1MonohullsThere are numerous types of monohulls;
displacement, semi-planing and planing, but this bulletin looks
only at the last two categories. The technology associated with
planing and semi-planing monohulls is generally mature. Recent
efforts in the development of semi-planing monohulls, however, have
led to larger length-to-beam ratios, pushing high-speed designs
toward long slender ships. These monohulls can be considered
advanced in that they are pushing the limit of the
state-of-the-art.
44.2.1.1Planing Monohulls
A planing hull has the majority of its weight supported by
dynamic lift with the small remaining part of the weight supported
by buoyancy or hydrostatic lift. These hullforms are typically of
the hard chine type with a Froude Number
> 0.9 or a Volumetric Froude Number
> 3.0. Another characteristic of planing hulls is the
occurrence of complete flow separation at the transom and the
sides. There are many variations of planing and semi-planing
monohulls which include; round bilge, hard chine, double chine and
stepped hulls. Cross sections of some of these are illustrated by
Figure 44-2.
State-of-the-Art Examples. Small combatant ships and high-speed
patrol craft of light displacement, and round bilge have been used
by the worlds navies since the early 20th Century. For the most
part, these designs finally gave way to hard chine hullforms and
then to double chine hullforms. Most of todays planing craft are of
the hard chine type.
Recent developments have pushed the fast ferry monohulls beyond
the 100 meter mark due to the trend towards larger capacity
vessels. The principal characteristics of a number of operating
vessels are shown in Table 44.II. Figure 44.3 shows the Aquastrada
Guizzo in operation.
Figure 44.2 - Types of Planing Monohulls
Table 44.II - Planing Monohulls
CharacteristicsGuizzo (Aquastrada)Albayzin (Mestral)NVG Asco
(Corsaire)MDV 1200
Pegasus
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (or Buses + Cars)101.8
14.5
2.12
9.5
27.93
1034
41
450
12696.2
14.6
2.1
8.9
21.6
946
35
450
84102
15.4
2.4
5.2
24
1100
37
500
148 (4 + 108)100
17.1
2.75
10.7
27.5
1200 est.
38
800
175 (6 + 106)
Figure 44.3 - Aquastrada
Specific Attributes. Planing and semi-planing monohull
technology is mature. Many designers and shipyards have experience
designing and building these vessels.
Construction of these hullforms is relatively simple.
Large useable volume in the transom area available for machinery
plant and propulsor integration and access.
Large deadweight capacity combined with relatively high
speeds.
Due to their maturity, there are numerous operating vessels from
which a wealth of operational statistics are available.
Specific Issues. Roll stability is usually an issue for
displacement monohulls, but not for typical planing monohulls due
to their wide beam. The trend toward high length-to-beam ratios
brings to light concerns about static and dynamic roll stability in
turns.
Typically, power plants and propulsors of high output are
necessary to achieve high speeds. Growth in size of such vessels is
limited by the need to operate at high enough speed to be in the
planing or semi-planing regime.
Heave and pitch motions and vertical accelerations of planing
and semi-planing vessels may be severe at high speed in rough
water. Thus, size may need to be larger than necessary for the
ridership, lowering the deadweight to displacement ratio. However,
active ride control has been shown to help in this regard.
Hull bottom slamming is also an issue for planing monohulls,
both from a passenger comfort and from a structural design point of
view.
44.2.2Multi-HullsFour different types of multi-hulled vessels
are described in this bulletin. The two general categories from
which the four types were derived are catamarans and trimarans.
Further dividing the catamaran category into three subcategories
yields the following; conventional (round bilge or hard chine),
wave-piercing and low wash (usually with round-bilge types).
Typical hull cross sections are illustrated by Figure 44.4. The use
of multi-hulls in marine transport has rapidly increased in the
last ten years mainly due to the large gain in arrangeable deck
area and advantages in powering and seakeeping over a monohull of
the same displacement The multi-hull concept is usually retained in
order to allow the use of slender hulls while maintaining adequate
stability. The concept is now being extended to an ever increasing
number of hulls (up to the pentamaran concept, for example).
44.2.2.1Conventional Catamaran
A catamaran is a twin hulled vessel which uses the separation of
slender hulls to gain low drag with acceptable transverse
stability. The twin hulls are typically symmetric, but can be
asymmetric. The hull shape can be of a round bilge type or with
hard chines depending upon the design speed.
State-of-the-Art Examples. Numerous catamarans are in commercial
operation. The characteristics of four representative vessels are
shown in Table 44-3. The top speed and size of these catamarans
have continued to increase mainly due to the improvements in
propulsion packages. Figure 44-5 shows a recent example of the
state-of-the-art, DELPHIN, an Auto Express 82 in operation.
