Thursday, November 27, 2008

Cockpit Coaming

So after the deck went on the last real job of building was to cut out the cockpit hole and line it with a coaming strip.  I wasn't looking forward to this part too much because while it is woodwork, its not the orthogonal, easy-to-measure joinery that I'm more accustomed to.

I made a template for the hole by turning one of the plan sheets over and on the plain back marking the centre line, deck beam positions and the run of the cockpit stringers.  I joined the tapering lines of the stringers with the curve of the dustbin lid at the aft end, and to an upturned bucket at the forward end.  I transferred the curves to the kayak by punching through the paper with an awl.  A little adjustment by eye was required to get a more pleasing line on the forward end before the line was followed by the jigsaw.

On the same day I prepared some pieces of ply, 120mm wide and 700mm long, cut across the outer grains of the ply (the way it bends easiest).  I laid these pieces on the driveway with an old towel over the top and soaked them with boiling water.  A few minutes later I filled the bucket that had acted as a template with sand and the wrapped the pieces (all stacked together) round the bucket and held them in place with a ratchet strap.

Two days later the ply was mostly dry and so I started to lay the curved pieces up on the kayak.  I was originally going to make the coaming out of two thicknesses of the 4mm ply on end, wrapped aroung the inside edge of the cockpit cutout.  This looked a little clunky though, so after mulling it over for a couple of days, I abandoned the inner layer.

So tonight I trimmed up the pieces with a jigsaw.  I marked line parallel to the deck with an offset block then partially flattened out the curved end pieces to trim them.  The straight side pieces were then trimmed to fit between the ends from ply with the outer grain running length ways.  For the bottom edge, I marked the back of the coaming where it was level with the bottm edge of the cockpit stringers down the sides, and with the bottom of the deck beams on the fore and aft centre line.  I faired a curve between the straight sides and the mid point and then cut it out hoping it would look OK when curved back on the boat.  This shape has meant the a very deep section to the coaming at the aft edge, which was the intention since there is no real provision for a separate back rest in this kayak.

After a dry fit test I mixed up the epoxy, pre-wet each joint surface and primed out any parts that would be no longer accessible.  I then added plenty of microfibres and used this to bong in the coaming.  I held everything in place with temporary screws, and on the end joints between the side and end pieces I used broad packers (covered in plastic parcel tape) under the screw to cover the edge and keep the faces flush.  The leftover epoxy and any squeeze out was then stuffed back into the gap between the deck and coaming to form a small fillet and improve the bond.  Its definitely warming up here now and for the first time I noticed the pot of epoxy getting really hot in my hand as the curing reaction started to happen.

To finish the coaming of I will trim the edges into a fair curve and fit a lip the the upper, outer edge to take a spray skirt.  I was going to use some steamed pine for this, but I think the curves are too severe to even bother trying.  Instead I'll soak some 10mm rope in epoxy and pin it in place, then fair it in with filler while fairing the rest of the outer hull.  And that's really all that is left to do.  Tape the deck seam, fair it in along with the other external tapes and then sand and sand and sand, and then paint.

Oh, and there's also the small matter of making a paddle...

Friday, November 21, 2008

Fully Decked

Progress has been slow, its been hard to grab much time in the last week or so. 

I have managed to get the deck on the kayak though.  I did this through last week, and at the weekend I planed of the excess around the edges and sanded any epoxy that squeezed out of the joint.

On Wednesday I managed to get into the garage for a brief moment to fit the PVC pipe ends that I'm using for hatches.  I stuck 3  small, curved face blocks around the underside of each of the holes to increase the gluing surface and held these in place with a small screw each.  I then added plenty of epoxy with microfibres to the glass tape the I had previously bonded to the tubes with PVC cement.  The fit in the holes was tight enough not to require any tape, pins or clamps.  I'll remove the temporary screws, clean up the excess resin and fillet and fill the deck/hatch transition when I'm ready to tape the deck/hull seam.

Finally, here's a shot of the copper pipe that I inserted in the bow to hold the toggle rope.

