561NR_2012-03

Hull in Aluminium Alloys, Design Principles,

Construction and Survey

March 2012

Rule Note NR 561 DT R00 E

Marine Division

92571 Neuilly sur Seine Cedex – France Tel: + 33 (0)1 55 24 70 00 – Fax: + 33 (0)1 55 24 70 25

Marine website: http://www.veristar.com Email: [email protected]

2012 Bureau Veritas - All rights reserved

ARTICLE 1

1.1. - BUREAU VERITAS is a Society the purpose of whose Marine Division (the "Society") is the classi-fication (" Classification ") of any ship or vessel or structure of any type or part of it or system therein col-lectively hereinafter referred to as a "Unit" whether linked to shore, river bed or sea bed or not, whetheroperated or located at sea or in inland waters or partly on land, including submarines, hovercrafts, drillingrigs, offshore installations of any type and of any purpose, their related and ancillary equipment, subseaor not, such as well head and pipelines, mooring legs and mooring points or otherwise as decided by theSociety.

The Society:• prepares and publishes Rules for classification, Guidance Notes and other documents (“Rules”);• issues Certificates, Attestations and Reports following its interventions (“Certificates”);• publishes Registers.

1.2. - The Society also participates in the application of National and International Regulations or Stand-ards, in particular by delegation from different Governments. Those activities are hereafter collectively re-ferred to as " Certification ".1.3. - The Society can also provide services related to Classification and Certification such as ship andcompany safety management certification; ship and port security certification, training activities; all activi-ties and duties incidental thereto such as documentation on any supporting means, software, instrumen-tation, measurements, tests and trials on board.

1.4. - The interventions mentioned in 1.1., 1.2. and 1.3. are referred to as " Services ". The party and/or itsrepresentative requesting the services is hereinafter referred to as the " Client ". The Services are pre-pared and carried out on the assumption that the Clients are aware of the International Maritimeand/or Offshore Industry (the "Industry") practices.1.5. - The Society is neither and may not be considered as an Underwriter, Broker in ship's sale or char-tering, Expert in Unit's valuation, Consulting Engineer, Controller, Naval Architect, Manufacturer, Ship-builder, Repair yard, Charterer or Shipowner who are not relieved of any of their expressed or impliedobligations by the interventions of the Society.

ARTICLE 22.1. - Classification is the appraisement given by the Society for its Client, at a certain date, following sur-veys by its Surveyors along the lines specified in Articles 3 and 4 hereafter on the level of compliance ofa Unit to its Rules or part of them. This appraisement is represented by a class entered on the Certificatesand periodically transcribed in the Society's Register.

2.2. - Certification is carried out by the Society along the same lines as set out in Articles 3 and 4 hereafterand with reference to the applicable National and International Regulations or Standards.

2.3. - It is incumbent upon the Client to maintain the condition of the Unit after surveys, to presentthe Unit for surveys and to inform the Society without delay of circumstances which may affect thegiven appraisement or cause to modify its scope.2.4. - The Client is to give to the Society all access and information necessary for the safe and efficientperformance of the requested Services. The Client is the sole responsible for the conditions of presenta-tion of the Unit for tests, trials and surveys and the conditions under which tests and trials are carried out.

ARTICLE 33.1. - The Rules, procedures and instructions of the Society take into account at the date of theirpreparation the state of currently available and proven technical knowledge of the Industry. Theyare not a standard or a code of construction neither a guide for maintenance, a safety handbookor a guide of professional practices, all of which are assumed to be known in detail and carefullyfollowed at all times by the Client.Committees consisting of personalities from the Industry contribute to the development of those docu-ments.3.2. - The Society only is qualified to apply its Rules and to interpret them. Any reference to themhas no effect unless it involves the Society's intervention.3.3. - The Services of the Society are carried out by professional Surveyors according to the applicableRules and to the Code of Ethics of the Society. Surveyors have authority to decide locally on matters re-lated to classification and certification of the Units, unless the Rules provide otherwise.

3.4. - The operations of the Society in providing its Services are exclusively conducted by way ofrandom inspections and do not in any circumstances involve monitoring or exhaustive verifica-tion.

ARTICLE 4

4.1. - The Society, acting by reference to its Rules:• reviews the construction arrangements of the Units as shown on the documents presented by the Cli-

ent;• conducts surveys at the place of their construction;• classes Units and enters their class in its Register;• surveys periodically the Units in service to note that the requirements for the maintenance of class are

met.

The Client is to inform the Society without delay of circumstances which may cause the date or theextent of the surveys to be changed.

ARTICLE 55.1. - The Society acts as a provider of services. This cannot be construed as an obligation bearingon the Society to obtain a result or as a warranty.5.2. - The certificates issued by the Society pursuant to 5.1. here above are a statement on the levelof compliance of the Unit to its Rules or to the documents of reference for the Services providedfor.In particular, the Society does not engage in any work relating to the design, building, productionor repair checks, neither in the operation of the Units or in their trade, neither in any advisory serv-ices, and cannot be held liable on those accounts. Its certificates cannot be construed as an im-plied or express warranty of safety, fitness for the purpose, seaworthiness of the Unit or of its valuefor sale, insurance or chartering.5.3. - The Society does not declare the acceptance or commissioning of a Unit, nor of its construc-tion in conformity with its design, that being the exclusive responsibility of its owner or builder,respectively.

5.4. - The Services of the Society cannot create any obligation bearing on the Society or constitute anywarranty of proper operation, beyond any representation set forth in the Rules, of any Unit, equipment ormachinery, computer software of any sort or other comparable concepts that has been subject to any sur-vey by the Society.

ARTICLE 66.1. - The Society accepts no responsibility for the use of information related to its Services which was notprovided for the purpose by the Society or with its assistance.

6.2. - If the Services of the Society cause to the Client a damage which is proved to be the directand reasonably foreseeable consequence of an error or omission of the Society, its liability to-wards the Client is limited to ten times the amount of fee paid for the Service having caused thedamage, provided however that this limit shall be subject to a minimum of eight thousand (8,000)Euro, and to a maximum which is the greater of eight hundred thousand (800,000) Euro and oneand a half times the above mentioned fee.The Society bears no liability for indirect or consequential loss such as e.g. loss of revenue, lossof profit, loss of production, loss relative to other contracts and indemnities for termination of oth-er agreements.6.3. - All claims are to be presented to the Society in writing within three months of the date when the Serv-ices were supplied or (if later) the date when the events which are relied on of were first known to the Client,and any claim which is not so presented shall be deemed waived and absolutely barred. Time is to be in-terrupted thereafter with the same periodicity.

ARTICLE 77.1. - Requests for Services are to be in writing.

7.2. - Either the Client or the Society can terminate as of right the requested Services after givingthe other party thirty days' written notice, for convenience, and without prejudice to the provisionsin Article 8 hereunder. 7.3. - The class granted to the concerned Units and the previously issued certificates remain valid until thedate of effect of the notice issued according to 7.2. here above subject to compliance with 2.3. here aboveand Article 8 hereunder.

7.4. - The contract for classification and/or certification of a Unit cannot be transferred neither assigned.

ARTICLE 88.1. - The Services of the Society, whether completed or not, involve, for the part carried out, the paymentof fee upon receipt of the invoice and the reimbursement of the expenses incurred.

8.2. Overdue amounts are increased as of right by interest in accordance with the applicable leg-islation.8.3. - The class of a Unit may be suspended in the event of non-payment of fee after a first unfruitfulnotification to pay.

ARTICLE 9

9.1. - The documents and data provided to or prepared by the Society for its Services, and the informationavailable to the Society, are treated as confidential. However:• clients have access to the data they have provided to the Society and, during the period of classifica-

tion of the Unit for them, to the classification file consisting of survey reports and certificates whichhave been prepared at any time by the Society for the classification of the Unit;

• copy of the documents made available for the classification of the Unit and of available survey reportscan be handed over to another Classification Society, where appropriate, in case of the Unit's transferof class;

• the data relative to the evolution of the Register, to the class suspension and to the survey status of theUnits, as well as general technical information related to hull and equipment damages, are passed onto IACS (International Association of Classification Societies) according to the association workingrules;

• the certificates, documents and information relative to the Units classed with the Society may bereviewed during certificating bodies audits and are disclosed upon order of the concerned governmen-tal or inter-governmental authorities or of a Court having jurisdiction.

The documents and data are subject to a file management plan.

ARTICLE 1010.1. - Any delay or shortcoming in the performance of its Services by the Society arising from an eventnot reasonably foreseeable by or beyond the control of the Society shall be deemed not to be a breach ofcontract.

ARTICLE 1111.1. - In case of diverging opinions during surveys between the Client and the Society's surveyor, the So-ciety may designate another of its surveyors at the request of the Client.

11.2. - Disagreements of a technical nature between the Client and the Society can be submitted by theSociety to the advice of its Marine Advisory Committee.

ARTICLE 1212.1. - Disputes over the Services carried out by delegation of Governments are assessed within theframework of the applicable agreements with the States, international Conventions and national rules.

12.2. - Disputes arising out of the payment of the Society's invoices by the Client are submitted to the Courtof Nanterre, France.

12.3. - Other disputes over the present General Conditions or over the Services of the Society areexclusively submitted to arbitration, by three arbitrators, in London according to the ArbitrationAct 1996 or any statutory modification or re-enactment thereof. The contract between the Societyand the Client shall be governed by English law.

ARTICLE 1313.1. - These General Conditions constitute the sole contractual obligations binding together theSociety and the Client, to the exclusion of all other representation, statements, terms, conditionswhether express or implied. They may be varied in writing by mutual agreement.13.2. - The invalidity of one or more stipulations of the present General Conditions does not affect the va-lidity of the remaining provisions.

13.3. - The definitions herein take precedence over any definitions serving the same purpose which mayappear in other documents issued by the Society.

BV Mod. Ad. ME 545 k - 17 December 2008

MARINE DIVISION

GENERAL CONDITIONS

RULE NOTE NR 561

NR 561Hull in Aluminium Alloys,

Design Principles, Construction and Survey

SECTION 1 GENERAL REQUIREMENTS

SECTION 2 MATERIALS

SECTION 3 JOINT DESIGN, WELD AND RIVETING SCANTLING

SECTION 4 CALCULATION PRINCIPLES OF HULL STRUCTURE AND SPECIAL FEATURES

SECTION 5 GLOBAL STRENGTH ANALYSIS OF HULL GIRDER AND CROSS DECK

SECTION 6 HULL LOCAL STRENGTH PRINCIPLES

SECTION 7 STRUCTURAL ARRANGEMENTS

SECTION 8 PILLARS

SECTION 9 HULL CONSTRUCTION AND SURVEY

APPENDIX 1 ALUMINIUM PROPERTIES

March 2012

Section 1 General Requirements

1 General 7

1.1 Application1.2 Exceptions1.3 Drawings and documents to be submitted1.4 Working process and inspection at works

Section 2 Materials

1 General 8

1.1 Application

2 Aluminium structure 8

2.1 Influence of welding on mechanical characteristics2.2 Extruded plating2.3 Material factor k2.4 Aluminium properties

3 Hull protection 9

3.1 Protection against corrosion

Section 3 Joint Design, Weld and Riveting Scantling

1 General 10

1.1 Application1.2 Weld and welding booklets

2 Scantling of welds 10

2.1 Butt welds2.2 Butt welds on permanent backing 2.3 Fillet welds in a lap joint2.4 Slot welds 2.5 Plug welding2.6 Fillet weld2.7 Welding between secondary and primary stiffeners2.8 Particular conditions applying to bilge keels

3 Typical joint preparation 14

3.1 Butt weld3.2 Butt weld on permanent backing3.3 Butt welds on temporary backing3.4 Fillet weld

4 Plate misalignment 15

4.1 Misalignment in butt weld4.2 Misalignment in cruciform connections

5 Riveting 15

5.1 General5.2 Choice of rivets5.3 Shape of aluminium-alloy rivets5.4 Execution of riveting

2 Bureau Veritas March 2012

6 Heterogeneous assembly steel / aluminium alloy 16

6.1 General 6.2 Riveting of members in aluminium alloy onto steel members6.3 Jointing systems other than classical riveting6.4 Transition joints by aluminium / steel cladded plates

7 Construction deformations 17

7.1 General

Section 4 Calculation Principles of Hull Structure and Special Features

1 General 18

1.1 Application

2 Calculation principles for plating 18

2.1 General2.2 Critical stresses

3 Calculation principles for secondary supporting members 19

3.1 Scantling3.2 Critical buckling stress for secondary stiffeners3.3 Checking criteria

4 Calculation principles for primary supporting members 21

4.1 Scantling4.2 Cut-outs and large openings4.3 Web stiffening arrangement for primary supporting members

5 Special features 23

5.1 Bow door and bow visor5.2 Rudders5.3 Water jet propulsion tunnel5.4 Foils and trim tab supports 5.5 Lifting appliances5.6 Strengthening for ice navigation

Section 5 Global Strength Analysis of Hull Girder and Cross Deck

1 General 25

1.1 Application

2 Longitudinal strength characteristics of hull girder - Monohull ship 25

2.1 General2.2 Strength characteristics2.3 Overall longitudinal bending stress

3 Global strength of catamaran (longitudinal and transverse) 26

3.1 General3.2 Global strength of simple deck platform catamaran3.3 Global strength of superstructure platform catamaran

March 2012 Bureau Veritas 3

Section 6 Hull Local Strength Principles

1 General 301.1 Local scantling1.2 Local load point location

2 Plating scantling 302.1 General2.2 Scantling

3 Secondary stiffener scantlings 323.1 General3.2 Span of stiffener3.3 Scantling

4 Primary stiffener scantling 334.1 General4.2 Scantling4.3 Curved primary stiffeners

5 General arrangement of brackets for secondary and primary stiffeners 345.1 General requirements5.2 Brackets for connection of perpendicular stiffeners5.3 Brackets ensuring continuity of secondary stiffeners5.4 Bracketless end stiffener connections5.5 Other type of end connections

Section 7 Structural Arrangements

1 General 37

1.1 Application

2 Bottom structure arrangements 37

2.1 General arrangement2.2 Longitudinal framing arrangement of single bottom2.3 Transverse framing arrangement of single bottom2.4 Double bottom arrangements2.5 Arrangement, scantling and connections of bilge keel

3 Side structure arrangement 39

3.1 General3.2 Stiffener arrangements3.3 Openings in the shell plating

4 Deck structure arrangements 39

4.1 General4.2 Stiffener arrangements4.3 Deck primary structure in way of launching appliances4.4 Opening arrangements4.5 Pillars arrangement under deck

5 Bulkhead structure arrangements 40

5.1 General5.2 Watertight bulkheads5.3 Non-tight bulkheads5.4 Bulkheads acting as pillars5.5 Bracketed stiffeners


6 Superstructure and deckhouse structure arrangements 41

6.1 Superstructure materials6.2 Connections of superstructures and deckhouses with the hull structure6.3 Structural arrangement of superstructures and deckhouses

7 Helicopter deck 41

7.1 General

Section 8 Pillars

1 General 42

1.1 Application

2 Critical buckling stresses 42

2.1 Buckling of pillars subjected to compression axial load

3 Pillar scantling 43

3.1 Maximum allowable axial load

Section 9 Hull Construction and Survey

1 General 45

1.1 Scope

2 Structure drawing examination 45

2.1 General

3 Hull construction 45

3.1 Shipyard details and procedures3.2 Materials3.3 Forming3.4 Welding 3.5 Non destructive examination of welds

4 Survey for unit production 48

4.1 General

5 Alternative survey scheme for production in large series 48

5.1 General5.2 Type approval5.3 Quality system documentation5.4 Manufacturing, testing and inspection plan (MTI plan)5.5 Society’s certificate

Appendix 1 Aluminium Properties

1 Mechanical properties 50

1.1 General



NR 561, Sec 1


SECTION 1 GENERAL REQUIREMENTS

1 General

1.1 Application

1.1.1 The requirements of this Rule Note are applicable toships having their hull and superstructure totally made ofaluminium alloy.

The purpose of this Rule Note is to define the generalrequirements for hull scantling, with respect to:

• material

• hull structure and welding calculation approach

• classification and /or certification process.

The requirements of this Rule Note apply in addition to theSociety Rules for the classification and/or certification ofships, in particular the requirements concerning:

• the loading cases

• the admissible stresses and/or safety coefficients.

Note 1: The Society Rules for the classification and/or certificationof ships means the Rules for the Classification and the Certificationof Yachts (NR500).

1.1.2 The scantling of superstructures built in aluminiumalloy and fitted on board a steel ship are to be checkedaccording to NR467 Rules for Steel Ships.

1.2 Exceptions

1.2.1 Ships with unusual design, speed or service, orintended to carry special cargoes not provided by the Rules,are examined on a case-by-case basis.

1.3 Drawings and documents to be submitted

1.3.1 As a rule, the drawings and documents to be submit-ted for hull structure review are listed in the Society Rulesfor the classification and/or certification of ships (see[1.1.1], Note 1).