Specific Attributes. Due to the twin hulls and the separation
between them, the catamaran has good inherent intact and damage
stability as demonstrated in recent accidents including the St.
Malo incident, April 17, 1995.
Large arrangeable deck area due to separation of hulls (allows,
in particular, to turn cars around for car ferries).
Hulls are large enough aft to allow integration of waterjet
propulsion and suitable for in-hull machinery arrangements.
Figure 44.4 - Typical Multi-Hulled Vessels
Table 44.III - Conventional CatamaransCharacteristicsHai Chang
(Austal)Juan Patrico
(INCAT K55)Westmaran
4200SDelphin
(Auto Express 82 m
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
Passengers
Cars (or Buses + Cars)40
11.5
1.4
N/A
4
N/A
32
338
None70.4
19.5
2.15
5.65
21.24
383 est.
45
294
5342.23
10
1.6
N/A
4
N/A
35
230
None82.3
23
2.5
6.5
24.0
1100 est.
37.5
600
175 (10 + 50)
Figure 44.5 - DELPHIN, Auto Express 82
Due to the slenderness ratio of the hulls, they are of low drag,
therefore, a catamaran has high performance capabilities. There are
numerous vessels operating from which good operational statistics
can be developed.
Specific Issues The wide beam of catamarans (or any multi-hull)
may cause difficulty in accessing some port facilities for which
they have not been designed.
Structural weight fraction is high due to cross-structure and
connections to the hulls.
Catamarans may experience high vertical accelerations and pitch
motions in head seas. Catamarans also are very stable in roll, but
because of this they may produce high lateral accelerations in beam
seas.
Performance is sensitive to hull separation, therefore, the wave
interaction between hulls needs to be investigated.
Slamming of wet-deck could occur if its height over the
waterline is not sufficient for the seas encountered on the
route.
44.2.2.2Wave Piercing CatamaransThe increasing need for
high-speed marine transport coupled with the fact that passengers
often experience discomfort on open ocean or exposed routes on
conventional catamarans, created a void which the wave-piercer was
developed to fill. Again, this hull form has twin hulls, but they
are long and slender with minimal freeboard and little buoyancy in
the bow section. This configuration allows the bows to cut or
pierce the waves reducing the tendency of the vessel to contour or
ride over the waves, thus providing lower pitch motions and
accelerations, while carrying similar deadweight. It should be
noted that some wave-piercers have a third half hull or bow
forward. The hull does not provide buoyancy to allow increased
deadweight, but does help mitigate wave slap and slam loads on the
cross-structure while operating in a sea state.
State-of-the-Art Examples Wave-piercing catamarans were
introduced in the early 1980s with the INCAT 28 m as the first to
operate on a commercial route. Since then, several companies have
developed their own approach to this type of design, the
characteristics of three of which are shown in Table 44-4. A photo
of the INCAT 78-m CONDOR 11 wave-piercers is shown in Figure
44.6.
Table 44.IV -Wave-Piercing CatamaransCharacteristicsCondor
11
(INCAT 78 m)Hayabusa (AMD 1500)Surf Express (Gold Coast)
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)77.5
26
3.4
7.2
17.28
785
35
600
150 (6 + 90)99.78
20
3.10
12.6
18.96
2200
30
460
94 (24)31.7
9.8
1.35
N/A
2.6
61.1
35
128
--
Figure 44.6 - CONDOR 11, INCAT 78 m Wave-piercer
Specific Attributes Heave and pitch motions and accelerations
are reduced while in head seas due to wave-piercing action of
sidehulls. Due to the twin hulls and the separation between them,
the vessel has good inherent intact and damage stability. They have
large useable deck area due to separation of hulls.
Hulls remain large enough aft to allow integration of waterjets
and propulsion machinery.
Due to slenderness of the hulls, they are efficient, therefore,
have high performance capability.
Due to their recent success, there are numerous operating
vessels from which good operational statistics can be
developed.
Specific Issues Construction is more difficult than with
conventional catamarans due to the structural complexity of the
forward hulls. The transition area from wave-piercing bow to the
more typical cross-section in way of the cross-deck starting point
is very structurally complex. Although the structure is more
complex, the structural weight fraction is similar to that of a
conventional catamaran.
The wide beam of wave-piercer catamarans is also an issue where
ports are not designed to harbor such vessels.
High roll or lateral accelerations or lateral jerky motions in
beam seas can also be experienced by wave-piercer catamarans due to
their inherently high lateral stability. Active ride control has
proven to be effective in controlling such effects.
