Section 1 General

1.1.1 The requirements of this Chapter are applicable to mono-hull craft of aluminium construction as defined in Pt 1, Ch 2, 2 Scope of the Rules.

1.2.1 The formulae contained within this Chapter are to be used in conjunction with the design loadings from Pt 5 Design and Load Criteria to determine the Rule scantling requirements.

1.3.1 Where the craft is of unusual design, form or proportions, or where the speed of the craft exceeds 60 knots the scantlings are to be determined by direct calculation.

1.3.2 The requirements of this Chapter may be modified where direct calculation procedures are adopted to analyse the stress distribution in the primary structure.

1.4.1 Clasifications Register (hereinafter referred to as 'LR') will consider direct calculations for the derivation of scantlings as an alternative and equivalent to those derived by Rule requirements in accordance with Pt 3, Ch 1, 3 Equivalents.

1.5.1 The symbols used in this Chapter are defined below and in the appropriate Section:

1.6.1 Where plating thicknesses as determined by the Rules require to be rounded then this is to be carried out to the nearest full or half millimetre, with thicknesses 0,75 and 0,25 being rounded up.

1.7.1 Dimensional tolerances for materials are to be in accordance with Ch 8 Aluminium Alloysof the Rules for the Manufacture, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials), or an acceptable National or International Standard.

1.7.2 The under thickness tolerance acceptable for classification is to be considered as the lower limit of a range of thickness tolerance which could be found in the normal production of a conventional rolling mill manufacturing material, on average, to the nominal thickness.

1.7.3 The Owners and Builders may agree in individual cases whether they wish to specify a more stringent under thickness tolerance than that given in Pt 7, Ch 3, 1.7 Dimensional tolerance 1.7.2.

1.7.4 The minus tolerance on sections (except for wide flats) is to be in accordance with a National or International Standard.

1.7.5 The thickness of plates and strip is to be measured at random locations whose distance from an edge is to be at least 25 mm. Local surface depressions resulting from imperfections and ground areas resulting from the elimination of defects may be disregarded provided that they are in accordance with the requirements of a National or International Standard.

1.7.6 The responsibility for maintaining the required tolerances and making the necessary measurements rests with the manufacturer/Builder. Occasional checking by the Surveyor does not absolve the manufacturer/Builder from the responsibility.

1.8.1 The basic grade of aluminium alloy is taken as marine grade 5083-0 with the following mechanical properties:

1.8.2 Where other alloy grades with differing mechanical properties are to be used, due allowance is given in the determination of the Rule requirement for plating thickness, section modulus, inertia and cross-sectional area by use of the following correction factors:

1. Plating thickness factor =

2. Section modulus and cross section area factor = k _a

where k _a is as defined in Pt 7, Ch 3, 1.5 Symbols and definitions 1.5.1.

1.9.1 Particular attention is to be given to the welding procedures for the welding of high strength sheet and plate. The 0,2 per cent yield strength values in the welded condition will, in general, be significantly less than in the unwelded condition. These reduced values are to be used in the determination of the Rule scantlings.

1.10.1 The requirements of Pt 7, Ch 3, 1.9 High strength sheet and plate are to be complied with. However, special consideration will be given to the use of un-welded strength properties for use in the determination of the Rule scantlings provided that suitable compensation is provided in way of welding on the face of the stiffener. This compensation can be provided by butt-straps or other acceptable arrangements, see also Pt 7, Ch 2, 4.25 Extruded `planking'.

1.10.2 The application of high strength extrusions is in general limited to superstructures, deckhouses, decks and bulkheads. Special consideration will be given to their use in other areas.

1.10.3 Butt welds and seams are to be carefully positioned clear of areas of high stress and where practicable are to be orientated parallel to the direction of the main stresses.

1.11.1 The effective geometric properties of rolled or built sections are to be calculated directly from the dimensions of the section and associated effective area of attached plating. Where the web of the section is not normal to the actual plating, and the angle exceeds 20^o, the properties of the section are to be determined about an axis parallel to the attached plating.

1.11.2 For stiffening members, the geometric properties of rolled or built sections are to be calculated in association with an effective area of attached load bearing plating of thickness t _p, in mm and a breadth b _e, in mm, b _e is as defined in Pt 7, Ch 3, 1.11 Effective width of attached plating 1.11.3 and Pt 7, Ch 3, 1.11 Effective width of attached plating 1.11.4.