Weld and welding booklets as requested in Sec 3, [1.2] arealso to be submitted for review.

1.3.2 Builder’s quality systems checking the general pro-duction fabrication and process are to be submitted forreview (see Sec 9).

1.4 Working process and inspection at works

1.4.1 Inspections needed by the Society during ship hullconstruction within the scope of the classification and/orcertification of ships built in unit production or in mass pro-duction are defined in Sec 9.

NR 561, Sec 2

SECTION 2 MATERIALS

Symbols

Rp0,2 : Proof stress (yield strength), in N/mm2, of theparent metal in delivery condition, as indicatedby the supplier

R’p0,2 : Proof stress (yield strength), in N/mm2, of the

parent metal in welded condition, as defined in[2.1.3] or [2.1.4]

Rm : Tensile strength, in N/mm2, of the parent metal indelivery condition, as indicated by the supplier

R’m : Tensile strength, in N/mm2, of the parent metal

in welded condition, as defined in [2.1.3] or[2.1.4]

E : Young’s modulus of aluminium, equal to70000 N/mm2

ν : Poisson ratio of aluminium, equal to 0,33.

1 General

1.1 Application

1.1.1 As a rule, the aluminium alloys used for the construc-tion of aluminium ships are as follows:

• For rolled or extruded products:

- series 5000: aluminium-magnesium alloy

- series 6000: aluminium-magnesium-silicon alloy

• For cast products:

- aluminium-magnesium alloy

- aluminium-silicon alloy

- aluminium-magnesium-silicon alloy.

In the early stages of the project, the shipyard is to submit tothe Society the characteristics of the materials they intend touse for the construction of the hull and of the structures. Inparticular, the temper of parent metal is to be indicated.

1.1.2 The characteristics of the materials to be used in theconstruction are to comply with the applicable require-ments of NR216 Rules on Materials and Welding for theClassification of Marine Units (see App 1).

Materials with different characteristics may be accepted,provided their specification (manufacture, chemical com-position, mechanical properties, welding, etc.) is submittedto the Society for approval.

1.1.3 In the case of structures subjected to low service tem-peratures or intended for other specific applications, thealloys to be employed are to be agreed by the Society.

2 Aluminium structure

2.1 Influence of welding on mechanical characteristics

2.1.1 Welding heat input lowers locally the mechanicalcharacteristics Rp0,2 and Rm of aluminium alloys hardenedby work hardening (series 5000 other than condition 0) orby heat treatment (series 6000).

2.1.2 Consequently, where necessary, a drop in themechanical characteristics of welded structures, withrespect to those of the parent material, is to be consideredfor the structure calculation in the heat-affected zone(HAZ).

As a general rule, the HAZ is to be taken extending over25 mm on each side of the weld axis.

2.1.3 Aluminium alloys of series 5000 (rolled and extruded)

Aluminium alloys of series 5000 in 0 condition (annealed)are not subject to a drop in mechanical strength in thewelded areas.

Aluminium alloys of series 5000 other than condition 0 aresubject to a drop in mechanical strength in the weldedareas. The mechanical characteristics to be considered arenormally those of condition 0.Note 1: Higher mechanical characteristics may be taken intoaccount, provided they are duly justified.

2.1.4 Aluminium alloys of series 6000Aluminium alloys of series 6000 are subject to a drop inmechanical strength in the vicinity of the welded areas.

The mechanical characteristics to be considered in thisHAZ are normally indicated by the supplier.

When no information is provided by the supplier, the valuesgiven in Tab 1 may be used.Note 1: Higher mechanical characteristics may be taken intoaccount, provided they are duly justified.

2.1.5 For welded constructions in hardened aluminiumalloys (series 5000 other than condition 0 and series 6000),higher characteristics than those in welded condition maybe considered, provided that welded connections arelocated in areas where stress levels are acceptable for thealloy considered in annealed or welded condition.

2.1.6 Young’s modulus and Poisson ratioUnless otherwise specified, the Young’s modulus and thePoisson ratio are to be taken, for aluminium alloy, respec-tively equal to 70000 N/mm2 and 0,33.


NR 561, Sec 2

Table 1 : Aluminium alloysAs welded mechanical characteristics

2.2 Extruded plating

2.2.1 Extrusions with built-in plating and stiffeners, referredto as extruded plating, may be used.

In general, the application is limited to decks, bulkheads,superstructures and deckhouses. Other uses may be consid-ered by the Society, on a case-by-case basis.

2.2.2 Extruded plating is preferably to be oriented so thatthe stiffeners are parallel to the direction of main stresses.

2.2.3 The structure continuity of plates and stiffeners is tobe ensured in way of weld end extruded panels. The endweld preparation and joints of extruded plating ends are tobe submitted for examination.

The crossing of extruded plating stiffeners with transverseprimary structure is to be submitted for examination, in par-ticular the connection of the secondary stiffeners to the pri-mary web transverse, and the connection of the primaryweb transverse to the extruded plating.

2.3 Material factor k

2.3.1 The material factor k for aluminium alloys is to beobtained from the following formula:

where:R’lim : Minimum of R’p0,2 and 0,7 R’m, in N/mm2.

2.3.2 In the case of welding of two different aluminiumalloys, the material factor k to be considered for the scant-lings is the greater material factor of the aluminium alloys ofthe assembly.

2.4 Aluminium properties

2.4.1 Mechanical properties of aluminium alloys are tocomply with the applicable requirements of NR216 Materi-als and Welding.For information, these properties are reminded in App 1.

3 Hull protection

3.1 Protection against corrosion

3.1.1 Corrosion protection of hull and superstructure is notcovered by the Classification and/or the Certification.It is incumbent upon the shipowner and the shipbuilder totake measures for the protection of materials against varioustypes of corrosion of aluminium alloy structure in marineatmosphere.

Basic following principles may be followed to ensure a cor-rosion protection:• adequate selection of alloys• structural design avoiding trap of sea water (drain hole,

wells, etc.)• control of the risks of galvanic corrosion• drying of stagnant sea-water and humidity retention

zones• regular inspection of sensible zones (batteries, heteroge-

neous assemblies, etc.)• regular maintenance of protective anodes.

As a rule, a protective coating is to be requested for alumin-ium structure built in 6000 series alloy in direct contactwith sea water, to prevent risk of uniform corrosion.

Aluminium alloyTemper

conditionR’p0,2 R’m

5000 series 0 Rp0,2 Rm

5000 series othervalues of

0 condition

6005 A(open sections)

T5 or T6 0,45 Rp0,2 0,6 Rm

6005 A(closed sections)

T5 or T6 0,50 Rp0,2 0,6 Rm

6060 (sections) (1) T5 0,43 Rp0,2 0,5 Rm

6061 (sections) T6 0,53 Rp0,2 0,6 Rm

6082 (sections) T6 0,45 Rp0,2 0,6 Rm

6106 (sections) T5 0,33 Rp0,2 0,54 Rm

(1) 6060 alloy is not to be used for structural members sus-taining dynamic loads (slamming and impact loads).The use of 6106 alloy is recommended in that case.

k 100R ′l im

-----------=


NR 561, Sec 3

SECTION 3 JOINT DESIGN, WELD AND RIVETING SCANTLING

1 General

1.1 Application

1.1.1 The requirements of this Section apply to the scant-ling and joint design of welded connections or riveting con-nections in aluminium hull structures.

Other equivalent standards may be accepted by the Society,on a case-by-case basis.

Note 1: Welding processes and inspection are dealt with in Sec 9.

1.1.2 Welding of various types of aluminium alloys is to becarried out by means of welding procedures approved forthe purpose.

1.1.3 The requirements of this Section apply also to hetero-geneous connection of aluminium alloy members with steelmembers by riveting, bi-metallic transition joints or othermeans.

1.1.4 Weld connections are to be executed according to:

• the approved hull construction plans, and

• the weld and welding booklets submitted to the Society.

Any details not specifically represented in the plans are, inany case, to comply with the applicable requirements of theSociety.

1.1.5 The method used to prepare the parts to be welded isleft to the discretion of each shipbuilder, according to itsown technology and experience.

These methods are to be reviewed during the qualificationof welding procedure, as defined in [1.2.2].

1.2 Weld and welding booklets

1.2.1 Weld booklet

A weld booklet, including the weld scantling such as throatthickness, pitch, design of joints, is to be submitted to theSociety for examination.

The weld booklet is not required if the structure drawingssubmitted to the Society contain the necessary relevant datadefining the weld scantling.

1.2.2 Welding booklet

A welding booklet including the welding procedures is tobe submitted to the Surveyor for examination (see Sec 9).

2 Scantling of welds

2.1 Butt welds

2.1.1 As a rule, butt welding is to be used for plate and stiff-ener butts and is mandatory for heavily stressed butts suchas those of the bottom, keel, side shell, sheerstrake andstrength deck plating, and bulkheads (in particular bulk-heads located in areas where vibrations occur).

2.1.2 All structural butt joints are to be full penetrationwelds completed by a backing run weld.

2.2 Butt welds on permanent backing

2.2.1 Butt weld on permanent backing may be acceptedwhere a backing run is not feasible.

In this case, the type of bevel and the gap between themembers to be assembled are to be such as to ensure aproper penetration of the weld on its backing.

2.3 Fillet welds in a lap joint

2.3.1 Fillet weld in a lap joint may be used only for mem-bers submitted to moderate stresses, taking into account thethroat thickness as defined in Fig 1 or Fig 2.

2.3.2 The width b, in mm, of overlapping is to be such that:

b ≥ 1,5 (t1 + t2) + 20.

Figure 1 : Fillet weld in lap joint

Figure 2 : Fillet weld in joggled lap joint

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NR 561, Sec 3

2.3.3 The ends are to be watertight, as far as practicable.

2.3.4 The weld closest to the shoulder may be intermittentexcept in liquid compartments and exposed areas.

2.4 Slot welds

2.4.1 Slot welding may be used where fillet welding is notpossible. The shape is shown in Fig 3 and Fig 4, dependingon the plate thickness.

Slot welds are to be, as far as practicable, parallel to thedirection of main stresses.

Figure 3 : Slot welding for t ≤ 12 mm

Figure 4 : Slot welding for t > 12 mm

2.4.2 Slot welding is not to be completely filled by theweld, and the width of the opening is to be such as to alloweasy fillet weld along its perimeter.

2.4.3 The distance L between extremities of two consecu-tive slot welds, as shown in Fig 5, is to be such that:

10 t ≤ L ≤ 200

where “t” is the plate thickness, in mm.

The maximum distance of L depends on the stresses of themembers.

Figure 5 : Distance between slot welds

2.5 Plug welding

2.5.1 Plug welding is to be used exceptionally, as a substi-tute to slot welding.

Plug welding is to be completely filled by the welding.

2.6 Fillet weld

2.6.1 Double continuous fillet weld location

As a general rule, double continuous fillet weld is to berequired in the following locations, as appropriate:

• boundaries of watertight plates

• primary and secondary stiffeners with the attached plat-ing at end connections or in way of brackets (end con-nection means the length extending over 20% of span atends)

• flange with web of built-up stiffeners at end connec-tions, in way of brackets, in way of flange knuckle andin way of rounded of face plate

• main engine and auxiliary machinery seatings

• bottom structure of high speed craft in way of jet roomspaces

• bottom structure in way of propeller blade

• structure in way of bilge keel, stabiliser, bow thruster,cranes, ...

2.6.2 Efficient length of fillet weld

The efficient length, in mm, of the lines of welding is givenby:

de = d − 20

where:

d : Actual length, in mm, of the line of welding.

2.6.3 Throat thickness of double continuous fillet weld

The minimum throat thickness tT of a double continuous fil-let weld, in mm, is to be obtained from the following for-mula:

tT = wF t

with:

tTmin ≤ tT ≤ 1,5 t

where:

wF : Welding factor for the various hull structuralconnections, defined in Tab 1

t : Actual thickness, in mm, of the thinner plate ofthe assembly

tTmin : Minimum throat thickness, in mm, taken, as arule, equal to 4 mm. This minimum value maybe taken equal to 3 mm when t is less than6 mm, provided it is covered by the weldingprocedures.

Note 1: The maximum throat thickness 1,5 t is intended only tolimit the welding energy content and to avoid the deterioration ofthe elements to weld.

The throat thickness tT may be increased for particular load-ing conditions.

In case of automatic welding with deep penetration, or incase of TIG welding, a reduction in the throat tT may beaccepted, subject to qualification of the welding procedure.

��

��

� � �

� > ��

��

��

��


NR 561, Sec 3

Table 1 : Welding factor wF for the various hull structural connections

Hull areaConnection

wF (1)of to

General,unless otherwise

specified in the Table

watertight plates boundaries 0,35

non-tight plates boundaries 0,20

strength decks side shell 0,45

webs ofordinary stiffeners

plating 0,13

plating at ends (2) 0,20

web of primary stiffener see [2.7]

web ofprimary stiffeners

plating and flange 0,20

plating and flange at ends (2) 0,30 (3)

bottom and inner bottom (in way of transversal and/or longitudinal bulkhead supported on tank top)

0,45

deck (for cantilever deck beam) 0,45

web of primary stiffeners 0,35

Structures located abaft 0,25 L from the fore end

ordinary stiffeners bottom and side shell plating 0,20

primary stiffeners bottom, inner bottom and side shell plating 0,25

Structures located in bottom slamming area or in the first third of

underside of cross deck of catamaran

ordinary stiffeners bottom plating 0,20

primary stiffeners bottom plating 0,25

Machinery space girders bottom and innerbottom plating

in way of main enginefoundations

0,45

in way of seating of auxiliary machinery

0,35

elsewhere 0,25

floors(except in way of main engine foundations)

bottom and innerbottom plating

in way of seating of auxiliary machinery

0,35

elsewhere 0,25

floors in way of main engine foundations

bottom plating 0,35

foundation plates 0,45

floors centre girder single bottom 0,45

double bottom 0,25

Superstructuresand

deckhouses

external bulkheads deck 0,35

internal bulkheads deck 0,13

ordinary stiffeners external and internal bulkhead plating 0,13

Pillars pillars deck pillars in compression 0,35

pillars in tension full penetration welding

Rudders primary element directly connected to solid parts or rudder stock

solid part or rudder stock 0,45

other webs each other 0,20

webs plating in general 0,20

top and bottom plates of rud-der plating

0,35

(1) For connections where wF ≥ 0,35, continuous fillet welding is to be adopted. See also [2.6.1].(2) Ends of ordinary stiffeners means the length extending over 20% of span at ends. Where end brackets are fitted, ends means the

area in way of brackets and at least 50 mm beyond the bracket toes. Where direct calculation are carried out, the end area is tobe considered on a case-by-case basis.

(3) Full penetration welding may be required, depending on the structural design and loads.


NR 561, Sec 3

2.6.4 Direct calculation of double continuous fillet weld

Where deemed necessary, the minimum throat thickness tT

of a double continuous fillet weld between stiffener weband associated plating and/or flange, in mm, may be deter-mined as follows:

where:

T : Shear force, in N, in the considered section ofthe stiffener

I : Inertia, in mm4, of the stiffener

τ : Admissible shear stress, in N/mm2, as defined inthe Society Rules for the classification and/orcertification of ships (see Sec 1, [1.1.1], Note 1)

tTmin : Minimum throat thickness defined in [2.6.3]

m : Value, in mm3, calculated as follows (see Fig 6):

• for weld between flange and web:

m = tf ⋅ bf ⋅ vf

• for weld between associated plate and web:

m = tp ⋅ bp ⋅ vp

Figure 6 :

2.6.5 Throat thickness of intermittent weldThe throat thickness tIT, in mm, of intermittent welds is to benot less than:

where:

tT : Throat, in mm, of the double continuous filletweld, obtained as defined in [2.6.3] or [2.6.4]

p : Pitch, in mm, of the fillet welds positioned onthe same side, measured as indicated in Tab 2

de : Efficient length, in mm, of the fillet welds, asdefined in [2.6.2]

t : Actual thickness, in mm, of the thinner plate ofthe assembly.

Table 2 : Pitch on intermittent fillet weld

2.6.6 Fillet weld in way of cut-outs

In way of cut-outs for the passage of stiffeners, the throatthickness tIT of the fillet welds located between cut-outs is tobe such that:

where:

de : Efficient length, defined in [2.6.2]

p, d : As shown in Fig 7.

Figure 7 : Fillet weld in way of cut-outs

tTT m⋅

2 I⋅ τ⋅---------------- tTmin≥ ≥

tp

tf

bf

vf

Neutralaxis

vp

tT

tT

bp

tIT tTpde

----- 1 5t,≤=

Type of intermittent fillet weldPitch

requirements

Staggered welds

d ≥ 75 mm (1)

p ≤ 3 d

Staggered welds subjected to dynamic loads

d ≥ 75 mmr ≥ 20 mm

Chain welds

d ≥ 75 mmp − d ≤ 200mm

(1) To reduce deformations, it is recommended to choosethe values of d according to the thickness.