44.2.2.3Low-Wash Catamaran
Due to increasing global environmental awareness, the low-wash
or low-wake catamaran hullform is becoming increasingly popular for
inland or sheltered routes, e.g., rivers or estuaries. The hulls
are generally symmetric with rounded sections and a high
length-to-beam ratio providing lower wake profiles.
State-of-the-Art Examples Low-wash vessels are typically in a
size range that is smaller than the conventional and wave-piercing
catamarans since they are typically designed to operate in
restricted waters. Due to the relative newness of these designs
there are only a few operating vessels, the leading particulars of
some of which are shown in Table 44.V. Two of the NQEA low wash
catamarans are shown in Figure 44.7.
Specific Advantages Although top speed is limited due to the
need to maintain the wave-making properties of the hull, these
vessels can operate at a higher speed in low wake areas than most
conventional or advanced marine vehicles.
Hull forms are designed for a low-wake profile, therefore, they
are very energy efficient and have low resistance properties.
Typically, operating on congested inland waters, these vessels
are designed to have good control and maneuverability.
Table 44.V - Low-Wash CatamaransCharacteristicsThames Class
(FBM)Castelo (FBM TransCat)Low-Wash (NQEA)
Length, m
Beam, m
Draft, m
Power, MW
Speed, kts
Passengers
Cars23
5.7
0.75
0.506
25
62
None44
11.8
1.4
1.896
25
496
None35
10.5
1.35
0.746
24
200
None
Figure 44.7 - NQEA Low-Wash CatamaransDue to the twin hulls and
the separation between them, the vessel has good inherent intact
and damage stability.
Again they have large useable deck area due to separation of
hulls.
Hulls remain large enough aft to allow integration of waterjets
and propulsion machinery.Specific Issues Since these vessels are
designed to operate in restricted water, they typically have a low
wet-deck clearance and would be subject to slamming as well as deck
wetness and high accelerations, if operated in open waters.
They are of relatively light density and may prove difficult,
therefore, to apply tgo car carrying ferries.
Higher speeds than those demonstrated (e.g., about 25 to 30 kts)
may be difficult to achieve while maintaining their low wake
capabilities.
44.2.2.4Trimarans
Trimarans are basically very slender monohulls fitted with small
sidehulls or outriggers to provide them with sufficient lateral
stability. The more recently proposed pentamaran concept operates
on the same principle. A proper balance between the slenderness
ratio of the main hull and the size and separation of the sidehulls
is needed to ensure a net benefit from a speed powering viewpoint.
Note that some vessels like the wave-piercing catamarans and the
tricat may look like trimarans, but really are catamarans as the
third central hull is normally not in contact with the water.
(Their third hull only provides additional buoyancy when
encountering large waves.)
State-of-the-Art Examples While trimarans have been around for
centuries, only recently has there been interest in pursuing
trimarans as viable options for ferry hullforms. The appearance in
1988, of the Ilan Voyager aroused interest in the trimaran concept.
There has also been interest shown by the UK and U.S. navies
including several prominent shipyards, in investigating the use of
a displacement trimaran hullform for frigates and corvette size
warships. This has also lead to designs for larger (~100 m)
trimaran passenger/car ferries. Some of the few operating trimarans
are shown in Table 44.VI. Figure 44.8 shows the Thames River Ferry
in operation.
Table 44.VI - Trimaran Passenger Vessels
CharacteristicsIlan VoyagerLay Consultants, Thames River
Ferry
Length, m
Beam, m
Draft, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)21.3
10
1.1
0.18
4.5
24
12
None17.5
5.5
0.8
0.35
15
20
60
None
Figure 44.8 - Thames River FerrySpecific Attributes Highly
efficient hullform allowing higher speed or lower installed power.
Sidehulls can easily provide adequate intact and damage stability
characteristics.
They also have large useable deck area due to separation of
hulls.
Good seakeeping qualities in all but quartering seas. Good
directional stability.Specific Issues Interest in this concept for
large vessels, such as ferries, is recent and there is, as of yet,
very little design and operational experience.
Structurally complex due to cross structures and outer hulls
(lack of design experience entails some risk).
Maneuvering is poor unless outer hulls are large enough for
propulsion units to be located within them.
Quartering seas cause problems for both seakeeping and
directional stability. There is a tendency for the vessels to
corkscrew.
Depending on the vessel, the utility of the outer hulls is
generally limited.
