Fishing Craft Technology

Unit 4 - Boat building materials and construction of boat

4.8. Construction of FRP boat
There are two types of FRP boat construction methods prevail through out the world. They are female mold and split mould technique method. Among these later method is popular in western countries. Hull moulding to be two piece structures laid up using split mould technique as follows:

• Two gel coats all over, applied by hand using “mohair” rollers and 100 mm paint brushes. Nominal thickness 0.5 mm gel type isophthalic. The whole of one side to be laid in one operation with no break, one gel after the other.
• One layer of 225 g/m2 chopped strand mat emulsion bonded, laid with isophthalic resin. Resin to glass ratio 1.8:1 by weight laid by hand using “wolly rollers” and aluminium “paddles” rollers.
• Operations (a) and (b) is to be carried out in one shift of work, i.e., within 24 hours. Cure time of 30 minutes minimum between gel coats and cure time of 60 minutes for 225 g/m2 layer.
• Main hull laminate has to commence not more than 24 h after application of 225 g/m2 layer.
• Three layers of 600 g/m2 chopped strand mat (CSM) emulsion bonded lay with resin all over. Resin to glass ratio 2:1 by weight. All three layers laid simultaneously in mat width strips transversely applied; stepped back by 50 mm steps from previous layers on the keel stem and transom join edges.
• One complex of 600 g/m2 (CSM) and 600 g/m2 woven roving and 600 g/m2 CSM laid simultaneously in mat width strips transversely applied, stepped back by 50 mm steps from previous layer on keel, stem and transom join edges.
• Three layers of 600 g/m2 CSM emulsion bonded lay with resin all over. Resin to glass ratio 2:1 by weight. All three layers laid simultaneously in mat width strips transversely applied, stepped back by 50 mm steps from previous layer on keel, stem and transom join edges.
• Bring mould halves together, bolt up all round, and arrange internal access and staging as required.
• Apply one layer of resin proof tape to join line all round.
• Repeat operation (a) to (f) throughout length of join line ensuring 50 mm overlaps increasing by 50 mm for each layer.
• Mark off hull with chalk or wax pencil for position of hull frames maximum spacing longitudinally 900 mm.
• Insert frames constructed of low density closed cell polyurethane foam, trapezoidal section base size 150 mm, tapering over 100 mm to top face of 100 mm. Frames to be contact adhesive bonded to hull.
• Over laminate frames with three layers of 600 g/m2 CSM with resin. Layers to lap over frame and onto hull with 50 mm, 250 mm and 400 mm laps each side.
• Frames to be extended through keel in way of bulkheads, fish hold, forefoot where practical frame to stop short in way of engine to allow fitting of engine bearers.
• Insert hull lifting blocks/plates for release from mould.
• Insert two main bulkheads constructed of 19 mm thick marine grade plywood vertical to datum and square to centerline. Plywood to be butt strapped on joints and glued and screwed. Bond bulkheads to frames on both sides with three layers of 600 g/m2 CSM with laps as per (1).
• Hull moulding is now ready to release from mould provided lifting blocks/plates have cured for 48 hours since insertion. Section (n) refers.
• On release from mould hull to be placed in fit out cradle or suitably chocked to prevent any distortion.
• Construction to be taken place by protected from sun, rain and in well ventilated dust-free atmosphere. All materials to be stored in similar conditions and to be suitable for use in tropical environments if appropriate and to be marine grade.
• Ballast to be located in the keel and bilge section in the form of steel punching set in resin and over laminated. Final trimming to be carried out after launch and inclining test.
• Hull protection to be included to stem shoe, keel iron and skeg.
• Galvanized steel strips to be fitted to bilge keels.

Deck:
The main deck to be constructed of cambered, hardwood, transverse beams nominally 150 mm × 75 mm and 60 mm as required and sheathed with 19 mm plywood over laminated with 1800 g/m2 of chopped strand mat, and to incorporate a non-slip finish. The deck also incorporated an engine removal hatch and access hatches to fish hold. All hatches to be fitted on coamings of at least 300 mm. Freeing ports to be cut in the bulwarks to allow free drainage of water overboard from deck. Bulwark height to be 610 mm minimum at side.
Gunwales:
Gunwales to be constructed in hardwood as outer section is 50× 50 mm and inner section is 150× 38 mm. Outer to be bolted to inner at approximately 900 mm centres using spacer blocks 120 mm deep × 100 mm thick.