To help out the few people who may actually try and build one of these things I’m going to offer up some more design details. One of the cool things about this method of using the stressed and bent plywood hull is that the general shape of the plywood skin pretty much defines the shape of the whole boat. The only real thing that you can change is the width of the deck at different points and how much V you want in the bow. Once the hull is stitched (or taped) together and you can bend it into whatever shape looks good to you. Rather than pre-defining the bulkheads and then forcing the hull to fit that shape, I let the shape of the hull define the shape of the bulkheads. So here’s all you really need to know, the deck width at the mast is 260mm, the deck width at the stern is 355mm, the max deck width is 370mm, and the front of the daggerboard box is 1525 mm from the bow. The V in the deck is 45 mm deep (at the mast). Note that Mothball one is slightly different than what I’m giving you here, but if I were to make it again this is what I’d use. The changes are small but would probably make a better boat.
So if you set those three deck widths it’s time to start making bulkheads. Bulkheads are really pretty easy to make, especially using the same thin ply used for the skin. You can cut out a bulkhead in about 60 sec, but the shape needs to be well defined. Mothball One has 11 bulkheads (including the solid transom bulkhead). Nine bulkheads are in the deck area and two are in the bow. Most of bulkheads have an inverted Y shape cut into them to reduce weight. To define the shape of the bulkheads measure that area on the boat as best you can and then draw the rough bulkhead onto a piece of cardboard making sure to make the bulkhead as square and symmetric as possible. Put the cardboard bulkhead in the boat and then trim it to make it fit as best you can. Then take the cardboard bulkhead and use it as a template to draw the plywood bulkheads. Again make sure the plywood bulkhead is square and symmetric. The skin will define the overall boat shape, but the bulkheads will ensure that the shape is square. If I were to do it again I’d probably add one additional bulkhead near the middle of the boat because that’s where the sides get stepped on a lot after you take a swim. Also note that the bulkhead below the mast should be solid to help create the two separate airtight tanks as defined by the Moth class rules. The daggerboard box has a bulkhead on each end of the box for added strength. Take a look at my older posts for some bulkhead pics.