44.2.3Small Waterplane Area VesselsThree types of small
waterplane area vessels can be defined. The SWATH (twin hulls) was
the first concept using reduced waterplane area, which is aimed at
decoupling the vessels motions from surface waves. Two recent
developments in the small waterplane area hullform include the
recently introduced semi-SWATH which is derived from a SWATH and
conventional catamaran hulls and the developmental/prototype HYSWAS
which is a combination of a small waterplane single hull and
hydrofoils, see Figure 44.9. The HYSWAS is discussed in more detail
under the subject of Hydrofoil Craft later in Section 3.5. French
and German companies have also developed low water-plane concepts
using three hulls, while Lockheed in the USA has developed a
similar concept using four hulls that they refer to as the SLICE
concept.
44.2.3.1SWATH (Small Waterplane Area Twin Hull)
As mentioned above, the basic idea of the SWATH concept is to
reduce the action of the waves on the vessel by reducing the
waterplane area to the minimum. Waves act on a ship primarily
through their intersection with the waterplane. As depth below the
surface of the water increases, the motions of the water due to
surface waves decreases sharply. The buoyancy of a SWATH is
concentrated in two large underwater bodies which, because of their
depth below the water surface, are much less subject to the action
of waves while the accommodations are concentrated in a platform
high above the water. Narrow (knife-like) struts link the
underwater body(ies) to the platform. Because waves impart energy
to a ship via the area of the hull which intersects the water
surface (waterplane area), the reaction of a vessel to waves is
directly proportional to the size of its waterplane area.
Therefore, reducing the waterplane area minimizes motions due to
waves.
State-of-the-Art Examples Some fairly large SWATH vessels (3000
to 5000 ton displacement) are in operation for military and
oceanographic missions.
The largest SWATH, the 11,000 ton cruise vessel Radisson Diamond
shows that there are essentially no limits to the size of the
concept. However, all of these larger vessels have relatively low
speed capability (e.g., less than 15 kts).
A number of high-speed passenger vessels are in operation. The
characteristics of these are shown in Table 44-7. Figure 44-10
shows the CLOUD X ready for launching.
Figure 44.9 - Typical Small Waterplane Area Vessels
Table 44.VII - SWATH Passenger Vessels
CharacteristicsSSC 40FBM Atlantic ClassNavatek 1Cloud X
Length, m
Beam, m
Draft, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)44
16
3.5
8
N/A
30.6
410
None37
13
2.7
4.1
180
31.7
400
None44
16
2.5
2
N/A
18
440
None37
18
3.4
5.7
340
30
365
None
Figure 44.10 - CLOUD X, SWATH
Specific Attributes Seakeeping is the number one attribute for
SWATH. These vessels can maintain speed in heavy seas where most
vessels would have reduced speed or could not operate at all.
The useable deck space is usually greater than monohulls of
comparable displacement as the motions are low essentially anywhere
on the ship. Some of the most successful applications have been for
dinner-cruise ferries.
Specific Issues The narrow struts sometimes make access to and
integration of the machinery plant difficult.
The top speed achievable by SWATH vessels remains limited as the
wetted surface, unlike most advanced hullforms, is increased rather
than reduced. Also, the narrow transom makes it unsuitable for
waterjet propulsion in most cases.
Damaged stability may become an issue for SWATH ships as their
reserve buoyancy is located high in the ship.
The operating draft, heel and trim of SWATH vessels are more
sensitive to overloading than is the case with conventional
catamarans due to the low waterplane area of the struts. Control of
fixed weight is very important to ensure that the vessel is
continuously operated close to its design draft and trim.
SWATH vessels have a large draft when compared with other
vessels of similar displacement.
SWATH vessels, as a result of the sensitivities mentioned above,
usually require active control of trim and heel.
44 2.3.2Semi-SWATH
A semi-SWATH is a hybrid of the forward half of a SWATH and the
aft end of a conventional catamaran. The combination results in
vessels with nearly equal seakeeping to that of regular SWATH
vessels, but with far superior speed/powering performance.
As a result of the catamaran type stern, the semi-SWATH concept
also allows the integration of waterjet propulsion, which is
usually the preferred choice for high-speed ferries.
State-of-the-Art Examples The first and largest semi-SWATH in
operation is the Stena HSS 1500 with a displacement of about 4000
ton and a deadweight of 1500 tons. This vessel is shown in Figure
44-11.
The leading particulars of a number of vessels which are in the
construction stage, or have recently been delivered, are shown in
Table 44.VIII.
Specific Attributes The principal attribute of a semi-SWATH
vessel is its seakeeping combined with a relatively low resistance
even to fairly high speeds (40+ knots).
The catamaran-like aft sections are more suitable for machinery
arrangement and especially for integrating waterjet propulsion.
