Sunday, February 28, 2010

Bulkheads notched and inside of the side panels epoxy coated

Notching the bulkheads to fit the chine logs drove me crazy. The plans do give some rough measurements, but because there is so much variation in the side bevels, some adjustment is necessary. It was late on Saturday night and I must have been tired, because nothing was going right with BH1. Fortunately a good night’s rest resolved the previous day’s problems, and the notching was completed OK. I didn’t take a pic because I didn’t think to…
In my previous post I showed the chinelogs being scarfed together as the Paulownia wasn’t long enough.
100_6932Here the chine logs are being attached to the bottom of the side panels. I needed 4 screws at the transom as the chine log had to be curved, and the clamps simply could not hold the curve. The packaging tape is pulling in the chine log slightly at this point due to the curve. You can’t see the chine logs under the side panels. The reason they are underneath is because they have to overlap the edge of the panels by 10mm and I needed to make sure that the panel aligned with the line I’d drawn on the chine log. The overlap is so they can be bevelled later to fit the bottom.
100_6934 Here you see the side edge of BH1 being bevelled. It also has a curve along its length, so the low angle block plane was again the "go to" tool. I reckon the block plane is just about the most useful tool in this build, next to the Japanese Dozuki saw. No complex tools are needed at all.
100_6922 I thought I’d throw this pic in. I’m drawing the back of the rasp along the glue faces of the rudder casing spacer block. This cuts a set of grooves which increase the surface area of the bond and makes a very strong joint. It’s an old trick I used when attaching cricket bat handles in a previous life.

100_6935 I’ve applied 3 coats of epoxy to the side panels, using the wet-on-wet technique. I masked off the surfaces that will need to to be bonded to the bulkheads and the gunwale strakes. In this shot you can see how the chinelogs overlap the side panels, and you get an idea of the curves along their lengths. Note the bulkheads stacked against the wall in the background.
The wet on wet method, saves a lot of sanding and dewaxing between coats*. It is recommended by West System epoxies as the previous coat is chemically bonded with the new coat. When the previous coat becomes tacky like masking tape, the next coat is ready to be applied. I used West system foam rollers as they can cope with the heat from the epoxy’s exothermic cure reaction as the ones from Bunnies just seem to disintegrate.

The insides will now just need a clean down with acetone to dewax the surface and then a sand before I apply the marine varnish, which will be when the hull is complete.

One of the things I was a little worried about using Paulownia is the softness of the timber and susceptibility to being dented. After coating with epoxy however, I can't even dent it with a finger nail, so I'm happy about that!

Next weekend should see me going 3D with the hull, which will be a big milestone. I guess they don't have kilometre stones?

*Edit: I've just read that West System don't recommend dewaxing with solvent. Only use water!


  1. Looks like it's going well! Keep up the good work. I think lots of people had problems with the BH notches, I know I did. Also, I second the simple tool-- I should've gotten a Japanese Backsaw right in the beginning, and I didn't. Much more precise, just as quick, and fast than a jigsaw. Maybe the jigsaw for the plywood, but the backsaw for everything else.

  2. Yes, the Japanese saws are wonderful because the kerf is so thin as a pencil line so you can actually cut along the line and your joint will fit. No more thinking about which side of the line to cut! I've had my two for years, using it to cut splices for cricket bat handles. Much more accurate than a table saw for when you have to cut timber that is irregular in shape.

    I too used a jigsaw for cutting out the shapes from the ply, but the Japanese saws would have been just as quick I think.