Construction - part nine

Mike Griffiths (guest blogger) sticks to his canoe building project

I forgot to post my tips on bulkhead fitting. The first is that you could consider using plastic ties for this part of the construction as it may be hard to remove the bulkhead ties after the epoxy fillets fixing them in place have cured. However my key piece of advice is – go up a drill size or two. The holes will be covered by the epoxy fillets on the inside and can be filled and sanded on the outside of the hull. This means that a larger size should not detract from the final finish but those bigger holes make threading the bulkhead ties simple rather than a nightmare struggle (you can tell I got to this solution after a bit of a fight). Otherwise – just concentrate on getting the bulkheads square to the line of the keel and nice and central.

Now to the sticky part. The first step in gluing the hull is to create epoxy and glass cloth fillets joining the planks at the bow and stern. My canoe construction bible specifies the use of wood flour as a filler for the epoxy – trust me on this – go with colloidal silica. This mix is simpler to manage and control – you will get better results. Having said that you will want to use wood flour on the fillets on the front (visible) side of the bulkheads to get a good colour match. Perhaps there is something to be said for getting in some practice before creating your first visible joint. I used masking tape to limit the width of the visible fillets although I think they will benefit from some additional sanding and shaping when I get a few minutes.

I made a few filleting tools from some scrap pieces of plywood picking my shapes and sizes at random so I was gratified to find that my hit and miss approach provided me with some pretty useful aids for spreading and shaping the epoxy mix.

I strayed from the instructions a little and used glass tape over the hidden bulkhead fillets as well as on the stem/stern fillets. The additional weight is trivial and I liked the idea of the extra adhesion following the fight to adjust the twist in a couple of the planks to get the bulkheads properly fitted. I also brushed some un-filled epoxy mix onto the plywood surfaces that were going to be joined by all of the fillets to soak into the top ply and so to ensure that the bond to the wood was optimal.

Once the fillets were cured I could turn the canoe upside down and set the trestles square and aligned – it was now time to glue the joints between the planks. Some of these joints are quite “open” on the underside while the last few inches at each end of the planks are pretty tightly closed with no visible gap to insert the epoxy mix. The tools of choice here are a syringe minus the sharp needle point and a pallet knife to slightly open the tighter joints for the epoxy glue to be pumped in. The glue is well mixed epoxy with a little filler. The specified consistency was “thin gravy”. Like the previous “jam” specification I was facing a potential transatlantic cultural gap here. I went with just a very small portion of filler in the mix and that seemed to work well. You need to work down the seams reasonably quickly and I found that mixing frequent lots of small batches of epoxy was best after my second batch went off at such speed that I lost the use of my first syringe. It would probably be a great idea to have an assistant available to mop up small runs but reality probably means that you are (like me) going to have to sand some of them out later.

Once the epoxy in the seams had cured I could assess the results. There were a good number of places where some additional epoxy would be required to completely fill the seams but I decided that this would be an easier task with the wire ties removed. So now was the time to pull out the 350 odd ties I had so laboriously threaded into the boat just a few days before. Like all the other tasks a few trials soon got me into a routine that sped up the work. You need three tools for this job – the needle nosed pliers used to put the ties in, a small pair of side cut wire cutters and (the surprise ingredient) an electrical soldering iron.

If you untwist a tie and then bend the two ends so they are once again vertical to the plank surface at the location of the hole they are easy to clip off on the outside of the hull more or less flush with the surface. Certainly without any “hooks” in their ends. Then it is a simple task to give the tie a yank with the pliers on the inside of the hull – and most will come straight out. One or two (more at the ends of the hull behind the bulkheads) will be held in place by epoxy – perhaps where they were inserted very close to a seam or there has been an unnoticed “dribble”. Here you use the soldering iron to warm up the wire to the point where the epoxy surrounding it starts to soften. Just a (very) few seconds of heating and out they come. I picked up this idea from reading around the stitch and glue boat building subject and in particular from Samuel Devlin's Boat Building book. Mr Devlin actually uses a car battery and a pair of jump leads rather than a namby pamby soldering iron but then he does generally work on a larger scale than my little lapstrake canoe. The same heating technique worked for most of the wires running through the stem and stern fillets as well – but not all, as the copper wire has a low tensile strength. It got me wondering about using steel wire at those points on the hull in any future project.

It did not seem a practical proposition to completely remove the ties holding the bulkheads in place although again I wondered if in future steel wire might work the trick here as well. However I threaded the bulkhead ties through larger holes than the rest of the ties and this made it simpler to cut them off flush with the outside of the hull. I could also bend some of them back into their holes below the hull surface. I found that I did not need to worry about the odd copper wire end poking up through the planks though as the copper is pretty soft and sands off easily with 80 grit paper.

After a couple of work sessions I had all of the wire ties removed. I was now the proud possessor of a canoe hull with nearly seven hundred holes in it – not all below the water line though.