Section 3 General construction process

3.1.1 Provision is made in this Section for the construction of craft built of fibre reinforced plastic using thermosetting materials. Craft built of fibre reinforced thermoplastic materials will be subject to individual consideration.

3.1.2 This Section contains the general Rule requirements to be complied with in the construction of fibre reinforced craft being built under survey. Where detailed requirements are not defined good boat building practices are to be applied.

3.1.3 Craft built of unusual materials or built using unusual techniques will be subject to individual consideration.

3.2.1 Curing agents, fillers and pigments are to be added strictly in accordance with the resin manufacturer's recommendations.

3.2.2 Before decanting, all resins are to be thoroughly mixed, deaerated and conditioned to at shop temperature in accordance with the resin manufacturer's instructions.

3.2.3 All measuring equipment is to be certified and suitable for the quantity of material being measured. Valid certificates of calibration are to form part of the quality control documentation.

3.2.4 Where pumping/metering equipment is used it is to be maintained in accordance with the manufacturer's instructions, and a valid certificate of calibration accuracy is to be retained in the quality control documentation.

3.2.5 Quality control records are to be maintained to provide traceability and identification of the resin and all additives used in the resin system. Batch numbers are to be identified.

3.2.6 Any additive used as a production aid must be that recommended by the resin manufacturer and is not to alter the mechanical properties or the characteristics of the cured laminate.

3.3.1 Production is to follow all necessary approved construction plans in accordance with the LR accepted quality plan.

3.3.2 Laminating is to be carried out by skilled operators, who are to be trained and qualified to the level required by the Builder's quality plan and are to be acceptable to LR.

3.3.3 Moulds are to be thoroughly cleaned, dried and allowed to attain the shop temperature before being treated with a suitable release system, see also Pt 8, Ch 2, 1.9 Mould construction 1.9.7.

3.3.4 The gel coat resin is to be applied by brush, roller or spraying equipment to give a uniform, nominal film thickness not exceeding 1,5 mm.

3.3.5 The period of exposure of the gel coat between gelation and the application of the first layer of reinforcement is, in general, to be as short as practicable. In no case is this to be longer than that recommended by the resin manufacturer for that particular resin system. Written confirmation of this is to be obtained and recorded in the Builder's quality control documentation.

3.3.6 Where a polyester or vinylester gel coat is used it is to be reinforced by a lightweight, powder bound reinforcement, generally not exceeding 300g/m² in weight, applied at a high resin content to give a glass content, by weight, of not greater than 0,286. This reinforcement is to be consolidated by gentle rolling. Care is to be taken not to damage the gel coat. A surface tissue may be incorporated within the gel coat, the details of which are to be clearly stated in the laminate schedule.

3.3.7 All mouldings are to be manufactured from layers of reinforcement, laid in the approved sequence and orientation, each layer being thoroughly impregnated and consolidated to give the required fibre content, by weight, in accordance with the approved plans.

3.3.8 In composite laminates, containing multiple layers of woven reinforcement, woven reinforcement may be laid on woven reinforcement provided that the inter-laminar shear strength is not less than 13,8 N/mm²; otherwise, a layer of random fibre reinforcement is to be laid alternately with the woven reinforcements.

3.3.9 Excessive exothermic heat generation caused by thick laminate construction is to be avoided. Where thick laminates are to be laid the Builder is to demonstrate to the Surveyor's satisfaction that the number of plies can be laid wet on wet and that the resultant temperature during the cure cycle does not have any deleterious effect on the mechanical properties of the cured laminate.

3.3.10 Laminating is to be carried out in a sequence such that the time lapse between the application of the successive layers is within the limits recommended by the resin manufacturer and documented in the quality control procedures for the particular resin system. Similarly, the time lapse between the forming and bonding of structural members is to be kept within these limits and, where this is not practicable, the surface of the laminate is to be prepared, in accordance with the resin manufacturer's instructions, to improve the bond.

3.3.11 When laminating is interrupted, and where other than an epoxy resin system is being used, the first of any subsequent layers of reinforcement to be laid in that area is to be of chopped glass fibre or other type of material to enhance the interlaminar strength properties of the laminate.

3.4.1 To ensure that the resultant thicknesses of the structure is not less than that required to comply with those indicated on the approved plans, the nominal fibre content, by weight, of the individual plies and overall laminate is to be controlled on the basis of the weight of the constituent materials.

3.4.2 Continuous monitoring of resin/reinforcement usage is required for ongoing fibre content verification and is to be recorded under the quality control system, see Ch 14, 5 Control of material quality for composite constructionof the Rules for Materials.

