rina partbchap04 reinforced plastic hulls charter yachts

Part BHull

Chapter 4

REINFORCED PLASTIC HULLS

SECTION 1 GENERAL REQUIREMENTS

SECTION 2 MATERIALS

SECTION 3 CONSTRUCTION AND QUALITY CONTROL

SECTION 4 LONGITUDINAL STRENGTH

SECTION 5 EXTERNAL PLATING

SECTION 6 SINGLE BOTTOM

SECTION 7 DOUBLE BOTTOM

SECTION 8 SIDE STRUCTURES

SECTION 9 DECKS

SECTION 10 BULKHEADS

SECTION 11 SUPERSTRUCTURES

SECTION 12 SCANTLINGS OF STRUCTURES WITH SANDWICH CONSTRUCTION

RINA Rules for Charter Yachts 133

Pt B, Ch 4, Sec 1

SECTION 1 GENERAL REQUIREMENTS

1 Field of application

1.1

1.1.1 Chapter 4 of Section B applies to monohull yachtswith a hull made of composite materials and a length L notexceeding 60 m, with motor or sail power with or withoutan auxiliary engine.

Multi-hulls or hulls with a greater length will be consideredcase by case.

In the examination of constructional plans, RINA may takeinto consideration material distribution and structural scant-lings other than those that would be obtained by applyingthese regulations, provided that structures with longitudinal,transverse and local strength not less than that of the corre-sponding Rule structure are obtained or provided that suchmaterial distribution and structural scantlings prove ade-quate, in the opinion of RINA, on the basis of direct test cal-culations of the structural strength. (See Pt B, Ch 1, Sec 1,par. 3.1)

2 Definitions and symbols

2.1 Premise

2.1.1 The definitions and symbols in this Article are validfor all the Sections of this Chapter.

The definitions of symbols having general validity are notnormally repeated in the various Sections, whereas themeanings of those symbols which have specific validity arespecified in the relevant Sections.

2.2 Symbols

2.2.1

γr : density of the resin; standard value 1,2 g/cm3;

γv : density of the fibres; standard value for glassfibres 2,56 g/cm3;

p : mass per area of the reinforcement of a singlelayer, in g/m2;

q : total mass per area of a single layer of the lami-nate, in g/m2;

gc : p/q = content of reinforcement in the layer; forlaminates in glass fibre the most frequent maxi-mum values of gc are the following, taking intoaccount that reinforcements are to be "wet" bythe resin matrix and compacted therein: 0,34for reinforcements in mat or cut filaments, 0,5for reinforcements in woven roving or cloth;

P : total mass per area of reinforcements in the lam-inate, in g/m2;

Q : total mass per area of the laminate, in gm2,excluding the surface coating of resin;

Gc : P/Q = content of reinforcement in the laminate;for laminates with glass fibre reinforcements thevalue of GC is to be not less than 0,30;

ti : thickness of a single layer of the laminate, inmm. In the case of glass reinforcements suchthickness is given by:

p being expressed in kg/m2;

tF : Σti = total thickness of the laminate.

2.3 Definitions

2.3.1

Reinforced plastic : a composite material consistingmainly of two components, amatrix of thermosetting resin andof fibre reinforcements, producedas a laminate through moulding;

Reinforcements : reinforcements are made up of aninert resistant material matrix ofthermosetting resin and of fibrereinforcements, encapsulated inthe matrix (resin) to increase itsresistance and rigidity. The rein-forcements usually consist ofglass fibres or other materials,such as aramid or carbon typefibres;

Single-skin laminate : reinforced plastic material with,in general, the shape of a flat orcurved plate, or moulded.

Sandwich laminate : material composed of two single-skin laminates, structurally con-nected by the interposition of acore of light material.

3 Plans, calculations and other infor-mation to be submitted

3.1

3.1.1 Plans with the scantlings, the layout and the majorstructures of the hull are to be submitted to RINA for exami-nation sufficiently in advance of commencement of thelaminating of the hull.

ti 0 33p 2 56,gc

------------- 1 36,– ,=


Pt B, Ch 4, Sec 1

The plans are to indicate the scantlings and the minimummechanical properties of the laminates as well as the per-centage in mass of the reinforcement in the laminate.

In general, the following plans are to be sent for examina-tion in triplicate.

• the midship section and the transverse sections with themain dimensions of the construction shown and, forconstructions with an engine, the design speed and thedesign acceleration aCG;

• longitudinal & trasversal section and relevant typicalconnections details;

• decks plan;

• construction of the bottom, floors, girders;

• double bottom;

• lamination schedule;

• watertight and subdivision bulkheads;

• superstructures;

• engine and auxiliary foundations.

• structure of stern/side door and relevant closing appli-ances;

• support structure for crane with design loads;

The above-mentioned plans are also to contain the relativelamination details, the percentage, in mass, of the reinforce-ment, the type of resin, core materials characteristics, thesandwich construction process and the type of structuraladhesive utilized (if any). In the case of reinforcementsother than glass, the minimum mechanical properties of thelaminate are to be indicated.

A list of all materials used in the construction including thecommercial name and the relevant characteristic of eachcomponent such as gel coat, resin, fibre reinforcement, corematerial, fire retardant additives or resins, adhesive, corebonding materials, details of the process of sandwich con-struction and details of the materials used for grantingreserve of buoyancy (and method of installation) shall besent with the initial submission of plan and copy of this listshall be provided to the attending Surveyor.The drawing list above is for guidance purposes only; inparticular, the same plan may be relative to one or more ofthe subjects indicated.

Furthermore, for documentation purposes, a copy of the fol-lowing plan is to be submitted:

- general arrangement;

- capacity plan;

- lines plan;

Where an *INWATERSURVEY (In-water Survey) notation isassigned the following plans and information are to be sub-mitted:

• Details showing how rudder pintle and bush clearancesare to be measured and how the security of the pintlesin their sockets are to be verified with the craft afloat.

• Details showing how stern bush clearances are to bemeasured with the craft afloat.

• Name and characteristics of high resistant paint, forinformation only.

3.2

3.2.1 In case a Builder for the construction of a new vesselof a standard design wants to use drawings alreadyapproved for a vessel similar in design and construction andclassed with the same class notation and the same naviga-tion, the drawings may not be sent for approval , but theRequest of Survey for the vessel shall be submitted enclosedto a list of the drawings the Builder wants to refer to andcopy of the approved drawings are to be sent to RINA.Attention is to be paid even to possible additional flagadministartions requirements, which may cause differencesin the constructions.

It's Builder responsability to submit for approval any modifi-cation to the approved plans prior to the commencement ofany work.

Plan approval of standard design vessels is only valid solong as no applicable Rule changes take place. When theRules are amended, the plans are to be submitted for newapproval.

4 Direct calculations 4.1 4.1.1 As an alternative to those based on the formulae inthis Chapter, scantlings may be obtained by direct calcula-tions carried out in accordance with the provisions ofChap. 1, Sec. 1 of these Rules. Chapter 1 provides schematisations, boundary conditionsand loads to be used for direct calculations.The scantlings of the various structures are to be such as toguarantee that stress levels do not exceed the allowable val-ues stipulated in Table 1. The values in column 1 are to beused for the load condition in still water, while those in col-umn 2 apply to dynamic loads.

Table 1

MemberAllowable stresses

1 2

Keel, bottom plating 0,4 σ 0, 8 σ

Side plating 0,4 σ 0,8 σ

Deck plating 0,4 σ 0,8 σ

Bottom longitudinals 0,6 σt 0,9 σt

Side longitudinals 0,5 σt 0,9 σt

Deck longitudinals 0,5 σt 0, 9 σt

Floors and girders 0,4 σt 0,8 σt

Frames and reinforced side stringers 0,4 σt 0,8 σt

Reinforced beams and deck girders 0,4 σt 0,8 σt

Note 1:σ(N/mm2): the ultimate bending strength for single-skin

laminates; the lesser of the ultimate tensilestrength and the ultimate compressive strengthfor sandwich type laminates. In this case theshear stress in the core is to be no greater than0,5 Rt where Rt is the ultimate shear strength ofthe core material;

σt(N/mm2): the ultimate tensile strength of the laminate.

136 RINA Rules for Charter Yachts

Pt B, Ch 4, Sec 1

5 General rules for design

5.1

5.1.1 The hull scantlings required in this Chapter are ingeneral to be maintained throughout the length of the hull.

For yachts with length L greater than 30 m, reduced scant-lings may be adopted for the fore and aft zones.

In such case the variations between the scantlings adoptedfor the central part of the hull and those adopted for theends are to be gradual.

In the design, care is to be taken in order to avoid structuraldiscontinuities in particular in way of the ends of super-structures and of the openings on the deck or side of theyacht.

For high speed hulls, a longitudinal structure with rein-forced floors, placed at a distance of not more than 2 m, isrequired for the bottom.

Such spacing is to be suitably reduced in the areas forwardof amidships subject to the forces caused by slamming.

5.2 Minimum thicknesses

5.2.1 The thicknesses of the laminates of the various mem-bers calculated using the formulae in this Chapter are to benot less than the values, in mm, in Table 2.

Table 2

The minimum values shown are required for laminates con-sisting of polyester resins and glass fibre reinforcements.

For laminates made using reinforcements of fibres otherthan glass (carbon and/or aramid, glass and aramid), lowerminimum thicknesses than those given in Table 2 may beaccepted on the basis of the principle of equivalence.

In such case, however, the thickness adopted is to be ade-quate in terms of buckling strength.

This thickness is, in any case, to be submitted to head officefor approval.

6 Construction

6.1 General

6.1.1 The construction process shall be in accordancewith Sec 3.

6.2 Details of construction

6.2.1 The following requirements refer to the details ofconstruction and structural connections that are most fre-quently used. Other solutions will be considered by RINAin individual cases, on the basis of a criterion of equiva-lence and, in any case, the good practice and the past expe-riences shall be followed. Details of construction shall berepresented in the structural plan.

6.2.2 As a general concept, the continuity of the structuralmembers is to be maintained and every change of sectionshall be gradual.

In the intersections between longitudinal and transversalmembers, the shallower member shall, in general, be con-tinuous under the primary member.

To ensure efficient load transmission, particular care is tobe given to the alignment of the structure and the fitting ofsuitable brackets e.g: side to deck (frames with beams),transom/bulkhead to bottom/deck (transom stiffeners withbottom/deck girders and deck/bottom girders with bulkheadstiffeners).

The Surveyor may require for additional bonding reinforce-ment in case of lack of alignment and for increased endbrackets, if deemed of non sufficient dimensions.

6.2.3 The plating stiffeners (e.g. longitudinals or floors)which are not prefabricated are to be laid up layer by layeron the same plating before polymerization; particular atten-tion is to be given to the bond and the structural continuityat the ends and intersection.

6.2.4 Discontinuities and hard points in the laminates areto be avoided and, to this end:

• variations in laminate thickness are to be by a gradualtaper from the greatest thickness to the smallest; as ageneral rule, there shall be a taper of at least 20 timesthe difference of thickness and, in case of connectionbetween single skin and sandwich construction, thecore material of sandwich shall be tapered too and thelength of this taper shall be at least twice the thicknessof the core itself.

• in way of edges (e.g. bottom edges), steps and similar inlaminates, the single layers are not to be stopped but areto be led beyond the edges for at least 30 mm; everylayer of reinforcement is to have its end staggered withrespect to that of the adjacent layer;

MemberSingle-skin laminate

Sandwichlaminate (1)

Keel, bottom plating 5,5 4,5/3,5

Side plating 5 4/3

Inner bottom plating 5 4,5/3,5

Strength deck plating 4 3/2

Lower deck plating 3 2/2

Subdivision bulkhead plating

2,5 2/2

Tank bulkhead plating 4,5 4/3

Side superstructures 2,5 2/2

Front superstructures 3 2,5/2,5

Girders-floors - 2/2

Any stiffeners - 2 (2)

(1) The first value refers to the external skin, the secondrefers to the internal skin

(2) Intended to refer to the thickness of the layers encapsu-lating the core


Pt B, Ch 4, Sec 1

6.2.5 In the laminates, woven rovings with a mass per area> 600 g/m2 are not to be superimposed directly, but are tobe separated by the interpositioning of a mat, preferablywith a mass per area of < 450 g/m2 so as to achieve a moreeffective bond.

