I've spent the past couple of weeks getting ready to put the hull of my Core Sound 17 Mk3 together, as there are a number of components that need to be worked on before the hull goes onto the building frame. The bulkheads have reinforcing pieces that are added to them, to give greater strength, and to provide location points for beams and stringers to be added later. For example, the aft end of the cabin has a piece of timber glued across it, angled to support the cockpit seating, and a couple of ply pieces which will hold the washboard (entrance to the cabin). I've dug out some of my old paintingclothes for this build. As the weather is getting a bit cooler I'm finding a T-shirt, flannel shirt and a windcheater is a good way of keeping warm enough for a day in the garage. The windcheater is from another life, in the 1990s, back when I made a living as a kite maker.  You can read a little bit about what I was doing back then here.

When putting the pieces together, I dry fit them first, using clamps and screws, and when I'm happy with the fit I will take the component apart, ready for gluing. The surfaces to be joined are first coated in unthickened epoxy, to soak all of the mating surfaces, and then a thickened mix of epoxy is added. The screws through the components lock everything together in the proper orientation, and then clamps are added around the edges, to make sure that the surfaces are forced together with the right amount of pressure. Sometimes I will use conventional clamps, but there are times then the longer wooden clamps that I made for my previous boat are handy, as they can reach further than conventional clamps. I will also use spring clamps, made from sections of PVC piping, where lots of clamps are needed, such as around the edges of the storage lockers in the bunks.

Using a double garage to build the boat is fantastic! The extra room has made is much easier to have several pieces glued up an curing while working on other pieces, and there's room to store finished pieces as well. Setting up a permanent ducted vacuum system has made it much easier to keep dust under control, expecially with sanders.

The hull components, and the cockpit sides, are longer than a single sheet of plywood, so they have to be joined. In the past I have joined plywood using scarf joints, where an 8:1 gradient is planed into the edge of two sheets of ply, and they are then joined together. This time, the CNC plywood pieces were joined with "finger joints", where the strength of the join derives from the deep fingers of the edges of the two plywood sheets meshing with each other. To make the joint as tight as possible, the first panel of plywood is placed on a large sheet of thick construction ply covered in a sheet of plastic. The hull piece is locked in place by driving a few screws through it, and into the construction ply below. The second piece is thenplaced alongside the first piece, with the fingers meshing at tightly as possible. Screws are then driven through that sheet as well, and then removed. The second piece is separated by about the width of the fingers, and the edges of the fingers are coated in unthickened epoxy. I run a bead of thickened epoxy around the fingers of the plywood that is still screwed onto the base, and then push the second piece of plywood back into place, wiggling it a little bit to make sure that it is firmly seated. If everything is where it is supposed to be, the screwholes in the second piece of plywood will line up with the screwholes in the base. When you start turning the screws it is easy to tell if they are located properly. Once they are all screwed down tight there is quite a bit of squeezed out glue from the finger joints, which I remove with a steel putty knife. The individual fingers are pushed down as well, to make sure that there is not a build-up of glue under the finger. If any more glue sqyeezed out I removed that as well. A sheet of plastic was laid over the completed join, and the sheets from the other side of the hull were laid over the first pair, matching edges and far corners, and the gluing process was repeated. This let me create two joined hull panels that were as symmetrical with each other as possible.  To make sure that the finger joints stayed as flat as possible I put another piece of plastic over the joint in the top sheets, lay a piece of timber about the width of the joint all the way across the panels, and then weighted the timber down with anything heavy that came to hand - bricks, lead, and an old water pump. After leaving the joints to cure for 24 hours, I took off the weights, removed the plastic, and took out the screws. So far I haven't had any screws get stuck, but if I do I will use the old technique of heating up the screw with a soldering iron, to soften the epoxy around it, and then back the screw out.

Once pieces have been glued, the glue has cured, and the screws removed, the holes have to be filled. I normally do this with a fairly lightly filled epoxy, putting a strip of making tape over the hole in the back of the panel, and laying the panel flat on the ground or a bench, so that the epoxy doesn't spread. After five or ten minutes I come back and see if I need to add any more epoxy to the hole, as it takes a bit of time for the epoxy to soak down into the hole and into the surrounding playwood. If I get the consistency right I won't need to fill those holes from the other side, as the epoxy will filled the hole all the way through to the masking tape. If there are holes that need to be filled on both sides, for example where there stringers glued onto both sides, I will either wait until the following morning to do the other side, or, if I am in a hurry, I will lightly cover the filled holes with masking tape and then turn the piece over to work on the holes on the other side.

So far, I haven't thrown out any brushes! For this build I'm following the practice of having three jars of acetone that I soak an epoxy brush in, with each jar progressively removing more of the epoxy. I then dab the brushg on paper towel to remove any residual acetone, and leave it to dry overnight before reusing the brush. Jar #1 is already getting pretty gunky, and I will soon have to leave this one open, to allow the remaining acetone to evaporate. I will then move jar #2 up to #1, move #3 to #2, and refill the original jar with new acetone and use it as the new #3. I look forward to seeing if this will work as well with rollers when I start coating panels. 

I've started doing the rough shaping of the centreboard blank. To get the top of the centreboad to the required rounded shape, I made a few passes with a circular saw to remove the larger excess pieces, and then cut the finer pieces of with a Japanese pull saw, finishing with a belt sander. The tip of the board has been cut off, ready for the 8KG lead tip which will replace it. I won't work on ther profile of the board until the tip arrives, to ensure that I get the shape right.

I spent a day or so sanding the pieces I have created so far, removing the excess epoxy from above the filled holes, and giving each face a sand with 80 grit, ready for epoxy coating.  The most difficult pieces to sand were the lower surfaces of the finger joints, these had unthickened epoxy to sand off as well as the thickened epoxy. A random orbital sander worked well for these, whereas a finishing sander had to be used when trying to get close to pieces with a stringer glued onto it.

In preparation for working on the glued hull pieces, I had to cut down some hoop pine to 19 x 25mm, and scarf join a couple of lengths to make stringers that were long enough for almost the full length of the hull sides. I used my Japanese pull saw to cut an 8:1 diagonal across the 19mm sides of these pieces, and then glued them together. The Hoop Pine I had was long enough for the lower chine, so it was just a matter of cutting these two to the correct length. Once the two side chine pieces were cured and sanded, I ran all four pieces through my router, putting a rounded edge on the two edges that wouldn't be glued to the hull. A rounded edge makes it easier to get a good coating of epoxy on the stringer, and as this stringer will be exposed in the cabin it is a good idea to have a slight curve rather than a sharp edge to bump into. Once that was done I used a plane to taper the forward end of all four stringers, working from 19mm at 91cm, down to only 2mm at the tip. This reduction is needed as the plywood will have a significant curve at the bow, and the reinforcing stringers would be to thick to allow the hull to take the correct shape when the pieces are joined if the stringers are left at full thickness all of the way until the end. I did contemplate using an electric plane, or a belt sander, to remove most of the wood, but I decided to do it with hand tools in order to make sure that I didn't remove too much material, which is easy to do in a few seconds with power tools.

Tomorrow I will be able to glue the hull stringers onto the hull pieces, getting one step closer to putting the hull together.