�

�

�

�

tIT tTpde

-----≥

��

�

�


NR 561, Sec 3

2.7 Welding between secondary and primary stiffeners

2.7.1 Continuous secondary stiffenersAs a general rule, the total resistant weld section AW, incm2, connecting the secondary stiffeners to the web of pri-mary members, is to be such that:

where:

ϕ : Coefficient to be taken equal to:

• 200 when the weld is parallel to the reac-tion exerted on primary members

• 160 when the weld is perpendicular to thereaction exerted on primary members

p : Design pressure, in kN/m2, acting on the sec-ondary stiffeners, as defined in the Society Rulesfor the classification and/or certification of ships(see Sec 1, [1.1.1], Note 1)

s : Spacing of the secondary stiffeners, in m

l : Span of the secondary stiffeners, in m

k : Greater value of the material factors for the sec-ondary stiffeners and primary members, asdefined in Sec 2, [2.3].

2.8 Particular conditions applying to bilge keels

2.8.1 Connection of the bilge keel (as defined in Sec 7,[2.5.1]) to the intermediate flat is to be made by continuouswelds, with a throat not less than, or equal to, the one of thecontinuous welds connecting the intermediate flat to thebilge strake.

Butt welds of the shell plating, intermediate flat and bilgekeel are to be suitably staggered.

To avoid shell plating being damaged, butt welds of theintermediate flat are to be made on a backing.

Butt welds of the bilge keel are not to extend up to the inter-mediate flat but are to stop on a scallop. The weld is to befree from defects in way of the scallop and, where neces-sary, the defects are to be ground.

3 Typical joint preparation

3.1 Butt weld

3.1.1 Permissible root gap j between elements to bewelded is to be defined during qualification tests of weldingprocedures and indicated in the welding booklet.

For guidance purposes, no root gap may be provided forbutt welds of plates less than 6 mm thick.

3.1.2 In the case of butt welds without backing, a backweldis recommended for thicknesses greater than, or equal to,6 mm.

In the other cases, a joint preparation with bevel, root gapand root face is to be provided.

3.1.3 In case of assembly of two plates of different thick-nesses, a taper x, having a minimum slope as shown on Fig8 or Fig 9, is to be adopted where:

• t1 ≤ 10 mm and t2 − t1 ≥ 3 mm, or

• t1 > 10 mm and t2 − t1 ≥ 4 mm

Figure 8 : Tapering on one face

Figure 9 : Tapering on both faces

Note 1: For connection of platings parallel to the direction of themain stresses, a minimum taper length x, such that x > 3 b, may bepermitted.

3.2 Butt weld on permanent backing

3.2.1 Butt welding on permanent backing may be acceptedwhere back welding is not feasible or in specific casesdeemed acceptable by the Society.

3.2.2 The gap j in the bottom of the groove, in mm, is notto exceed (see Fig 10):

• for t ≤ 6: j = t

with:

α = 0o and t1 = t + 1 ≤ 6 mm

• for 6 < t ≤ 20: j = 6 mm

with:

α = 20o and t1 = 6 mm

• for t > 20: j = 10 mm

with:

α = 15o and t1 = 10 mm.

3.2.3 For extruded sections with an integrated melting bathfor backing, preparation before welding is defined duringthe qualification of welding procedures.

AW ϕpsl 1 s2l------–

⎝ ⎠⎛ ⎞ k10 3–≥

��

��

�� ≥ ��

�

�

��

� ≥ ��


NR 561, Sec 3

Figure 10 : Butt weld on permanent backing

3.3 Butt welds on temporary backing

3.3.1 Preparation before welding of the butt welds carriedout on temporary backing is to be defined during the quali-fication of welding procedures.

3.4 Fillet weld

3.4.1 ClearanceThe clearance j between elements to be welded, as definedin Fig 11, is to be as follows:

j ≤ 1 mm for t ≤ 8 mm

j ≤ 2 mm for t > 8 mm

For greater clearances, the throat thickness tT is to beincreased by half the clearance j.

Figure 11 : Clearance

Figure 12 : Clearance and preparation

Figure 13 : Clearance and preparation

3.4.2 Preparation

Where the thickness exceeds 8 mm, a preparation may berecommended, as shown in Fig 12 and Fig 13.

In any case, a root face device of 3 mm minimum is to beprovided.

4 Plate misalignment

4.1 Misalignment in butt weld

4.1.1 The misalignment between plates of equal thicknessis to be less than 10% of the plate thickness, without beinggreater than 3 mm.

4.2 Misalignment in cruciform connections

4.2.1 In the case of cruciform joint, as shown in Fig 14,misalignment “m” is to be such that:

m ≤ t / 2

where:

t = Max (t1 , t2)

The maximum allowable misalignment “m” may berequired smaller in case of highly stressed cruciform joints.

5 Riveting

5.1 General

5.1.1 This Article defines the conditions of riveting of hullsand structures made of aluminium alloy.

Riveting strength data sheets are to be submitted to the Soci-ety. Additional sample tests of riveted joints representativeof the hull construction may be required, if deemed neces-sary. As a general rule, the samples are tested under tensile,compressive and shear forces (see also NR216 Materialsand welding, Ch 3, Sec 2, [3]).

�

α

��

��

�

α

� �

� � �

�

≥ �

� � �

�

≥ �


NR 561, Sec 3

Figure 14 : Cruciform connection

5.2 Choice of rivets

5.2.1 For the riveting of series 5000 aluminium-magnesiumalloys, the grade of the rivet is to have magnesium contentnot exceeding 3,5%.

5.3 Shape of aluminium-alloy rivets

5.3.1 Diameters of rivets (versus the thickness of the thinnermember to be riveted), diameters of hole perforations, man-ufacturing tolerances and shape of the heads of rivets aregiven in Tab 3, Fig 15 and Fig 16.

Slight departure from the above dimensions may beaccepted, to the satisfaction of the Surveyor.

5.3.2 For riveting of massive parts and accessories, the holediameter may be increased by 2 mm.

5.4 Execution of riveting

5.4.1 The rivet holes are to be spaced regularly with a verylow tolerance (0,1 to 0,2 mm). Holes are to be drilled.

5.4.2 The number of rows of rivets and the pitch betweenrivets depend on the relative strength required for the joint.

The pitch is to be such that:

2,5 d ≤ pitch ≤ 6 d, where d is the rivet diameter.

For riveting with several rows, the row spacing is to be, as arule, equal to:

• the pitch for chain-riveting, and

• 0,75 time the pitch for staggered riveting.

5.4.3 Cold-riveting may be performed with well annealedrivets up to 14 mm in diameter for grade 5052 rivets. Forlarger diameters, hot-riveting is to be used (at400oC ± 25oC). In some special cases, large diameterAlSiMg rivets may be used directly after hardening.

The holding dolly is to be heavier than that used for a steelrivet of the same diameter.

6 Heterogeneous assembly steel / aluminium alloy

6.1 General

6.1.1 This Article defines the conditions for heterogeneousassembly for hulls and structures made of aluminium alloysand steel.

Figure 15 : Manufactured heads

t1

m

t2

��

�

�

��

�

�

��

�

��

�� ≤ �� ≥ ��

��

≤ ��

��

≥ ��

�

��

α

α � �� ≥ ��α � �� α � �� ≤ ��

��

≤ ��

��

≥ ��

�� ≤ �� ≥ ��


NR 561, Sec 3

Figure 16 : Riveted heads

6.2 Riveting of members in aluminium alloy onto steel members

6.2.1 Correct insulation between steel and aluminium is tobe ensured by means of joints, washers and plastic or rub-ber tubes, or any other equivalent solution.

6.2.2 As far as practicable, the rivet is to be of the samecomposition as the aluminium alloy used for the structure.

6.2.3 Requirements of [5.3] apply. Diameters of rivets aregiven in Tab 3 according to the thickness of the member inaluminium alloy.

6.2.4 Requirements of [5.4] apply otherwise.

6.3 Jointing systems other than classical riveting

6.3.1 Any jointing system other than classical riveting (highperformance fixation, etc.) may be used with the Society'sagreement.

6.4 Transition joints by aluminium / steel cladded plates

6.4.1 The use of transition joints made of aluminium / steelcladded plates or profiles may be considered with the Soci-ety's agreement.

6.4.2 Transition joints are to be type-approved (see NR480Approval of the Manufacturing Process of Metallic Materi-als, Sec 8).

7 Construction deformations

7.1 General

7.1.1 Shrinkage heats to reduce hull construction deforma-tion are not advisable for 5000 series alloy with metallurgi-cal temper other than O-H111 and for 6000 series alloy.

Table 3 : Rivets in aluminium alloy

��

��

��

�

�

��

��

�

��

��

�

��

�

��

��

�

��

Diameter of the rivets, in mm Reaming of rivet holes, in mm Thickness of plates and sections, in mm

Radius r,in mmNominal value d Minimum value Maximum value Minimum value Maximum value

4 3,9 4,0 4,1 4,2 from 1,5 to 2,0 0,2

5 4,9 5,0 5,1 5,2 from 2,0 to 2,5 0,2

6 5,9 6,0 6,1 6,2 from 2,5 to 3,0 0,3

8 7,8 8,0 8,1 8,2 from 3,0 to 4,0 0,4

10 9,8 10,0 10,1 10,2 from 4,0 to 6,0 0,4

12 11,8 12,0 12,1 12,2 from 5,0 to 8,0 0,5

14 (1) 13,8 14,0 14,1 14,2 from 6,0 to 10,0 0,6

16 15,8 16,0 16,1 16,2 from 7,0 to 12,0 0,05 d

18 17,8 18,0 18,1 18,2 from 9,0 to 14,0 0,05 d

20 19,8 20,0 20,2 20,3 from 10,0 to 15,0 0,05 d

22 21,8 22,0 22,2 22,3 from 11,0 to 16,0 0,05 d

24 23,8 24,0 24,2 24,3 from 12,0 to 17,0 0,05 d

(1) Maximal diameter of rivet recommended for cold use.Note 1: A manufactured head may be associated with different types of riveted heads.Type C rivets of diameter 10 mm or more may have flat points.


NR 561, Sec 4

SECTION 4 CALCULATION PRINCIPLES OF HULL STRUCTURE

AND SPECIAL FEATURES

Symbols

E : Young modulus of aluminium, as defined in Sec 2

ν : Poisson’s coefficient, as defined in Sec 2

Rp0,2 : Proof stress (yield strength) of the parent metalin delivery condition, in N/mm2, as defined inSec 2, Symbols

R’p0,2 : Proof stress (yield strength) of the parent metalin welded condition, in N/mm2, as defined inSec 2, Symbols

hw : Height of the web, in mm. For bulb sections, theheight is to be measured without the bulb

tw : Thickness of the web, in mm

bf : Breath of the flange or the bulb, in mm

tf : Thickness of the flange or the bulb, in mm.

1 General

1.1 Application

1.1.1 Hull structural members are to be examined underthe effect of global hull girder loads (forces and momentswhich result from effects of local loads acting on the ship asa whole and considered as a beam), and the effect of localloads (pressure and forces directly applied to the individualstructural members).

1.1.2 The purpose of the present Section is to define thecalculation principles of structural members and the specialfeatures.

The global hull girder scantling and the local hull scantlingare defined in Sec 5 and Sec 6, respectively.

The special feature arrangements are defined in Article [5].

1.1.3 Definitions

The requirements of the present Section are provided forlongitudinal and transverse framing systems, according tothe following definitions:

• secondary supporting members: members straight sup-porting plates

• primary supporting members: members supporting sec-ondary members.

Note 1: Other types of framing systems are to be examined on acase-by-case basis by the Society.

2 Calculation principles for plating

2.1 General

2.1.1 The thickness of plating is to be such as to satisfy therequired strength under the local loads and under the hullgirder loads.

The scantlings under local loads are to be determined asdefined in Sec 6.

The scantlings under global hull girder loads are to bedefined such as to satisfy:

• the overall longitudinal bending stress check as definedin Sec 5, and

• the buckling check as defined in the present Article anddepending on the type of hull global stresses acting onthe plate panel considered (in-plane compression stressacting on one or two sides and/or shear stress).

2.1.2 Plate buckling analysis

The three following cases, corresponding, as a general rule,to the loading induced by global loads on hull girder andcross deck of catamaran (see Sec 5), may be considered:

• panel submitted to compression/bending stress

• panel submitted to shear stress

• panel submitted to compression stresses on its twosides.

Note 1: For buckling analysis, plate panels are considered as beingsimply supported. For specific designs, other boundary conditionsmay be considered at the Society’s discretion, provided that thenecessary informations are submitted for review.

Note 2: The sign convention for normal stresses are positive for ten-sion and negative for compression.

2.1.3 The plate panels to be checked under buckling crite-ria are mainly:

• Under compression due to global hull bending:

- bottom and/or deck plating

- side shell plating, in the upper area below strengthdeck

- side shell plating, in the lower area above bottom


NR 561, Sec 4

• Under compression due to transverse global bending ofcatamaran induced by torsion:

- bottom and deck plating of cross deck of catama-rans, in way of transverse primary beams and bulk-heads

• Under shear:

- side shell plating

- primary transverse structure bulkheads of cross deckof catamarans.

2.1.4 Buckling check criteria

The safety factors, equal to the ratio between the criticalstresses calculated in [2.2] and the actual stress induced bythe effect of global loads on hull girder and cross deck ofcatamaran, are to be not less than the minimum safety fac-tors defined in the Society Rules for the classification and/orcertification of ships (see Sec 1, [1.1.1], Note 1).

2.2 Critical stresses

2.2.1 The critical buckling stresses of panel submitted tocompression/bending stress and to shear stress is to beobtained as defined the Society Rules for the classificationand or certification of ships.

3 Calculation principles for secondary supporting members

3.1 Scantling

3.1.1 The section modulus and the shear area of secondarysupporting members are to be defined taking into accountthe local loads and, when the stiffener is submitted to over-all longitudinal bending and/or to global strength of cata-maran, the hull girder loads.

The scantling under local loads is to be as defined in Sec 6.

The scantling under hull girder loads is to be defined:

• in order to ensure an inertia and section moduli of thehull girder transverse section as defined in Sec 5, and

• such as to satisfy:

- the actual overall longitudinal bending stress asdefined in Sec 5, and

- the buckling check as defined in the present Articlein relation to the overall longitudinal (or transversal,for catamaran) bending stresses.

3.1.2 Recommended dimensions

As a rule, the dimensions of secondary supporting membersare to fulfil the following conditions:

• for flat bar:

• for T-sections and angles:

3.1.3 Geometric properties

a) Geometric properties

The geometric properties of secondary supporting mem-bers (Inertia, modulus and shear section) are to be cal-culated by direct approach.

b) Attached plating for local load analysis

The width bp of the attached plating, to be consideredfor the calculation of the secondary stiffener geometricproperties, is to be taken, in m, equal to:

• where the plating extends on both sides of the sec-ondary stiffener:

bp = s

• where the plating extends on one side of the secondarystiffener (i.e. secondary stiffener bounding an opening):

bp = 0,5 s

with:

s : Spacing, in m, of secondary stiffeners.

c) Attached plating for buckling analysis

The width be of the attached plating, to be consideredfor the calculation of the secondary stiffener geometricproperties, is to be taken, in m, equal to:

• where no local buckling occurs on the attached plat-ing:

be = s

• where local buckling occurs on the attached plating:

to be taken not greater than s

with:

s : Spacing, in m, of secondary stiffeners

σA : Global hull girder compression stress σX orσY, in N/mm2, acting on the plate panel,defined in Sec 5, according to the directionx or y considered.

hw

tw

------ 15 k≤

hw

tw

------ 33 k≤

bf

tf

---- 21 k ≤

bftfhwtw

6-----------≥

be2 25,

βe

----------- 1 25,βe

2-----------–

⎝ ⎠⎛ ⎞ s=

βestp

--- σA

E------103=


NR 561, Sec 4

3.2 Critical buckling stress for secondary stiffeners

3.2.1 General

The critical buckling stress is to be obtained, in N/mm2,from the following formulae:

where:

σE = min (σE1, σE2, σE3)

σE1 : Euler column buckling stress, in N/mm2, givenin [3.2.2]

σE2 : Euler torsional buckling stress, in N/mm2, givenin [3.2.3]

σE3 : Euler web buckling stress, in N/mm2, given in[3.2.4].