6.2.6 The structural materials (e.g. plywood) fitted in thelaminates (as insert or backing pad) for increasing the localstrength in way of the attachment of fitting are to have cleanand prepared surfaces so as to achieve a satisfactory bondand have beveled edges. Joints between successive layerare to be overlapped.

Single skin lamination in way of the attachments of fittingsmay be accepted provided that the local thickness is 1,5times the adjacent thickness, with the additional layers lam-inated beyond the extremities of the surrounding stiffeners.Sandwich structures shall be taken to single skin structuresin way of the attachment of fittings and suitably reinforced.

6.2.7 Where through hull fittings are provided, particularcare is to be taken to seal the hull laminate. In case of sand-wich structures, backing pad of suitable dimensions are tobe provided in order to avoid concentration of forces. Oth-erwise, the core in way of the fittings may be replaced witha solid or high density core always sealing the hull lami-nate.

6.2.8 Where the strength of a stiffener is impaired by anyopening or holes for drainage, compensation is to be pro-vided. In any case, as a general rule, the depth of drainageholes in the stiffeners shall not exceed 30% of the depth ofthe stiffener and shall be positioned at the quarter span ofthe stiffener; furthermore, in general, openings into web'sstiffeners are to have a depth not exceeding half of thedepth of the web and are to be so located that the edges arenot less than 25% of the web depth from the face laminate.

The length of these openings shall be not greater than thedepth of the web or 60% of the secondary member spacing,whichever is greater. Details to be sent for approval.

6.2.9 The corners of all openings are to be well rounded,with the openings supported on all sides. Openings ondecks are to be supported by beams and deck girdersarranged on the edges.

The edges of cut-outs for openings in single-skin laminatesare to be well sealed. Where they are exposed to liquids orto humid environments, they are to be sealed with two lay-

ers of mat of 450 g/m2 or its equivalent.

The edges of cut-outs for openings in sandwich laminatesare to be closed with a stiffener of thickness not less thanthat of the external skin. If no epoxide resin is used for thelamination, the first layer of such laminate is to be applied

with a mat of mass not exceeding 450 g/m2.

6.2.10 Pipes and cables passing through spaces filled withexpanded material are to be situated in plastic conduits soas to make removal and replacement easier.

6.2.11 The joints of the single layers of reinforcement of alaminate are to be overlap joints (see Figures 1, 2 and 3)and the joint of each layer is to be staggered with respect tothe two adjacent layers.

Figure 1 : Hull centreline structure

Figure 2 : Open type skeg

Bottom Keel

Bottom

Connectionzone


Pt B, Ch 4, Sec 1

Figure 3 : Typical transom boundaries

Figure 1: typycal for yachts fitted with skeg . Where a skegis not fitted, a centre line stiffener/girder is to be added.

Figure 2: open skeg If a deeper open skeg is provided, dia-phragm plates with upper closing flange may be required,with skeg filled up with foam.

Figure 3: Typical transom boundaries.

6.2.12 As far as the side shell and bottom shell connectionconcerns, a chine reinforcement shall always be provided;a structural foam infill shall be provided between the sideshell and the bottom shell along the chine line. Chine railsare to be over laminated on the inner surface of the hull. Incase of sandwich structures, they shall be returned to singleskin laminates al chine rail. Chine details are to be submit-ted for approval (enclosed to the drawing "typical Details").

6.3 Connections of laminates

6.3.1 GeneralConnections of laminates are to be made with joints that donot affect the strength and structural continuity of the lami-nates themselves.

Before proceeding with any connection the surfaces onwhich the layers are placed are to be cleaned thoroughlyand then brushed with a wire brush in order to raise thefibres of the laminate as much as possible. If a surface iscovered by gel coat, this is to be removed completely.

Laminates may be connected mechanically with corrosionresistant bolts, rivets or screws spaced at intervals such asnot to affect the effectiveness of the joint. Thin washers oflarge diameter are to be used under both the head and thenut of the bolts. An adhesive of suitable type having sealingcharacteristic may be incorporated within the joint. In anycase, the edges of the laminate and the holes are to be ade-quately sealed.

6.3.2 Butt-jointsButt joints are to be carried out as shown in Figure 4, whichis relevant to the joint of the keel of a prefabricated hull inhalves.

Figure 4

6.3.3 Hull to deck connection

Examples of watertight connection, of overlap type, for theconnection of an upper deck to a separately prefabricatedhull side are shown in Figures 5 and 6. Different solutionsmay be accepted.

The connection is obtained interposing, between the con-tact areas of the laminates to be joined, a compliant resin(or similar sealing adhesive product) and a mat on resin andoverlapping the joint itself, e.g. on the internal side of thehull, a butt strap made of laminate having a thickness notless than half of the lesser of the two laminates.

As an alternative to such a butt strap, a bolt connection maybe adopted, generally using steel bolts or rivets having adiameter d not less than the lesser thickness of the laminatesto be connected, spacing equal to 10 d and zigzag distribu-tion.

The head and the nut of the bolts and the riveting of rivetsare to be against a thin washers of large diameter. An adhe-sive of suitable type having sealing characteristic may beincorporated within the joint. In any case, the edges of thelaminate and the holes are to be adequately sealed and boltnuts are to remain securely fastened after tightening.

In narrow spaces, such as the stem in the zone of connec-tion between the deck and the hull, below the bulwark,dedicated holes are to be cut in order to reach the space tobe laminated.

Figure 5

B / 10 min


Pt B, Ch 4, Sec 1

Figure 6

6.3.4 House/Deck connectionAdequate support under the ends of houses is to be pro-vided in the form of webs, pillars or bulkheads in conjunc-tion with reinforced deck beams. The connection of thehouse to the deck is to be done avoiding stress concentra-tion and providing an adequate load distribution

6.3.5 Corner jointsCorner joints are normally used to connect stiffeners to plat-ing (longitudinals, frames, internal mouldings etc.) or forboundary connections of bulkheads (see Figure 7).

Figure 7

The scantlings of such connections are to be as follows:

• Ω shaped stiffeners: plate laminate connected to platinghaving a width not less than 50 mm (25 mm for the first

layer) plus 20 mm for each: 1000 g/m2 of subsequentlayers;

a) b) c)

d)

Seam accessiblefrom one side only

Pre-fabricatedsection


Pt B, Ch 4, Sec 1

• other stiffeners: two angle bars, each having side andscantlings as above except where stiffeners are of ply-wood, in which case the angle bars are to have a thick-ness not less than 0,25 t, t being the thickness of theplywood, but in any case no less than 2 mm;

• bulkheads: connections to the plating by means of twoangle bars, one on each side and each having:• side = 50 mm for the first layer plus 40 mm for each

1000 g/m2 of the subsequent layers;• thickness = 2 mm, or if greater, = 0,5 tmin, where tmin

is the lesser thickness of the layers to be connected.

The thickness of such angle bars, in the case of plywoodbulkheads, is to be equal to 2 mm or, if greater, equal to0,25 t, t being the thickness of the plywood.

Where access is not possible from one side, the only anglebar fitted is to have scantlings equivalent to those of the twoangle bars mentioned above.

The bulkheads to hull connections shall be realized by fill-ing with compliant resin or similar filler the contact zonebetween hull (girders and/or floors) and the bulkhead. Samearrangement in the upper connection between bulkheadand deck. Furthermore, the core of the stiffeners abovewhich the bulkheads are fitted is recommended to be ofhigh density type in way of the bulkheads.

Details of the compliant resins for structural filleting appli-cation to be used in the construction and the over bondingis to be submitted. Characteristics of compliant resins to beenclosed to the list required in par 3.1.1.

6.4 Engine exhaust

6.4.1 Engine exhaust discharge arrangements made oflaminates are to be of the water injection type with a nor-mal service temperature of approximately 70° C and a max-imum temperature not exceeding 120° C.

6.4.2 The resins used for the lamination are to be typeapproved and to have adequate resistance to heat and tochemical agents as well as a high deflection temperature.As a general rule, the exhaust ducts are to be internallycoated with two layers of mat of 600 g/m2 laminated withvinylester resin; a flame-retardant or self-extinguishing poly-ester resin with a low deflection at high temperature may beaccepted. Details of these resins are to be enclosed to thelist required in par 3.1.1 and general characteristic to bereported on relevant drawings.

6.4.3 Additives or pigments which may impair themechanical properties of the resin are not to be used.

6.4.4 laminated with a flame-retardant or self-extinguishingpolyester resin.

6.5 Tanks for liquids

6.5.1 Structural tanks, i.e. those that are part of the hulland intended to contain fuel oil or lube oil, are to be madefrom single-skin laminates. Minimum thickness is to be notless than 10 mm. For other tanks, the minimum allowedthickness of single skin laminates is 4,5mm.

The tank is to be isolated from the rest of the hull by meansof diaphragms made of laminates arranged inside all the(longitudinal and/or transverse) stiffeners such that, in theevent of damage to the stiffener laminate, the liquid con-tained cannot leak (from inside the stiffener) outside thetank.

Sandwich type laminates may be accepted subject to condi-tions laid down by RINA, and provided that, in any case,the thickness of the inner skin in contact with the liquid isnot less than 10 mm and that internal diaphragms arearranged separating the tank from the rest of the hull.

Internal structure and laminate are to be coated with a resinresistant to hydrocarbons and externally with one which isself-extinguishing, both resins being certified by the Manu-facturer (details of these resins to be enclosed to the listrequired in par 3.1.1).

Mechanical tests are to be carried out on samples of thelaminate "as is" shall be and after immersion in the fuel oilat ambient temperature for a week. After immersion themechanical properties of the laminate are to be not lessthan 80% of the values of the samples "as is". The samplesshall be sealed the on all sides (with the hydrocarbonsresistant resin or gealcoat as used in the construction) inorder to have produce a good tests.

The edges of the samples are to be adequately sealed inorder to prevent the infiltration of fuel oil inside the lami-nate.

6.5.2 Where the tank is formed by plywood bulkheads, itssurface is to be completely protected against the ingress ofliquid by means of a layer of laminate of thickness of atleast 4 mm.

6.5.3 Tanks, complete with all pipe connections, are to besubjected to a hydraulic pressure test with a head above thetank top equal to h, as defined in Chap. 1, Sec. 5, or to theoverflow pipe, whichever is the greater.

At the discretion of RINA, leak testing with an air pressureof 0,15 bar may be accepted as an alternative, provided thatit is possible, using liquid solutions of proven effectivenessin the detection of air leaks, to carry out a visual inspectionof all parts of the tanks with particular reference to pipeconnections.


Pt B, Ch 4, Sec 2

SECTION 2 MATERIALS

1 General

1.1

1.1.1 In addition to those in this Section, provisionsregarding the characteristics and test and quality controlprocedures for the manufacture of composite materials arealso specified in Part D, Chap 6 of these Rules.

1.1.2 The basic laminate considered in this Chapter iscomposed of an unsaturated resin, in general polyester, andof glass fibre reinforcements in the form of mat alternatedwith woven roving. The construction may consist of a sin-gle-skin laminate, a sandwich laminate, or a combination ofboth.

The reinforcement contained in the laminate is not less than30% by weight; it is laid-up by hand, by mechanical pre-impregnation, or by spraying.

Laminates having a different composition or special systemsof lay-up will be considered by RINA on a case-by-casebasis upon submission of technical documentation illustrat-ing details of the procedure.

