Construction - part ten

Mike Griffiths (guest blogger) is he shaping up?


My posts telling the story of my stitch and glue lapstrake canoe construction are likely to slow as the main stages in the construction come to and end and I start in on the sanding and finishing. Before we get to that stage though there is still quite a lot of work to do preparing for (just about) the final addition to the structure - the gunwales. I still had to add some epoxy to the joints that had not been completely filled but first I deviated from the instructions. I knew that the European oak inwales and outwales were probably going to be a little bit difficult to bend and that this would stress the top plank in particular as they were bent to the boat's final curves. I decided to add a small fillet to both the top two plank joints behind the bulkheads - I also added a narrow glass cloth reinforcing strip. Why the addition? Well, as a first time builder, I could not be sure that those rather tight joints had been completely filled with glue and the last thing I wanted to happen was a joint failure.




With these additions in place, I then topped up the plank joints that were not completely filled the first time. The construction book suggests that you should use a slightly thicker mix than the glue used for the first shot but to apply it in the same way - using a syringe. I decided on a different tack and thickened my epoxy with lots of colloidal silica. I then used a pallet knife to push the thickened mix into the joints - using the knife to level off to what I hoped should be the correct hull lines.




Perhaps foolishly,I did all of this epoxy work in the lowest ambient temperature so far - which had an interesting effect. The epoxy cured nicely in the usual 24 hours or so but a few days later I noticed that there was an 'amine blush' on the surface. This waxy layer needs to be cleaned off with detergent and water. It is strange stuff though and I will try and avoid a re-occurrence by working at higher temperatures in future.




I took advantage of generally higher outdoor temperatures of the next couple of days to move the canoe hull back to the barn while I first of all cleaned my office and then started work on the inwales and outwales. First off, I sanded off any epoxy that had extruded from the scarfed joints and then I inspected each length of oak to decide which piece was going to do which duty. I then used the router to round over the top and bottom edges of the outwales. I found it was best to clamp two lengths side by side to give me a good platform to rest the router base on. After routing, I sanded the top and bottom edge to remove any saw marks left over from ripping the lengths from the original plank.

While I want to finish the corners of the inwales, I could not round them at this stage as the pieces needed to be fitted to the boat before I could determine the locations of the decks and the seats. I want to leave the inwales square under the decks for maximum adhesion and I will also need to fit "doublers" to increase the width of the inwales where the seats will be fitted. It is not clear yet if I will leave this finishing until after the inwales are glued in place or if I will try and sort them out before that.




I then set about clamping one of the outwales to the outer edge of the canoe hull so that I could cut it to length. First off, this looked somewhat tricky as the oak lath had to bend in three dimensions to follow the curve of the top plank as well as the twist of the hull. In practice it turned out to be fairly steady although a couple of extra arms would have been helpful from time to time. When the outwale was clamped and cut to length I could admire the improved curve of the hull - not quite perfect yet but definitely smoother.

Offering up the first outwale

I then clamped the second outwale in position and cut that to length. The next task was to stretch a string along the length of the hull to measure the mitre angle that would need to be cut between the inwales where they met at the stem and stern. With this measure I could cut the first mitre on the first inwale and then start working it into the boat. The involved removing each clamp holding the outwale in turn and the adjusting it to hold the inwale in place as well. One I neared the other end of the canoe I could mark and make the cut to complete the inwale and to set it snugly in place.

With the inwale in place, the top edge of the hull on that beam took on a very pleasing curve from end to end. Then it was just a case of following the same routine with the other inwale. Wow do you need a lot of clamps to build a canoe. It is very clear that I will need all that I have just to glue one gunwale into position if I want a good fit.

After that I was out of time and could not start in on gluing the gunwales into place. In any case, it was clear from my efforts so far that I was going to need an assistant for this particular process. Next weekend I am visiting the UK which means no work on the canoe but it will allow me the opportunity to pick up some materials difficult to obtain locally - some good yacht varnish and some coloured epoxy top coat for the outside of the hull. In the mean time the gunwales can stay clamped in place which might reduce some of the tension in the wood and make the gluing less of a fight - well maybe.

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.