3.2.2 Euler column buckling of axially loaded stiffeners

The Euler column buckling stress is obtained, in N/mm2,from the following formula:

3.2.3 Euler torsional buckling of axially loaded stiffeners

The Euler torsional buckling stresses is obtained, in N/mm2,from the following formula:

where:

Iw : Sectorial moment of inertia, in cm6, of the stiff-ener about its connection to the attached plating:

• for flat bars:

• for T-sections:

• for angles and bulb sections:

Ip : Polar moment of inertia, in cm4, of the stiffenerabout its connection to the attached plating:

• for flat bars:

• for stiffeners with face plate:

It : St. Venant’s moment of inertia, in cm4, of thestiffener without attached plating:

• for flat bars:

• for stiffeners with face plate:

m : Number of half waves, to be taken equal to theinteger number such that (see also Tab 1):

KC :

C0 : Spring stiffness of the attached plating:

Table 1 : Number m of half wavesfor torsional buckling of axially loaded stiffeners

3.2.4 Euler web buckling of axially loaded stiffeners

The Euler buckling stress σE3 of the stiffener web is obtained,in N/mm2, from the following formulae:

• for flat bars:

• for T-sections, angles and bulb sections:

3.3 Checking criteria

3.3.1 The critical buckling stress σc , as defined in [3.2.1]of the secondary stiffener are to comply with the followingformula:

σc ≥ σ ⋅ SF

where:

σ : Actual compression stress in the stiffener, inN/mm2, induced by the overall longitudinalbending and/or by the global strength of cata-maran as defined in Sec 5

SF : Safety factor as defined in the Society Rules forthe classification and/or certification of ships(see Sec 1, [1.1.1], Note 1).

σc σE= for σER'p0 2,

2------------≤

σc R'p0 2, 1R'p 0 2,

4σE

------------–⎝ ⎠⎛ ⎞= for σE

R'p0 2,

2------------>

σE1 π2EIe

Ael2

-----------10 4–=

σE2π2 EIw

104 Ipl2

------------------KC

m2------- m2+

⎝ ⎠⎛ ⎞ 0 385, E

It

Ip

---+=

Iwhw

3 tw3

36------------10 6–=

Iwtfbf

3hw2

12----------------10 6–=

Iwbf

3hw2

12 bf hw+( )2------------------------------- [tfbf

2 2bfhw 4hw2+ +=

+ 3twbfhw] 10 6–

Iphw

3 tw

3-----------10 4–=

KC 0 < KC < 4 4 ≤ KC < 36 36 ≤ KC < 144

m 1 2 3

Iphw

3 tw

3----------- hw

2 bftf+⎝ ⎠⎛ ⎞ 10 4–=

Ithwtw

3

3-----------10 4–=

It13--- hwtw

3 bftf3 1 0 63,

tf

bf

----–⎝ ⎠⎛ ⎞+ 10 4–=

m2 m 1–( )2 KC≤ m2 m 1+( )2<

KCC0l

4

π4EIw

--------------106=

C0Etp

3

2 73, s--------------10 3–=

σE3 55tW

hW

-------⎝ ⎠⎛ ⎞

2

104=

σE3 27tW

hW

-------⎝ ⎠⎛ ⎞

2

104=


NR 561, Sec 4

4 Calculation principles for primary supporting members

4.1 Scantling

4.1.1 The section modulus and the shear area of primarysupporting members are to be defined by the sameapproach than for the secondary supporting membersdefined in Article [3], taking into account the requirementsof the present Article.

4.1.2 Geometric properties for local load analysis

The geometric properties of primary supporting membersare to be calculated by direct approach, taking into consid-eration item a) and/or item b):

a) Web of primary member directly welded on theattached plating:

The width bP of the attached plating to be considered forthe yielding check of primary supporting members ana-lysed through beam structural models is to be taken, inm, equal to:

• where the plating extends on both sides of the pri-mary supporting member:

bP = min (s; 0,2l)

• where the plating extends on one side of the primarysupporting member (i.e. primary supporting memberbounding an opening):

bP = min (0,5 s; 0,1l)

b) Web of primary member not directly welded on theattached plating (floating frame):

The attached plating is normally to be disregarded forthe calculation of the primary supporting member geo-metric properties.

4.2 Cut-outs and large openings

4.2.1 General

Cut-outs and large openings in primary supporting memberwebs may be taken into account as defined in the present[4.2], when deemed necessary.

4.2.2 Cut-outs in web

The web shear area of primary supporting members is totake into account the section reduction due to cut-outs pro-vided for secondary stiffeners, if relevant.

Cut-outs for the passage of secondary stiffeners are to be assmall as possible and well rounded with smooth edges.

In general, the height of cut-outs is to be not greater than50% of the height of the primary supporting member.

4.2.3 Location of cut-outs in web

As a general rule, where openings such as lightening holesor duct routing for pipes, electrical cables, ..., are cut in pri-mary supporting members, they are to be equidistant fromthe face plate and the attached plate. As a rule, their heightis not to be greater than 20% of the primary supportingmember web height.

The length of openings is to be not greater than:

• at the end of primary member span: 25% of the distancebetween adjacent openings

• elsewhere: the distance between adjacent openings.

Openings may not be fitted in way of toes of end brackets.

4.2.4 Large openings

In case of large openings as shown in Fig 1, the secondarystresses in primary supporting members are to be consid-ered for the reinforcement of the openings, where deemednecessary.

The secondary stresses may be calculated in accordancewith the following procedure.

Figure 1 : Large openings inprimary supporting members - Secondary stresses

Members (1) and (2) are subjected to the following forces,moments and stresses:

MA

MMBQA

Q QB

R/2

1

2 BA

R

2

1

d

FK2 QT

- F

K1 QT

m2

m1

FMA MB+

2d----------------------=

m1MA MB–

2--------------------- K1=

m2MA MB–

2--------------------- K2=


NR 561, Sec 4

where:

MA, MB : Bending moments, in kN.m, in sections A and Bof the primary supporting member

m1, m2 : Bending moments, in kN.m, in (1) and (2)

d : Distance, in m, between the neutral axes of (1)and (2)

σF1, σF2 : Axial stresses, in N/mm2, in (1) and (2)

σm1, σm2 : Bending stresses, in N/mm2, in (1) and (2)

QT : Shear force, in kN, equal to QA or QB, which-ever is greater

τ1, τ2 : Shear stresses, in N/mm2, in (1) and (2)

w1, w2 : Net section moduli, in cm3, of (1) and (2)

S1, S2 : Net sectional areas, in cm2, of (1) and (2)

Sw1, Sw2 : Net sectional areas, in cm2, of webs in (1) and(2)

I1, I2 : Net moments of inertia, in cm4, of (1) and (2)with attached plating

The combined stress σC calculated at the ends of members(1) and (2) is to be obtained from the following formula:

The combined stress σC is to comply with the checking cri-teria defined in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).Where these checking criteria are not complied with, thecut-out is to be reinforced by:

• continuous face plate (see Fig 2), or

• straight face plate (see Fig 3), or

• compensation of the opening by increase of the webthickness t1(see Fig 4).

Other arrangements may be accepted provided they aresupported by direct calculations submitted to the Society forreview.

Figure 2 : Stiffening of large openingsin primary supporting members - Solution 1



Inserted plate

4.3 Web stiffening arrangement for primary supporting members

4.3.1 Webs of primary supporting members are generallyto be stiffened where the height, in mm, is greater than 30 t,(t being the web thickness, in mm, of the primary support-ing member), by web stiffeners spaced not more than 75 t.

Where deemed necessary, tripping brackets are to be fitted:

• at the toe of end brackets

• in way of concentrated loads, and

• in way of flange knuckle

with a maximum spacing not greater than four secondarystiffener spacings.

σF1 10FS1

-----=

σF2 10 FS2

-----=

σm1m1

w1

-------103=

σm2m2

w2

-------103=

τ1 10K1QT

Sw1

-------------=

τ2 10K2QT

Sw2

-------------=

K1I1

I1 I2+--------------=

K2I2

I1 I2+--------------=

σC σF σm+( )2 3τ2+=

0,5 H1,5 H

H

t1 t

H

H


NR 561, Sec 4

4.3.2 The section modulus of web stiffeners of non-water-tight primary supporting members is to be not less than thevalue obtained, in cm3, from the following formula:

w = 2,5 s2 t

where:

s : Length, in m, of the web stiffeners supportingthe primary member

t : Web thickness, in mm, of the web stiffenerssupporting the primary member.

4.3.3 As a general rule, tripping brackets welded to the faceplate (see Fig 5), to avoid its buckling, are generally to bespaced not more than 2 m and fitted:

• at rounded and knuckle face plates

• at the toe of end brackets

• in way of cross ties

• in way of concentrated loads

• every fourth spacing of secondary stiffeners.

Where the width of the symmetrical face plate is greaterthan 200 mm, backing brackets are to be fitted in way of thetripping brackets.

Figure 5 : Primary tripping bracket

4.3.4 The arm length d of the tripping brackets, in m, is tobe not less than the greater of the following values:

where:

b : Height, in m, of the tripping brackets, as shownin Fig 5

st : Spacing, in m, of the tripping brackets

t : Thickness, in mm, of the tripping brackets.

4.3.5 Tripping brackets with a thickness, in mm, less than22 times the length, in m, of the free edge of the bracket areto be flanged or stiffened by a welded face plate.

The sectional area, in cm2, of the flanged edge or the faceplate is to be not less than 10 times the length, in m, of thefree edge of the bracket.

5 Special features

5.1 Bow door and bow visor

5.1.1 Plate and secondary stiffenersThe scantlings of plates and secondary stiffeners of bowdoor and bow visor are to be not less than the scantlings ofplates and secondary stiffeners of the fore part of the hullobtained according to the Society Rules for the classifica-tion and/or certification of ships (see Sec 1, [1.1.1], Note 1).

5.1.2 Primary supporting members, securing and supporting devices

Primary supporting members and securing and supportingdevices scantlings are to be determined as defined in Pt B,Ch 9, Sec 5 of NR467 Rules for Steel Ships.

The allowable stresses, in N/mm2, to be taken into accountto check these elements are as follows:

• allowable normal stress:

σALL = 50 / k

• allowable shear stress:

τALL = 35 / k

• allowable equivalent stress:

σVM, ALL = 65 / k

• allowable nominal pressure:

σB, ALL = 0,8 R’p0,2

where:

k : Material factor, as defined in Sec 2, [2.3].

5.1.3 Attention is drawn to the additional statutory regula-tions that may be requested by the Flag Authorities.

5.2 Rudders

5.2.1 Rudder blade and rudder stock scantling are to bechecked case by case by the Society, on the basis of NR467,Rules for Steel Ships, Pt B, Ch 10, Sec 1.

The material factors k and k1 considered in the scantling for-mulae of NR467 are to be taken equal to the followingvalue:

5.3 Water jet propulsion tunnel

5.3.1 The drawings of water jet duct, ship supporting struc-ture, thrust bearing, as well as shell openings and local rein-forcements are to be submitted for examination.

The pressure in water jet ducts, the forces and momentsinduced by the water jet to the ship structure and the calcu-lation procedure from the designer are to be specified.

In no case the scantlings are to be taken less than therequirements for:

• the surrounding hull structure defined in the presentRule Note

• the requirements defined in NR396 Rules for the Classi-fication of High Speed Craft, Ch 3, C3.9.2.

b

d

d 0 38b,=

d 0 85b st

t---,=

k k1235R ′

p0 2,

------------= =


NR 561, Sec 4

5.4 Foils and trim tab supports

5.4.1 Foils and trim tab supports are not covered within thescope of classification and/or certification.

Forces and moments induced by these elements, as well asthe designer calculation, are to be submitted for the exami-nation of the surrounding ship structure reinforcements.

As a general rule, attachment structure of foils to the shipstructure are to be located within watertight compartmentor equivalent.

5.5 Lifting appliances

5.5.1 As a rule, the welded fixed parts of lifting appliancesfitted into the hull and their local reinforcements are con-sidered as integral part of the hull and are to be checked.

The forces and moments transmitted by the crane to theship structure are to be submitted to the Society.

For crane having a safe working load F less than 50 kN, andwhen the deadweights of the crane are unknown, the bend-ing moment M, in kN⋅m, induced by the crane pedestal tothe hull is to be taken equal to:

M = 2,2 F x0

where:x0 : Maximum jib radius of the crane, in m.Cranes having a safe working load greater than 50 kN are tobe examined on a case-by-case basis.

Local reinforcements and hull structure surrounding thecrane pedestal are to be checked by direct calculations, tak-ing into account the permissible stresses defined for localstructure scantling in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).

When inserted plates are provided in deck, side shell orbulkheads in way of crane foundation, these inserts are tohave well radiused corners and are to be edge-preparedprior to welding.

5.6 Strengthening for ice navigation

5.6.1 When requested by the Owner, an additional iceclass notation may be assigned according to NR467, Rulesfor Steel Ships, Pt A, Ch 1, Sec 2, [6.10].Hull strengthening required for the assignment of this addi-tional class notation is defined in NR467, Rules for SteelShips, Pt E, Ch 8. The minimum yield stress of the material,ReH, considered in scantling formulae of NR467 Rules is tobe taken, for aluminium, equal to the proof stress in thewelded condition R’

p0,2.


NR 561, Sec 5

SECTION 5 GLOBAL STRENGTH ANALYSIS OF HULL

GIRDER AND CROSS DECK

1 General

1.1 Application

1.1.1 Global hull longitudinal girder strength

As a rule, for monohull ships and for floats of catamarans,the global hull girder longitudinal strength is to be exam-ined as defined in [2] in the following cases:

• ships with length greater than 40 m, or

• ships having large openings in decks or significant geo-metrical structure discontinuity at bottom or deck, or

• ships with transverse framing systems, or

• ships with deck structure made of small plate thick-nesses and large spacing of secondary stiffeners, or

• ships with important deadweight, or

• where deemed appropriate by the Society.

Note 1: For ships not covered by the above cases, the hull girderstrength is considered satisfied when local scantlings are in accord-ance with requirements defined in Sec 6.

1.1.2 Global transverse strength of catamaran

As a rule, the global transverse strength of catamaran is tobe examined as defined in [3] for all types of catamaran.

1.1.3 Finite element calculation

The global strength analysis may also be examined with aFinite Elements Analysis submitted by the designer. In thiscase, and where large openings are provided in side shelland/or in transverse cross bulkhead of catamaran, a specialattention is to be paid to ensure a realistic modelling of thebending and shear strength of the window jambs betweenwindows.

2 Longitudinal strength characteristics of hull girder - Monohull ship

2.1 General

2.1.1 The calculation of the hull girder strength characteris-tics is to be carried out taking into account all the longitudi-nal continuous structural elements of the hull.

A superstructure extending over at least 0,4 L may generallybe considered as contributing to the longitudinal strength.

The transverse sectional areas of openings such as deckhatches, side shell ports, side shell and superstructure doorsand windows, in the members contributing to the longitudi-nal hull girder strength, are to be deduced from the consid-ered transverse section.

Lightening holes, draining holes and single scallops in lon-gitudinal stiffeners need not be deduced if their height isless than 0,25 hW without being greater than 75 mm, wherehW is the web height, in mm, of the considered longitudinal.

2.2 Strength characteristics

2.2.1 Section modulusThe section modulus in any point of a transverse sectionalong the hull girder is given, in m3, by the following for-mula:

where:IY : Moment of inertia, in m4 of the transverse sec-

tion considered, calculated taking into accountall the continuous structural elements of thehull contributing to the longitudinal strength asdefined in [2.1], with respect to the horizontalneutral axis

z : Z co-ordinate, in m, of the considered point inthe transverse section above the base line

N : Z co-ordinate, in m, of the centre of gravity ofthe transverse section, above the base line.

2.2.2 Section moduli at bottom and deckThe section moduli at bottom and at deck are given, in m3,by the following formulae:• at bottom:

• at deck:

where:IY , N : Defined in [2.2.1]VD : Vertical distance, in m, equal to:

VD = zD − N

zD : z co-ordinate, in m, of the deck,above the base line.

2.3 Overall longitudinal bending stress

2.3.1 The overall longitudinal bending stress in any point ofa transverse section, in N/mm2, is obtained by the followingformula:

ZAIY

z N–----------------=

ZABIY

N----=

ZABIY

VD

------=

σAMV

ZA

-------=


NR 561, Sec 5

where:

MV : Vertical overall bending moment of combina-tion global loads, in kN⋅m, calculated as indi-cated in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1],Note 1)

ZA : Section modulus, in m3, calculated according to[2.2.1].

2.3.2 Stress checkThe overall longitudinal bending stress calculated accord-ing to [2.3.1] is to be in accordance with the permissibleglobal stress and the safety factor for buckling as defined inthe Society Rules for the classification and/or certification ofships (see Sec 1, [1.1.1], Note 1).Note 1: The safety factor for buckling is the ratio between the criti-cal stress, determined as defined in Sec 4, [2.2] for plate and in Sec4, [3.2] for stiffeners, and the actual overall longitudinal bendingstress calculated as defined in [2.3].

3 Global strength of catamaran (longitudinal and transverse)

3.1 General

3.1.1 Type of calculation approach for catamaranThe global strength of catamaran is to be examined:

• according to [2]: The moment of inertia IY is to be calcu-lated for only one float. A platform between floatsextending over at least 0,4 L is to be considered for thecalculation of IY, with the area bR and bWD as defined inFig 3

and, for torsion strength check:

• according to [3.2] (simple deck platform), for catamaranhaving platform structure connecting the two floatsmade by transverse primary members only, or

• according to [3.3] (superstructure platform), for catama-ran having platform structure connecting the two floatsmade by a superstructure and main transverse bulkheads.