Like a SWATH, semi-SWATH vessels offer a great deal of
arrangeable deck space.
Specific Issues Although not quite as sensitive as SWATH
vessels, semi-SWATH vessels are somewhat sensitive to overloading
and trim. The small waterplane of the forward section makes it more
sensitive, in particular, to forward trim. However, this concept is
fairly new and more operational experience is needed to assess its
future.
44.2.4Hydrofoil Craft44.2.4.1Conventional Hydrofoil
CraftHydrofoil craft have been around since the late 1800s with
major advancements only occurring in the last half century
mirroring that of the aerospace industry. These advances have
allowed the development of reliable and efficient hydrofoils to be
built and put into profitable service. Recent advancements have
allowed for a departure from the typical monohull hydrofoil to
catamaran hydrofoils, both of which are discussed in this
chapter.
The hulls of hydrofoil craft are lifted out of the water by
either surface-piercing or fully submerged foil systems. These
systems are illustrated in Figure 44-12. Both types of foil systems
are prevalent in military and commercial operations throughout the
world. The surface-piercing foil system is self-stabilizing with
regard to hull height and attitude above the water. Thus, they will
cause the vessel to respond to surface waves in pitch, heave and
roll and require more limited sea-state operational restrictions.
The fully submerged hydrofoil,
Figure 44.11 - Stena HSS 1500, Semi-SWATH
Table 44.8 - Semi-SWATH Passenger VesselsCharacteristicsStena
HSS 1500Stena HS 900Seajet 250
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Cars + Buses)124
40
4.5
13
70
4000 est.
44
1500
375 (50 + 100)88
28
3.7
12.6
34
1650 est.
40
900
212 (10 + 154)76
23
3.4
8.05
30
890 est.
44
450
120
Figure 44.12 - Surface Piercing and Fully Submerged
Hydrofoils
Table 44.IX - Hydrofoil Passenger VesselsCharacteristicsBoeing
Jetfoil 929-100RHS-160FKometa-MTFoilcat
Length, m
Beam, m*
Draft, m**
Hull Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers27.4
9.5
5 (-)
--
5.534
110
42
19031.2
6.7(12.6)
3.76 (1.7)
--
2.8
91.5
34.5
23835.1
(11)
3.6 (1.7)
--
1.64
58.9
31
10235
12
4.7 (2.55)
4.2
8.95
150 est.
45
403
(*) The number in parenthesis is the foil width for
surface-piercing hydrofoils.
(**) The draft indicated is the hullborne and (foilborne)
draft.
Figure 44.13 - Jetfoil at Speed in a Seawayis not
self-stabilizing and requires an active control system. Since, in
this situation, the hull is nearly decoupled from the water
surface, craft with fully submerged foils are not as limited by
sea-state and provide a very comfortable ride. The hullform used is
usually a monohull or a catamaran. Since the hull lifts out of the
water, the hull shape has only a second order importance. However,
the hull needs to be designed to minimize resistance while
accelerating through the take-off hump and a hard-chine planing
hull is usually preferred. Also, the hull needs to be able to
structurally withstand wave impact in heavy seas and an emergency
landing without damage due to slamming.State-of-the-Art
Examples
There are numerous military and commercial craft in operation
throughout the world. The leading particulars of some of these are
shown in Table 44-9. One of the most famous hydrofoils, the Boeing
Jetfoil, is shown in Figure 44-13.
Specific Attributes
High speed is possible once foilborne due to low wetted areas
and high lift-to-drag ratio achieved.
Good seakeeping and low motions for the fully submerged
hydrofoils with almost no degradation of speed with respect to sea
state. These craft are also highly maneuverable at speed.
Surface-piercing hydrofoils can use a more conventional hull and
propulsion system similar to those on planing monohulls.
Specific Issues
Deadweight is limited because foils support the entire weight of
the vessel. Thus, these vessels may only be used effectively in
passenger ferry service. It should be noted that there are numerous
naval applications for these hullforms, but, in all cases, the
concept is not efficient in very large size applications.
Since the hull is lifted a significant distance out of the water
with the fully-submerged hydrofoil concept, the integration of the
propulsion system is complex. Waterjets or propellers may be used,
but, in the foilborne mode of operation, propellers are generally
more efficient. Additionally, a second propulsion system for
hullborne operations is often required. These are high cost
platforms due to these complexities combined with the automatic
flight-control system required for the foils.
Construction is difficult due to structural complexities of
attaching the foils to the hull and designing a hull of minimum
weight, to take the applicable environmental loads especially
slamming loads during emergency landing.