All of the materials making up the laminates are to haveproperties suitable for marine use in the opinion of theManufacturer. The products used in the production of thelaminates, whether single-skin or sandwich (resins, rein-forcements, stiffeners, cores, etc.), are to be type approvedby RINA; any structural parts in plywood are to be madewith material type approved by RINA. At the discretion ofthe latter, material type approved by other recognised Soci-eties may be accepted.

2 Definitions and terminology

2.1

2.1.1

Mat : Reinforcements made up of regu-larly distributed filaments on theflat with no particular orientationand held together by a bond so asto form a mat that can be rolledup. The filaments may be cut to apre-determined length or continu-ous.

Roving : Made up of parallel filaments.

Woven Roving : Made from the weaving of roving.Due to their construction theyhave continuous filaments.Woven rovings of different typesexist and can be differentiated by:the type of roving used in warp

and weft, the name of the distri-bution per unit of length, respec-tively in warp and weft.

Mat -woven Roving : Combined reinforcement madeup of a layer of mat with cut fila-ments superimposed on a layer ofwoven roving by stitching orbonding.

Hybrid : Reinforcement having fibres oftwo or more different types; a typ-ical example is that of glass fibrewith aramid type fibre.

Unidirectional : Reinforcement made up of fibresthat follow only one directionwithout interweaving.

Biaxial : Reinforcement made up of fibresthat follow two directions (0°-90°), without interweaving.

Quadriaxial : Reinforcement made up of paral-lel fibres in the direction of fillingand warp (0°, 90°) and in twooblique directions (+ 45°).

3 Materials of laminates

3.1 Resins

3.1.1 Resins used are to be of type approved by RINA formarine use.

Resins may be for laminating, i.e. form the matrix of lami-nates, or for surface coating (gel coat); the latter are to becompatible with the former, having mainly the purpose ofprotecting the laminate from external agents.

Polyester-orthophthalic type gel coat resins are not permit-ted. In the case of a hull constructed with a sandwich lami-nate on a male mould, the water resistance of the externalsurface will be the subject of special consideration.

Resins are to have the capacity for "wetting" the fibres of thelaminate and for bonding them in such a way that the lami-nate has suitable mechanical properties and, in the case ofglass fibre, not less than those indicated in 3.6.

The resins used are in general of the polyester, polyestervi-nylester or epoxide type; in any case, the resin is to have anultimate elongation of not less than 3,0% if on the surfaceand 2,5% if in the laminate.

Compliant resins used in different structural applicationsare, as a general rule, to be used always in conjunction withover bonding lamination. The acceptance of structural fil-lets of compliant resins alone, without over bonding lami-nation will be subject to special consideration after analysis


Pt B, Ch 4, Sec 2

of test results submitted by the manufacturer demonstratingequivalent strength to over bonding laminates.

Resins are to be used within the limits and following theinstructions supplied by the Manufacturer.

3.1.2 Resins additivesResin additives (catalysts, accelerators, fillers, wax additivesand colour pigments) are to be compatible with the resinsand suitable for their curing process. Catalysts which initi-ate the curing process of the resin and the acceleratorswhich govern the gelling and setting times are to be suchthat the resin sets completely in the environmental condi-tions in which manufacture is carried out. The Manufac-turer's recommendations for the level of catalyst andaccelerator to be mixed into the resins are to be followed.

The inert fillers are not to significantly alter the properties ofthe resin, with particular regard to the viscosity, and are tobe carefully mixed distributed in the resin itself in such away that the laminates have the minimum mechanicalproperties stated in these requirements.

Such fillers are not to exceed 13% (including 3% of anythixotropic filler) by weight of the resins.

The color pigments are not to affect the polymerizationprocess of the resin, are to be added to the resin as acolored paste and are not to exceed the maximum amount(in general 5%) recommended by the Manufacturer. Thethixotropic fillers of the resins for surface coating are not toexceed 3% by weight of the resin itself.

Details of the resins additives are to be enclosed in the listrequired in Sec 1, par 3.1.1.

3.1.3 Flame-retardant additivesWhere the laminate is required to have fire-retarding orflame-retardant characteristics, details of the proposedarrangements are to be submitted for examination.

Where additives are adopted for this purpose, they are to beused in accordance with the Manufacturer's instructions.

The results of tests performed by independent laboratoriesverifying the required characteristics are to be submitted.

Where fire-retarding or flame-retardant characteristics arerequired by the flag Administration, such properties are tobe approved by the relevant Administration, or by RINAwhen authorized by the former.

Details of flame-retardant additives are to be enclosed inthe list required in Sec 1, par 3.1.1.

3.2 Reinforcements

3.2.1 GeneralAll fibre reinforcements are to be of type approved byRINA. The reinforcement used and their characteristics areto be enclosed to the list required in Sec 1 par 3.1.1.

The reinforcements taken into consideration in theserequirements are mainly of fibres of three types: glass fibre,aramid type fibre and carbon type fibre.

The use of hybrid reinforcements obtained by coupling theabove-mentioned fibres is also foreseen.

Structures can be obtained using reinforcements of one ormore of the above-mentioned materials.

In the latter case the laminates may be made in alternatelayers, i.e. made up of layers of one material or using hybridreinforcements.

In any event, the manufacturing process is to be approvedin advance by RINA, and to this end a technical report is tobe sent illustrating the processes to be followed and thematerials (resins, reinforcements, etc.) used.

Reinforcements made of materials other than the precedingmay be taken into consideration on a case-by-case basis byRINA, which will stipulate the conditions for their accept-ance.

The materials are to be free from imperfections, discolora-tion, foreign bodies, moisture and other defects and storedand handled in accordance with the manufacturer's recom-mendations.

3.2.2 Glass fibreThe glass generally used for the manufacture of reinforce-ments is that called type "E", having an alkali content of notmore than 1%, expressed in Na2O.

Reinforcements manufactured in "S" type glass may also beused.

Such reinforcements are to be used for the lamination inhull resin matrices, with the procedure foreseen by theManufacturer, such that the laminates have the samemechanical properties required in the structural calcula-tions and for "E" type glass, these not being less than thoseindicated in 3.6.

Reinforcements in glass fibre are generally foreseen in theform of: continuous filament or chopped strand mat, roving,unidirectional woven roving and in combined products i.e.made up of both mat and roving.

3.2.3 Aramid type fibresReinforcements in aramid type fibres are generally used inthe form of roving or cloth of different weights (g/m2).

Such reinforcements can be used in the manufacture ofhulls either alone or alternated with layers of mat or rovingof "E" type glass.

Hybrid reinforcements, in which the aramid type fibres arelaid at the same time, in the same layer as "E" type glassfi-bres or carbon type fibres, may also be used.

3.2.4 Carbon-graphite fibresCarbon-graphite type fibres means those which are atpresent called "carbon" type, used in the form of productssuitable to be incorporated as reinforcements by themselvesor together with other materials like glass fibres or aramidtype fibres, in resin matrices for the construction of struc-tural laminates.

3.3 Core materials for sandwich laminates

3.3.1 Core materials are to be of type approved by RINA;these materials shall be used in accordance with manufac-turer's instructions and the method used in the sandwichconstruction shall be forwarded for information purposesenclosed to the list required in Sec 1, par 3.1.1.

The materials considered in these requirements are rigidexpanded foam plastics and balsa wood.


Pt B, Ch 4, Sec 2

Particular care is to be given to the handle of these materi-als which shall be in accordance to the manufacturer's rec-ommendations.

The use of other materials will be taken into considerationon a case-by-case basis by RINA, which will decide theconditions for acceptance on the basis of a criterion ofequivalence.

Polystyrene can only be used as buoyancy material.

3.3.2 "Rigid expanded foam plastics" means expandedpolyurethane (PUR) and polyvinyl chloride (PVC).

These materials, just as other materials used for cores, are tobe of the closed-cell type, resistant to environmental agents(salt water, fuel oils, lube oils) and to have a low absorptionof water characteristics.

Furthermore, they are to maintain a good level of resistanceup to the temperature of 60°C, and if worked in nonrigidsheets made up of small blocks, the open weave backingand the adhesive are to be compatible and soluble in theresin of the laminate.

3.3.3 Balsa wood is to be chemically treated againstattacks by parasites and mould and oven dried immediatelyafter cutting.

Its humidity is to be no greater than 12%; if worked in non-rigid sheets made up of small blocks, the open weave back-ing and the adhesive are to be compatible and soluble inthe resin of the laminate.

The balsa wood is to be laid-up with its grain at right-anglesto the fibres in the surface laminates.

3.3.4 The ultimate tensile strength of the core materials isto be not less than the values indicated in Table 1. Suchcharacteristic is to be ascertained by tests; in any case, corematerials for laminates having an ultimate tensile strength<0,4 N/mm2 are not acceptable.

3.3.5 For the constructions of sandwich structures with thedry vacuum bagging techniques core bonding paste are tobe used; their characteristics are to be enclosed in the list asper Sec 1, par 3.1.1. The construction procedures of suchsandwich structures will be subject to special considera-tion.

Table 1

3.4 Adhesive and sealant material

3.4.1 These materials are to be accepted by RINA beforeuse. Detail to be submitted enclosed to the list required inSec 1 par 3.1.1.

3.5 Plywood

3.5.1 Plywood for structural applications is to be marineplywood type approved by RINA.

Where it is used for the core of reinforcements or sandwichstructures, the surfaces are to be suitably treated to enablethe absorption of the resin and the adhesion of the laminate.

3.6 Timber

3.6.1 The use of timber is subject to special considerationby Head Office. In general, the designer will have to indi-cate on submitted drawings the assumed characteristicssuch as strength and density.

3.7 Repair compounds

3.7.1 Materials used for repairs are to be accepted byRINA before use.

For acceptance purposes, the manufacturer is to submit fullproduct details, and user instructions, listing the types ofrepair for which the system is to be used.

Dependent on the proposed uses, RINA may require sometests.

3.8 Type approval of materials

3.8.1 Recognition by RINA of the suitability for use (typeapproval) of materials for hull construction may berequested by the Manufacturer. The type approval of res-ins, fibre products of single-skin laminates and core materi-als of sandwich laminates is carried out according to therequirements set out in the relevant RINA Rules.

Table 2 lists the typical mechanical properties of fibrescommonly used for reinforcements.

4 Mechanical properties of laminates

4.1 General

4.1.1 The minimum mechanical properties in N/mm2 oflaminates made with reinforcements of "E" type glass fibremay be obtained from the formulae given in Table 3 as afunction of GC of the laminate as defined in Section 1.

These values are based on the most frequently used lami-nates made up of reinforcements of mat and roving type.

In the above-mentioned Table, the values indicated arethose corresponding to GC = 30, the minimum valueallowed of the content of glass reinforcement.

The minimum mechanical properties of the glass laminatesfound in testing, as a function of GC, are to be no less thanthe values obtained from the formulae of the above-men-tioned Table.

Materiale Density (kg/m3)Ultimate tensile

strength (N/mm2)

Balsa

96 1,1

144 1,64

176 2,1

Polyvinyl chloride (PVC)

55 0,73

90 1,3

Polyurethane(PUR)

60 0,4

90 0,5


Pt B, Ch 4, Sec 2

Laminates with reinforcements of fibres other than glass,described in 3.2, are to have mechanical properties that arein general greater than or at least equal to those given inTable 3, the reinforcement content being equal. RINAreserves the right to take into consideration possible lami-nates having certain properties lower than those given inTable 3, and will establish the procedures and criteria forapproval on case by case.

The scantlings indicated in this Chapter are based on thevalues of the mechanical properties of a laminate madewith reinforcements in "E" type glass, with a reinforcementcontent equal to 0,30.

Whenever the mechanical properties of the reinforcementare greater than those mentioned above, the scantlings maybe modified in accordance with the provisions of 3.6.2below.

The mechanical properties and the percentage of reinforce-ment are to be ascertained, for each yacht built, from testson samples taken preferably from the hull or, alternatively,having the same composition and prepared during the lam-ination of the hull ( for the tests to be carried out, s ee Pt D,Ch 6, Sec.3).

