Building a Northumbrian Coble in Clinker Ply

The Next Couple Weeks

stem notch

The keelson is notched into the bottom of the stem, so I had to chisel the notch out. This has to be done quite accurately so ensure the stem is square and straight. After a good long while I got it finished and when I tried it it fitted basically perfectly. I clamped it up and was ready to drill holes for screws when I realized that the screws I'd bought were too long. I went and bought some 2 inch number 14 screws and screwed the whole thing together and I was impressed with how solid it was.

transom knee

Using a collection of clamps and blocks of wood I got the transom knee clamped to the transom and got the screw holes drilled and countersunk. The drilling was a bit of a challenge because the drill got hot extremely quickly. I had to stop several times each hole and let it cool to avoid clouds of smoke. I did a similar thing in the keelson and then screwed it all together with some massive number 14, 3 inch screws.

Backbone in place

Once I'd glued all these bits together it was finally time to mount the backbone in the moulds. I had to file a couple of the notches a bit but then aligned everything and screwed the keelson in place with a screw into each mould. I also screwed the top of the stem to the strongback and added some supports for the transom. This made the whole assembly much more sturdy and held the moulds in place.

Keelson beveled

The next step was to cut the bevel for the garboard. The goal is to have the plank sit flush against the bevelled keelson all the way along and on each of the moulds. Most of it was pretty straightforward but getting the stem right was a bit more of a pain. I should have tested it using something wider than the batten I did use, and as a result there were a couple bits near the base of the stem that were a bit hollow, but the epoxy will fill the gap when I glue the plank on, so it's not a structural issue.


More Spiling

Connecting the Dots

Now I was finally ready to spile the first plank! Spiling is a grand little technique used to transfer a weird curving shape, like a plank, onto something flat, like a sheet of plywood. To do this you affix a strip of wood roughly in the place the plank will go and then get a compass (of the drafting variety, not the navigation type). Putting the point of the compass on a point along the edge of where the plank should be, you draw an arc on the board you put in place. After doing this periodically all along the edges you take the spiling board and put it on the sheet of plywood. Then take the compass, making sure it's still set to the same radius, and put it first on one side of an arc, draw an arc on the plywood, and then move it to the other side of the first arc and draw another arc on the plywood. Where these two new arcs intersect is the center of the circle/arc, and also exactly (theoretically) where the edge of the plank is! After doing this all along you just trace a line between the points using a batten to make sure the line is fair (a smooth curve). After the outline of the plank is drawn it was really easy to cut it out using my fantastic japanese rip saw. That thing cuts through plywood like crazy. On a full blade stroke it can go a good 3cm. I only have about 3.5 inches clearance above the floor when I'm cutting the plywood but it still seems to go pretty quickly. I timed it and it took like 10 minutes to do the ~3m cut, but it seems faster when I'm doing it. This saw is also great because it can cut things flush without damaging the surface. I can cut the ends of the planks right flush against the transom in seconds with great ease.

Amazingly it fit! I was very pleased. Now that I had the plank cut out I was able to bevel the transom. That really wasn't a bit deal, and I'd left enough wood for the bevel too which was good to find out. I put in a bunch of stainless screws along the keelson, stem, and a couple into the transom and when I was sure everything fit I broke out the epoxy. I first brushed a coat of straight epoxy on the contact areas and then covered that with some thickened epoxy. The idea is that the unthicked epoxy penetrates the wood better and so you get a better bond.

The next garboard went similarly well. For some reason both of the next planks were fine for most of their length but at the bow they curved up about 1cm above where they should have. Since they were both the same I think that it's due to some problem with my spiling board. I was using some sections of baseboard to spile but just after I finished the 4th plank one of the joins exploded and so now I'm using some thin stips of plywood which I hope will fit the curves better and give me better accuracy.

End of a plank

4 planks glued


Head on view

My giant compass

For the garboards I used my little 6" drafting compass and it seemed to work fine but then for the next two planks it was too small to get a nice arc, and the bigger the arc the more accurate. I checked if Staples had any suitably large compasses but they did not, plus even their small ones were incredibly expensive, so I decided to make my own. After about 10 minutes work I had something that seemed nice and solid and plenty big enough. I used a bit of extra epoxy to glue a nail into one arm to give it a good pivot point and clamped a pencil to the other and it worked great. I later changed to a mechanical pencil because it always has the same size line, and with the original pencil I ended up having to figure out where in the 1mm thick line I should actually put points.

Each of the planks needs a bevel, like the keelson. This is pretty easy to cut, but at the bow they also need a "gain" which is a bit of a notch cut out in the bevel so that the boards lie flush with each other. I used my dozuki (my third japanese saw, for doing very fine work) and a chisel to cut these and they seemed to come out pretty well. I think they'll look very nice when they are all sanded and painted. Speaking of paint, I managed to pick up a tin of paint in pretty much just the colour I want for the sheer strake for $4 since it was a mistint.

For the #2 planks I put some screws and wooden blocks between the molds to hold the join together while I glued it. I think for the next ones I'll try using a wooden batten as well in the hope that it will apply pressure more evenly and make things more fair.

go back Carry On!