3.7.2 Where required, plans giving details of the proposed structural modifications or repairs are to be submitted for approval, prior to execution.
3.8 Inspection
3.8.1 It is the builder’s responsibility to carry out the inspections required in accordance with the accepted quality control system.
3.8.2 The Surveyors will monitor the builder’s quality control records and carry out inspections of work in progress during their periodical visits.
3.8.3 During inspections, all deviations are to be dealt with under the builder’s agreed quality procedures.
3.9 Acceptance criteria
3.9.1 Classification is dependent upon the work being carried out in accordance with the approved plans and the requirements of an accepted quality system.
3.9.2 The workmanship is to be to the satisfaction of the attending Surveyor. This will include the verification of the quality control documentation and the remedial action associated with all defects and deficiencies recorded.
3.9.3 Proposed deviations from the approved plans are subject to IRS approval. An amended plan is to be submitted for approval prior to any such changes being introduced.
Section 4
4.2.5 The production plan is to identify allowable tolerances for the alignment of the primary structural components.
4.2.6 To ensure efficient load transmission, intercostals, single skin bulkheads are to be aligned to within half the thickness of the thinner bulkhead. In the case of sandwich construction the tolerance requirements will be individually considered dependent upon the sandwich panel dimensions and the construction of the continuous member. In general, the webs of the intercoastal sandwich panel member are to be aligned within 5 mm. Where poor alignment has been identified, additional boundary bonding reinforcements are to be applied as agreed with the attending Surveyor. Any deviations and details of the remedial action taken are to be recorded in the builder's quality control documentation.
4.2.7 To ensure efficient transmission of shear loads, the alignment tolerance of intercoastal ‘top hat’
stiffener webs is, in general, to be within half of the web thickness. Where poor alignment is identified, additional reinforcements are, in general, to be incorporated into the stiffener webs as agreed with the attending Surveyor. Such deviations and details of the remedial action taken are to be recorded in the builder's quality control documentation.
4.3 Continuity
4.3.1 Continuity of all primary structural members is to be maintained and abrupt changes of section are to be avoided. All longitudinal girders and stiffeners are to be continuous through their supporting members.
Brackets ending at unsupported sandwich panels are to be tapered smoothly to zero and the panels skin laminate to be locally reinforced at the end of the bracket.
Girders are to be fitted with bracket or tapered gradually at ends. See Fig. 1.5.1
4.3.2 Special consideration is to be given to the inter-section of longitudinal and transverse members. In general the ratio between the depths of the intersecting members is to be 2:1. The shallower member is to be continuous under the supporting members.
4.3.3 Alternative proposals to the requirements given in 4.3.2 will be subject to special consideration alongwith details for maintaining the continuity of reinforcements at intersections in both directions which are to be submitted. Where stiffeners are of similar dimensions the primary member is to be continuous. In general, the section modulus of the continuous material is to be maintained.
4.4 Openings
4.4.1 All openings are to have well rounded corners and are to be supported on all sides. Cut edges of openings are to be sealed to prevent the ingress of moisture.
4.4.2 All hatch openings are to be supported by a system of transverse and longitudinal stiffeners, the details of which are to be submitted for approval.
4.4.3 The requirements for closing arrangements and outfit are given in Chapter 4, Section 3.
4.4.4 All deck openings are to have corner radii as specified in Section 6.4.3.
4.4.5 For details of sealing the edges of openings and sandwich panels, see 4.9.
4.5 Through bolting and bolted connections
4.5.1 Bolting arrangements are, in general, to be in accordance with 4.5 to 4.7. The details of all through bolted structural connections including bolt material, proposed number and spacing are to be indicated on the relevant construction plans submitted for approval. The design of the joint is to be suitable for its intended purpose with a sufficient number of bolts to satisfactorily close the joint.
4.5.2 All fastenings are to be of a suitable marine grade and are to be of a non-corrosive material or protected against corrosion.
4.5.3 In general, large headed bolts or large diameter thick washers are to be used to prevent localised crushing damage during tightening.
4.5.4 Where mechanical fastenings are used, the torque is to be indicated on the plans submitted for approval.
4.5.5 In sandwich constructions, inserts of a material capable of resisting crushing are to be fitted in accordance with 4.7.
4.5.6 The diameter of a fastening is not to be less than the thickness of the thinner component being fastened, with a minimum of 6 mm.
4.5.7 Bolted connections are, in general, to be bonded along all mating surfaces using an accepted structural adhesive, applied in accordance with the manufacturer’s requirements. Where connections rely solely on the shear resistance of the connecting bolts the spacing is not to exceed 3 x the bolt diameter. In areas where subsequent access will either be limited or not possible, self- locking nuts are to be provided.