1.11.3 The effective width of attached plating to secondary members b _e is to be taken as but not greater than s. σ_a is not to be taken as greater than 169 N/mm² for aluminum alloy. E, s and σ_a are as defined in Pt 7, Ch 3, 1.5 Symbols and definitions 1.5.1.

1.11.4 The effective breadth of attached plating to primary support members (girders, transverses, webs, etc.) b _e is to be taken as bf, where b and f are as defined in Pt 3, Ch 2, 3.2 Geometric properties of sections 3.2.1.

1.11.5 Where primary stiffening members support areas of plating of the extruded plank type, or the floating frame system is used, the effect of the plating attached to the secondary stiffening members is to be ignored when calculating the actual section modulus and inertia of the primary stiffening members, i.e. the full section modulus and inertia are to be provided by the primary stiffening member only, see also Pt 7, Ch 2, 4.26 Aluminium/steel transition joints.

1.12.1 Special consideration will be given to the use of materials other than aluminium alloy. Details of the type of material, the specification to which it was manufactured and its mechanical properties are to be submitted for appraisal.

1.13.1 The use of FRP in construction is to be in accordance with Pt 8 Hull Construction in Composite.

1.14.1 The thickness of plating as determined by the Rules may be reduced where significant curvature exists between the supporting members. In such cases a plate curvature correction factor may be applied:

See Figure 3.1.1 Convex curvature.

1.15.1 The thickness of plating as determined by the Rules may be reduced when the panel aspect ratio is taken into consideration. In such cases a panel aspect ratio correction factor may be applied:

1.16.1 The requirements for the thickness of plating, t _p, is, in general, to be in accordance with the following:

s, γ, β, p, σ_a are as defined in Pt 7, Ch 3, 1.5 Symbols and definitions 1.5.1.

1.17.1 The requirements for section modulus, inertia and web area of stiffening members are in general to be in accordance with the following:

1. Section modulus:

   
   where

   Φz	=	section modulus coefficient dependent on the loading model assumption taken from Table 3.1.1 Section modulus, inertia and web area coefficients
   f σ	=	limiting bending stress coefficient for stiffening member given in Table 7.3.1 Limiting stress coefficients for local loading in Chapter 7.

   p, s, _e and σ_a are as defined in Pt 7, Ch 3, 1.5 Symbols and definitions.

2. Inertia:

   
   where

   ΦI	=	inertia coefficient dependent on the loading model assumption taken from Table 3.1.1 Section modulus, inertia and web area coefficients
   f δ	=	limiting deflection coefficient for stiffener member given in Table 7.2.1 Limiting deflection ratio in Chapter 7.

   p, s, _e, and E are as defined in Pt 7, Ch 3, 1.5 Symbols and definitions 1.5.1.

3. Web area:

   
   where

   ΦA	=	web area coefficient dependent on the loading model assumption taken from Table 3.1.1 Section modulus, inertia and web area coefficients
   f τ	=	limiting shear stress coefficient for stiffener member given in Table 7.3.1 Limiting stress coefficients for local loading

   p, s, _e, and τ_a are as defined in Pt 7, Ch 3, 1.5 Symbols and definitions 1.5.1.

1.18.1 From structural stability and local buckling considerations, the proportions of stiffening members are, in general, to be in accordance with Table 3.1.2 Stiffener proportions.

1.19.1 The effective length of span, _e, of a stiffening member is generally less than the overall length, , by an amount which depends on the design of the end connections. The span points, between which the value of _e is measured, are to be determined as follows:

1. For rolled or built-up secondary stiffening members:

   The span point is to be taken at the point where the depth of the end bracket, measured from the face of the secondary stiffening member, is equal to the depth of the member, see Figure 3.1.2 Span points. Where there is no end bracket, the span point is to be measured between primary member webs.

2. For primary support members:

   The span point is to be taken at a point distant, b _e from the end of the member, where

   

where b _e, b _b, d _w and d _B are as shown in Figure 3.1.2 Span points.

1.19.2 Where the stiffener member is inclined to a vertical or horizontal axis and the inclination exceeds 10^o, the span is to be measured along the member.

1.19.3 Where the stiffening member is curved then the span is to be taken as the effective chord length between span points.

1.19.4 Where there is a pronounced turn of bilge, chine or the structure is significantly pitched, the span may be measured as in Figure 3.1.2 Span points.

1.19.5 It is assumed that the ends of stiffening members are substantially fixed against rotation and displacement. If the arrangement of supporting structure is such that this condition is not achieved, consideration will be given to the effective span to be used for the stiffener.