Table 2

Table 3

The values of the mechanical properties are to be no lessthan those used for the scantling of the structures.

Where certain values are in fact found to be lower thanthose used for the scantlings, but no lower than 85% of thelatter, RINA reserves the right to accept the laminate subjectto any conditions for acceptance it may stipulate.

4.2 General

4.2.1 Coefficients relative to the mechanical properties of laminates

The values of the coefficients Ko and Kof relative to themechanical properties of the laminates that appear in theformulae of the structural scantlings of the hull in this Chap-ter are given by:

Specific gravityTensile modulus of elastic-

ity N/mm2

Shear modulus of elasticity N/mm2 Poisson’s ratio

E Glass 2,56 69000 28000 0,22

S Glass 2,49 69000 (1) 0,20

R Glass 2,58 (1) (1) (1)

Aramid 1,45 124000 2800 0,34

LM Carbon 1,8 230000 (1) (1)

IM Carbon 1,8 270000 (1) (1)

HM Carbon 1,8 300000 (1) (1)

VHM Carbon 2,15 725000 (1) (1)

(1) Values supplied by the Manufacturer and agreed upon with RINA prior to use

1 2

Rm = ultimate tensile strength = 1278 G2c - 510 Gc + 123 85

E = tensile modulus of elasticity = (37 Gc - 4,75) . 103 6350

Rmc = ultimate compressive strength = 150 Gc + 72 117

Ec = compressive modulus of elasticity = (40 Gc - 6) . 103 6000

Rmf = ultimate flexural strength = (502 G2c + 107) 152

Et = flexural modulus of elasticity = (33,4 G2c + 2,2) . 103 5200

Rmt = ultimate shear strength = 80 Gc + 38 62

G = shear modulus of elasticity = (1,7 Gc + 2,24) . 103 2750

Rmti = ultimate interlaminar shear strength = 22,5 - 17,5 Gc 17

Ko 85 Rm⁄=


Pt B, Ch 4, Sec 2

where Rm and Rmf are the values, in N/mm2, of the ultimatetensile and flexural strengths of the laminate. Such valuesmay be calculated with the formulae in Table 3 for glassfibre reinforcements or obtained from mechanical tests onsamples of the laminate for other types of laminate.

Therefore, in the case of laminates with glass fibre havingGC = 30 (minimum allowed), it Is to be assumed that::

The values Ko and Kof are to be taken as not less than 0,5and 0,7, respectively, except in specific cases consideredby RINA on the basis of the results of tests carried out.

For laminates of sandwich type structures the coefficient isgiven by the formula:

where Rm is the ultimate tensile strength, in N/mm2, of thesurface laminate.

Kof152Rmf

----------

0 5,

=

Ko 1=

Kof 1=

Kof′ 85

Rm

------

0 5,

=


Pt B, Ch 4, Sec 3

SECTION 3 CONSTRUCTION AND QUALITY CONTROL

1 Shipyards or workshops

1.1 General

1.1.1 All construction are to be built using materials andworking process approved or accepted by RINA.

The Builder has to obtain the approval or acceptance of thematerials he uses; furthermore it is the Builder responsibilityto ensure that all the materials are used in accordance withthe manufacturer's instruction and recommendations.

Shipyards or workshops for hull construction are to be suit-ably equipped to provide the required working environ-ment according to these requirements, which are to becomplied with for the recognition of the shipyard or work-shop as suitable for the construction of hulls in reinforcedplastic. This suitability is to be ascertained by a RINA Sur-veyor, the responsibility for the fulfilment of the require-ments specified below as well as all other measures for theproper carrying out of construction being left to the ship-yard or workshop.

When it emerges from the tests carried out that the shipyardor workshop complies with the following provisions, usestype approved materials, and has a system of productionand quality control that satisfies the RINA Rules, so as toensure a consistent level of quality, the shipyard or work-shop may obtain from RINA a special recognition of suita-bility for the construction of reinforced plastic hulls.

The risks of contamination of the materials are to bereduced as far as possible; separate zones are to be pro-vided for storage and for manufacturing processes. Alterna-tive arrangements of the same standard may be adopted.

Compliance with the requirements of this Section does notexempt those in charge of the shipyard or workshop fromthe obligation of fulfilling all the hygiene requirements forwork stipulated by the relevant authorities.

1.2 Moulding shops

1.2.1 Where hand lay-up or spray lay-up processes areused for the manufacture of laminates, a temperature ofbetween 16° and 32°C is to be maintained in the mouldingshop during the lay-up and polymerisation periods. Smallvariations in temperature may be allowed, at the discretionof the RINA Surveyor, always with due consideration beinggiven to the resin Manufacturer's recommendations.Where moulding processes other than those mentionedabove are used, the temperatures of the moulding shop areto be established accordingly.

The relative humidity of the moulding shop is to be kept aslow as possible, preferably below 70%, and in any caselower than the limit recommended by the resin Manufac-turer. Significant changes in humidity, such as would lead

to condensation on moulds and materials, are to beavoided.

Instruments to measure the humidity and temperature are tobe placed in sufficient number and in suitable positions. Ifnecessary, due to environmental conditions, an instrumentcapable of providing a continuous readout and record ofthe measured values may be required.

Ventilation systems are not to cause an excessive evapora-tion of the resin monomer and draughts are to be avoided.

The work areas are to be suitably illuminated. Precautionsare to be taken to avoid effects on the polymerisation of theresin due to direct sunlight or artificial light.

1.3 Storage areas for materials

1.3.1 Resins are to be stored in dry, well-ventilated condi-tions at the temperature recommended by the resin Manu-facturer. If the resins are stored in tanks, it is to be possibleto stir them at a frequency for a length of time indicated bythe resin Manufacturer. When the resins are stored outsidethe moulding shop, they are to be brought into the shop indue time to reach the working temperature required beforebeing used.

Catalysts and accelerators are to be stored separately inclean, dry and well-ventilated conditions in accordancewith the Manufacturer's recommendations.

Fillers and additives are to be stored in closed containersthat are impervious to dust and humidity.

Reinforcements, e.g. glass fibre, are to be stored in dust-freeand dry conditions, in accordance with the Manufacturer'srecommendations. When they are stored outside the cut-ting area, the reinforcements are to be brought into the lat-ter in due time so as to reach the temperature of themoulding shop before being used.

Pre-impregnated reinforcements are to be stored in an areaset aside for the purpose. The quality control documenta-tion is to keep a record of the storage and depletion of thestock of such reinforcements.

Materials for the cores of sandwich type structures are to bestored in dry areas and protected against damage; they areto be stored in their protective covering until they are used.

1.4 Identification and handling of materials

1.4.1 In the phases of reception and handling the materialsare not to suffer contamination or degradation and are tobear adequate identification marks at all times, includingthose relative to RINA type approval. Storage is to be soarranged that the materials are used, whenever possible, inchronological order of receipt. Materials are not to be usedafter the Manufacturer's date of expiry, except when the lat-ter has given the hull builder prior written consent.


Pt B, Ch 4, Sec 3

2 Hull construction processes

2.1 General

2.1.1 The general requirements for the construction ofhand lay-up or spray lay-up laminates are set out below;processes of other types (e.g. by resin transfer, vacuum orpressurised moulding with mat and continuous filaments)are to be individually recognised as suitable by RINA.

2.2 Moulds

2.2.1 Moulds for production of laminates are to be con-structed with a suitable material which does not affect theresin polymerisation and are to be adequately stiffened inorder to maintain their shape and precision in form. Theyare also not to prevent the finished laminate from beingreleased, thus avoiding cracks and deformations. During construction, provision is to be made to ensure sat-isfactory access such as to permit the proper carrying out ofthe laminating.

Moulds are to be thoroughly cleaned, dried and brought tothe moulding shop temperature before being treated withthe mould release agents, which are not to have an inhibit-ing effect on the gel coat resin.

2.3 Laminating

2.3.1 The gel coat is to be applied by brush, roller orspraying device so as to form a uniform layer with a thick-ness of between 0,4 and 0,6 mm. Furthermore, it is not tobe left exposed for longer than is recommended by theManufacturer before the application of the first layer of rein-forcement. A lightweight reinforcement, generally not exceeding amass per area of 300 g/m2, is to be applied to the gel coatitself by means of rolling so as to obtain a content of rein-forcement not exceeding approximately 0,3.

In the case of hand lay-up processing, the laminates are tobe obtained with the layers of reinforcement laid in thesequence indicated in the approved drawings and eachlayer is to be thoroughly "wet" in the resin matrix and com-pacted to give the required weight content.

The amount of resin laid "wet on wet" is to be limited toavoid excessive heat generation.

Laminating is to be carried out in such a sequence that theinterval between the application of layers is within the lim-its recommended by the resin Manufacturer.

Similarly, the time between the forming and bonding ofstructural members is to be kept within these limits; wherethis is not practicable, the surface of the laminate is to betreated with abrasive agents in order to obtain an adequatebond.

When laminating is interrupted so that the exposed resingels, the first layer of reinforcement subsequently laid is tobe of mat type.

Reinforcements are to be arranged so as to maintain conti-nuity of strength throughout the laminate. Joints betweenthe sections of reinforcement are to be overlapped and stag-gered throughout the thickness of the laminate.

In the case of simultaneous spray lay-up of resin and cutfibres, the following requirements are also to be compliedwith:

• before the use of the simultaneous lay-up system, theManufacturer is to satisfy himself of the efficiency of theequipment and the competence of the operator;

• the use of this technique is limited to those parts of thestructure to which sufficiently good access may beobtained so as to ensure satisfactory laminating;

• before use, the spray lay-up equipment is to be cali-brated in such a way as to provide the required fibrecontent by weight; the spray gun is also to be calibrated,according to the Manufacturer's instruction manual,such as to obtain the required catalyst content, the gen-eral spray conditions and the appropriate length of cutfibres. Such length is generally to be not less than 35mm for structural laminates, unless the mechanicalproperties are confirmed by tests; in any event, thelength of glass fibres is to be not less than 25 mm;

• the calibration of the lay-up system is to be checkedperiodically during the operation;

• the uniformity of lamination and fibre content is to besystematically checked during production.

The manufacturing process for sandwich type laminates istaken into consideration by RINA in relation to the materi-als, processes and equipment proposed by the Manufac-turer, with particular regard to the core material and to itslay-up as well as to details of connections between prefabri-cated parts of the sandwich laminates themselves. The corematerials are to be compatible with the resins of the surfacelaminates and suitable to obtain strong adhesion to the lat-ter (Manufacturer’s instructions to be followed).

Attention is drawn, in particular, to the importance ofensuring the correct carrying out of joints between panels.

Where rigid core materials are used, then dry vacuum bag-ging techniques are to be adopted. Particular care is to begiven to the core bonding materials and to the holes pro-vided to ensure efficient removal of air under the core.Bonding paste is to be visible at these holes after vacuumbagging.

2.4 Hardening and release of laminates

2.4.1 On completion of the laminating, the laminate is tobe left in the mould for a period of time to allow the resin toharden before being removed. This period may vary,depending on the type of resin and the complexity of thelaminate, but is to be at least 24 hours, unless a differentperiod is recommended by the resin Manufacturer.

The hull, deck and large assemblies are to be adequatelybraced and supported for removal from the moulds as wellas during the fitting-out period of the yacht.

After the release and before the application of any specialpost-hardening treatment, which is to be examined byRINA, the structures are to be stabilised in the mouldingenvironment for the period of time recommended by theresin Manufacturer. In the absence of recommendations,the period is to be at least 24 hours.


Pt B, Ch 4, Sec 3

2.5 Defects in the laminates

2.5.1 The manufacturing processes of laminates are to besuch as to avoid defects, such as in particular: surfacecracks, surface or internal blistering due to the presence ofair bubbles, cracks in the resin for surface coating, internalareas with non-impregnated fibres, surface corrugation, andsurface areas without resin or with glass fibre reinforce-ments exposed to the external environment.