3.4.3 A method of validating the completed laminate thickness is to be agreed between the Builder and Surveyor. Where electronic thickness measurement methods are employed, the equipment is to be calibrated against a laminate of identical construction. Alternatively a series of areas are to be identified within the craft where samples can be taken to validate the thickness of the laminate (e.g. in way of overboard discharges/ seawater intakes/deck openings etc.).

3.5.1 The laminate schedule is to clearly define the logical sequence of production and is to identify the specific materials to be used.

3.5.2 The schedule is to define the extent of each reinforcement and state relevant details regarding overlapping, staggering thicknesses and tailoring of reinforcements.

3.5.3 Progressive thickness measurements in accordance with Pt 8, Ch 2, 3.4 Fibre content 3.4.3 are to be recorded as part of the quality control documentation and, where required, additional reinforcements are to be laid to attain the required thickness.

3.5.4 Areas of local deficiency requiring additional reinforcement and areas that have been found to be increased thickness are to be recorded in the quality control documentation.

3.6.1 The equipment for spray deposition of resin and glass fibres is to be inspected during the Workshop Inspection and a sample panel produced. Documentary evidence of maintenance, calibration, catalyst content, fibre length and overall fibre content by weight are to be entered into the quality control documentation. The spray pattern is to give an even distribution, as recommended by the manufacturer of the equipment and is to be to the satisfaction of the attending Surveyor.

3.6.2 Special consideration is to be given to the production environment, ventilation equipment and quality control arrangements to ensure that the finished product meets the requirements of the approved plans.

3.6.3 Unless the mechanical properties are confirmed by testing, the chopped fibre length for a structural laminate is to be not less than 35 mm. In no case is the fibre length to be less than 25 mm.

3.6.4 Spray equipment is only to be operated by trained and competent personnel. Training certification is to form part of the quality control documentation. The use of spray lay-up is to be limited to the parts of the structure to which sufficient access can be obtained to ensure satisfactory laminating.

3.6.5 The weights of resin and reinforcement used is to be monitored continuously to check the glass/resin ratio. Samples are also be taken on a regular basis to validate the calibration of the equipment.

3.6.6 Where spray lay-up is used to back up the gel coat the weight of sprayed fibre is not to exceed 300 g/m², applied at a high resin content to give a glass content by weight, of not greater than 0,286. This should be consolidated by gentle rolling. This first layer of reinforcement is to be allowed to cure to a trimming state before proceeding with the remainder of the laminate.

3.6.7 Consolidation is to be carried out as soon as is practicable after spray deposition. In general, this is to be carried out when a weight of reinforcement equivalent to a thickness of 2 - 3 mm has been deposited. The thickness of the resulting laminate is to be periodically checked and recorded.

3.6.8 Particular attention is to be given to localised thinning of the laminate in way of chines, coamings, knuckles and openings. Further deposition may be required in such areas to compensate for any reduction in thickness. Alternatively, layers of other equivalent reinforcements may be laid to achieve the required local thickness.

3.7.1 After completion of the lay-up, the moulding is to be left in the mould for a period to allow the resin to cure before being removed. This period can vary with ambient temperature, the type of resin and the complexity of the moulding, but is to be not less than 12 hours or that recommended by the resin manufacturer.

3.7.2 Care is to be exercised during removal from the mould to ensure that the hull, deck and other large assemblies are adequately braced and supported to avoid damage to and maintain the form of the moulding.

3.7.3 Where female moulds are adopted, all primary stiffening and transverse bulkheads are to be installed prior to removal from the mould unless agreed otherwise on the approved construction schedule and plans.

3.7.4 Mouldings are not to be stored outside of the workshop environment until they have attained the stage of cure recommended by the resin manufacturer for that particular resin. Provision is to be made for mouldings to be protected against adverse weather conditions.

3.7.5 Mouldings are, in general, to be stabilised in the moulding environment for at least 24 hours, or that recommended by the resin manufacturer before the application of any special cure treatment, details of which are to be submitted for approval.

3.8.1 The degree of cure of mouldings is to be measured using a Barcol impressor model GYZJ 934-1 in accordance with BS 2782: Part 10: Method 1001: 1977 (1989) or other equivalent National or International Standard. Alternative equivalent standards of hardness measurement will be considered.

3.8.2 The hardness meter is to be regularly checked for calibration during use. A calibration certificate is to form part of the quality control documentation.

3.8.3 Removal from the mould is not to be attempted until a minimum Barcol reading recommended by the resin manufacturer or a value of 20 has been attained. Subsequently, the moulding is not to be moved outside of the controlled environment until a minimum Barcol reading recommended by the resin manufacturer of 35 (or equivalent) has been recorded.