The global strength of multihulls having more than twofloats are to be examined on a case-by-case basis.

3.2 Global strength of simple deck platform catamaran

3.2.1 GeneralThe global strength of simple deck beam given in [3.2.2] to[3.2.3] may be considered for ships having:

• a platform made by simple deck with transverse stiffen-ers, and

• a shear rigidity of the transverse stiffeners negligible inrelation to its bending rigidity, and

• deck beams extending over the breadth of each float.

3.2.2 Deck beam analysisThe reaction force Fi , in N, in way of each deck beam i, andthe corresponding bending moment Mi , in N⋅m, are to becalculated as follows (see Fig 1):

Fi = ω ⋅ ri ⋅ di

Mi = Fi ⋅ li / 2

where:

ω : Rotation angle, in rad, of one hull in relation tothe other, around a transverse axis passingthrough G, equal to:

Mtt : Torsional moment, in kN⋅m, as defined in theSociety Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1)

ri : Stiffness of each deck beam i, in N/m, equal to:

di : Abscissa, in m, of the deck beam i with respectto G:

di = xi − a

li : Span of deck beam i, in m, between the innerfaces of the hulls

Ii : Bending inertia of deck beam i, in cm4

Ei : Young’s modulus of deck beam i, in N/mm2

xi : Abscissa, in m, of deck beam i with respect toorigin O

a : Abscissa, in m, of the centre of gravity G withrespect to the origin O

3.2.3 Checking criteria

For each beam i, the shear and bending stresses, calculatedtaking into account the reaction force Fi and the bendingmoment Mi defined in [3.2.2], are to be in compliance withthe criteria defined in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).

When deemed necessary, a buckling check of the platformplate under compression stresses induced by the bending ofthe deck beams may be carried out in accordance with Sec 4,[2].

3.3 Global strength of superstructure platform catamaran

3.3.1 General

The global strength analysis of superstructure platform maybe carried out by a beam model as shown on Fig 2, takinginto account the bending and shear stiffnesses of the differ-ent primary transverse bulkheads (and main beams) and ofone float.

The transverses main beams are fixed in way of the innerside shell of the other float.

Any other justified global analysis may be considered.

ωMtt

ridi2

∑------------------=

ri12EiIi

l3

i

--------------10 2–=

arixi∑

ri∑---------------=


NR 561, Sec 5

Figure 1 : Transverse strength of catamaran

Figure 2 : Cross deck of catamarans - Model principle

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NR 561, Sec 5

3.3.2 Main transverse cross deck modelEach resisting transverse member between floats is consid-ered as a beam in the global model, taking into account:• its bending inertia about an horizontal axis (depending

mainly on the web height of the transverse cross beamor bulkhead, the roof deck thickness and the thicknessof the underside of the cross deck)

• its vertical shear inertia (depending on the web height ofthe transverse cross beams or bulkheads and their thick-ness)

• its span between inner side shell of floats.

3.3.3 Float modelThe float is modelled as a beam having, as far as possible:• vertical and horizontal bending inertiae, and• a shear inertia, and• a torsional inertia about longitudinal float axis,

close to the actual float values.

The transverse sections of the float to be considered are totake into account all the longitudinal continuous members(plates and longitudinal stiffeners) in the areas bR and bWD

(see Fig 3) defined as follows:bR : Breadth equal to 10% of the roof longitudinal

lengthbWD : Breadth equal to 10% of the cross deck longitu-

dinal length.

Figure 3 : Hull girder strengthAreas to be taken into account for

continuous members (plates and stiffeners)

3.3.4 Wave model loadingThe torsional moment exerted on the cross deck andinduced by encountered waves in quarteing sea may berepresented by two vertical forces F, equal in magnitudeand opposite in direction, as shown in Fig 2.

The magnitude of the force F, in kN, is to be taken equal to:

F = MWT / LWL

where:MWT : Torsional moment, in kN⋅m, as defined in the

Society Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1)

LWL : Length, in m, of the float at full load water line.Note 1: As a general rule, two successive loading cases are to betaken into account: the case as shown in Fig 2 and the same casewith forces in opposite direction.

3.3.5 Digging in wave loadingThe digging in wave loading corresponds to the situationwhere the catamaran sails in quartering head sea and hasthe fore end of the floats burying themselves into theencountered waves.

The vertical and horizontal forces loading the floats and tobe considered in the beam model defined in [3.3.1] aredefined in the Society Rules for the classification and/or cer-tification of ships.

3.3.6 Main structure check

a) Float structure

The longitudinal strength of the floats is to be checkedas indicated in [2], considering the vertical bendingmoments and the vertical shear forces deduced from thebeam model analysis defined in [3.3.1] under platformtorsional loading defined in [3.3.4] and [3.3.5]. Thebending moment and the shear force distribution alongthe float are shown in Fig 5.

The global longitudinal stresses calculated according to[2.3.1] are to be checked according to [2.3.2].

b) Primary transverse structure

Each resisting transverse cross member between floats(cross beams, bulkheads) is checked against bendingand shear strengths, taking into account the bendingmoments and shear forces resulting from the beammodel analysis defined in [3.3.1].

The values of bending moments and shear forces to beconsidered are the one calculated in the transversebeams of the beam model, in way of the modelled float.

The transverse distribution of vertical bending momentsand vertical shear forces is shown in Fig 4.

Figure 4 : Transverse distribution ofbending moments and shear forces

��

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NR 561, Sec 5

Particular attention is to be paid to:• shear buckling check of transverse bulkheads• compression/bending buckling check of wet deck

and cross deck plating in areas where the bendingmoment is maximum.

The stresses in each resisting transverse memberbetween floats are to be in accordance with the permis-

sible global stresses and the safety factors for bucklingas defined in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).

Note 1: The safety factor for buckling is the ratio between the criti-cal stress, determined in Sec 4, [2.2] for plates and in Sec 4,[3.2] for stiffeners, and the actual stresses in the transversemembers.

Figure 5 : Overall loads in the float

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NR 561, Sec 6

SECTION 6 HULL LOCAL STRENGTH PRINCIPLES

Symbols

s : Spacing, in m, of the secondary or primary stiff-ener under consideration

l : Span, in m, as defined in [3.2], of the secondaryor primary stiffener under consideration

k : Material factor, defined in Sec 2, [2.3]μ : Aspect ratio coefficient of the elementary plate

panel, equal to:

σlocam : Local permissible bending stress, in N/mm2, asdefined in the Society Rules for the classifica-tion and/or certification of ships (see Sec 1,[1.1.1], Note 1), depending on the type of load(hydrodynamic or dynamic)

τlocam : Local permissible shear stress, in N/mm2, asdefined in the Society Rules for the classifica-tion and/or certification of ships (see Sec 1,[1.1.1], Note 1), depending on the type of load(hydrodynamic or dynamic)

p : Local loads (wave loads, dynamic loads andpressure in tanks), in kN/m2, as defined in theSociety Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1)

m : End stiffener condition coefficient, defined in[3.1.3].

1 General

1.1 Local scantling

1.1.1 The present Section deals with the local scantling ofplatings and secondary and primary stiffeners under lateralpressures.Note 1: The scantling of platings and secondary and primary stiff-eners contributing to the overall longitudinal strength of the hullgirder and to the overall transverse strength of transverse cross deckof catamaran are also to be checked as defined in Sec 5.

1.1.2 Local loadsThe lateral pressures taken into account for the scantlingdefined in the present Rule Note are those defined in theSociety Rules for the classification and/or certification ofships (see Sec 1, [1.1.1], Note 1), i.e.:

• wave loads• dynamic loads:

- bottom slamming pressures for high speed ships,when slamming may occur

- side shell impacts (and cross deck impacts for multihull) for all types of ships

• deck loads and superstructure pressure

• bulkhead and tank loads

• wheel loads.

1.2 Local load point location

1.2.1 Wave loadsUnless otherwise specified, the wave loads are to be calcu-lated:

• for plate panels:

at the lower edge of the plate panels

• for longitudinal stiffeners:

at mid-span of the stiffeners

• for transverse stiffeners:

at the lower (pS lower) and upper (pS upper) points of the stiff-eners.

1.2.2 Dynamic loadsUnless otherwise specified, the dynamic loads are to be cal-culated:

• for plate panels:

at mid-edge of the plate panels

• for longitudinal and transverse stiffeners:

at mid-span of the stiffeners.

Note 1: As a general rule, side shell primary stiffeners and crossdeck primary stiffeners are examined with wave loads only, withouttaking into account the side shell and cross deck impacts.

2 Plating scantling

2.1 General

2.1.1 Local scantlings of platings are to be checked underthe following loads:

• for bottom platings: wave loads and bottom slammingpressures (when slamming may occur)

• for side shell and cross deck platings: wave loads andside shell impacts

• for deck platings: the greater value between wave loadsand minimum loads, and, when applicable, wheeledloads

• for superstructure platings: the greater value betweenwave loads and minimum loads.

Note 1: When they are sustaining compression loads induced byoverall longitudinal or transverse stresses, the platings are also to bechecked against buckling criteria as defined in Sec 5.

μ 1 1, 0 5, s2

l2

----⎝ ⎠⎛ ⎞–= 1≤


NR 561, Sec 6

2.1.2 For each plate, the scantling is obtained consideringsuccessively the different loads sustained by the plate(defined in [2.1.1]) and the relevant associated permissiblestresses defined in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).

2.2 Scantling

2.2.1 Plating subjected to lateral pressure

As a rule, the thickness of plating sustaining lateral pressureis to be not less than the value obtained, in mm, from thefollowing formula:

where:

coeff : Coefficient equal to:

• in case of wave load, bottom slamming,pressure in tank or on bulkhead:

coeff = 1

• in case of impact pressure on side shells andcross deck of catamaran:

- if l’ / 0,6 ≤ 1 + s’:

coeff = 1

- if l’ / 0,6 > 1 + s’:

coeff = (1 + s’)−1/2

with:

l’ : Longer side, in m, of the plate panel

s’ : Shorter side, in m of the plate panel.

2.2.2 Plating subjected to wheeled loads

a) The thickness of plate panels subjected to wheeledloads is to be not less than the value obtained, in mm,from the following formula:

where:

CWL : Coefficient to be taken equal to:

where l/s is to be taken not greater than 3

l’, s’ : Lengths, in m, of, respectively, the longerand the shorter sides of the plate panel

AT : Tyre print area, in m2. In the case of doubleor triple wheels, AT is the print area of thegroup of wheels.

AT is not to be taken less than the valuegiven in the Society Rules for the classifica-tion and/or certification of ships (see Sec 1,[1.1.1], Note 1)

n : Number of wheels on the plate panel, takenequal to:

• 1 in the case of a single wheel

• the number of wheels in a group ofwheels in the case of double or triplewheels

P0 : Wheeled force, in kN, as defined in the Soci-ety Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1).

b) For vehicles with the four wheels of the axle located ona plate panel as shown in Fig 1, the thickness of deckplating is to be not less than the greater of the valuesobtained, in mm, from the following formulae:

t = t1

t = t2 (1 + β2 + β3 + β4)0,5

where:

t1 : Thickness obtained, in mm, from item a)with n = 2, considering one group of twowheels located on the plate panel

t2 : Thickness obtained, in mm, from item a)with n = 1, considering one wheel locatedon the plate panel

β2, β3, β4: Coefficients obtained from the following for-mulae, replacing i by 2, 3 and 4, respec-tively (see Fig 1):

• for αi < 2:

βi = 0,8 (1,2 − 2,02 αi + 1,17 αi2 − 0,23 αi

3)

• for αi ≥ 2:

βi = 0

with αi = xi / b

xi : Distance, in m, from the wheelconsidered to the referencewheel (see Fig 1)

b : Dimension, in m, of the platepanel side perpendicular to theaxle.

Figure 1 : Four wheel axle located on a plate panel

t 22 4, coeff μ s pσ locam

--------------⋅ ⋅=

t CW L 2 35nP0k,=

CWL 2 15, 0 05 l ′s ′----,– 0 02 4 l ′

s′----–

⎝ ⎠⎛ ⎞ α0 5,, 1 75α0 25,,–+=

αAT

ls------=

X2 X3

X4

2 1 3 4

a

b


NR 561, Sec 6

3 Secondary stiffener scantlings

3.1 General

3.1.1 Loading cases

Local scantlings of secondary stiffeners are to be checkedunder the following loading cases:

• for bottom secondary stiffeners: wave loads and bottomslamming pressures (when slamming may occur)

• for side shell and cross deck secondary stiffeners: waveloads and side shell impacts

• for deck secondary stiffeners: the greater value betweenwave loads and minimum loads, and, when applicable,wheeled loads

• for superstructure secondary stiffeners: the greater valuebetween wave loads and minimum loads.

Note 1: When they are sustaining compression loads induced byoverall longitudinal or transverse stresses, the secondary stiffenersand their attached platings are also to be checked against bucklingcriteria as defined in Sec 5.

3.1.2 Permissible stresses

For each secondary stiffener, the scantling is obtained con-sidering independently the different loads sustained by thestiffener (defined in [3.1.1]) and the relevant permissiblestresses defined in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).

3.1.3 End stiffener conditions

The connection of secondary stiffeners with surroundingsupporting structure is to be taken into account in the calcu-lation of the rule stiffener section moduli.

The following three hypotheses on end stiffener conditionsare taken into consideration in the scantling formulae, usinga coefficient m equal, successively, to:

• for fixed end condition: m = 12

The cross-section at the ends of the stiffener cannotrotate under the effect of the lateral loads (as a rule, thesecondary stiffeners are considered with fixed ends).

• for simply supported end condition: m = 8

The cross-section at the ends of the stiffener can rotatefreely under the effect of the lateral loads.

• for intermediate conditions: m = 10

The cross-section at the ends of the stiffener is in anintermediate condition between fixed end conditionand simply supported end condition.

3.2 Span of stiffener

3.2.1 The span l of the stiffeners considered in the scant-ling formulae is to be measured as shown in Fig 2 to Fig 4.

Figure 2 : Stiffener without brackets

Figure 3 : Stiffener with a stiffener at one end

Figure 4 : Stiffener with a bracket and a stiffenerat one end

3.2.2 For open floors, when a direct beam calculation tak-ing into account all the elements of the open floor is notcarried out, the span l of the upper and lower secondarystiffeners connected by one or two strut(s) is to be takenequal to 0,7 l2 instead of l1 (see Fig 5).

Figure 5 : Span of stiffeners in case of open floors

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NR 561, Sec 6

3.3 Scantling

3.3.1 Secondary stiffeners under wave loads

As a rule, the section modulus Z, in cm3, and the shear areaAsh, in cm2, of the secondary stiffeners sustaining laterallocal loads are to be not less than the values obtained fromthe following formulae:

• for longitudinal stiffeners and transverse deck stiffeners:

• for vertical transverse stiffeners:

with:

psupper , pslower : Wave loads at lower and upper calcula-tion point of the vertical stiffener anddefined in the Society Rules for the classifi-cation and/or certification of ships (see Sec1, [1.1.1], Note 1)

where:

coeff, coeft: Reduction coefficients as defined in the SocietyRules for the classification and/or certificationof ships (see Sec 1, [1.1.1], Note 1).

3.3.2 Secondary stiffeners under bottom slamming

As a rule, the section modulus Z, in cm3, and the shear areaAsh, in cm2, of the secondary stiffeners sustaining lateral bot-tom slamming pressures are to be not less than the valuesobtained from the following formulae:

where:

coeff, coeft: Reduction coefficients as defined in the SocietyRules for the classification and/or certificationof ships (see Sec 1, [1.1.1], Note 1).

3.3.3 Secondary stiffeners under side shell impacts

As a rule, the section modulus Z, in cm3, and the shear areaAsh, in cm2, of the secondary stiffeners sustaining lateral sideshell impacts are to be not less than the values obtainedfrom the following formulae:

where:

coeff, coeft: Reduction coefficients equal to:

coeff = 0,3 (3 l2 − 0,36) / l3 with l ≥ 0,6 m

coeft = 0,6 / l, without being taken greater than 1.

3.3.4 Struts for open floorsAs a general rule, the scantling of the struts is to be checkedby direct calculation, taking into account the compressionand/or the tensile force Q, in kN, calculated as follows:

• compression force:

• tensile force:

where:

PBottom : Local loads (wave loads and/or dynamic loads),in kN/m2, applied on the ship bottom, as definedin the Society Rules for the classification and/orcertification of ships (see Sec 1, [1.1.1], Note 1)

PDBottom : Local loads, in kN/m2, applied on the ship dou-ble bottom, as defined in the Society Rules forthe classification and/or certification of ships(see Sec 1, [1.1.1], Note 1)

PBallast : Ballast local loads at mid-height of the shipdouble bottom, in kN/m2, as defined in theSociety Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1)

l2 : Span of the upper and lower secondary stiffen-ers, as defined in Fig 5.