4.5.8 In general, all structural, bolted connections are to use reeled lines of bolts in accordance with the requirements given in Table 4.5.8.
Table 4.5.8 : Minimum bolt pitch requirements in bonded and bolted connections
Location Pitch
Watertight connections
- below static load waterline 10 db
Connections in hull above static load waterline to deck 15 db
Hull to deck connections
- bonded with structural adhesive - bolted with mastic sealant (see note 2)
15 db
8 db
Connections in deckhouses 20 db
Deckhouse to deck connections - bonded with structural adhesive - bolted with mastic sealant (see note 2)
15 db
8 db
Minimum distance between reeled lines of bolts 3 db
Minimum distance from centreline of line of bolts to free edge 2 db
Notes:
1. db is the diameter of the bolt
2. Internal boundary sealing angle to be provided.
4.5.9 All structural, single line, bolted connections without adhesive bonding are to be in accordance with the requirements given in Table 4.5.9.
Table 4.5.9 : Minimum bolt pitch requirements in bolted structural connections
Location Pitch
Manhole covers to fuel tanks 6 db
Manhole covers to water tanks 8 db
Covers over void tanks/cofferdams 10 db
Bolted access hatches in decks 10 db
Bolted watertight door frames 8 db
Window frames 8 db
Notes:
1. db is the diameter of the bolt.
2. Internal boundary sealing angle to be provided.
4.5.10 Care is to be taken to avoid distortion of the frame when window frames are bolted into the structure of the Ship. Where necessary, uneven surfaces are to be locally built upto the satisfaction of the attending Surveyor.
4.5.11 Bolt holes are to be drilled, without undue pressure at break through, having a diametric tolerance of two percent of the bolt diameter. Where bolted connections are to be made watertight the hole is to be sealed with resin and allowed to cure before the bolt is inserted.
4.5.12 In areas of high stress or where unusual bolting configurations are proposed, testing on the basis of equivalence with the above Rules, may be required.
4.6 Through hull fittings
4.6.1 Where fittings penetrate the hull envelope, care is to be taken to seal the hull laminate with resin or other suitable compound. See 4.9.
4.6.2 The areas in way of penetrations for fittings in sandwich construction are, in general, to comply with the requirements of 4.7. Where the requirements cannot be complied with, the core is to be replaced locally with a solid core or very high density foam core with compressive properties commensurate with the loads imposed by the securing arrangements. In areas where localised crushing of a sandwich core is likely to occur, large diameter washers, compression tubes or inserts or a combination of these may to be provided.
4.6.3 All bolted fittings are to be bedded down using a suitable mastic, details of which are to be indicated on the plans for approval.
4.7 Backing bars (inserts) and tapping plates
4.7.1 The requirements for backing plates and bars will be individually considered, on the basis of the loading imposed, details of which are to be indicated on the submitted plans.
4.7.2 Metallic plates and bars are to be suitably protected against corrosion.
4.7.3 Tapping plates may be encapsulated within the laminate, laminated to or bolted to the structure. Where tapping plate edges or corners are likely to give rise to hard spots or stress concentrations the edges are to be suitably rounded.
4.7.4 Where tapping plates are placed on foam cores the plate is to be mounted on a suitable foundation to prevent the movement of the tapping plate during drilling operations.
4.7.5 Direct calculations regarding the scantlings of tapping plates are to be provided at the plan appraisal stage.
4.8 Exposed edges
4.8.1 The exposed edges of all openings cut in single skin laminate panels are to be suitably sealed.
Where such edges are in wet spaces or under water the edges of such openings are to have rounded edges and are to be sealed by two plies of 450 g/m2 chopped strand mat (or equivalent) reinforcements.
4.8.2 Exposed edges of openings cut in sandwich panels are to be suitably sealed. The cut edges are, in general, to be sealed with a weight of reinforcement not less than that required for the outer skin of the sandwich. Where other than an epoxy resin system is used the first layer of such reinforcement is to be chopped strand mat with a weight not exceeding 450 g/m2.
4.9 Local reinforcement
4.9.1 Areas subject to local loads or increased stress are to be suitably reinforced, details of which are to be indicated on the submitted plans.
4.9.2 The hull is to be locally increased by minimum 50% in thickness in way of rudder tubes, propeller brackets, etc. Details of such reinforcements are to be submitted. Local reinforcement is in general to extend under the adjacent supporting structure and then tapered gradually to the base laminate thickness over a distance of minimum 20 times the difference in thickness.
