I will wait on warmer weather to undertake the major surgery of cutting the boat and glassing in the fittings (maybe in March?) which I will post then. Many thanks to all who commented, made suggestions, sent photos etc., especially Chris-UK, Richard Moss and Mike @ Rockpool.
Step 1. Determine where to place the joints. The kayak is 512cm long, and 170 cm in from bow and stern clears both hatches, and leaves adequate room for the footrest (fore) and a day hatch compartment behind the seat aft. It also means that each piece will be under 6 foot! I'm planning on locating the (male) tenons and latches on the shorter ends and the (female) mortices and catch plates on the longer mid-section.
Step 2. Make a suitable bulkhead template. Measure the cross sections at both points and make a cardboard template that fits the LARGER of the two cross-sections. Then mark on where the mortise and tenons will go, so they fit within the smaller bulkhead perimeter. The reason is that you can then use the same pattern for both ends, and just need to trim the bulkheads to the hull cross section. At the same time I marked the (approximate) latch positions to make sure there is sufficient clearance for glassing in between the mortise/tenons.
Step 3. Make a plug for a suitable tenon. You need to choose a simple shape which will mate cleanly but firmly. I chose a tapered fish paste jar with no lips, overhangs, decorations etc. This was waxed and coated with PVA release agent, and filled with casting resin. I floated a stubby candle in the centre to save on resin and cut down on heat build-up during curing (the wax melts and can be poured out once “green” leaving a hollow centre. Fill the form brim-full and top with a sheet of wax/PVA’d glass to get a perfectly flat base. Once cured fill any cracks/bubbles or pin-pricks with filler, and clean-up with 400/600 grit paper. Make three.
Step 4. Assemble your mould. Trace the bulkhead onto the underside of a piece of float glass with a marker pen. Glue your (three) tenons in position with silicone, mask off the laminating area with brown parcel tape – leaving an extra 2-3 cm all round for trimming, and wax and coat with PVA release. Use the template to mark and cut out your chopped strand matt (CSM). I used four layers of 300g/m2 per bulkhead, i.e. x 4 = 16 in total. Cut separate pieces for the mortise/tenons (circles) and cut “flower petals” to ensure good fits around the complex shapes. For heavy-duty use or on a bigger boat, I’d suggest 5 or even 6 CSM layers.
Step 5. Colour your gel coat with pigment to match the boat and apply a decent layer. I mixed about 250g per bulkhead giving 0.5-1mm thickness. Hold your glass to the light to identify thin patches. Pay attention to where the tenon plugs join the glass to ensure a decent bead with no pin holes or bubbles. A tooling gel coat (tougher, for mould making) might be a good idea. Allow to tack-off.
Step 6. Start to laminate on top of the tacked gel coat. Paint a layer of catalysed polyester resin onto the gel coat, add the first CSM, wet-out the tenon “caps” and stipple the sides onto the gel coat well. Accurate cutting out and trimming of the CSM gives a tight fit which helps to accommodate the sharp radii. I catalysed about 450g of resin for each bulkhead. Work quickly and stipple well – you will need a stiff brush to stipple as the shape is too small and complex to use a wetting-out roller.
Step 7. Allow the bulkhead to CURE COMPLETELY on the glass. I lifted the first one whilst green, and it DEFORMED. I tossed it and made a new one and left it 36 hours on the mould, it remained perfectly flat!!! Clean up with a bit of 400/600 grit paper, mask the edges with parcel tape and wax and PVA again. Repeat Steps 5 & 6 to give a male bulkhead to the female already made. Again, allow to fully cure. Split the two, remove the parcel tape and trim to the tape line with a mini-grinder and wash. You now have a matching pair of bulkheads. Make a second pair, either by laminating a mate for each of the existing, or by starting from scratch again.
Step 8. Make a plug for the latch recesses. I made an MDF plug to make five at a time I’m using five per end – one on each hull chine and one on the deck centre line. This seems fairly standard as long as they are evenly spaced around the circumference – the obvious location to avoid is the keel line. At £12+VAT a pop they are not cheap, and six seems excessive. The latches I’m using are the same as Rockpool, from http://www.protex.com. The recess is deep enough for the latch to be flush with the deck. In this case the latch is 20mm high when closed, and the deck is ~5mm thick so the recesses are 16mm deep. I allowed 2mm per side and 5mm per end clearance. The plug then was given a coat of polyester resin to seal the MDF and waxed and PVA’d.
Step 9. Laminate the latch recess boxes. I used a pigmented gel coat of 1mm + to match the boat colour (black in this case) and 4 layers of 300g/m2 CSM on the base (where the screws will go) and two on the sides and flanges. This will be added to when the recesses are glassed into the deck underside and rear of the bulkheads. I laminated them as a group, and had to really stipple well to avoid bubbles and voids. I’ll probably make an additional set and choose the ten best as a means of QC. The set was cut into individual pairs with a mini grinder, and the flanges trimmed and roughened on a grinding wheel.
The components are now assembled, comprising two each pairs of male/female bulkheads and ten sets of two-piece latch recesses, together with latches, catch plates and s/steel screws, washers and lock nuts.
Cost to date:
1 kg gel coat (~£7), 2.5 kg polyester resin (£10) and 4m2 of CSM (1.2 kg - £6) plus ~£12 for sundry bits n’ bobs (acetone, pigment, wax, PVA etc) = £ 35. The latches cost £15 each incl. catch plate and VAT plus shipping, and another £1.00 for 5 each nuts, bolts and washers – so the total material cost is likely to come in at around £250. I suppose I’ve invested about 10 hours time over several evenings so far, with the same to go.
Coming soon…
Jigging and cutting the boat, trimming and glassing in the bulkheads and latch recesses, and fitting the latches.
Cheers
Steve