Surface-piercing hydrofoil craft are much less expensive, but
operation is limited to coastal or partially protected routes. They
sometimes employ active ride control systems to ameliorate motions
due to the wave-foil interaction.
b)HYSWAS
Description
The Hydrofoil Small Waterplane Area Ship (HYSWAS) concept is a
hybrid between the SWATH and Hydrofoil concepts. A single hull with
a small waterplane area and a large underwater body is fitted with
a fully-submerged foil system to provide partial lift as well as
active control (especially in roll).
This concept is intended to improve speed/powering
characteristics compared to conventional SWATH vessels as wetted
area is reduced, while keeping the positive attributes of small
waterplane area.
State-of-the-Art
There are no operational HYSWAS yet, but some prototypes show
great promise and are delineated in Table 44-10. Plans for large
vessels capable of carrying 1000 tons deadweight are being
considered as part of Japans Techno-Superliner program The
prototype TSL-F for this program is shown in Figure 44-14.
Table 44-10
HYSWAS VesselsCharacteristicsTSL-F PrototypeSea Quest
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts17.1
6.2
3.1/1.6
Unknown
2.8
38
418.2
3.7
3.0/?
4.0
0.6
12
35
Specific Attributes
HYSWAS offers a good combination of high-speed and excellent
seakeeping.
The foils act to unwet the underside of the platform and a
significant part of the strut linking the platform to the
underwater body. They also provide the means of actively
controlling the vessels motions, especially in roll.
Small wake when foilborne.
Specific Issues
HYSWAS machinery installation poses the same challenges as with
SWATH vessels; the narrow struts make the installation and access
to the machinery difficult.
Craft stability at speed is entirely dependent upon the control
of the foils, as for hydrofoil craft having fully-submerged foils.
Control at low speed is more of a challenge.
Foilborne speeds are relatively high, thus extrapolation to
large vessels would require targeting very high speeds (60+ kts)
and large propulsion plants.The vessels have relatively deep draft,
while off foils.
Figure 44-14. TSL-F HYSWAS
44.2.5Hovercrafta)Air Cushion Vehicles (ACVs)
Description
Air Cushion Vehicles are essentially hovercraft with rectangular
platforms supported by a cushion of pressurized air, the escape of
which is impeded by flexible skirts attached around the whole
periphery of the platform, as illustrated in Figure 44-15. The
pressurized air, which supports 100% of the weight of the vehicle,
is usually provided by dedicated lift fans. Propulsion is usually
provided by air propellers.
The platforms reduced contact with the water results in low
resistance at high speed.
State-of-the-Art Examples
Most air cushion vehicles being built today are for military
use, but the SRN.4 has been a very successful car ferry for more
than 28 years. This vehicle is shown in Figure 44-16. Smaller
passenger ferries are also available on the market (see Table
44-11).
Figure 44-15. Air Cushion Vehicle (ACV)
Figure 44-16. The Venerable SRN.4
Table 44-11 - Air Cushion VehiclesCharacteristicsSRN.4
Mk3AP.1-88LCAC*
Length, m
Beam, m
Draft, m
Cushion Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)56.4
23.2
0
1.5
11.3
300
65
418
6024.4
11.0
0
1.37
1.4
40.8
50
101
026.8
14.3
0
1.5
11.8
154
50
*
*
* Note the Landing Craft, Air Cushion (LCAC) is a U.S. Navy
Amphibious Assault Landing Craft.
Specific Attributes
The principal specific attribute of the ACV is its amphibious
capability which enables it to operate from a variety of unprepared
beaches and with minimal terminal facilities.
The amphibious capability also enables them to operate in
shallow waters, even over sand banks, and over marsh land or
various types of terrain inaccessible by conventional means. This,
in some instances, can significantly reduce the time in transit by
reducing the length of a route.
The air cushion allows these craft to operate efficiently at
high-speed (50+ kts) as it considerably reduces frictional
resistance.
Specific Issues
To maintain its amphibious capability, air propellers are used
for propulsion. The high cost and low efficiency of air propellers
compared to marine propulsors in this application is an issue.
There is also a high noise level generated by such propellers which
could cause problems for operating on certain routes.
Since the lift power is dictated by the overall weight of the
vehicle, lightweight (aerospace) technology is usually required,
thus making the price of ACVs high compared to other types of
advanced marine vehicles.
The inflatable skirts used to contain the cushion of pressurized
air are subject to significant wear when used at high speed and,
particularly, when operating over land. Their maintenance is,
therefore, a specific issue that must be adequately planned and
addressed by an operator.
Directional stability can be a problem.
Air-cooled engines are most often required as there is no
connection with the water.