Any defects are to be eliminated by means of appropriaterepair methods to the satisfaction of the RINA Surveyor.

Dimensions and tolerances are to conform to the approvedconstruction documentation.

2.5.2 The responsibility for maintaining the required toler-ances rests with the Builder.

Monitoring and random checking by the Surveyor does notabsolve the Builder from this responsibility.

2.6 Checks and tests

2.6.1 Checks and tests are to be arranged during the lami-nation process by the hull builder, in accordance with therelevant quality system, and by the RINA Surveyor.

The hull builder is to maintain a constant check on the lam-inate.

Any defects found are to be eliminated immediately.

In general the following checks and tests are to be carriedout:

a) check of the mould before the application of the releaseagent and of the gel coat;

b) check of the thickness of the gel coat and the uniformityof its application;

c) c) check of the resin and the amount of catalyst, accele-rator, hardener and various additives;

d) check of the uniformity of the impregnation of reinfor-cements, their lay-up and superimposition;

e) check and recording of the percentage of the reinforce-ment in the laminate;

f) checks of any post-hardening treatments;

g) general check of the laminate before release from themould;

h) check and recording of the laminate hardness beforerelease from the mould;

i) check of the thickness of the laminate which, in general,is not to differ by more than 15% from the thicknessindicated in approved structural plans;

j) mechanical tests on laminates taken from the hull orprepared during the lamination of the hull (in accor-dance with Pt D, Ch 6, Sec 3).

The thicknesses of the laminates are, in general, to be meas-ured at not less than ten points, evenly distributed acrossthe surface.

The above-mentioned checks and tests are to be carried outas a rule in the presence of a RINA Surveyor; where theshipyard has a system of production organisation and qual-ity control certified by RINA, the checks may be carried outdirectly by the shipyard without the presence of a RINA Sur-veyor.

2.6.2 Where ultrasonic thickness gauges are used, relevanttools are to be calibrated against an identical laminate (ofmeasured thickness).

2.6.3 As a general rule, a method of validating the com-plete laminate tickness is to be agreed between the Builderand the Surveyor.


Pt B, Ch 4, Sec 4

SECTION 4 LONGITUDINAL STRENGTH

1 General

1.1

1.1.1 The structural scantlings prescribed in this sectionare also intended as appropriate for the purposes of the lon-gitudinal hull strength of a yacht having length L notexceeding 40 m for monohull yacht or 35 m for catamaransand openings on the strength deck of limited size. For yachts of greater length and/or openings of size greaterthan the breadth B of the hull and extending for a consider-able part of the length of the yacht, a test of the longitudinalstrength is required.

The procedures for such test will be stipulated by RINA on acase-by-case basis in relation to the quality of the laminatesand the layout of the yacht.

As a guide, the criteria used by RINA for tests of longitudi-nal hull beam strength are shown below.

1.2

1.2.1 To this end, longitudinal strength calculations are tobe carried out considering the load and ballast conditionsfor both departure and arrival.

2 Bending stresses

2.1

2.1.1 In addition to satisfying the minimum requirementsstipulated in the individual Chapters of these Rules, thescantlings of members contributing to the longitudinalstrength of monohull yacht and catamarans are to achieve asection modulus of the midship section at the bottom andthe deck such as to guarantee stresses not exceeding theallowable values. Therefore:

where:

Wf, Wp : section modulus at the bottom and the deck,respectively, of the transverse section in m3

MT : design total vertical bending moment defined inChap. 1, Sec. 5.

f : 0,33 for planing yachts

f : 0,25 for displacement yachts

σl : the lesser of the values of ultimate tensile andultimate compressive strength, in N/mm2, of thebottom and deck laminate.

2.2

2.2.1 In order to limit the flexibility of the hull structure,the moment of inertia J of the midship section, in m4, is gen-erally to be not less than the value given by the followingformulae:

J = 200 . MT . 10-6 for planing vessesls

J = 230 . MT . 10-6 displacement yachts.

2.3 Calculation of strength modulus

2.3.1 Reference is to be made to Table 1 for plating andTable 2 for longitudinals for calculation of the midship sec-tion modulus.

Table 1

Where there is a sandwich member, the two skins of thelaminate are to be taken into account for the purposes ofthe longitudinal strength only with their own characteris-tics. The cores may be taken into account only if they offerlongitudinal continuity and appreciable strength againstaxial tension-compression.

For each transverse section within the midship region, thesection modulus, in m3, is given by:

where:

P :

A :

F :

tp, tm, tf, Ep, Em, Ef,: values defiined in Table 1

tps, tms, tfs, Eps, Ems, Efs, Ips, Ims, Ifs, tpa, tma, tfa, Epa, Ema, Efa,Hpa,Hma, Hfa, np, nm, nf: values defiined in Table2

Im, C’ : length, in m, defined in Figure 1.

σf fσl≤

σp fσl≤

σfMT

1000 Wf

----------------------- N mm2⁄=

σpMT

1000 Wp

------------------------ N mm2⁄=

Deck Side shell Bottom

Mean thickness, in mm tp tm tf

Young’s modulus, in N/mm2 Ep Em Ef

Wp1Ep

----- C' P C'6----- A 1 F P–

F 0 5 A⋅,+---------------------------+

⋅ ⋅+⋅ 10 3–⋅ ⋅=

Wf1Ef

---- C' P C'6----- A 1 F P–

F 0 5 A⋅,+---------------------------+

⋅ ⋅+⋅ 10 3–⋅ ⋅=

tp B Ep np Ips tps Eps tpa Hpa Epa⋅ ⋅+⋅ ⋅( )⋅+⋅ ⋅

2 tm Im Em nm tms Ims Ems tma Hma Ema⋅ ⋅+⋅ ⋅( )⋅+⋅ ⋅[ ]

tfB2--- Ef nf Ifs tfs Efs tfa Hfa Efa⋅ ⋅+⋅ ⋅( )⋅+⋅ ⋅


Pt B, Ch 4, Sec 4

Table 2

Figure 1

3 Shear stresses

3.1

3.1.1 The shear stresses in every position along the lengthL are not to exceed the allowable values; in particular.

where:

Tt : total shear stress in kN defined in Chap. 1, Arti-cle 5.4

f : defined in 2

τ : shear stress of the laminate, in N/mm2

Αt : actual shear area of the transverse section, inm2, actual shear area of the transverse section,in m2, to be calculated considering the net areaof side plating and of any longitudinal bulk-heads excluding openings.

Deck Side shell Bottom

Flange

Mean thickness, in mm tps tms tfs

Young’s modulus, in N/mm2 Eps Ems Efs

Breadth in mm Ips Ims Ifs

Web

Equivalent thickness in Section I, in mm tpa tms tfa

Young’s modulus, in N/mm2 Epa Ems Efa

Height in mm Hpa Hma Hfa

Number of longitudinals np nm nf

Tt

At

----- 10 3– f τ⋅≤⋅


Pt B, Ch 4, Sec 5

SECTION 5 EXTERNAL PLATING

1 General

1.1

1.1.1 Bottom and side plating may be made using bothsingle-skin laminate and sandwich structure.

When the two solutions are adopted for the hull, a suitabletaper is to be made between the two types.

Bottom plating is the plating up to the chine or to the upperturn of the bilge.

When the side thickness differs from the bottom thicknessby more than 3 mm, a transition zone is to be foreseen.

.


2.1

2.1.1

S : larger dimension of the plating panel, in m

s : spacing of the ordinary longitudinal or trans-verse stiffener, in m

p : scantling pressure, in kN/m2, given in Chap. 1,Sec. 5

Kof, Ko : factors defined in Sec. 2 of this Chapter.

3 Keel

3.1

3.1.1 The keel is to extend the whole length of the yachtand have a breadth bCH, in mm, not less than the valueobtained by the following formula:

The thickness of the keel is to be not less than the value tCH,in mm, obtained by the following formula:

t being the greater of the values t1 e t2, in mm, calculated asspecified in 5 assuming the spacing s of the correspondingstiffeners.

Appraising s, and dead rise edge > 12° is considered as astiffener.

The thickness tCH is to be gradually tapered transversally, tothe thickness of the bottom and in the case of hulls having aU-shaped keel, the thickness of the keel is to extend, trans-versally, as indicated in Figure 2 b) in Section 1, taperingwith the bottom plating.

In yachts with sail and ballast keel, the thickness of the keelfor the whole length of the ballast keel is to be increased by

30%; this increase is to extend longitudinally to fore and aftof the ballast for a suitable length.

When the hull is laminated in halves, the keel joint is to becarried out as shown in Figure 5 in Section 1 or in a similarway.

4 Rudder horn

4.1

4.1.1 When the rudder is of the semi-spade type, such asType I B shown in Chapter 1, Section 2, Figure 2, the rele-vant rudder horn is to have dimensions and thickness suchthat the moment of inertia J, in cm4, and the section modu-lus Z, in cm3, of the generic horizontal section of the sameskeg, with respect to its longitudinal axis are not less thanthe values given by the following formulae:

where:

A : the rudder area, in m2, acting on the horn;

h : the vertical distance, in mm, from the skeg sec-tion to the lower edge of the pintle (rudderheel);

V : maximum design speed of the yacht, in knots.

5 Bottom plating

5.1

5.1.1 The thickness of bottom plating is to be not less thanthe greater of the values t1 e t2, in mm, calculated with thefollowing formulae:

where:

k1 : 0,26, when assuming p=p1

: 0,15, when assuming p=p2.

ka : coefficient as a function of the ratio S/s given inTable 1.

The thickness of the plating of the bilge is, in any event, tobe taken as not less than the greater of the thicknesses of thebottom and side.

The minimum bottom shell thickness is to extent to thechine line or 150mm above the statical load waterline,whichever is the greater.

bCH 30L=

tCH 1 4t,=

J A h2 V2⋅ ⋅36

------------------------10 3–=

Z A h V2⋅ ⋅55

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

t1 k1 ka s kof p0 5,⋅ ⋅ ⋅ ⋅=

t2 16 s kof D0 5,⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 5

If the plating has a pronounced curve, as for example in thecase of the hulls of sailing yachts, the thickness calculatedwith the formulae above may be reduced multiplying by (1- f/s), f being the distance, in m, between the connectingbeam and the two extremities of the plating concerned andthe surface of the plating itself. This reduction may not beassumed less than 0,70.

In sailing yachts with or without auxiliary engine in way ofthe ballast keel, when the width of the latter is greater thanthat of the keel, the thickness of the bottom is to beincreased to the value taken for the keel.

Table 1

6 Side plating and sheerstrake plating

6.1

6.1.1 A sheerstrake plate of height h, in mm, not less than0,025 L and thickness tc, in mm, not less than the value inthe following formula is to be fitted:

where t is the greater of the thicknesses t1 e t2, calculated asstated in 6.2 below.

6.2 Side plating

6.2.1 The thickness of side plating is to be not less than thegreater of the values t1 e t2, in mm, calculated with the fol-lowing formulae:

where k1 and ka are as defined in 5.1.

7 Openings in the shell plating

7.1

7.1.1 Sea intakes and other openings are to be wellrounded at the corners and located, as far as possible, out-side the bilge strakes and the keel. Arrangements are to besuch as to ensure continuity of strength in way of openings.

The edges of openings are to be suitably sealed in order toprevent the absorption of water.

7.2

7.2.1 Openings in the curved zone of the bilge strakesmay be accepted where the former are elliptical or fittedwith equivalent arrangements to minimise the stress con-centration effects.

7.3

7.3.1 The internal walls of sea intakes are to have externalplating thickness increased by 2 mm, but not less than 6mm.

8 Local stiffeners

8.1

8.1.1 The thickness of plating determined with the forego-ing formulae is to be increased locally, generally by at least50%, in way of the propulsion engine bedplates, stem (thethickness is not required to be greater than that of the keelin this case), propeller shaft struts, rudder horn or trunk, sta-bilisers, anchor recesses, etc.

