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Plywood
By May 9th I was ready to make the bottom. I used 3/16" birch plywood. This concerned me a bit though my stitch-and-glue book acknowledged people successfully used it. I love the way this ply looks, and also liked the lightness. But the veneer layer is very thin, and once it is broken on either side there is virtually no strength. So far it has worked out very well though. I made paper patterns.
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Patterns for the bottom ply |
These patterns verified that the ply pieces would work. A single 4x8 sheet was cut into three strips and the third strip cut in half on an angle so the bottoms with one scarf joint could be made.
My issues with the scarfing jig were a) my circular saw blade didn't quite go through both layers, and more importantly b) I got curves in the joint because the plywood wasn't completely clamped down across the full width. I figured out how to address this about the time I was done making the sides. Once the scarf joints had set, I clamped the bottom pieces on and marked for the cut to within 1/8" or so of the actual shape. One of the surprises I'd noticed when shaping the keelson and stringers was that along the keelson, I could use a completely straight edge from the transom almost to the stem, leaving a small curved gap (clearly visible in Figures 17 and 20 below). So I decided to stay with that "plan", later making a filler out of plywood aft of the daggerboard trunk, and continuing the mahogany piece that completed the stem back to the daggerboard trunk to fill that gap (more below). Marking and cutting was simple along the chine, and really simple along the keelson except for the last bit of the bow.
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Test fit/marking of bottoms, to cut them close to size before gluing them on |
Another problem was caused by the fact that toward the bow, the angle at the chine became nearly nothing as the bottoms angled more toward the vertical. I liked the ease of the technique of gluing the bottom on, and then shaving the edges to fit the side angle, and doing the same with the sides. But with the chine angle near the bow, that would expose a really long/wide area of the edge of the side plywood. In the end I decided on an approach that some may not like, and maybe there was a better solution: I shaved the bottom to the chine to be lapped by the side until forward of rib 1, where instead I cut the bottom to the precise edge of the chine, later doing the same with the sides. The resulting notch/discontinuity is visible below and clearly shows on the completed boat.
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The bottom overhangs the chine until rib 1, where I started cutting it to the line of the chine to avoid showing too much edge of the side plywood |
At any rate, with the bottom pieces cut as nearly to shape as was safe, I glued them on. This was fun, as the curves of the boat started to move from imagination to the visible realm. I coated the insides with epoxy completely, and then the contact areas on the frame. I put 3/8" brass woodscrews in every foot or so, just to use as clamps, later removing them and plugging the holes, so only trouble spots needed extra clamps.
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Bottom pieces glued on, with the final curve at the bow a challenge to get tight! |
Below you can clearly see the bottom plywood overhanging the chine, and the gap over the keelson created by using a completely straight edge on the bottom piece there.
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View from the stern with bottom glued on. Screws were just clamps, later removed and plugged. |
By May 14th I'd completed shaping the bottom flush at the chine (a little belt sander, a little wood rasp, a little orbital sander-patience was never my strong suit, but no show-stopper mistakes occurred). It was time to repeat the process for the sides. It turned out I could just get the pieces I needed with one more 4x8 birch sheet and two scarf joints using the leftover from the first sheet. But in retrospect this was foolish, as I needed to buy a 3rd sheet for the decks anyway and could have done it then with just one scarf joint.
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Paper patterns for the sides |
One of the less pleasant events of the project occurred during this phase. after gluing the strips at the scarf joints, and marking them, I was cutting one of them with the saber saw (btw, of all the tools I used, circular saw, table saw, router, drill, belt and circular sanders and even a bit of band saw, the saber saw came out the hero, used for notching the formers and jigs, and all these curves). The piece slipped off the edge of the table and hit the ground, and snapped the inner veneer so the piece hung together just by the outer veneer. After some impressive cussing, I glued a piece of ply across the inside of the joint and quit for the day; if you ever look inside under the bow of the boat, that's why there is a scab on one side only across the forward scarf joint.
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Helper jig for getting the side pieces clamped in place to mark them |
The sides were screwed and occasionally clamped on, like the bottoms. The filler piece in the gap over the after keelson was also glued on at this step. The transition in the handling of the chine joint is clearly visible below; the sides have not yet been shaped at the chine but the forward part had to be precisely cut before gluing, whereas the rest just had to be close.
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The sides are glued on. Freed and Upright |
One of the most enjoyable days was May 18th, taking the boat off of the strongback. Fortunately I'd remembered, before gluing on the sides, to break all points loose from the attachment vertical 2x4s where glue had dripped onto them, and also break the temporary formers loose all around. I also removed the screws from the vertical 2x4s to the ribs before putting the sides on at any point where they would be difficult to access afterwards. So early that morning I started removing the wood screws through the formers into the stringers, and then removing the screws from the upright 2x4s to the ribs, to the point where the hull was free and just sitting on the remaining uprights.
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Ready for birth, free of the strongback |
After a massive cleanup of the whole garage area (did I mention I have a patient wife?) I took the hull off, cleared the table, and set it upright on some carpet strips. I was delighted with the lines.
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Free from the strongback, right-side up for the first time |
Fiberglass and squeegees Final steps before glassing the bottom included finishing the stem. This was a challenging piece, as the mahogany strips I used (two of them, 1/8" thick so they would take the curve required) transitioned from filling in the gap between the bottoms forward of the daggerboard, to lapping over the forward edges of the bottom and side plywood.
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First of two mahogany strips to complete the stem/cutwater |
With a little wood rasp and orbital (can't remember whether I hauled the belt sander out on this at any point) and with the side edges all trimmed up and rounded around the transom, the hull is ready for a coat of epoxy. I decided to do it that way, coating, sanding, and then glassing after that because I also needed to fill the screw holes and the gaps around down the centerline with epoxy/sawdust putty.
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Ready for epoxy on the bottom of the hull |
Next: Glassing the Hull
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