4 Primary stiffener scantling

4.1 General

4.1.1 Loading casesScantlings of primary stiffeners are to be checked under thefollowing loading cases:

• for bottom primary stiffeners: wave loads and bottomslamming pressures (when slamming may occur)

• for side shell primary stiffeners: wave loads

• for deck primary stiffeners: the greater value betweenwave loads and minimum loads, and, when applicable,wheel loads

• for superstructure primary stiffeners: the greater valuebetween wave loads and minimum loads.

Note 1: When they are sustaining compression loads induced byoverall longitudinal or transverse stresses, the primary stiffeners andtheir attached platings are also to be checked against buckling cri-teria as defined in Sec 5.

4.1.2 Permissible stressesFor each primary stiffener, the scantling is obtained consid-ering independently the different loads sustained by thestiffener (defined in [3.1.1]) and the relevant permissiblestresses defined in the Society Rules for the classificationand/or certification of ships (see Sec 1, [1.1.1], Note 1).

Z 1000coeff psl2

mσ locam

-------------------=

Ash 5coeft pslτlo cam

-------------=

Z 1000coeff3pSlower 2pSupper+( )sl2

60σlocam

---------------------------------------------------------=

Ash 5coeft0 7pslower, 0 3psu pper,+( )sl

τlocam

-------------------------------------------------------------------=

Z 1000coeffpsl2

m σlocam⋅-----------------------=


-------------=

Z 1000coeffpsl2

mσ locam

-------------------=


-------------=

Qsl2

4------- PBo ttom PDBotto m+( )=

Q2sl2PBallas t

4---------------------------=


NR 561, Sec 6

4.1.3 Attached plating bucklingDepending on the compression stress level in the attachedplating induced by the loading cases defined in [4.1.1], itmay be necessary to check the buckling of the attachedplating along the primary stiffener span, according to therequirements of Sec 4, [2].

4.2 Scantling

4.2.1 As a rule, the section modulus Z, in cm3, and theshear area Ash, in cm2, of the primary stiffeners sustaininglateral wave loads or bottom slamming pressures are to benot less than the values obtained for the secondary stiffen-ers, taking [4.1.1] into account.

4.3 Curved primary stiffeners

4.3.1 The curvature of primary supporting members may betaken into account by direct analysis.

In case of 2-D or 3-D beam structural model, the curvedprimary supporting members may be represented by anumber N of straight beams, N being adequately selected tominimize the spring effect in way of knuckles.

The stiffness of knuckle equivalent springs is considered asminor from the point of view of the local bending momentand the shear force distribution when the angle betweentwo successive beams is not more than 3°.

5 General arrangement of brackets for secondary and primary stiffeners

5.1 General requirements

5.1.1 As a general rule, brackets are to be provided at thestiffener ends when the continuity of the web and the flangeof the stiffeners is not ensured in way of their supports.

5.1.2 Arm lengths of end brackets are to be equal, as far aspracticable.

5.1.3 The section of the end bracket web is generally to benot less than that of the supported stiffener web.

5.1.4 The section modulus of the end bracket is to be atleast equal to the section modulus of the stiffener supportedby the bracket.

When the bracket is flanged, the section modulus is to beexamined in way of the flange as well as in way of the endof the flange.

5.1.5 Bracket flangesAluminium brackets having a thickness, in mm, less than22 Lb are to be flanged or stiffened with a welded face plate,such that:

• the sectional area, in cm2, of the flanged edge or theface plate is at least equal to 10 Lb

• the width, in mm, of the bracket flange is not less than50 (Lb + 1)

• the thickness of the bracket flange is not less than that ofthe bracket web

where:

Lb : Length, in m, of the free edge of the bracket.

5.1.6 When a face plate is welded on end brackets to bestrengthened, this face plate is to be symmetrical.

In such a case, the following arrangements are to be com-plied with, as a rule:

• the face plates are to be snipped at the ends, with a totalangle not greater than 30°

• the width of the face plates at ends is not to exceed25 mm

• the face plates being 20 mm thick or above are to betapered at ends over half the thickness

• the radius of the curved face plates is to be as large aspossible

• a collar plate is to be fitted in way of the bracket toes

• the fillet weld throat is to be not less than t/2, where t isthe thickness of the bracket toe.

5.2 Brackets for connection of perpendicular stiffeners

5.2.1 Typical brackets for connection of perpendicular stiff-eners are shown from Fig 6 to Fig 11.

As a general rule, brackets are to be in accordance with therequirements given in [5.1].

In addition, and where no direct calculation is carried out,the length d, in mm, as defined from Fig 6 to Fig 11, is to beas a rule such that:

d ≥ 1,5 hs

where:

hs : Height, in mm, of the supported stiffener.

When a bracket is provided to ensure the simultaneous con-tinuity of two (or three) stiffeners of equivalent stiffness, thebracket scantling is to be examined by direct calculation,taking into account the balanced bending moment in theconnection of the two (or three) stiffeners.

Figure 6 : Bracket at upper end ofsecondary stiffeners on plane bulkhead

d

d

hs


NR 561, Sec 6

Figure 7 : Bracket at lower end ofsecondary stiffeners on plane bulkhead

Figure 8 : Other bracket arrangement at lower end of secondary stiffeners on plane bulkhead

5.3 Brackets ensuring continuity of secondary stiffeners

5.3.1 Where secondary stiffeners are cut in way of the pri-mary supporting members, brackets (or equivalent arrange-ments) are to be fitted to ensure the structural continuity asdefined in Fig 12. Their section moduli and their sectionalareas are to be not less than those of the secondary stiffeners.

The bracket thickness is to be not less than that of the sec-ondary stiffeners and dimension d of each bracket is to beas a rule not less than 1,5 hS .

Figure 9 : Connection of perpendicular stiffenersin the same plane

Figure 10 : Connection of stiffenerslocated in perpendicular planes

Figure 11 : Lower bracket of main frames

Figure 12 : End connection of secondary stiffenersBacking bracket

d

d

hs

A

A

Section A-A

d

hs

d

d

hs

dhs

d d

hs


NR 561, Sec 6

5.4 Bracketless end stiffener connections

5.4.1 Case of two stiffeners

In the case of bracketless crossing between two primarysupporting members (see Fig 13), the thickness tb of thecommon part of the webs, in mm, is to be not less than thegreater value obtained from the following formulae:

where:

Sf1, Sf2 : Flange sections, in mm2, of member 1 andmember 2, respectively

σ1, σ2 : Normal stresses, in N/mm2, in flanges of mem-ber 1 and member 2, respectively.

Figure 13 : Bracketless connectionsbetween two primary supporting members

Figure 14 : Bracketless connectionsbetween three primary supporting members

5.4.2 Case of three stiffeners

In the case of bracketless crossing between three primarysupporting members (see Fig 14) and when the flange conti-nuity is ensured between member 2 and member 3, thethickness tb of the common part of the webs, in mm, is to benot less than:

When the flanges of member 2 and member 3 are not con-tinuous, the net thickness of the common part of the webs isto be as defined in [5.4.1].

5.4.3 Stiffening of common part of webs

When the minimum value of heights h1 and h2 of member 1and member 2 is greater than 60 tb, the common part of thewebs is generally to be stiffened.

5.4.4 Lamellar tearing in way of flanges

When lamellar tearing of flanges is likely to occur, a 100%ultrasonic testing of the flanges in way of the weld may berequired after welding.

5.5 Other type of end connections

5.5.1 Where end connections are made according to Fig15, a stiffener with sniped ends is to be fitted on connectionweb, when:

a > 60 t

where:

a : Dimension, in mm, measured as shown on Fig 15

t : Web thickness, in mm.

Figure 15 : End connection with stiffener

tbSf1σ1

0 4h2Rp0 2,′,

---------------------------=

tbSf2σ2

0 4h1R ′p 0 2,,

-----------------------------=

tb max t1 t2,( )=

Member 2

Member 1

h1tb

h2

Member 2

Member 1

Member 3

h1tb

h2

tbSf1 σ1

0 4h2 Rp0 2,′,

---------------------------=

�

�

��

�


NR 561, Sec 7

SECTION 7 STRUCTURAL ARRANGEMENTS

1 General

1.1 Application

1.1.1 The requirements of the present Section apply to lon-gitudinally and transversely frame structure arrangements ofships built in aluminium alloy for:

• single and double bottoms

• sides and decks

• transverse and longitudinal structures

• superstructures and deckhouses.

2 Bottom structure arrangements

2.1 General arrangement

2.1.1 The bottom structure is to be checked by theDesigner to make sure that it withstands the loads resultingfrom the dry-docking of the ship or the lifting by crane.These loading cases are not within the scope of the classifi-cation and/or certification.

2.1.2 For ships considered by the Flag Administration aspassenger ships, it might be necessary to provide a continu-ous double bottom. In such a case, the relevant require-ments of NR467 Rules for Steel Ships are applicable.

2.1.3 Provision is to be made for the free passage of waterfrom all the areas of the bottom to the suctions, by means ofscallops in floors and bottom girders.

2.1.4 Additional girders and floors may be fitted in theengine room to ensure adequate rigidity of the structure,according to the recommendations of the engine supplier.

2.1.5 If fitted, solid ballast is to be securely positioned. Ifnecessary, intermediate girders and floors may be required.The builder is to check that solid ballast material is compat-ible with the aluminium alloys used.

2.2 Longitudinal framing arrangement of single bottom

2.2.1 As a general rule, ships with a longitudinally framedsingle bottom are to be fitted with a continuous or intercos-tal centre girder welded to the floors.

2.2.2 Where side girders are fitted locally in lieu of the cen-tre girder, they are to be extended over a sufficient distancebeyond the ends of the centre girder and an additional stiff-ening of the bottom in the centreline area may be required.

2.2.3 Where face plates of floors and bottom girders are atthe same level, the face plate of the stiffer member is gener-ally to be continuous. Butt welds of face plates are to pro-vide strength continuity.

2.2.4 Centre and side bottom girders are to be extended asfar as possible towards the ends of the hull.

2.2.5 As a rule, bottom girders are to be fitted in way ofeach line of pillars. If it is not the case, local longitudinalmembers are to be provided.

2.2.6 Longitudinal secondary stiffeners are generally to becontinuous when crossing primary members.

2.2.7 Cut-outs fitted in the web of floors for the crossing ofbottom longitudinals are to be taken into account for theshear analysis of floors.

2.3 Transverse framing arrangement of single bottom

2.3.1 Requirements of [2.1] apply also to transverse fram-ing in single bottom.

2.3.2 In general, the height, in m, of floors at the centrelineshould not be less than B/16. In the case of ships with con-siderable rise of floors, this height may be required to beincreased so as to ensure a satisfactory connection to theframes.

2.3.3 The ends of floors at side are to be located in linewith side transverse members.

In some particular cases, it may be accepted that floor endsat side be welded on a primary longitudinal member of theside shell or of the bottom.

2.3.4 Openings and cut-outs in the web of bottom girdersfor the crossing of floors are to be taken into account for thefloor shear analysis.

2.4 Double bottom arrangements

2.4.1 Double bottom heightAs a general rule, the double bottom height is to be:

• sufficient to ensure access to any part of the bottom, and

• not less than 0,7 m in way of the centre girder.

2.4.2 Where the height of the double bottom varies, thevariation is generally to be made gradually and over an ade-quate length; the knuckles of inner bottom plating are to belocated in way of floors.

Where such arrangements are not possible, suitable longitu-dinal structures such as partial girders, longitudinal bracketsetc., fitted across the knuckle, are to be fitted.


NR 561, Sec 7

2.4.3 Arrangement of floorsFloors are to be provided:• watertight in way of watertight transverse bulkheads• reinforced in way of double bottom steps.

In longitudinally framed bottoms, plate floors or verticalstiffeners are generally to be provided in way of bottomand/or inner bottom longitudinal secondary stiffeners.

2.4.4 Where the double bottom height exceeds 0,9 m, webof floors are to be strengthened by vertical stiffeners spacednot more than 1 m apart.These stiffeners may consist of:• either bottom girders welded to the floors, or• flat bars with a width equal to one tenth of the floor

depth and a thickness equal to the floor thickness.

2.4.5 Watertight floors are to be fitted with stiffeners havinga section modulus not less than that required for tank bulk-head vertical stiffeners.

2.4.6 In case of open floors consisting in a frame con-nected to the bottom plating and a reverse frame connectedto the inner bottom plating, the construction principle is tobe as shown on Fig 1.

2.4.7 Longitudinal secondary stiffeners

Bottom and inner bottom longitudinal secondary stiffenersare generally to be continuous through the floors.

2.5 Arrangement, scantling and connections of bilge keel

2.5.1 Arrangement

Bilge keels may not be welded directly on the shell plating.An intermediate flat, or doubler, is required on the shellplating.

The thickness of the intermediate flat is to be equal to that ofthe bilge strake.

The ends of the bilge keels are to be sniped at an angle of15° or rounded with a large radius. They are to be locatedin way of a transverse bilge stiffener. The ends of the inter-mediate flat are to be sniped at an angle of 15°.

The arrangement shown in Fig 2 is recommended.

The arrangement shown in Fig 3 may also be accepted.

Figure 1 : Open floor - Transverse framing system

Figure 2 : Bilge keel arrangement Figure 3 : Bilge keel arrangement

shell plating


NR 561, Sec 7

2.5.2 Materials

The bilge keel and the intermediate flat are to be made ofaluminium having the same yield stress as that of the bilgestrake.

2.5.3 Welding

Welding of bilge keel with intermediate flat is to be inaccordance with Sec 3.

3 Side structure arrangement

3.1 General

3.1.1 In a transverse framing system, structure of sides ismade of transverse frames, possibly supported by horizontalstringers.

3.1.2 In a longitudinal framing system, structure of sides ismade of secondary longitudinal stiffeners supported by ver-tical primary supporting members.

3.1.3 Where the sheerstrake (connection between sideshell and deck plate) is rounded, the radius, in mm, is to benot less than 15 tS , where tS is the thickness, in mm, of thesheerstrake.

3.2 Stiffener arrangements

3.2.1 Secondary stiffeners are normally to be continuousthrough primary supporting members.

Otherwise, the detail of the connection is examined by theSociety on a case-by-case basis.

3.2.2 In general, the section modulus of ‘tweendeck framesis to be not less than that required for frames located imme-diately above.

3.2.3 Transverse web frames and secondary side frames areto be attached to floors and to deck beams by brackets orany other equivalent structure (see Sec 6, [5]).

3.2.4 For transverse framing system, the attention of theDesigner is drawn on the risk of buckling of side shell platepanels at ends of frames. Extra thicknesses or additional ver-tical intercostal stiffeners may be requested on the sideshell.

3.3 Openings in the shell plating

3.3.1 Openings in side shell are to be well rounded at thecorners and located, as far as practicable, well clear ofsuperstructure ends.

3.3.2 Large-sized openings are to be adequately compen-sated by means of insert plates of increased thickness. Suchcompensations are to be partial or total, depending on thestresses occurring in the area of the openings.

3.3.3 Openings for stabilizer fins are considered by theSociety on a case-by-case basis. The sea chest thickness isgenerally to be equal to that of the local shell plating.

3.3.4 Secondary stiffeners cut in way of openings are to beattached to local structural members supported by the con-tinuous adjacent secondary stiffeners, or any other equiva-lent arrangement.

4 Deck structure arrangements

4.1 General

4.1.1 Adequate continuity of decks (plates and stiffeners) isto be ensured in way of:

• stepped strength decks

• changes in the framing system

• large openings.

4.1.2 Deck supporting structures under cranes and wind-lass are to be adequately stiffened.

4.1.3 Pillars or other supporting structures are generally tobe fitted under heavy concentrated loads on decks.

4.1.4 Stiffeners are to be fitted in way of the ends and thecorners of deck houses and partial superstructures.

4.1.5 Beams fitted at side of a deck hatch are to be effi-ciently supported by at least two deck girders located ateach side of the deck opening.

4.2 Stiffener arrangements

4.2.1 Deck longitudinals are to be continuous in way ofdeck beams and transverse bulkheads.

Other arrangements may be considered, provided adequatecontinuity of longitudinal strength is ensured.

4.3 Deck primary structure in way of launching appliances

4.3.1 The scantling of deck primary structure supportinglaunching appliances used for survival craft or rescue boatsis to be determined by direct calculations, taking intoaccount the loads exerted by the launching appliances, tobe taken equal to the safe working load of the launchingappliances.

The combined stress, in N/mm2, in the primary structure isnot to exceed the smaller of R’p0,2 / 2,2 and R’m / 4,5.

4.3.2 The attention is drawn on any possible specificrequirement that could be issued by the Flag Administrationwith respect to a structural fire protection.

4.4 Opening arrangements

4.4.1 The deck openings are to be as much spaced apart aspossible.

As practicable, they are to be located as far as possible fromthe highly stressed deck areas or from the stepped deckareas.


NR 561, Sec 7

4.4.2 Extra thicknesses or additional reinforcements may berequested where deck openings are located:

• close to the primary transverse cross bulkheads on cata-marans

• in areas of deck structural singularity (stepped deck...)