8.2

8.2.1 Where the aft end is shaped such that the bottomplating aft has a large flat area, RINA may require the localplating to be increased and/or reinforced with the fitting ofadditional stiffeners.

8.3

8.3.1 The thickness of plating is to be locally increased inway of inner or outer permanent ballast arrangements asindicated in 3.1.1.

8.4

8.4.1 The thickness of the transom is to be not less thanthat of the side plating for the portion above the waterline,or less than that of the bottom for the portion below thewaterline.

Where water-jets or propulsion systems are fitted directly tothe transom, the scantlings of the latter will be the subject ofspecial consideration.

In such case a sandwich structure with marine plywoodcore of adequate thickness is recommended.

9 Cross-deck bottom plating

9.1

9.1.1 The thickness is to be taken, the stiffener spacing sbeing equal, no less than that of the side plating.

Where the gap between the bottom and the waterline is sosmall that local wave impact phenomena are anticipated,an increase in thickness and/or additional internal stiffenersmay be required.

S/s Ka

1 17,5

1,2 19,6

1,4 20,9

1,6 21,6

1,8 22,1

2,0 22,3

>2 22,4

tc 1 30t,=

t1 k1 ka s kof p0 5,⋅ ⋅ ⋅ ⋅=

t2 12 s kof D0 5,⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 6

SECTION 6 SINGLE BOTTOM

1 General

1.1

1.1.1 This Section stipulates the criteria for the structuralscantlings of a single bottom, which may be of either longi-tudinal or transverse type.

1.2 Longitudinal structure

1.2.1 A centre girder is to be fitted. In the case of a keelwith a dead rise > 12°, the centre girder may be omitted butin such case the fitting of a longitudinal stringer is required.

Where the breadth of the floors exceeds 6 m, sufficient sidegirders are to be fitted so that the distance between themand the centre girder or the side does not exceed 3 m.

1.2.2 The bottom of the engine room is to be reinforcedwith a suitable web floor consisting of floors and girders;the latter are to extend beyond the engine room for a suita-ble length and are to be connected to any existing girders inother areas.

1.2.3 Additional bottom stiffeners are to be fitted in way ofthe propeller shaft struts, the rudder and the ballast keel.

1.3 Transverse structure

1.3.1 The transverse framing consists of ordinary stiffenersarranged transversally (floors) and placed at each framesupported by girders, which in turn are supported by trans-verse bulkheads or reinforced floors.

1.3.2 A centre girder is to be fitted. In the case of a keelwith a dead rise > 12°, the centre girder may be omitted butin such case the fitting of a longitudinal stringer is required.

Where the breadth of the floors exceeds 6 m, sufficient sidegirders are to be fitted so that the distance between themand the centre girder or the side does not exceed 3 m.

1.3.3 The bottom of the engine room is to be reinforcedwith a suitable web floor consisting of floors and girders;the latter are to extend beyond the engine room for a suita-ble length and are to be connected to any existing girders inother areas.

1.3.4 Additional bottom stiffeners are to be fitted in way ofthe propeller shaft struts, the rudder and the ballast keel.

1.3.5 Floors are to be fitted in way of reinforced frames atthe sides and reinforced deck beams.

Any intermediate floors are to be adequately connected tothe ends


2.1

2.1.1

s : spacing of ordinary longitudinal or transversestiffeners, in m;

p : scantling pressure, in kN/m2, given in Chap. 1,Sec.5;

Ko : coefficient defined in Sec. 2 of this Chapter.

3 Longitudinal type structure

3.1 Bottom longitudinals

3.1.1 The section modulus of longitudinal stringers is to benot less than the value Z, in cm2, calculated with the fol-lowing formula:

where:

k1 : 1,5 assuming p=p1

: 1 assuming p=p2

S : conventional span of the longitudinal stiffener,in m, equal to the distance between floors.

3.2 Floors

3.2.1 The section modulus of the floors at the centreline ofthe span S is to be not less than the value ZM, in cm3, calcu-lated with the following formula.

where:

k1 : 2,4 assuming p = p1

1,2 assuming p = p2

b : half the distance, in m, between the two floorsadjacent to that concerned

S : conventional floor span equal to the distance,in m, between the two supporting members(sides, girders, keel with a dead rise edge >12°).

In the case of a U-shaped keel or one with a dead rise edge≤12° but > 8° the span S is always to be calculated consid-ering the distance between girders or sides; the modulus ZM

may, however, be reduced by 40%.

If a side girder is fitted on each side with a height equal tothe local height of the floor, the modulus may be reducedby a further 10%.

Z k1 s S2 Ko p⋅ ⋅ ⋅ ⋅=

ZM k1 b S2 Ko p⋅ ⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 6

3.3 Girders

3.3.1 Centre girder

When the girder forms a support for the floor, the sectionmodulus is to be not less than the value ZPC, in cm3, calcu-lated with the following formula:

where:

k1 : defined in 3.2.

b’PC : half the distance, in m, between the two sidegirders if supporting or equal to B/2 in theabsence of supporting side girders

S : conventional girder span equal to the distance,in m, between the two supporting members(transverse bulkheads, floors).

Whenever the centre girder does not form a support for thefloors, the section modulus is to be not less than the valueZPC, in cm3, calculated with the following formula:

where:


b’PC : half the distance, in m, between the two sidegirders if present or equal to B/2 in the absenceof side girders

S : distance between the floors.

3.3.2 Side girders

When the side girder forms a support for the floor, the sec-tion modulus is to be not less than the value ZPL, in cm3,calculated with the following formula:

where:


b’PL : half the distance, in m, between the two adja-cent girders or between the side and the girderconcerned

S : conventional girder span equal to the distance,in m, between the two supporting members(transverse bulkheads, floors).

Whenever the side girder does not form a support for thefloors, the section modulus is to be not less than the valueZPL, in cm3, calculated with the following formula:

where:


b’PL : half the distance, in m, between the two adja-cent girders or between the side and the adja-cent girder

S : distance between the floors, in m.

4 Transverse type structures

4.1 Ordinary floors

4.1.1 The section modulus for ordinary floors is to be notless than the value Z, in cm3, calculated with the followingformula:

where:

k1 : defined in 3.1

S : conventional span in m, of the floor equal to thedistance between the members which support it(girders, sides).

4.2 Centre girder

4.2.1 The section modulus of the centre girder is to be notless than the value ZPC, in cm3, calculated with the follow-ing formula:

where:

k1 : defined in 3.2

bPC : half the distance, in m, between the two sidegirders if supporting or equal to B/2 in theabsence of supporting side girders

S : conventional span of the centre girder, equal tothe distance, in m, between the two supportingmembers (transverse bulkheads, floors).

4.3 Side girders

4.3.1 The section modulus is to be not less than the valueZPL, in cm3, calculated with the following formula:

where:

k1 : defined in 3.2

bPL : half the distance, in m, between the two adja-cent girders or between the side and the girderadjacent to that concerned

S : conventional girder span equal to the distance,in m, between the two members which supportit (transverse bulkheads, floors).

5 Constructional details

5.1

5.1.1 The centre girder and side girders are to be con-nected to the stiffeners of the transom by means of suitablefittings.

ZPC k1 bPC S2 Ko p⋅ ⋅ ⋅ ⋅=

ZPC k1 bPC′ S2 Ko p⋅ ⋅ ⋅ ⋅=

ZPL k1 bPL′ S2 Ko p⋅ ⋅ ⋅ ⋅=

ZPL k1 bPL′ S2 Ko p⋅ ⋅ ⋅ ⋅=

Z k1 s S2 Ko p⋅ ⋅ ⋅ ⋅=

ZPC k1 bPC S2 Ko p⋅ ⋅ ⋅ ⋅=

ZPL k1 bPL S2 Ko p⋅ ⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 7

SECTION 7 DOUBLE BOTTOM

1 General

1.1

1.1.1 This Section stipulates the criteria for the structuralscantlings of a double bottom, which may be of either lon-gitudinal or transverse type.

The longitudinal type structure is made up of ordinary rein-forcements placed longitudinally, supported by floors.

The fitting of a double bottom with longitudinal framing isrecommended for planing and semi-planing yachts.

1.1.2 The fitting of a double bottom extending from thecollision bulkhead to the forward bulkhead of the machin-ery space, or as near thereto as practicable, is requested foryacht of L > 50 m.

1.1.3 The dimensions of the double bottom, and in partic-ular the height, are to be such as to allow access for inspec-tion and maintenance.

In floors and in side girders, manholes are to be provided inorder to guarantee that all parts of the double bottom canbe inspected at least visually.

The height of manholes is generally to be not greater thanhalf the local height in the double bottom. When manholeswith greater height are fitted, the free edge is to be rein-forced by a flat iron bar or other equally effective reinforce-ments are to be arranged.

Manholes are not to be placed in the continuous centregirder, or in floors and side girders below pillars, except inspecial cases at the discretion of RINA.

1.1.4 Openings are to be provided in floors and girders inorder to ensure down-flow of air and liquids in every part ofthe double bottom.

Holes for the passage of air are to be arranged as close aspossible to the top and those for the passage of liquids asclose as possible to the bottom.

The edges of the holes are to be suitably sealed in order toprevent the absorption of liquid into the laminate.

Bilge wells placed in the inner bottom are to be watertightand limited as far as possible in height and are to have wallsand bottom of thickness not less than that prescribed forinner bottom plating.

In zones where the double bottom varies in height or isinterrupted, tapering of the structures is to be adopted inorder to avoid discontinuities.

2 Minimum height

2.1

2.1.1 The height of the double bottom is to be sufficient toallow access to all areas and, in way of the centre girder, isto be not less than the value hdF, in mm, obtained from thefollowing formula:

The height of the double bottom is in any event to be notless than 700 mm. For yacht less than 50 m in length RINAmay accept reduced height.

3 Inner bottom plating

3.1

3.1.1 The thickness of the inner bottom plating is to be notless than the value t1, in mm, calculated with the followingformula:

where:

s : spacing of the ordinary stiffeners, in m

kof : coefficients for the properties of the materialdefined in Sec. 2.

For yachts of length L <50 m the thickness is to be main-tained throughout the length of the hull.

For yachts of length L > 50 m, the thickness may be gradu-ally reduced outside 0,4 L amidships so as to reach a valueno less than 0,9 t1 at the ends.

Where the inner bottom forms the top of a tank intended forliquid cargoes, the thickness of the top is also to complywith the provisions of Sec. 10.

4 Centre girder

4.1

4.1.1 A centre girder is to be fitted, as far as this is practi-cable, throughout the length of the hull.

The thickness of the core of a sandwich type centre girder isto be not less than the following value tpc, in mm:

where kof is defined in Sec. 2.

Where a single-skin laminate is used for the centre girder,the thickness is to be not less than twice that defined above.

hdf 28B 32 T 10+( )+=

t1 1 3 0 04L, 5s 1+ +( )kof for gle skin laminate–sin,=

t1 0 04L, 5s 1+ +( )kof for sandwich laminate=

tpc 0 125L, 3 5,+( )kof=


Pt B, Ch 4, Sec 7

5 Side girders

5.1

5.1.1 Where the breadth of the floors does not exceed 6m, side girders need not be fitted.

Where the breadth of the floors exceeds 6 m, side girdersare to be arranged with thickness equal to that of the floors.

A sufficient number of side girders are to be fitted so that thedistance between them, or between one such girder and thecentre girder or the side, does not exceed 3 m.

The side girders are to be extended as far forward and aft aspracticable and are, as a rule, to terminate on a transversebulkhead or on a floor or other transverse structure of ade-quate strength.

Watertight girders are to have thickness not less than thatrequired in Sec. 10 for tank bulkheads

5.2

5.2.1 Where additional girders are foreseen in way of thebedplates of engines, they are to be integrated into thestructures of the yacht and extended as far forward and aftas practicable.