The low length-to-beam ratio required for stability reasons
results in high hump drag, thus ACVs are suitable mostly for
high-speed operations or post-hump operations.
Long exposure to the cobblestone like motions of ACVs can
generate fatigue for their riders although they do not result as
much in sea sickness as do the lower frequency motions of a
conventional vessel.
b)ACV With Aft Skegs (ACVAS)
Description
The ACVAS is a hovercraft that is very similar to a conventional
ACV, but is fitted with skegs at the aft end of each side skirt in
order to give it a foothold in the water for (more efficient)
marine propulsion.
State-of-the-Art Examples
This concept is still in the development stage. There are no
production craft on the market, but some developmental prototypes
and designs exist. The characteristics of one of these is shown in
Table 44-12. A photo of this same craft is shown in Figure
44-17.
Table 44.12 -ACVAS VesselCharacteristicsSumidagawa
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Speed, kts
Passenger20.0
7.9
0.5
3.7
0.8
30
80
Specific Attributes
The concept has low frictional resistance due to the air
cushion, as for conventional ACVs although this is tempered by the
presence of the skegs. Compared to an ACV, the ACVAS benefits from
its foot in the water as it can be fitted with marine propellers or
waterjets for propulsion, with a far greater propulsive efficiency
than air propellers and reduced noise as a result.
Another benefit of the access to the water is the use of
water-cooled engines instead of air-cooled engines for propulsion
power.
Specific Concerns
The ACVAS looses the amphibious capability of the pure ACV
although it can still operate in shallow water, particularly, if
waterjets are used.
The concept is still at a developmental stage, but shows great
promise.
Other comments applicable to ACVs also apply here.
Figure 44-17. Sumidagawa ACVAS During Operations
c)Surface Effect Ship
Description
A Surface Effect Ship (SES) is a hovercraft that combines the
twin rigid sidehulls of a catamaran with the flexible seals of an
ACV fore and aft to contain, beneath the platform, a cushion of
pressurized air. This cushion supports typically 80% or more of the
weight of the craft and results in a significant reduction in
resistance at high speeds. A sketch of the concept is shown in
Figure 44-18.
State-of-the-Art Examples
The first SESs appeared some 35 years ago and a fairly large
number of SES passenger ferries are now in operation around the
world. The principal characteristics of three of these are shown in
Table 44-13.
The largest SES built to-date is a 70-m prototype built by
Mitsubishi and Mitsui for the Techno-Superliner program, shown in
Figure 44-19.
Plans for large cargo/container vessels up to 5000 tons of
deadweight are also being considered.
Specific Attributes
As with ACVs, the SES concept aims at reducing friction drag by
reducing the wetted surface of the hull.
Table 44.13 - SES VesselsCharacteristicsUT928HM 527TSLA-70
Length, m
Beam, m
Draft, m
Power, mW
Displacement, t
Speed, kts
Passengers38
12
2.6/1.0
5.1
150
48
35027
10
2.6/1.7
2.7
87
36
20070
19
3.5/1.1
30
Unknown
54
None*
* Prototype, designed to carry 200 t deadweight.
Like the ACVAS, the contact with the water allows the use of
marine propellers or waterjets as well as water cooled engines.
The sidehulls also provide the SES with lateral stability. This
allows higher length-to-beam configurations than ACVs which result
in a greater flexibility for operating efficiently at medium speeds
(lower hump drag).
SES are, therefore, suitable for a wide range of speeds, but
particular so for high speeds (>40 kts).
Figure 44-18. Surface Effect Ship (SES)
Figure 44-19. TSLA 70 Surface Effect Ship
Specific Issues
The added complexity and maintenance of lift fans, lift engines
and end seals is often viewed as a penalty compared to what can be
achieved with simpler catamarans, but those need to be traded
against the much higher speed/power performance offered by SES.
Although the flexible skirts used at both ends of the cushion
are much smaller than on fully skirted ACVs, their maintenance is
still an important consideration for an operator.
Very long exposure to the cobblestone like motions of an SES may
generate fatigue for the rider although they are not quite as prone
to generate seasickness as the lower frequency motions usually
encountered on conventional vessels.