Monday, November 10, 2008


For me, part of the fun in making my own stuff is in finding alternative uses for everyday items, or alternatively, finding an everyday item to use out of context as a cheaper alternative for the 'proper' part.

The toggle eye I mounted into the bow of the kayak serves two purposes. Firstly, it must reinforce the hull and prevent the pull on the toggle rope from deforming the hull or pulling loose. Secondly, it must separate the hole through the hull from the airtight chamber formed ahead of the forward bulkhead. For this purpose, I employed a short length of 15mm copper pipe. I carefully marked the angles after boring a hole with a 16mm spade bit and cut the ends with a regular hacksaw. I scuffed the surface with 60 grit paper to allow the epoxy to key into the copper. The pipe is encased in a large block of epoxy/microfibre blend, which once cured, I filed back the ends about 1mm each side to be flush with the hull.

Kayak hatch covers are available from lots of outdoor, marine and specialist kayak shops, but the cost in the region of $100 upwards each. I don't need to use the airtight compartments ans storage, I just want to make sure they are dry, and if not (epoxy isn't totally waterproof, although it does take lengthy immersion to get any noticeable absorption) I need to be able to sponge out and air the compartments. To this end, I purchased a couple of 90mm storm water pipe covers. The consist of a short length of 90mm PVC pipe (about 70mm long) with one end open and the other covered by a removable, threaded cap. Again, epoxy wont bond to PVC and I didn't want to rely on simply scuffing the surface of such a large join. I think I read of the vague details of this process, but I made up the details myself.

Firstly I cut a length of glass tape just long enough to wrap round the pipe. I then cut it length ways down the centre. I laid 2 long strips of masking tape, sticky side up, on the workbench and stuck a half-width of glass tape to each, keeping the edges as straight as possible. I then piped a generous line of PVC solvent down the centre of each piece of glass tape. This was then wrapped around a piece of pipe, keeping the 'good' edge of the glass tape parallel with and just below the bottom of the threaded section. The masking tape keeps the glass in contact wit the PVC and allows pressure to be applied so that the solvent is partly absorbed in the glass weave. When I come to mount the pipes in the deck, I'll then add epoxy to the glass tape which will get a good bond with the part of the glass that is not already embedded in the PVC cement. The pipe and caps are grey, but I'll spray the caps with black enamel and any pipe showing above deck will be faired in with an epoxy fillet, primed and painted the same colour as the rest of the boat.


I seem to be falling behind with the blog entries. I think the main reason is that I want photos to help describe a process or an idea, but either don't take them (because I forget or the process is too messy to involve an expensive digital camera) or because I get a bit fed up with the whole download - crop - resize - rename - upload process involved in posting them.

So here's a text only catchup...

On Wednesday I managed to screw the remaining forward portion of deck in place and I removed the still-damp towel to let the wood dry whilst in its new curve.

On Thursday and Friday I was too tired and did nothing - sometimes you just need a break.

On Saturday I only had a couple of hours, so I marked out the position just ahead of the forward bulkhead where I wanted to mount an inspection hatch and then I unscrewed the deck. This took a while. I then trimmed the deck up to within half a carpenter's pencil width of the hull with a new neat cutting jigsaw blade. I then swapped to the thin curve-cut blade and cut out the inspection hatch hole. I also prepared a piece to become an eye for the bow toggle - more of this later.

On Sunday I epoxied in the toggle eye and primed out the underside of the deck with plain epoxy. This was a hassle because it was very windy and all sorts of dust and leaves blew into the garage entrance and stuck the the tacky deck. Also, the wet of the resin caused the deck to try and curve back in the opposite direction of what was required. I quickly mixed up some epoxy and microfibre blend which I applied to the inwales, cockpit stringers , forward deck beam and forward bulkhead. Then it was on with the deck and in with all those screws again. Earlier my son Samuel had helped me take all the screws out of the scrap pads, put shiny brown parcel tape on one side of the pads and then put all the screws back in again so screwing down the deck could be achieved whilst the epoxy was still workable.

Tuesday, November 4, 2008

Torture Chamber

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.