Girders of height no less than that of the floors are to be fit-ted under the bedplates of main engines.

Engine foundation bolts are to be arranged, as far as practi-cable, in close proximity to girders and floors.

Where this is not possible, transverse brackets are to be fit-ted.

6 Floors

6.1

6.1.1 The thickness of the core of sandwich type floors tm,in mm, is to be not less than the following value:

where kof is defined in Sec. 2.

Where a single-skin laminate is used for floors, the thick-ness is to be not less than twice that calculated above.

Watertight floors are also to have thickness not less thanthat required in Sec. 10 for tank bulkheads.

6.2

6.2.1 When the height of a floor exceeds 900 mm, verticalstiffeners are to be arranged. In any event, solid floors or equivalent structures are to bearranged in longitudinally framed double bottoms in the fol-lowing locations.• under buklheads and pillars• outside the machinery space at an interval no greater

than 2 m• in the machinery space under the bedplates of main

engines• in way of variations in height of the double bottom.

Solid floors are to be arranged in transversely framed dou-ble bottoms in the following locations:• under bulkheads and pillars• in the machinery space at every frame • in way of variations in height of the double bottom• outside the machinery space at 2 m intervals.

7 Bottom and inner bottom longitudi-nals

7.1

7.1.1 The section modulus of bottom stiffeners is to be noless than that required for single bottom longitudinals stipu-lated in Sec. 6. The section modulus of inner bottom stiffeners is to be noless than 85% of the section modulus of bottom longitudi-nals.

Where tanks intended for liquid cargoes are arranged abovethe double bottom, the section modulus of longitudinals isto be no less than that required for tank stiffeners as statedin Sec. 10.

tm 0 125L, 1 5,+( )kof=


Pt B, Ch 4, Sec 8

SECTION 8 SIDE STRUCTURES

1 General

1.1

1.1.1 Where tanks intended for liquid cargoes arearranged above the double bottom, the section modulus oflongitudinals is to be no less than that required for tank stiff-eners as stated in Sec. 10.

The longitudinal type structure consists of ordinary stiffen-ers placed longitudinally supported by reinforced frames,generally spaced not more than 2 m apart, or by transversebulkheads.

The transverse type structure is made up of ordinary rein-forcements placed vertically (frames), which may be sup-ported by reinforced stringers, by decks, by flats or by thebottom structures.

Reinforced frames are to be provided in way of the mastand the ballast keel, in sailing yachts, in the machineryspace and in general in way of large openings on theweather deck.


2.1

2.1.1

s : spacing of ordinary longitudinal or transversestiffeners, in m;

p : scantling pressure, in kN/m2, defined in Part B,Chap. 1, Sec. 5 ;

Ko : factor defined in Sec. 2 of this Chapter.

3 Ordinary stiffeners

3.1

3.1.1 The section modulus of the frames is to be not lessthan the value Z, in cm3, calculated with the following for-mula:

where:

k1 : 1,75 assuming p=p1

: 1,1 assuming p=p2

S : conventional frame span, in m, equal to thedistance between the supporting members.

The ordinary frames are to be well connected to the ele-ments which support them, in general made up of a beamand a floor.

3.2 Longitudinals

3.2.1 The section modulus of the side longitudinals is tobe not less than the value Z, in cm3, calculated with the fol-lowing formula:

where:k1 : 1,9 assuming p=p1

: 1 assuming p=p2

S : conventional span of the longitudinal, in m,equal to the distance between the supportingmembers, in general made up of reinforced fra-mes or transverse bulkheads.

4 Reinforced beams

4.1 Reinforced frames

4.1.1 The section modulus of the reinforced frames is to benot less than the value calculated with the following for-mula:

where:k1 : 1 assuming p=p1

: 0,7 assuming p=p2

KCR : 2,5 for reinforced frames which support ordi-nary longitudinal stiffeners, or reinforced string-ers;

: 1,1 for reinforced frames which do not supportordinary stiffeners;

s : spacing, in m, between the reinforced frames orhalf the distance between the reinforced framesand the transverse bulkhead adjacent to theframe concerned;

S : conventional span, in m, equal to the distancebetween the members which support the rein-forced frame.

4.2 Reinforced stringers

4.2.1 The section modulus of the reinforced stringers is tobe not less than the value calculated with the following for-mula:

where:k1 : defined in 4.1KCR : 2,5 for reinforced stringers which support ordi-

nary vertical stiffeners (frames); : 1,1 for reinforced stringers which do not sup-

port ordinary vertical stiffeners;

Z k1 s S2 Ko p⋅ ⋅ ⋅ ⋅=

Z k1 s S2 Ko p⋅ ⋅ ⋅ ⋅=

Z k1 KCR s S2 Ko p⋅ ⋅ ⋅ ⋅ ⋅=

Z k1 KCR′ s S2 Ko p⋅ ⋅ ⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 8

s : spacing, in m, between the reinforced stringersor 0,5 D in the absence of other reinforcedstringers or decks;

S : conventional span, in m, equal to the distancebetween the members which support thestringer, in general made up of transverse bulk-heads or reinforced frames.


Pt B, Ch 4, Sec 9

SECTION 9 DECKS

1 General

1.1

1.1.1 This Section lays down the criteria for the scantlingsof decks, plating and reinforcing or supporting structures.

The reinforcing and supporting structures of decks consist ofordinary reinforcements, beams or longitudinal stringers,laid transversally or longitudinally, supported by lines ofshoring made up of systems of girders and/or reinforcedbeams, which in turn are supported by pillars or by trans-verse or longitudinal bulkheads.

Reinforced beams together with reinforced frames are to beplaced in way of the mast in sailing yachts.

In sailing yachts with the mast resting on the deck or on thedeckhouse, a pillar or bulkhead is to be arranged in way ofthe mast base.


2.1

2.1.1

pdc : calculation deck, meaning the first deck abovethe full load waterline, extending for at least 0,6L and constituting an efficient support for thestructural elements of the side; in theory, it is toextend for the whole length of the yacht;

s : spacing of ordinary transverse or longitudinalstiffeners, in m;

h : scantling height, in m, the value of which isgiven in Part B, Chap. 1, Sec. 5;

Ko, Kof : factor defined in Sec. 2 of this Chapter.

3 Deck plating

3.1 Weather deck

3.1.1 The thickness of the weather deck plating, consider-ing that said deck is also a strength deck, is to be not lessthan the value t, in mm, calculated with the following for-mula:

On yachts of L > 30 m a stringer plate is to be fitted withwidth b, in m, not less than 0,025 L and thickness t, in mm,not less than the value given by the formula

where ka is defined in 5.1 in Sec. 5.

3.2 Lower decks

3.2.1 The thickness of decks below the weather deckintended for accommodation spaces is to be not less thanthe value calculated with the formula:

where ka is defined in 5.1 in Sec. 5.

Where the deck is a tank top, the thickness of the deck is, inany event, to be not less than the value calculated with theformulae given in Sec.10 for tank bulkhead plating.

4 Stiffening and support structures for decks

4.1 Ordinary stiffeners

4.1.1 The section modulus of the ordinary stiffeners ofboth longitudinal and transverse (beams) type is to be notless than the value Z, in cm3, calculated with the followingequation:

where:C1 : 1 for weather deck longitudinals

: 0,63 for lower deck longitudinals: 0,56 for beams.

4.2 Reinforced beams

4.2.1 The section modulus for girders and for ordinaryreinforced beams is to be not less than the value Z, in cm3,calculated with the following equation:

where:b : average width of the strip of deck resting on the

beam, in m. In the calculation of b any open-ings are to be considered as non-existent

S : conventional span of the reinforced beam, in m,equal to the distance between the two support-ing members (pillars, other reinforced beams,bulkheads).

4.3 Pillars

4.3.1 Pillars are, in general, to be made of steel or alumin-ium alloy tubes, and connected at both ends to plates sup-ported by efficient brackets which allow connection to thehull structure by means of bolts. Details to be sent forapproval.The section area of pillars is to be not less than the value A,in A, in cm2, given by the formula:

t 0 15, ka s kof L10 5,⋅ ⋅ ⋅ ⋅=

t 0 2, ka s kof L10 5,⋅ ⋅ ⋅ ⋅=

t 0 13, ka s kof L10 5,⋅ ⋅ ⋅ ⋅=

Z 14 s S2 h kof C1⋅ ⋅ ⋅ ⋅ ⋅=

Z 15 b S2 h ko⋅ ⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 9

where:Q : load resting on the pillar, in kN, calculated with

the following formula:

where:A : area of the part of the deck resting

on the pillar, in m2.h : scantling height, defined in 2.1.1.

λ : the ratio between the pillar length and the mini-mum radius of gyration of the pillar cross-sec-tion.

C : 1 for steel pillars

: 1,6 for aluminium alloy pillars.

4.3.2 Pillars are to be fitted on main structural members.Wherever possible, deck pillars are to be fitted in the samevertical line as pillars above and below, and effectivearrangements are to be made to distribute the load at theheads and heels of all pillars.

4.3.3 The attachment of pillars to sandwich structuresshould, in general, be through an area of single skin lami-nate. Where this is not practicable and the attachment ofthe pillar has to be by through bolting through a sandwichstructure then a wood, or other suitable solid insert is to befitted in the core in way.

A Q C⋅12 5, 0 045λ,–---------------------------------------=

Q 6 87, A h⋅ ⋅=


Pt B, Ch 4, Sec 10


SECTION 10 BULKHEADS

1 General

1.1

1.1.1 The number and position of watertight bulkheadsare, in general, to be in accordance with the provisions ofChapter 1 of Part B.

The scantlings indicated in this Section refer to bulkheadsmade of reinforced plastic both in single-skin and in sand-wich type laminates.

Whenever bulkheads, other than tank bulkheads, are madeof wood, it is to be type approved marine plywood and thescantlings are to be not less than those indicated in Chapter5 of Part B.

Pipes or cables running in through watertight bulkhead areto be fitted with suitable watertight glands.

2 Symbols

2.1

2.1.1

s : spacing between the stiffeners, in m

S : conventional span, equal to the distance, in m,between the members that support the stiffenerconcerned

hs, hB : as defined in Part B, Chap. 1, Sec. 5

ko, kof : as defined in Sec. 2 of this Chapter.

3 Plating

3.1

3.1.1 The watertight bulkhead plating is to have a thick-ness not less than the value tS in mm, calculated with thefollowing formula:

The coefficient k1 and the scantling height h have the valuesindicated in Table 1.

Table 1

4 Stiffeners

4.1 Ordinary stiffeners

4.1.1 The section modulus of ordinary stiffeners is to benot less than the value Z, in cm3, calculated with the fol-lowing formula:

The values of the coefficient c and of the scantling height hare those indicated in Table 2.

4.2 Reinforced beams

4.2.1 The horizontal webs of bulkheads with ordinary ver-tical stiffeners and reinforced stiffeners in the bulkheadswith ordinary horizontal stiffeners are to have a sectionmodulus not less than the value Z, in cm3, calculated withthe following formula:

where:

C1 : 10,7 for subdivision bulkheads

: 18 for tank bulkheads

b : width, in m, of the zone of bulkhead resting onthe horizontal web or on the reinforced stiffener

h : scantling height indicated in Table 2.

Table 2

5 Tanks for liquids

5.1

5.1.1 See Sec 1 par 6.5.

tS k1 s kof h0 5,⋅ ⋅ ⋅=

Bulkhead k1 h (m)

Collision bulkhead 5,8 hB

Watertight bulkhead 5,0 hB

Deep tank bulkhead 5,3 hs

Bulkhead h (m) c

Collision bulkhead hB 0,78

Watertight bulkhead hB 0,63

Deep tank bulkhead hs 1

Z 13 5, s S2 h c ko⋅ ⋅ ⋅ ⋅ ⋅=

Z C1 b S2 h ko⋅ ⋅ ⋅ ⋅=

Pt B, Ch 4, Sec 11


SECTION 11 SUPERSTRUCTURES

1 General

1.1

1.1.1 First tier superstructures or deckhouses are intendedas those situated on the uppermost exposed continuousdeck of the yacht, second tier superstructures or deckhousesare those above, and so on.