1.20.1 Secondary members, that is longitudinals, beams, frames and bulkhead stiffeners forming part of the hull structure, are to be effectively continuous and are to be suitably bracketed at their end connections. Where it is desired to adopt bracketless connections, the proposed arrangements will be individually considered, see also Pt 7, Ch 2, 4.12 Weld connection of strength deck plating to sheerstrake and Table 2.4.5 Secondary member end connections welds in Chapter 2.

1.20.2 Where bracketed end connections are fitted in accordance with these requirements, they may be taken into account in determining the effective span of the member.

1.20.3 The scantlings of secondary member end connections are to be in accordance with Pt 7, Ch 3, 1.21 Scantlings of end brackets.

1.21.1 Where a longitudinal strength member is cut at a primary support and the continuity of strength is provided by brackets, the scantlings of the end brackets are to be such that their section modulus and effective cross-sectional area are not less than those of the member. Care is to be taken to ensure correct alignment of the brackets on each side of the primary member.

1.21.2 In other cases the scantlings of the bracket are to be based on the modulus as follows:

1. Bracket connecting stiffener to primary member - modulus of the stiffener.

2. Bracket at the head of a main transverse frame where frame terminates - modulus of the frame.

3. Brackets connecting lower deck beams or longitudinals to the main frame in the forward 0,5L _R - modulus of the frame.

4. Elsewhere - the lesser modulus of the members being connected by the bracket.

1.21.3 The web thickness and face flat area of end brackets are not in general to be less than those of the connecting stiffeners. Additionally, the stiffener proportion requirements of Pt 7, Ch 3, 1.18 Geometric properties and proportions of stiffener sections are to be satisfied.

1.21.4 Typical arrangements of stiffener end brackets are shown diagrammatically in Figure 3.1.3 Stiffener end brackets.

1.21.5 The lengths, a and b of the arms are to be measured from the plating to the toe of the bracket and are to be such that:

1. a + b ≥ 2,0 _b

2. a ≥ 0,8 _b

3. b ≥ 0,8 _b

where a and b are the actual lengths of the two arms of the bracket, in mm, measured from the plating to the toe of the bracket.

In no case is _b to be taken as less than twice the web depth of the stiffener on which the bracket scantlings are to be based.

1.21.6 The free edge of the bracket is to be stiffened where any of the following apply:

1. The section modulus, Z, exceeds 500 cm³.

2. The length of free edge exceeds 40 times the bracket thickness.

3. The bracket is fitted at the lower end of main transverse side framing.

1.21.7 Where a face flat is fitted, its breadth, b _f, is to be not less than:

but not less than 40 mm

1.21.8 Where the edge is stiffened by a welded face flat, the cross-sectional area of the face flat is to be not less than:

1. 0,017 k _a b _f T _B cm² for offset edge stiffening.

2. 0,014 k _a b _f T _B cm² for symmetrically placed stiffening.

   b f

   =

   breadth of face flat, in mm

   T B

   =

   the thickness of the bracket, in mm

   k a

   =

   is as defined in Pt 7, Ch 3, 1.5 Symbols and definitions 1.5.1.

1.21.9 Where the stiffening member is lapped onto the bracket, the length of overlap is to be adequate to provide for the required area of welding. In general, the length of overlap is not to be less than , or the depth of stiffener, whichever is the greater.

1.21.10 Where the free edge of the bracket is hollowed out, it is to be stiffened or increased in size to ensure that the modulus of the bracket through the throat is not less than that of the required straight edged bracket.

1.21.11 The arrangement of the connection between the stiffener and the bracket is to be such that at no point in the connection is the actual modulus reduced to less than that of the stiffener with associated plating.

1.21.12 The design of end connections and their supporting structure is to be such as to provide adequate resistance to rotation and displacement of the joint.

1.22.1 The requirements for section modulus and inertia (if applicable) of primary members are given in the appropriate Chapter. The scantling requirements for primary member end connections in dry spaces and in tanks of all craft types are generally to comply with the requirements of Pt 7, Ch 3, 1.21 Scantlings of end brackets, taking Z as the section modulus of the primary member.

1.22.2 Primary members are to be so arranged as to ensure effective continuity of strength, and abrupt changes of depth or section are to be avoided. Where members abut on both sides of a bulkhead, or on other members, arrangements are to be made to ensure that they are in alignment. Primary members in tanks are to form a continuous line of support and wherever possible, a complete ring system.