• in way of the fixing of out-fittings.

4.4.3 As a rule, all the deck openings are to be fitted withrounded corners. Generally, the corner radius is not to beless than 5% of the transverse width of the opening.

4.4.4 Corner radiusing, in the case of two or more openingsathwart ship in one single transverse section, is consideredby the Society on a case-by-case basis.

4.5 Pillars arrangement under deck

4.5.1 Pillars are to be connected to the inner bottom at theintersection of floors and bottom girders and at deck at theintersection of deck beams and deck girders.

Where it is not the case, an appropriate local structure (par-tial floors, partial bottom girders, partial deck beams or par-tial deck girders) is to be fitted to support the pillars.

4.5.2 As a general rule, heads and heels of pillars are to beattached to the surrounding structure by means of continu-ous welding and brackets.

A doubling plate attached to the surrounding structure maybe provided so that the loads are well distributed, except inthe case of pillars which may also work under tension. Ingeneral, the thickness of the doubling plate is not to be lessthan 1,5 times the thickness of the pillar.

4.5.3 Where pillars are made of steel or stainless steel, theirconnection to the hull structure is to be made of bi-metallicjoints or equivalent systems. These systems are to be type-approved.

4.5.4 Manholes may not be cut in the web of bottom gird-ers and floors located below the heels of pillars.

4.5.5 Tight or non-tight bulkheads may be considered aspillars, provided their scantling complies with [5.4].

4.5.6 Pillar scantling

Scantling of the pillars are to comply with the requirementsof Sec 8.

5 Bulkhead structure arrangements

5.1 General

5.1.1 Bulkheads may be horizontally or vertically stiffened.

Stiffening of horizontally framed bulkheads consists of hori-zontal secondary stiffeners supported by vertical primarysupporting members.

Stiffening of vertically framed bulkheads consists of verticalsecondary stiffeners which may be supported by horizontalstringers.

5.1.2 The structural continuity of the vertical and horizon-tal primary supporting members with the surrounding sup-porting hull structures is to be carefully ensured.

5.1.3 As a general rule, transverse bulkheads are to be stiff-ened, in way of bottom and deck girders, by vertical stiffen-ers in line with these girders, or by an equivalent system.

Where a deck girder is not continuous, the bulkhead verti-cal stiffener supporting the end of the deck girder is to bestrong enough to sustain the bending moment transmittedby the deck girder.

5.2 Watertight bulkheads

5.2.1 The number and the location of watertight bulkheadsare to be in accordance with the relevant requirements ofthe damage stability criteria or the general arrangement asdefined in the Society Rules for the classification and/or cer-tification of ships (see Sec 1, [1.1.1], Note 1).

5.2.2 Crossing through watertight transverse bulkheads ofbottom, side shell or deck longitudinal stiffeners is to beclosed by watertight collar plates.

5.2.3 Stiffeners of watertight bulkheads are to end in way ofhull structure members, and are to be fitted with end brack-ets.

Where this arrangement is made impossible due to hulllines, any other solution may be accepted provided embed-ding of the bulkhead secondary stiffeners is satisfactorilyachieved.

5.2.4 The secondary stiffeners of watertight bulkheads inthe ‘tweendecks may be snipped at ends, provided theirscantling is increased accordingly.

5.3 Non-tight bulkheads

5.3.1 As a rule, non-tight bulkheads not acting as pillars areto be provided with vertical stiffeners being, at a maximum:

• 0,9 m apart, for transverse bulkheads

• two frames apart, with a maximum of 1,5 m, for longitu-dinal bulkheads.

5.3.2 Wash bulkheads

As a rule, the total area of the openings in a tank wash bulk-head is to be between 10% and 30% of the total area of thewash bulkhead.

5.4 Bulkheads acting as pillars

5.4.1 As a rule, bulkheads acting as pillars (i.e thosedesigned to sustain the loads transmitted by a deck struc-ture) are to be provided with vertical stiffeners being, at amaximum:

• two frames apart, when the frame spacing does notexceed 0,75 m

• one frame apart, when the frame spacing is greater than0,75 m.


NR 561, Sec 7

5.4.2 A vertical stiffening member is to be fitted on thebulkhead in line with the deck primary supporting membertransferring the loads from the deck to the bulkhead.

This vertical stiffener is to be calculated with the applicablerequirements defined for pillars (see Sec 8), taking intoaccount, for the associated plating, a width equal to 30 timesthe plating thickness.

5.5 Bracketed stiffeners

5.5.1 The bracket scantlings at ends of bulkhead stiffenersare carried out by direct calculation, taking into account thebending moments and shear forces acting on the stiffenersin way of the brackets, as defined in Sec 6, [5].

6 Superstructure and deckhouse structure arrangements

6.1 Superstructure materials

6.1.1 Special attention is to be given to any specificrequirements from the Flag Administration about the struc-tural materials and the structural fire protection in the super-structures.

6.2 Connections of superstructures and deckhouses with the hull structure

6.2.1 Superstructure and deckhouse frames are to be fitted,as far as practicable, in way of deck structure and are to beefficiently connected.

Ends of superstructures and deckhouses are to be efficientlysupported by bulkheads, diaphragms, webs or pillars.

Where hatchways are fitted close to the ends of superstruc-tures, additional strengthening may be required.

6.2.2 Connection to the hull deck of the corners of super-structures and deckhouses is considered by the Society on acase-by-case basis. Where necessary, local reinforcementsmay be required.

6.2.3 As a general rule, the side plating at ends of super-structures is to be tapered into the side shell bulwark or thesheerstrake of the strength deck.

Where a raised deck is fitted, the local reinforcement inway of the step is to extend, as a general rule, over at least3-frame spacings.

6.3 Structural arrangement of superstructures and deckhouses

6.3.1 Web frames, transverse partial bulkheads or otherequivalent strengthening of each superstructure tier are tobe arranged, where practicable, in line with the transversereinforced structure below.Web frames are also to be arranged in way of large open-ings, tender davits, winches, provision cranes and otherareas subjected to local loads.

6.3.2 OpeningsAll the openings in superstructures and deckhousesexposed to greenseas are to be fitted with sills or coamingsas defined in the Society Rules for the classification and/orcertification of ships (see Sec 1, [1.1.1], Note 1).

The attention of the Shipowners, Shipyards and Designer isdrawn on the fact that the flag Administration may requestapplication of National Rules.

6.3.3 Access and doorsAccess openings cut in side plating of enclosed superstruc-tures are to be fitted with doors having a strength equivalentto the strength of the surrounding structure.

Special consideration is to be given to the connection of thedoors to the surrounding structure.

Securing devices which ensure watertightness are toinclude tight gaskets, clamping dogs or other similar appli-ances, and are to be permanently attached to the bulkheadsand doors. These doors are to be operable from both sides.

6.3.4 Construction detailsThe vertical stiffeners of the superstructure and deckhousewalls of the first tier (directly located above the freeboarddeck) are to be attached to the decks at their ends.

Brackets are to be fitted at the lower end and, preferablytoo, at the upper end of the vertical stiffeners of exposedfront bulkheads of engine casings and superstructures.

7 Helicopter deck

7.1 General

7.1.1 Structure of the helicopter deck located on super-structure weather deck or on platform permanently con-nected to the hull structure is to be examined according toNR467 Rules for Steel Ships, Pt B, Ch 9, Sec 10.The value of Ry (minimum yield stress of the material con-sidered, in N/mm2) used in the scantling formulae of NR467Rules for Steel Ships is to be taken equal to R’

lim as definedin Sec 2, [2.3.1].

7.1.2 Attention is drawn on any possible specific require-ment that could be issued by the Flag Administration withrespect to structural fire protection.


NR 561, Sec 8

SECTION 8 PILLARS

Symbols

A : Cross-sectional area, in cm2, of the pillar

I : Minimum moment of inertia, in cm4, of the pil-lar in relation to its principal axis

E : Young’s modulus of aluminium, equal to70000 N/mm2

l : Span, in m, of the pillar

f : Fixity condition coefficient, to be obtained fromTab 1

Rp 0,2 : Proof stress (yield strength), in N/mm2, of theparent metal in delivery conditions, as definedby the supplier

Rp 0,2’ : Proof stress (yield strength), in N/mm2, of theparent metal in welded conditions as defined inSec 2

σE : Euler pillar buckling stress, in N/mm2, to beobtained from the following formula:

σCB : Global pillar buckling stress, in N/mm2

σCL : Local pillar buckling stress, in N/mm2.

1 General

1.1 Application

1.1.1 The requirements of this Section apply to pillars(independent profiles or bulkhead stiffeners) made of alu-minium alloys.

1.1.2 The present Section only deals with the bucklingcheck of the pillars (the general requirements relating to pil-lar arrangement are given in Sec 7, [4.5]).

1.1.3 Calculation approachFor aluminium pillars, the pillar buckling stresses σCB andσCL , in N/mm2, and the maximum allowable axial load PC ,in kN, are to be successively examined according the twofollowing methods:

• global column buckling, and

• local buckling.

1.1.4 Compression axial loadWhere pillars are vertically aligned, the compression axialload FA , in kN, is equal to the sum of the loads supportedby the pillar considered and those supported by the pillarslocated above, multiplied by a load factor r.

The load factor depends on the relative position of each pil-lar with respect to that considered (i.e. the number of tiersseparating the two pillars).

The compression axial load in the pillar is to be obtained, inkN, from the following formula:

where:

AD : Area, in m2, of the portion of the deck or theplatform supported by the pillar considered

ps : Pressure on deck, in kN/m2, as defined in theSociety Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1).

pL : Local loads, in kN, if any

r : Load factor depending on the relative positionof each pillar above the one considered, to betaken equal to:

• r = 0,9 for the pillar immediately above thepillar considered

• r = 0,9i > 0,478 for the ith pillar of the lineabove the pillar considered

Qi : Vertical local load, in kN, supported by the ith

pillar of the line above the pillar considered, ifany.

2 Critical buckling stresses

2.1 Buckling of pillars subjected to compression axial load

2.1.1 Global critical column buckling stressThe global critical column buckling stress σCB of pillarsmade of aluminium alloy is to be obtained, in N/mm2, fromthe following formula:

where:

C : Coefficient to be taken equal to one of the fol-lowing formulae or deduced from Fig 1:

• for alloys serie 5000:

• for alloys serie 6000:

where:

σE π2EI

A fl( )2----------------10 4–=

FA ADps pL ri

∑ Qi+ +=

σCBRp0 2 ′,

0 85, 0 25 fl AI

-------------⎝ ⎠⎛ ⎞,+

---------------------------------------------------- C⋅=

11 λ 1 λ+( )2 0 68 λ⋅,( )–+ +---------------------------------------------------------------------------

1

1 λ 1 λ+( )2 3 2 λ⋅,( )–+ +------------------------------------------------------------------------

λ Rp 0 2, ′σE

-------------=


NR 561, Sec 8

2.1.2 Local critical buckling stressThe local critical buckling stress σCL of pillars made of alu-minium alloy is to be obtained, in N/mm2, from the follow-ing formula:

σCL = 2 Rp 0,2’ C

where:C : Coefficient as defined in [2.1.1], with:

σEi : Euler local buckling stress, in N/mm2, to betaken equal to:• for circular tubular pillars:

t : Pillar thickness, in mmD : Pillar outer diameter, in mm

• for rectangular tubular pillars:

b : Greatest dimension of the cross-section, in mm

t : Plating thickness in relation to b,in mm

• for built up pillars, the lesser of:

hW , tW : Web height and web thickness,respectively, of built-up section,in mm

bF , tF : Face plate width and face platethickness, respectively, of built-up section, in mm.

3 Pillar scantling

3.1 Maximum allowable axial load

3.1.1 The maximum allowable axial load PC, in kN, is thesmaller of the following values:

PC = σCB ⋅ A ⋅ 10−1

PC = σCL ⋅ A ⋅ 10−1

Table 1 : Coefficient f

λRp 0 2, ′

σEi

-------------=

σEi 12 5 E206000--------------------

⎝ ⎠⎛ ⎞ t

D----

⎝ ⎠⎛ ⎞ 104,=

σEi 78E

206000--------------------

⎝ ⎠⎛ ⎞ t

b---

⎝ ⎠⎛ ⎞

2

104=

σEi 78 E206000--------------------

⎝ ⎠⎛ ⎞ tW

hW

-------⎝ ⎠⎛ ⎞

2

104=

σEi 32 E206000--------------------

⎝ ⎠⎛ ⎞ tF

bF

-----⎝ ⎠⎛ ⎞

2

104=

Conditions of fixity

f 0,5 (1) 0,7 1,0 2,0 1,0 2,0

(1) End clamped condition may only be considered when the structure in way of pillar ends can not rotate under the effect of loadings.


NR 561, Sec 8

Figure 1 : Coefficient C

��

��

��

��

��

��

��

��

��

�

��

��

��

��

��

��

��

��

��

� � � � � � �

λ

��

��


NR 561, Sec 9

SECTION 9 HULL CONSTRUCTION AND SURVEY

1 General

1.1 Scope

1.1.1 The purpose of this Section is to define hull construc-tion and survey requirements within the scope of the classi-fication of ships and/or certification of ship hulls required tobe built in compliance with to the applicable Society'sClassification Rules and surveyed during construction bythe Society.

The scope of classification is defined in NR467 Rules forSteel Ships, Part A.

2 Structure drawing examination

2.1 General

2.1.1 The structure drawing examination is to be carriedout in accordance with the present Rule Note and the appli-cable Society Rules for the classification and/or certificationof ships (see Sec 1, [1.1.1], Note 1).

2.1.2 The type of aluminium alloys, including grade, tem-per and minimum proof stress, is to be specified by theshipyard on the structure drawings.

2.1.3 The details of the welded and/or riveting connectionsbetween the main structural elements, including throatthicknesses and joint types, are to be specified by the ship-yard on the structure drawings or in the weld booklet, asdefined in Sec 3, [1.2.1].

3 Hull construction

3.1 Shipyard details and procedures

3.1.1 The following details are to be submitted by the Ship-yard to the Society:

• design office and production work staff

• production capacity (number of units per year, numberof types, sizes)

• total number of hull units already built.

3.1.2 The following procedures are to be submitted by theShipyard to the Society:

• Traceability

• procedure to ensure traceability of materials, con-sumables and equipment covered by the Society’sRules (from the purchase order to the installation orplacing on ship)

• data to ensure traceability of the production means(describing the different steps such as inspection orrecording during production)

• handling of non-conformities (from the reception ofmaterials or equipment to the end of construction)

• handling of client complaints and returns to after-sales department.

• Construction

• procedure to ensure that the hull is built in accordancewith the approved drawings, as defined in [2]

• procedure to precise the equipment references, thereferences to any equipment approval, the suppliers'technical requirements, the precautions to be takenwhen installing the equipment

• builder’s inspection process and handling of defects

• procedure to ensure that the remedial measuresconcerning the defects and deficiencies noticed bythe Surveyor of the Society during the survey aretaken into account.

Procedures are also to define:

- the precautions to be taken to comply with thesuppliers and Society requirements in order notto cause, during installation, structure damagesaffecting structural strength and watertightness,and

- the preparations to be made on the hull in antic-ipation of installation.

3.2 Materials

3.2.1 The following details about materials used are to besubmitted by the Shipyard to the Society:

• list of aluminium alloys used for plates, stiffeners, fillerproducts etc., with their references and suppliers’ identi-fication

• references of existing material approval certificates

• material data sheets containing, in particular, the suppli-ers’ recommendations on storage use.

3.2.2 The storage conditions of materials and welding con-sumables are to be in accordance with the manufacturers’recommendations, in dry places without condensation andclear of the ground

All the materials are to be identifiable in the storage site(quality of aluminium alloy and welding consumables, ref-erence of batches and type of approval certificate, ...)

The builder is to provide an inspection to ensure that theincoming plates, stiffeners and consumables are in accord-ance with the purchase batches and that defective materialshave been rejected.


NR 561, Sec 9

3.3 Forming

3.3.1 Forming operations are to be in accordance with thematerial manufacturer's recommendation or recognisedstandard.

3.4 Welding

3.4.1 Welding booklet

A welding booklet, including the welding procedures, fillerproducts and the design of joints (root gap and clearance),as well as the sequence of welding provided to reduce to aminimum restraint during welding operations, is to be sub-mitted to the Surveyor for examination.

Moreover, the welding booklet is:

• to indicate, for each type of joint, the preparations andthe various welding parameters

• to define, for each type of assembly, the nature and theextent of the inspections proposed, in particular those ofthe non-destructive testing such as dye-penetrant testsand, if needed, those of the radiographic inspection.

3.4.2 Welding consumables, procedures and welder qualifications

The various welding procedures and consumable materialsare to be used within the limits of their approval and inaccordance with the conditions of use specified in therespective approval documents.

• Welding filler product

• The choice of the welding filler metal is to be madetaking into account the welding procedure, theassembly and the grade of aluminium alloy corre-sponding to the parent metal.