Where the distance from the hypothetical freeboard deck tothe full load waterline exceeds the freeboard that can hypo-thetically be assigned to the yacht, the reference deck forthe determination of the superstructure tier may be the deckbelow the one specified above, see Ch 1, Sec 1, [4.3.2].

When there is no access from inside superstructures anddeckhouses to 'tweendecks below, reduced scantlings withrespect to those stipulated in this Section may be acceptedat the discretion of RINA.

2 Boundary bulkhead plating

2.1

2.1.1 The thickness of the boundary bulkheads is to benot less than the value t, in mm, calculated with the follow-ing formula:

s : spacing between the stiffeners, in mh : conventional scantling height, in m, the value

of which is to be taken not less than the valueindicated in Table 1.

Kof : factor defined in Sec 2.

Table 1

In any event, the thickness t is to be not less than the valuesshown in Table 2 of Sec. 1 of this Chapter.

3 Stiffeners

3.1

3.1.1 The stiffeners of the boundary bulkheads are to havea section modulus not less than the value Z, in cm3, calcu-lated with the following formula:

where:h : conventional scantling height, in m, defined in

2 .1Ko : factor defined in Sec 2s : spacing of the stiffeners, in mS : span of the stiffeners, equal to the distance, in

m, between the members supporting the stiff-ener concerned.

4 Superstructure decks

4.1 Plating

4.1.1 The superstructure deck plating is to be not less thanthe value t, in mm, calculated with the following formula:

where:s : spacing of the stiffeners, in mKof : factor defined in Sec 2h : conventional scantling height, in m, defined in

2.1.

4.2 Stiffeners

4.2.1 The section modulus Z, in cm3, of both the longitudi-nal and transverse ordinary deck stiffeners is to be not lessthan the value calculated with the following formula:

where:S : conventional span of the stiffener, equal to the

distance, in m, between the supporting mem-bers

s, h, Ko : as defined in 3.1.Reinforced beams (beams, stringers) and ordinary pillars areto have scantlings as stated in Sec. 9.

Type of bulkhead h (m)

1st tier front 1,5

2nd tier front 1,0

Other bulkheads wherever situated 1,0

t 3 7, s KOf h0 5,⋅ ⋅ ⋅=

Z 5 5, s S2 h Ko⋅ ⋅ ⋅ ⋅=

t 3 7, s KOf h0 5,⋅ ⋅ ⋅=

Z 5 5, s S2 h Ko⋅ ⋅ ⋅ ⋅=

Pt B, Ch 4, Sec 12

SECTION 12 SCANTLINGS OF STRUCTURES WITH SANDWICHCONSTRUCTION

1 Premise

1.1

1.1.1 The sandwich type laminate taken into considerationin this Section is made up of two thin laminates in rein-forced plastic bonded to a core material with a low densityand low values for the mechanical properties.

The core material is, in general, made up of balsa wood,plastic foam of different densities or other materials (honey-comb) which deform easily under pressure or traction butwhich offer good resistance to shear stresses.

The thicknesses of the two skins are negligible compared tothe thicknesses of the core.

The thickness of the core is to be not less than 6 times theminimum thickness of the skins.

The thicknesses of the two skins are to be approximatelyequal; the thickness of the external skin is to be no greaterthan 1,33 times the net thickness of the internal skin.

The moduli of elasticity of the core material are negligiblecompared to those of the skin material.

Normal forces and flexing moments act only on the externalfaces, while shear forces are supported by the core .

The scantlings indicated in the following Articles of thisSection are considered valid assuming the above-men-tioned hypotheses.

The scantlings of sandwich structures obtained differentlyand/or with core materials or with skins not correspondingto the above-mentioned properties will be considered caseby case on the principle of equivalence, on submission offull technical documentation of the materials used and anytests carried out.

2 General

2.1 Laminating

2.1.1 Where the core material is deposited above a prefab-ricated skin, as far as practicable the former is to be appliedafter the polymerisation of the skin laminate has passed theexothermic stage.

2.1.2 Where the core is applied on a pre-laminated sur-face, even adhesion is to be ensured.

2.1.3 When resins other than epoxide resins are used, thelayer of reinforcement in contact with the core material is tobe of mat.

2.1.4 Prior to proceeding with glueing of the core, the lat-ter is to be suitably cleaned and treated in accordance withthe Manufacturer's instructions.

2.1.5 Where the edges of a sandwich panel are to be con-nected to a single-skin laminate, the taper of the panel isnot to exceed 30°. In zones where high density or plywood insert plates arearranged, the taper is not to exceed 45°.

2.2 Vacuum bagging

2.2.1 Where the vacuum bagging system is used, details ofthe procedure are to be submitted for examination. The number, scantlings and distribution of venting holes inthe panels are to be in accordance with the Manufacturer'sinstructions.

The degree of vacuum in the bagging system both at thebeginning of the process and during the polymerisationphase is not to exceed the level recommended by the Man-ufacturer, so as to avoid phenomena of core evaporationand/or excessive monomer loss.

2.3 Constructional details

2.3.1 In general the two skins, external and internal, are tobe identical in lamination and in resistance and elasticityproperties.In way of the keel, in particular in sailing yachts with a bal-last keel, in the zone where there are the hull appendages,such as propeller shaft struts and rudder horns, in way ofthe connection to the upper deck and in general where con-nections with bolts are foreseen, as a rule, single-skin lami-nate is to be used.

The use of a sandwich laminate in these zones will be care-fully considered by RINA bearing in mind the properties ofthe core and the precautions taken to avoid infiltration ofwater in the holes drilled for the passage of studs and bolts.

The use of sandwich laminates is also ill-advised in way ofstructural tanks for liquids where fuel oils are concerned.

Such use may be accepted by increasing the thickness ofthe skin in contact with the liquid, as indicated in Section10.

3 Symbols

3.1

3.1.1 S : conventional span of the strip of sandwich lam-

inate equal to the minimum distance, in m,


Pt B, Ch 4, Sec 12

between the structural members supporting thesandwich (bulkheads, reinforced frames);

p : scantling pressure, in kN/m2, as defined in PartB, Chap. 1, Sec. 5;

h : scantling height, in m, given in Part B, Chap. 1,Sec. 5;

Rto : ultimate tensile strength, in kN/m2, of the exter-nal skin;

Rti : ultimate tensile strength, in kN/m2, of the inter-nal skin;

Rco : ultimate flexural strength, in kN/m2, of theexternal skin;

Rci : ultimate flexural strength, in kN/m2, of the inter-nal skin;

t : ultimate shear strength, in kN/m2, of the corematerial of the sandwich;

h : net height, in mm, of the core of the sandwich.

4 Minimum thickness of the skins

4.1

4.1.1 The thickness of the skin laminate is to be sufficientto obtain the section modulus prescribed in the followingArticles; furthermore, it is to have a value, in mm, not lessthan that given by the following formulae:

a) Bottom

b) Side and weather deck

where:

to : thickness of the external laminate of the sand-wich

ti : thickness of the internal laminate of the sand-wich.

Thicknesses less than the minimums calculated with theabove formulae, though not less than those in Table 2, maybe accepted provided they are sufficient in terms of buck-ling strength.

In the case of a sandwich structure with a core in balsawood or polyurethane foam and other similar products, thecritical stress σCR, in N/mm2, given by the following for-mula, is to be not less than 1,1 σC:

essendo:

EF : compressive modulus of elasticity of the lami-nate of the skin considered, in, in N/mm2;

EA : compressive modulus of elasticity of the corematerial of the skin considered, in N/mm2;

GA : shear modulus of elasticity of the core material,in N/mm2;

σC : actual compressive strength on the skin consid-ered, in N/mm2

ν : Poisson coefficient of the laminate of the skinconsidered.

5 Bottom

5.1

5.1.1 The section moduli ZSo e ZSi, in cm3, correspondingto the external and internal skins, respectively, of a strip ofsandwich of the bottom 1 cm wide are to be not less thanthe values given by the following formulae:


: 0,4 assuming p=p2

The moment of inertia of a strip of sandwich 1 cm wide is tobe not less than the value IS, in cm4, given by the followingformula:

where:R : the greater of the ultimate compressive strengths

of the two skins, in N/mm2;ES : the mean of the four values of the compressive

and shear moduli of elasticity of the two skins,in N/mm2;

Z : ZSo or ZSi , in cm3, whichever is the greater.

The net height of the core ha, in mm, is to be not less thanthe value given by the formula:


: 0,2 assuming p=p2

6 Side

6.1

6.1.1 The section moduli ZSo and ZSi, in cm3, correspond-ing to the external and internal skins, respectively, of a stripof sandwich of the side 1 cm wide are to be not less thanthe values given by the following formulae:


: 0,4 assuming p=p2

to 0 50, 2 2, 0 25L,+( )⋅=

ti 0 40, 2 2, 0 25L,+( )⋅=

to 0 45, 2 2, 0 25L,+( )⋅=

ti 0 35, 2 2, 0 25L,+( )⋅=

σCR 0 4,EF EA GA⋅ ⋅( )

1 ν2–-------------------------------

1 3⁄

⋅=

ZSo k1 p S2 1Rco

-------⋅ ⋅ ⋅=

ZSi k1 p S2 1Rti

------⋅ ⋅ ⋅=

IS 40 S Z RES

----⋅ ⋅ ⋅=

hak1 p S⋅ ⋅

τ--------------------=

ZSo k1 p S2 1Rco

-------⋅ ⋅ ⋅=

ZSi k1 p S2 1Rti

------⋅ ⋅ ⋅=


Pt B, Ch 4, Sec 12

The moment of inertia of a strip of sandwich of the side 1cm wide is to be not less than the value IS, in cm4, given bythe following formula:

ù

where R and ES are as defined in Art. 5:



: 0,2 assuming p=p2

7 Decks

7.1

7.1.1 The section moduli ZSo and ZSi, in cm3, correspond-ing to the external and internal skins, respectively, of a stripof sandwich of the deck 1 cm wide are to be not less thanthe values given by the following formulae:

However, the modulus ZSo may be assumed not greaterthan that required for the side in 6.1, having the same .

The moment of inertia of a strip of sandwich 1 cm wide is tobe not less than the value IS, in cm4, given by the followingformula:

where R and ES are as defined in Art.5:

The net height of the core ha, in mm, is to be not less thanthe value given by the following formula:

8 Watertight bulkheads and boundary bulkheads of the superstructure

8.1

8.1.1 The scantlings shown in this Article apply both tosubdivision bulkheads and to tank bulkheads.

They may also be applied to boundary bulkheads of thesuperstructure assuming for h the relevant value indicatedin Chap. 4, Sec. 11.

The section modulus ZS, in cm3, and the moment of inertiaIS, in cm4, of a strip of sandwich 1 cm wide are to be notless than the values given by the following formulae:

where:

R : the greater of the ultimate compressive shearstrengths of the two skins, in N/mm2;

ES : the mean of the values of the compressive mod-uli of elasticity of the two skins, in N/mm2;


IS 40 S Z RES

----⋅ ⋅ ⋅=

hak1 p S⋅ ⋅

τ--------------------=

ZSo 15 h S2 1Rco

-------⋅ ⋅ ⋅=

ZSi 15 h S2 1Rti

------⋅ ⋅ ⋅=

IS 40 S Z RES

----⋅ ⋅ ⋅=

ha7 h S⋅ ⋅

τ------------------=

ZS 15 h S 1R---⋅ ⋅ ⋅=

IS 40 S Z RES

----⋅ ⋅ ⋅=

ha7 h S⋅ ⋅

τ------------------=


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