1.22.3 The members are to have adequate lateral stability and web stiffening and the structure is to be arranged to minimise hard spots and other sources of stress concentration. Openings are to have well rounded corners and smooth edges and are to be located having regard to the stress distribution and buckling strength of the panel.

1.22.4 Primary members are to be provided with adequate end fixity by end brackets or equivalent structure. The design of end connections and their supporting structure is to be such as to provide adequate resistance to rotation and displacement of the joint and effective distribution of the load from the member.

1.22.5 Where the primary member is supported by structure which provides only a low degree of restraint against rotation, the member is generally to be extended beyond the point of support and thereafter tapered and/or scarfed into the adjacent structure over a distance generally not less than two frame spaces.

1.22.6 Where primary members are subject to concentrated loads, particularly if these are out of line with the member web, additional strengthening may be required.

1.22.7 The thickness of the bracket is to be not less than that of the primary member web. The free edge of the bracket is to be stiffened.

1.22.8 Where a deck girder or transverse is connected to a vertical member on the shell or bulkhead, the scantlings of the latter may be required to be increased to provide adequate stiffness to resist rotation of the joint.

1.22.9 Where a member is continued over a point of support, such as a pillar or pillar bulkhead stiffener, the design of the end connection is to be such as to ensure the effective distribution of the load into the support. Proposals to fit brackets of reduced scantlings, or alternative arrangements, will be considered.

1.22.10 Connections between primary members forming a ring system are to minimise stress concentrations at the junctions. Integral brackets are generally to be radiused or well rounded at their toes. The arm length of the bracket, measured from the face of the member, is to be not less than the depth of the smaller member forming the connection.

1.23.1 Where structural members pass through the boundary of a tank, and leakage into the adjacent space could be hazardous or undesirable, full penetration welding is to be adopted for the members for at least 150 mm on each side of the boundary. Alternatively a small scallop of suitable shape may be cut in the member close to the boundary outside the compartment, and carefully welded all round.

1.24.1 Primary members are to be supported by tripping brackets. The tripping brackets supporting asymmetrical sections are to be spaced no more than two secondary frames apart. The tripping brackets supporting symmetrical sections are to be spaced no more than four secondary frames apart.

1.24.2 Tripping brackets are in general required to be fitted at the toes of end brackets and in way of heavy or concentrated loads such as the heels of pillars. See also LR's Guidance Notes for Structural Details.

1.25.1 Where openings are cut in the web, the depth of opening is not to exceed 50 per cent of the web depth, and the opening is to be so located that the edges are not less than 25 per cent of the web depth from the face plate. The length of opening is not to exceed the web depth or 60 per cent of the secondary member spacing, whichever is the greater, and the ends of the openings are to be equidistant from the corners of cut-outs for secondary members. Where larger openings are proposed, the arrangements and compensation required will be specially considered.

1.25.2 Openings are to have smooth edges and well rounded corners.

1.26.1 The arrangement of material is to be such as will ensure structural continuity. Abrupt changes of shape or section, sharp corners and points of stress concentration are to be avoided.

1.26.2 Where members abut on both sides of a bulkhead or similar structure, care is to be taken to ensure good alignment.

1.26.3 Pillars and pillar bulkheads are to be fitted in the same vertical line wherever possible, and elsewhere arrangements are to be made to transmit the out of line forces satisfactorily. The load at head and heel of pillars is to be effectively distributed and arrangements are to be made to ensure the adequacy and lateral stability of the supporting members.

1.26.4 Continuity is to be maintained where primary members intersect and where the members are of the same depth, a suitable gusset plate is to be fitted, see Figure 3.1.4 Primary member intersection.

1.26.5 End connections of structural members are to provide adequate end fixity and effective distribution of the load into the supporting structure.

1.26.6 The toes of brackets, etc. are not to land on unstiffened panels of plating. Special care is to be taken to avoid notch effects at the toes of brackets, by making the toe concave or otherwise tapering it off, see also LR's Guidance Notes for Structural Details.

1.26.7 Particular attention is to be paid to the design of the end bracket toes in order to minimise stress concentrations. Sniped face plates which are welded onto the edge of primary member brackets are to be carried well around the radiused part of the bracket toe and are to incorporate a taper not exceeding one in three. Where sniped face plates are welded adjacent to the edge of primary member brackets, adequate cross sectional area is to be provided through the bracket toe at the end of the snipe. In general, this area measured perpendicular to the face plate, is to be not less than 60 per cent of the full cross-sectional area of the face plate, see Figure 3.1.5 Bracket toe construction.