3.9.1 Changes in laminate thickness are to be made using a gradual taper. The length of such taper is, in general, not to be less than 20 times the difference in thickness. Where the construction changes from sandwich laminate to a solid laminate, the thickness of the core material is, in general, to be reduced by a gradual taper of not less than 2:1.

3.9.2 Framing and stiffening sections are to be built up layer by layer in accordance with an approved procedure, particular attention being given to ensure a satisfactory bond and structural continuity at the ends and intersections.

3.9.3 Discontinuities and hard points in the structure are to be avoided, and where the strength of a stiffening member is impaired by any attachment of fittings, openings, drainage arrangements, etc. compensation is to be provided.

3.9.4 Where items are prefabricated outside the mould, they are to be connected by boundary angles formed by layers of reinforcement, structural fillets or other approved method. Where structural fillets are proposed, the scantlings and arrangements will be specially considered.

3.9.5 Polyester, vinylester or epoxide resin may be used in bonded joints, provided that the joint is so designed that the resin bond is in shear. The contact area is to be as large as practicable and the surfaces are to be suitably prepared in accordance with the resin manufacturer's instructions.

3.9.6 The submitted plans are to clearly define the laminate sequence at corner joints. In general, corner laminates are to be boxed and all cuts are to be alternately staggered to avoid a fault line. At corner joints vertical and horizontal laminates are to be laid alternately and butts are to be staggered accordingly.

3.9.7 The submitted plans are to clearly define the details of scarfed joints. In general, scarfs are not to not be steeper than a 12:1 taper. Scarf joints may be either ground or stepped and may be single or double taper. Where single taper scarf joints are proposed, a sealing laminate is to be provided, details of which are to be submitted. Where stepped joints are proposed care is to be taken to ensure that over-cutting does not occur. All joints are to be arranged so that they can be reinforced internally to maintain structural continuity of the laminate.

3.9.8 Lap joints may be bolted or adhesively bonded, or both. They may be single or double lapped dependent upon the specific application.

3.9.9 Where tray mouldings form part of the integral structure of the craft, full details are to be indicated on the submitted plans. Information regarding tolerances is to be presented together with details of all adhesives and proposed bonding-in techniques. Particular attention is to be given to the design so as to maintain the structural continuity of the webs of any stiffening members.

3.9.10 The hulls of all craft with a service speed of 25 knots or greater are to be moulded as required by Pt 8, Ch 3, 3.15 Hull laminate arrangement.

3.9.11 Chine details are to be clearly indicated on the submitted plans. Spray rails may form part of the structural laminate or may be installed as a laminated or bolted appendage. Where the chine is a laminated appendage, provision is to be made for a sacrificial ply at which failure may occur without undue damage to the remaining structure of the hull. Sandwich structures are to be returned to single skin laminates at chine rails unless agreed otherwise on the approved construction plans. Chine rails are to be infilled and over laminated on the inner surface of the hull. Additional reinforcement is to be laminated into the chine area in accordance with Pt 8, Ch 3, 3.8 Chine reinforcement.

3.9.12 Reinforcements are to be arranged to maintain continuity of strength throughout the laminate. Joints in each layer of reinforcement are, in general, to be overlapped. The length of the overlap is dependent upon the type of reinforcement but is not to be less than 50 mm. The position of the joints in the laminate is to be staggered, in general by 150 mm, to maintain as near uniform laminate thickness as practicable. Tests may be required to demonstrate continuity of strength when bi-directional, multi-axial or cross plied reinforcements are used.

3.9.13 As an alternative to overlapping as required by Pt 8, Ch 2, 3.9 Laminate detail 3.9.12, individual consideration will be given, on the basis of test results, to partial butting of reinforcements manufactured with a salvedge. For such reinforcements the salvedge tails are to be laid on top of each other to provide continuity. Butts in the same vertical plane are to be separated by not less than five passing plies.

3.9.14 Laminate overlapping and staggering arrangements may require to be tested at the discretion of the Surveyor.

3.9.15 Laminates may be fastened mechanically provided that the fastenings are of a corrosion resistant metal and are spaced and positioned so as not to impair the efficiency of the joint. The fastenings are to be of an acceptable type and, where washer plates are used, they are to be of a compatible material. The edges of the laminates and the fastening holes are to be sealed.

3.9.16 Where plywood and timber members are to be matted onto, or encapsulated within, the laminate, the surface of the wood is to be suitably prepared prior to bonding.

3.9.17 For details of through hull fittings, see Pt 8, Ch 2, 5.6 Through hull fittings.