4.10 Hull to deck connections
4.10.1 Details of the hull to deck connection, the method of bonding and the tolerances are to be indicated on the submitted plans.
4.10.2 Hull to deck connections are to be, in general, bolted and over-bonded. A suitable mastic or sealing compound is to be incorporated within the joint.
4.10.3 The bolting details are to be reeled lines of bolts pitched as specified in Tables 4.5.8 and 4.5.9, as applicable. Suitable large diameter thick washers are to be used under both the head and the nut.
4.10.4 Where a mastic is not used, sealing plies are to be applied on the inside of the hull.
4.10.5 The weight of the over-bonding reinforcement is, in general, not to be taken as less than equivalent to the lighter of the component members being connected, and in no case less than equivalent to three plies of 600 g/m2 chopped strand mat.
4.10.6 Substantial beam knees are to be provided to maintain structural continuity between the transverse deck and hull stiffening.
4.10.7 The watertight integrity, continuity and strength of the connection is not to be impaired by the attachment of the hull fender.
4.11 Exhaust systems
4.11.1 Exhaust systems, manufactured from FRP, are to be of the water injected type with a normal operating temperature of 60o to 70oC.
4.11.2 Exhaust pipes, silencers and water separators are to be of a type approved design, installed strictly in accordance with the manufacturer’s requirements.
4.11.3 Where a type approved system is not used, the arrangement will be considered on an individual basis. Resins used in the manufacture of exhaust systems are to be of a type approved by IRS and are to have good heat and chemical resistance properties with a high deflection temperature under load. A vinylester resin is to be used, but a fire retardant polyester resin, having a high heat distortion temperature, will be considered. Test samples may be required dependent upon the proposed arrangement, temperatures and materials.
4.11.4 It is recommended that pigments and additives are not used unless it can be demonstrated that the mechanical properties of the resin system remain unaffected. Resins used are not to show any embrittlement with age.
4.11.5 Special consideration is to be given to post curing of such systems to obtain optimal characteristics.
4.11.6 Due to the weight of water contained within the system, exhaust pipes and fittings are to be efficiently supported.
4.11.7 Exhaust boxes are to be lined with a minimum of two plies of 600 g/m2 chopped strand mat (or equivalent) using a suitable fire retardant/high temperature resin.
4.11.8 For engineering aspects of exhaust systems reference is to be made to Chapter 12, Section 3.1.4.
4.12 Ballast
4.12.1 The provision of permanent ballast is not to adversely affect the surrounding structure.
4.12.2 Where a resin compound is to be poured into a void space, care is to be taken to minimise the generation of heat that may affect the mechanical and weathering characteristics of the structural laminate.
4.12.3 Details of all ballast materials and the proposed method of installation are to be indicated on the submitted plans.
4.13 Limber holes
4.13.1 Provision is to be made to drain areas likely to accumulate liquids, details of which are to be indicated on the submitted plans.
4.13.2 The size, shape and position of limber holes are not to affect the structural strength of the stiffening members in which they are fitted. Limber holes are, in general, to be positioned at the quarter span of the stiffener.
4.13.3 In way of limber holes, “Top Hat” stiffeners are to be boxed, so that, water does not pass through stiffener hollows to other parts of the vessel.
4.14 Integral tanks (requirements for coatings)
4.14.1 The surfaces of integral tanks are to be provided with a barrier to reduce the ingress of liquid.
The details of the proposed system are to be indicated on the submitted plans.
4.14.2 Fresh water tanks are to be coated with a non-toxic and non-tainting coat of resin that is recommended by the resin manufacturer for potable water tanks.
4.14.3 The design and arrangement of oil fuel tanks is to be such that there is no exposed horizontal section at the bottom that could be exposed to a fire. Other fire protection arrangements for oil fuel tanks will be specially considered. For details of fire protection requirements see Chapter 10.
4.14.4 Where plywood bulkheads form part of a tank boundary, the surface is to be completely protected against the ingress of moisture with a minimum of 5 mm thickness of laminate to provide an effective fluid barrier.
4.14.5 Where outfit items are to be laminated to the tank surface, the heavy coating of resin is to be applied afterwards and the laminated brackets sealed to prevent the ingress of moisture.
4.14.6 The scantlings of integral oil fuel and water tanks are to be in accordance with Sections 7, 8 and 9.
4.14.7 Integral tanks are to be tested in accordance with Chapter 4, Section 4.6.
4.15 Reserve buoyancy
4.15.1 Details of materials to be used and the method of installation of reserve buoyancy are to be indicated on the submitted plans.
4.15.2 Where necessary, buoyancy materials are to be over-laminated in-situ to prevent the ingress of moisture.