Tuesday, November 4, 2008
The main method of construction on the kayak up to this point has been stitch and tape. Pieces of plywood have been cut to shape and stitched together along there edges with cable ties before a permanent fixing of glass fibre tape and epoxy resin was applied. Another related method is called tortured ply, where compound curves are forced into the plywood. Its relatively easy to get a sheet of ply to bend in one direction at a time, so boats designed for this method of construction have panels shaped as sections of cones or cylinders. But the deck on the kayak is convex across the beam but has a concave sheer, the profile of the top edge of the side panels.
Last night I started putting on the deck on the forward end of the kayak. I screwed an oversize sheet in place at the halfway length of the cockpit. this allowed be to strap the middle section of the sheet roughly and draw an outline to trim the sheet to - still oversize but now by 30-50mm all round.
More screws were placed along the inwales working from the midships forward, and the stresses on the screws got greater as the curve was formed. I used scrap ply packers under each screw to prevent the deck springing back and popping all the screws through. As I approached the forward bulkhead the gap between the inwale and the deck was getting bigger and something needed to be done. I persevered for a while with a couple of ratchet straps holding things down, but it wasn't going to work.
At this point I took of the ratchet straps and then rearranged 3 straps over the top of an old towel that was soaked in hot water. The idea is that the warm and wet environment softens the fibres of the ply and makes it more agreeable to the compound curves being forced upon it. Wooden packers over the inwales concentrated the ratchet straps' force in the right direction while rags protected the deck and hull from the heavy metal hooks and ratchets. While tightening all this lot up, holding the ply with one hand and most of my body and tensioning a strap with the other hand, there was a pinging noise and a sharp pain in my shoulder. The torture victim had fought back.
I don't know what the outcome of all this was, I dared not look in the garage this morning so I'll conduct the post mortem tonight.