44.2.6Wing-in-Ground Effect (WIG) Craft
A WIG, wingship or ekranoplan is an aircraft which takes
advantage of the fact that a wing, operating in close proximity to
the ground or water surface, will experience a reduction in
lift-induced drag. However, during one cycle of operation, a WIG
encompasses three corners of the lift pyramid. At taxi it is a
displacement vessel, at take-off and landing it is a planing craft
and then a power augmented ram wing and, finally, during cruise it
is an aircraft in ground effect, a purely aerodynamic vehicle. A
WIG may also operate at higher altitudes to circumvent traffic or
small land masses for short periods of time. The ram wing and
channel flow wing craft are hybrid vehicles which use aerodynamic
lift to achieve high speeds. It is essentially a low-aspect ratio
wing with the trailing edge virtually touching the surface and
endplates sealing the wing tips to the surface. Both the WIG and
ram wing types are described in this bulletin.
a)WIGs
Description
WIGS are generally a mix between a seaplane hull and low aspect
ratio wings which have been shown to obtain efficient speeds up to
400 kts within ground effect. When in the cruise mode, no part of
the vessel is in contact with the water as illustrated in Figure
44-20. Although the beneficial effects of ground effect on the
lift-to-drag ratio of aircraft have been observed since the Wright
Brothers, WIG specific research and development has only really
occurred within the last 30 years. Most of this research was done
in Russia and has only recently been released.
State-of-the-Art Examples
Following the opening of the iron curtain, a flood of
information about Russian ekranoplans hit the western world. This
information has shown that it is physically possible to build and
operate a large WIG such as the Caspian Sea Monster. One of the
more notable achievements in the use of ground effect was the 1929
flight of the German DoX Flying Boat across the Atlantic within
ground effect. Some commercial applications of WIGs are presently
being considered in Germany, Japan, France and the United States.
The characteristics of some examples of WIGs are shown in Table
44-14. It should be noted that, except for the Ekranoplan shown in
Figure 44-21, none of these craft have been operated
commercially.
Specific Attributes
The ability of the WIG to fully leave the surface of the water
allows it to operate in the aircraft speed regime which is, at a
minimum, twice that of the typical high-speed marine craft.
Specific Issues
There are no commercially operated WIGs. They are basically
still in the demonstration stage, although the western world has
greatly benefited from the research and development accomplished in
the former Soviet Union.
Because WIGs are very similar to aircraft, their structure and
mechanical systems are of higher complexity than the structure of a
typical marine craft.
WIGS are operationally limited by sea states and winds for
take-off and landing.
Numerous regulatory issues would need to be addressed prior to
implementation of these craft as passenger carrying vehicles.
Figure 44-20. Wing-in-Ground Effect Craft
Figure 44-21. A.90.150 Ekranoplan in Flight
Table 44-14 - WIG VehiclesCharacteristicsTAF VIII-5A.90.150
EkranoplanXTW-2
Length, m
Beam, m*
Power, mW**
Displacement, t
Speed, kts
Passengers19.8
8.5
1.2
9.2
95
1558
31.5
11.0
125
216
15018.5
12.72
0.448
3.6
100
14
(*) The beam indicated designates the wing span of the WIG.
(**) The power indicated is the cruise power only.
b)Ram and Channel Flow Wing Craft
Description
Operating Ram wing or Channel Flow wing craft are not truly
aerodynamic craft, but are supported by a combination of
hydrostatic, hydrodynamic and aerodynamic forces. These craft also
tend to by multi-hulled vessels using the cross deck structure as
the wing and the hulls to cap the wings. A ram wing operates by
creating dynamic overpressure on the bottom side of the wing to
increase the lift-to-drag ratio when at operational speed. The
channel flow wing operates similar to a WIG in that the trailing
end of the wing is open.
State-of-the-Art Examples
The theory behind ram and channel flow wing craft is not new.
Applications have included very high-speed catamarans (>100 kts)
used in offshore power boat racing. Only recently has there been
any commercial applications of these designs albeit at much lower
speeds. The particulars for two of these designs are summarized in
Table 44-15. One of these is the Quadrimaran shown in Figure
44-22.
Specific Attributes
The ability of the ram or channel wing craft to utilize both
aero and hydrodynamic lift allows them to operate in the upper end
of the speed regime.
Specific Issues
There are only a few commercially operated craft and these have
not been operating for a long period of time.
Ram and channel flow wings may be structurally and mechanically
complex when compared to typical multi-hull hullforms.
Table 44-15 - Ram Wing VesselsCharacteristicsWild
ThingQuadrimaran
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
Passengers30
11
Unknown
1.2
2.25
80
45
14925
10.4
0.4
Unknown
1.25
216
40+
150
Figure 44-22. Quadrimaran, Channel Flow Wing Craft
EMBED Word.Picture.8
EMBED Word.Picture.8
PAGE 44-2
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_1046024938.doc
_1046191452.doc
HYSWAS
SWATH
FWD
AFT
SEMI-SWATH
_1046023871.doc
ROUND BILGE
HARD CHINE
WAVE-PIERCER
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