1.27.1 Where the stiffeners of the double bottom floors and transverse bulkheads are unconnected to the secondary members and offset from them, see Figure 3.1.6 Arrangement with offset stiffener, the collar arrangement for the secondary members are to satisfy the requirements of Pt 7, Ch 3, 1.28 Arrangements at intersection of continuous secondary and primary members. In addition, the fillet welds attaching the lugs to the secondary members are to be based on a weld factor of 0,44 for the throat thickness. To facilitate access for welding the offset stiffeners are to be located 50 mm from the slot edge furthest from the web of the secondary member. The ends of the offset stiffeners are to be suitably tapered and softened.

1.27.2 Alternative arrangements will be considered on the basis of their ability to transmit load with equivalent effectiveness. Details of the calculations made and testing procedures are to be submitted.

1.28.1 Cut-outs for the passage of secondary members through the webs of primary members, and the related collaring arrangements, are to be designed to minimise stress concentrations around the perimeter of the opening and in the attached hull envelope or bulkhead plating. The critical shear buckling stress of the panel in which the cut-out is made is to be investigated. Cut-outs for longitudinals will be required to have double lugs in areas of high stress.

1.28.2 The cross-sectional areas of connections are to be determined from the load transmitted through each component in association with its appropriate permissible stress.

1.28.3 The load transmitted through the intersection arrangement is to be determined using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft respectively.

1.28.5 The arrangement of lug/collar/direct connection to the primary web stiffener determines the load apportioned to each component. The effect on each component of the intersection is to be assessed, as appropriate, for shear and direct stress. Where the web stiffener is not connected to the secondary member, the load, P, is transmitted through the lug/collar/direct connection.

1.28.6 The breadth of cut-outs is to be as small as practicable, with the top edge suitably radiused. Cut-outs are to have smooth edges, and the corner radii are to be as large as practicable. Where the web depth is greater than 100 mm the corner radii are to be a minimum of 20 per cent of the breadth of the cut-out or 20 mm, whichever is the greater, and for large cut-outs greater than 250 mm deep, the web plate connection to the hull envelope, or bulkhead, should end in a smooth tapered `soft toe'. Recommended shapes of cut-out are shown in Figure 3.1.7 Cut-outs and connections, but consideration will be given to other shapes on the basis of maintaining equivalent strength and minimising stress concentration, see also LR's Guidance Notes for Structural Details.

1.28.7 Consideration is to be given to the provision of adequate drainage and unimpeded flow of air and water when designing the cut-outs and connection details.

1.28.8 Asymmetrical secondary members are to be connected on the heel side to the primary member web plate. Additional connection by lugs on the opposite side may be required.

1.28.9 Symmetrical secondary members are to be connected by lugs on one or both sides, as necessary.

1.28.10 Where the primary member stiffener is connected to the secondary member it is to be aligned with the web of the secondary member, except where the face plate of the latter is offset and abutted to the web, in which case the stiffener connection is to be lapped.

1.28.11 Fabricated longitudinals having the face plate welded to the underside of the web, leaving the edge of the web exposed, are not recommended for side shell and longitudinal bulkhead longitudinals. Where it is proposed to fit such sections, a symmetrical arrangement of connection to transverse members is to be incorporated. This can be achieved by fitting backing structure on the opposite side of the transverse web or bulkhead.

1.28.12 Where a bracket is fitted to the primary member web plate in addition to a connected stiffener it is to be arranged on the opposite side to, and in alignment with the stiffener. The arm length of the bracket is to be not less than the depth of the stiffener, and its cross-sectional area through the throat of the bracket is to be included in the calculation of the area of the primary web stiffener in way of the connection.

1.28.13 Alternative arrangements will be considered on the basis of their ability to transmit load with equivalent effectiveness. Details of the calculations made and testing procedures are to be submitted.

1.29.1 Manholes, lightening holes and other cut-outs are to be avoided in way of concentrated loads and areas of high shear. In particular, manholes and similar openings are not to be cut in vertical or horizontal diaphragm plates in narrow cofferdams or in floors and double bottom girders close to their span ends, or below the heels of pillars, unless the stresses in the plating and the panel buckling characteristics have been calculated and found satisfactory.

1.29.2 Manholes, lightening holes and other openings are to be suitably framed and stiffened where necessary.

1.29.3 Air and drain holes, notches and scallops are to be kept at least 200 mm clear of the toes of end brackets and other areas of high stress. Openings are to be well rounded with smooth edges. Closely spaced scallops are not permitted. Widely spaced air or drain holes may be accepted, provided that they are of elliptical shape, or equivalent, to minimise stress concentration and are, in general, cut clear of the weld connection.