The welding consumables are to be in accordancewith NR216 Materials and Welding.

• Welding filler products are generally to be approvedby the Society and are of type as defined in NR216Materials and Welding, Ch 5, Sec 2 or of other typesaccepted as equivalent by the Society.

• The filler products used are to be mentioned in thewelding booklet or in the welding specification ofthe construction concerned.

• Arc welding of aluminium alloys is to be carried outunder an inert atmosphere, using either a refractoryelectrode (TIG process) or a consumable electrode(MIG process).

• Automatic or semi-automatic weld may be used forprefabricated panels and on building slip for theconnection of blocks.

• Whenever the thicknesses are greater than or equalto 4 mm, butt weld of hull plating or of resistantmembers is to be carried out in two opposed runsminimum, in order to eliminate transverse flaws.

• For welding of thicknesses greater than 8 mm, anefficient heating of the plates to be connected is tobe carried out in order to prevent risks of condensa-tion (pre-heating at about 70°C).

• Qualification of welders: welders for manual weldingand for semi-automatic welding processes are to beproperly trained and are to be certified by the Societyaccording to the procedures given in NR476 ApprovalTesting of Welders unless otherwise agreed.

• Qualification of weldings procedures: requirements forthe approval of welding procedures are to be as definedin NR216 Materials and Welding, Ch 5, Sec 4.

3.4.3 Weather protection

Welding operations in open air are to be avoided.

It is recommended to carry out the welding of the greatestpossible number of items in shelter.

Adequate protection from the weather is to be provided toparts being welded; in any event, such parts are to be dry.

In welding procedures using bare, cored or coated wireswith gas shielding, the welding is to be carried out inweather protected conditions, so as to ensure that the gasoutflow from the nozzle is not disturbed by winds anddraughts.

3.4.4 Butt connection edge preparation

The edge preparation is to be of the required geometry andcorrectly performed.

Preparation of edges and adjusting are to comply with thetolerances indicated in the welding booklet.

3.4.5 Surface condition

The surfaces to be welded are to be free from moisture andother substances, such as mill scale, oil, grease or paint,which may produce defects in the welds.

Effective means of cleaning are to be adopted. The metal isto be properly degreased prior to the welding by means of asolvent inert for the metal.

Before welding, a mechanical cleaning of the edges to bewelded is also to be carried out by means of brushing (stain-less steel brush) or scraping. Chemical pickling may also beused.

3.4.6 Assembling and gap

The setting appliances and system to be used for positioningare to ensure an adequate tightening adjustment and anappropriate gap of the parts to be welded, while allowingmaximum freedom for shrinkage to prevent cracks or otherdefects due to excessive restraint.

The provisions taken for the layout of joints, the adjustmentof elements, the nature and the execution order of welds areto be such that they minimize the deformations.

The gap between the edges is to comply with the requiredtolerances or, when not specified, is to be in accordancewith the normal good practice.

Where stiffener ends are butt welded, the weld is to extendover the full section. Chamfers may be needed, in particularfor bulb sections. If both sections have a different height,the strength continuity is to be restored by means of abracket (or equivalent arrangement).


NR 561, Sec 9

3.4.7 Welding sequences and interpass cleaningWelding sequences and direction of welding are to bedetermined so as to minimise deformations and preventdefects in the welded connections.

After each run, the slag is to be removed by means of ametal brush and the grease is to be removed by an appropri-ate cleaning. The same precaution is to be taken when aninterrupted weld is resumed or when two welds are to beconnected.

Where a welding is interrupted, the end of the joint is to becarefully grounded and an overlapping of welding linesover 20 mm is necessary.

3.5 Non destructive examination of welds

3.5.1 GeneralThe yard Inspector department is to inspect the aspect, sur-face, uniformity and thickness of the welds (the throats ofthe fillet welds are to be checked by means of gauges).Where defects are found, the weld is to be repaired inagreement with the Surveyor.

The extent, distribution and methods of non-destructivetesting (visual, dye-penetrant and radiographic inspection),as well as the quality standards adopted by the shipyard andapplied to the construction, are to be defined at the initialstages of construction and presented in a document submit-ted to the Surveyor in charge of the survey. Note 1: Non-destructive tests are to be carried out by certifiedqualified personnel or by recognised bodies in compliance withappropriate standards.

Note 2: Welding inspection of watertight welds in oil fuel tanks isto be carried out carefully due to the difficulty in repairing in serv-ice such types of welding.

3.5.2 Weld categoriesWelds are classified in the three following categories defin-ing the extent and distribution of non-destructive testing(defined in [3.5.4]) as well as the acceptance criteria:• special category: for welds where cracks may lead to the

loss of the ship• first category: for butt welds of shell and butt or fillet

welds of longitudinal members, primary elements, struc-ture transverse bulkheads, engine seating and rudders

• second category: for welds other than those belongingto the special or first categories.

Choice of the categories for hull and superstructure welds isto be made by the yard before the construction starts(according to the level of stresses, the consequences of acrack and the location of the welds, in particular theiraccessibility for survey and repair), and submitted to theSociety for review.

3.5.3 Inspection methodsThe three main methods of inspection to be considered are:

a) Visual inspection: the inspection of welds intends tocheck the absence of unacceptable visual defects andthe conformity of welds as defined in the examinedstructure drawings (type, location, throat thickness)

b) Dye-penetrant testing

c) Radiographic inspection.

As far as possible, the radiographic inspection of aluminiumbutt welds is to be carried out by means of X-rays. Where itis difficult to make radiography (in particular due to accessi-bility), a gamma-ray inspection may be used.

For gamma-ray inspection, the following main precautionsare to be taken in order to obtain a fine image and anacceptable contrast:

• fine grain film

• reinforcing screen

• density in the range 2,5 to 4,5

• the image quality given by the image quality indicator(IQI) is to be such that:

- the minimum diameter of the visible hole is equalto 5% of the assembly thickness, for IQI with hole

- the minimum diameter of the visible wire is equalto 2% of the assembly thickness, for IQI withwires.

Alternatively, preliminary runs, showing that the imagequality obtained with the proposed gamma-ray inspection isalmost equivalent to that which may be obtained in X-rayinspection for the same range of thicknesses, may beaccepted.

Such preliminary checking, which are to be carried outbefore gamma-ray inspection is used on the hull and struc-ture, may consist in comparative tests between X-ray andgamma-ray on typical welded samples. In this respect, thesamples used for the qualification of welders or of the weld-ing procedures can be used.

3.5.4 Extent of non-destructive examinationThe following extents are to be taken into account for theweld inspections carried out by the shipyard:

a) Special category weld:

• visual inspection: full length visual inspection ofevery weld

• Butt welds: full length radiographic inspection (itmay be reduced in the case of automatic welding,subject to the agreement of the Surveyor), and fulllength dye-penetrant testing

• Fillet welds: full length dye-penetrant testing.

b) First category weld:

• Visual inspection: full length visual inspection ofevery weld

• Butt welds: dye-penetrant testing is to be carried outon the weld lengths submitted to radiographicinspection, and on any suspicious length revealedduring visual inspection.

For radiographic inspection, the number N of radio-graphs is to be not less than the length of the ship, inm, (for multihull, N is to be not less than n times thelength of the ship, in m, where n is the number ofhulls). The location of these radiographs is deter-mined by the yard with the Surveyor’s agreementand is to be mainly localized at the cross-welds andon highly stressed welds.

• Fillet welds: as a rule, dye-penetrant testing may becarried out at random. The extent of this random checkis to be defined in accordance with the Surveyor.


NR 561, Sec 9

c) Second category weld:

• Visual inspection: full length visual inspection ofevery weld.

Where defects are detected, the extent of the inspec-tion is to be increased as agreed by the yard and theSurveyor.

3.5.5 Acceptance criteriaCriteria for the acceptance of weld defects are to be definedby the yard at the initial stage of construction and submittedto the Surveyor’s agreement.

The following main weld imperfections and their accept-ance limit, taking into account the weld category as definedin [3.5.2], are to be described:

• excessive weld metal or convexity

• excessive asymmetry of fillet weld or overlap

• local lack of fusion or incomplete penetration

• excessive penetration

• exposed or internal local porosity

• linear misalignment for butt welds or incorrect root gapfor fillet welds.

The criteria may be based on recognized national or inter-national standards applicable to structures in aluminiumalloys, and finished welds are to be, on the whole, free fromcracks and lack of fusion.

4 Survey for unit production

4.1 General

4.1.1 The survey includes the following steps:

• survey at yard with regards to general requirements of [3]

• structure drawing examination (see [2])

• survey at yard during unit production with regards toapproved drawings, yard's response to comments madeby the Society during structure review examination andconstruction requirements.

These can only focus on the construction stage in progressduring the survey. It is to the responsability of the inspectiondepartment of the yard to present to the Surveyor anydefects noted during the construction of the ship.

5 Alternative survey scheme for production in large series

5.1 General

5.1.1 Where the hull construction is made in large series,an alternative survey scheme may be agreed with the Soci-ety for hull to be surveyed as far as Classification is con-cerned or hull to be certified by the Society on voluntarybasis.

5.1.2 The general requirements for the alternative surveyscheme, BV Mode I, are given in the Society's Rule NoteNR320 as amended.

5.1.3 The alternative survey scheme comprises the follow-ing steps:

• type approval

• yard's recognition based on initial audit and periodicalaudits

• certificate of conformity issued by the yard and submit-ted to the Society for endorsement.

5.2 Type approval

5.2.1 General

The type approval of a hull made of aluminium alloy andbuilt in large series comprises:

• examination, in accordance with the present Rule Noteand the Society Rules for the classification and/or certifi-cation of ships (see Sec 1, [1.1.1], Note 1), of drawingsand documents defining the main structural compo-nents of the hull

• examination of certain items of equipment and their fit-tings if requested by the Society Rules for the classifica-tion and/or certification of ships (see Sec 1, [1.1.1],Note 1)

• inspection of the first hull (or a hull representing thelarge series production).

5.2.2 Examination of drawings

The structure drawing examination is to be carried out asdefined in [2].

5.2.3 Examination of certain items of equipment

The equipment requiring a particular drawing examinationis defined in the Society Rules for the classification and/orcertification of ships (see Sec 1, [1.1.1], Note 1). As a gen-eral rule, this equipment consists mainly in portholes, deckhatches and doors.

This examination may be carried out as defined in theSociey’s Rules or through an homologation process, at thesatisfaction of the Society.

5.2.4 Inspection

The purpose of the inspection, carried out by a Surveyor ofthe Society according to [3] on the initial hull of the series(or a representative hull of the series), is to make surveys atyard during unit production with regards to approved draw-ings, yard's response to comments made by the Society dur-ing structure review examination and constructionrequirements .

5.2.5 Type Approval Certificate

A Type Approval Certificate (TAC) is issued for the initialhull covered by the type approval procedure.

5.3 Quality system documentation

5.3.1 The quality system documentation submitted to theSociety is to include the information required in [3.1] and inNR320 as amended.


NR 561, Sec 9

5.4 Manufacturing, testing and inspection plan (MTI plan)

5.4.1 For each type of hull , the manufacturing, testing andinspection plan is to detail specifically:• Materials:

Special requirements of the supplier (storage conditions,type of checks to be performed on incoming productsand properties to be tested by the yard before use).• Storage conditions:

Information about storage sites (ventilation condi-tions to avoid condensation, supplier data sheetsspecifying the storage conditions, listing documentsto record arrival and departure dates for consign-ment).

• Reception:Information about consignment (traceability of con-signment specifying date of arrival, type of inspec-tion, check on product packaging, types of specifictests performed).

• Traceability:Description of the yard process to ensure traceabilityof the materials from the time of the reception to theend of the production operations.

• Hull construction:Description of the yard process to ensure that the scant-lings and construction meet the rule requirements inrelation to the approved drawings.

• Installation of internal structure:

Information about the main operations of the internalstructure installation.

• Equipment:

The main equipment to be covered by the rules of theSociety are portholes, windows and deck hatches,watertight doors, independent tanks and rudders, thescheduled tests and traceability on the equipment uponarrival and/or after installation.

• Testing and damage reference documents:

For all the previously defined MTI plan processes, pro-cedures are to be written, defining the types of tests orinspections performed, the acceptance criteria and themeans of handling nonconformities.

5.5 Society’s certificate

5.5.1 Certificate of recognition

After completion of the examination, by the Society, of thequality assurance manual, the MTI plan and the yard audit,a Certificate of recognition may be granted as per the provi-sions of NR320 as amended.

5.5.2 Certificate of conformity

Each hull may be certified individually upon request madeto the Society.


NR 561, App 1

APPENDIX 1 ALUMINIUM PROPERTIES

1 Mechanical properties

1.1 General

1.1.1 The mechanical properties of aluminium alloys arereminded in Tab 1 and Tab 2, for information only.

Note 1: The present Tables come from NR216 Materials and Weld-ing, Ch 3, Sec 2, January 2011 issue. It may be necessary to ensurethat these Tables are still the same than those defined in the issue inforce of NR216 Materials and Welding.

Table 1 : Mechanical properties for rolled products with 3 mm ≤ t ≤ 50 mm

Grade Temper conditionThickness t

(mm)Yield strength Rp 0,2 min

(N/mm2)Tensile strength Rm min

or range (N/mm2)

Elongation min (%) (1)

A50 mm A5d

5083

0 3 ≤ t ≤ 50 125 275 - 350 16 14

H112 3 ≤ t ≤ 50 125 275 12 10

H116 3 ≤ t ≤ 50 215 305 10 10

H321 3 ≤ t ≤ 50 215 - 295 305 - 385 12 10

5383

O 3 ≤ t ≤ 50 145 290 17

H116 3 ≤ t ≤ 50 220 305 10 10

H321 3 ≤ t ≤ 50 220 305 10 10

5059

O 3 ≤ t ≤ 50 160 330 24

H1163 ≤ t ≤ 20 270 370 10 10

20 < t ≤ 50 260 360 10 10

H3213 ≤ t ≤ 20 270 370 10 10

20 < t ≤ 50 260 360 10 10

5086

O 3 ≤ t ≤ 50 95 240 - 305 16 14

H1123 ≤ t ≤ 12,5 125 250 8

12,5 < t ≤ 50 105 240 9

H116 3 ≤ t ≤ 50 195 275 10 (2) 9

5754 O 3 ≤ t ≤ 50 80 190 - 240 18 17

5456

O3 ≤ t ≤ 6,3 130 - 205 290 - 365 16

6,3 < t ≤ 50 125 - 205 285 - 360 16 14

H116

3 ≤ t ≤ 30 230 315 10 10

30 < t ≤ 40 215 305 10

40 < t ≤ 50 200 285 10

H321

3 ≤ t ≤ 12,5 230 - 315 315 - 405 12

12,5 < t ≤ 40 215 - 305 305 - 385 10

40 < t ≤ 50 200 - 295 285 - 370 10

(1) Elongation in 50 mm applies for thicknesses up to and including 12,5 mm and in 5d for thicknesses over 12,5 mm.(2) 8% for thicknesses up to and including 6,3 mm.


NR 561, App 1

Table 2 : Mechanical properties for extruded products with 3 mm ≤ t ≤ 50 mm

Grade Temper condition Thickness t (mm)Yield strength Rp 0,2 min

(N/mm2)Tensile strength Rm min

or range (N/mm2)

Elongation min (%) (1) (2)

A50mm A5d

5083

0 3 ≤ t ≤ 50 110 270 - 350 14 12

H111 3 ≤ t ≤ 50 165 275 12 10

H112 3 ≤ t ≤ 50 110 270 12 10

5383

0 3 ≤ t ≤ 50 145 290 17 17

H111 3 ≤ t ≤ 50 145 290 17 17

H112 3 ≤ t ≤ 50 190 310 13

5059 H112 3 ≤ t ≤ 50 200 330 10

5086

0 3 ≤ t ≤ 50 95 240 - 315 14 12

H111 3 ≤ t ≤ 50 145 250 12 10

H112 3 ≤ t ≤ 50 95 240 12 10

6005A

T5 3 ≤ t ≤ 50 215 260 9 8

T63 ≤ t ≤ 10 215 260 8 6

10 < t ≤ 50 200 250 8 6

6060 (3) T5t ≤ 5 120 160 10 10

5 < t ≤ 25 100 140 10 10

6061 T6 3 ≤ t ≤ 50 240 260 10 8

6106 T5 t ≤ 6 200 250 10 10

6082

T5 3 ≤ t ≤ 50 230 270 8 6

T63 ≤ t ≤ 5 250 290 6

5 < t ≤ 50 260 310 10 8

(1) The values are applicable for longitudinal and transverse tensile test specimens as well.(2) Elongation in 50 mm applies for thicknesses up to and including 12,5 mm and in 5d for thicknesses over 12,5 mm.(3) 6060 alloy is not to be used for structural members sustaining dynamic loads (slamming and impact loads). The use of 6106

alloy is recommended in that case.


NR 561, App 1


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