1.30.1 The quality of welding and general workmanship of fittings and attachments as given in Pt 7, Ch 3, 1.31 Bilge keels and ground bars and Pt 7, Ch 3, 1.32 Other fittings and attachments are to be in accordance with Pt 7, Ch 2, 3.7 Acceptance criteria.

1.31.1 It is recommended that bilge keels are not to be fitted in the forward 0,3L _R region on ships intended to navigate in ice conditions.

1.31.2 Bilge keels are to be attached to a continuous ground bar as shown in Figure 3.1.8 Bilge keel construction. Butt welds in shell plating, ground bar and bilge keels are to be staggered.

1.31.3 The thickness of the ground bar is to be not less than the thickness of the bottom shell or 8 mm, whichever is the greater, but need not be taken as greater than 15 mm.

1.31.4 The material class, grade and quality of the ground bar are to be similar to those of the adjacent shell plating.

1.31.5 The ground bar is to be connected to the shell with a continuous fillet weld and the bilge keel to the ground bar with a light continuous fillet weld.

1.31.6 Direct connection between ground bar butt welds and shell plating, and between bilge keel butt welds and ground bar is to be avoided.

1.31.7 The end details of bilge keels and intermittent bilge keels, where adopted, are to be as shown in Figure 3.1.9 Bilge keel end design.

1.31.8 The ground bar and bilge keel ends are to be tapered or rounded. Where the ends are tapered, the tapers are to be gradual with ratios of at least 3:1, see Figure 3.1.9 Bilge keel end design(a) and (b). Where the ends are rounded, details are to be as shown in Figure 3.1.9 Bilge keel end design(c). Cut-outs on the bilge keel web within zone 'A' (see Figure 3.1.9 Bilge keel end design(b)) are not permitted.

1.31.9 The end of the bilge keel web is to be between 50 mm and 100 mm from the end of the ground bar, see Figure 3.1.9 Bilge keel end design(a).

1.31.10 An internal transverse support is to be positioned as close as possible to halfway between the end of the bilge keel web and the end of the ground bar, see Figure 3.1.9 Bilge keel end design(b).

1.31.11 Where an internal longitudinal stiffener is fitted in line with the bilge keel web, the longitudinal stiffener is to extend to at least the nearest transverse member outside zone 'A', see Figure 3.1.9 Bilge keel end design(b). In this case, the requirement of Pt 7, Ch 3, 1.31 Bilge keels and ground bars 1.31.10 does not apply.

1.31.12 For craft over 65 m in length, L _R, holes are to be drilled in the bilge keel butt welds. The size and position of these holes are to be as illustrated in Figure 3.1.8 Bilge keel construction. Where the butt weld has been subject to non-destructive examination the stop hole may be omitted.

1.31.13 Bilge keels of a different design from that shown in Figure 3.1.8 Bilge keel construction and Figure 3.1.9 Bilge keel end design will be specially considered.

1.31.14 Within zone 'B' (see Figure 3.1.9 Bilge keel end design(a)), welds at the ends of the ground bar and the bilge plating, and at the ends of the bilge keel web and ground bar, are to have weld factors of 0,44 and 0,34 respectively. These welds are to be ground and to blend smoothly with the base materials.

1.31.15 A plan of the bilge keels is to be submitted for approval of material grades, welded connections and detail design.

1.32.1 Gutterway bars at the upper deck are to be so arranged that the effect of main hull stresses on them is minimised.

1.32.2 Minor attachments, such as pipe clips, staging lugs and supports, are generally to be kept clear of toes of end brackets, corners of openings and similar areas of high stress. Where connected to asymmetrical stiffeners, the attachments may be in line with the web providing the fillet weld leg length is clear of the offset face plate or flange edge. Where this cannot be achieved the attachments are to be connected to the web, and in the case of flanged stiffeners they are to be kept at least 25 mm clear of the flange edge. On symmetrical stiffeners, they may be connected to the web or to the centreline of the face plate in line with the web.

1.32.3 Where necessary in the construction of the craft, lifting lugs may be welded to the hull plating but they are not to be slotted through. Where they are subsequently removed, this is to be carried out by mechanical cutting close to the plate surface, and the remaining material and welding ground off. After removal the area is to be carefully examined to ensure freedom from cracks or other defects in the plate surface.