Tuesday, February 12, 2008

Assembling the Crossbeams

Laminating the solid Doug fir stringers to the ply parts of the crossbeams requires a bit of advance planning, due to the shape of the parts. The beams consist of a vertical plywood web with a curve along the top edge and a horizontal plywood floor with the curve along the leading edge. This shape allows for a good-looking finished beam with a sloping fairing on the front face to decrease windage and the slamming effects of wave tops when beating to weather.

Due to the curve on these ply parts and the size of the stringers, which are cut to an angle matching the fairing, getting a good glue joint with epoxy requires good clamping technique. Here at Boatsmith we use a very effective method we have developed on other big laminating jobs, involving making temporary clamping blocks and glueing them to the parts using an industrial CA glue with a quick-dry accelerator. This glue will hold the blocks in position on the finished parts and is strong enough to withstand clamping pressure on sprung parts like this while the epoxy glue mixture used in the lamination cures. After the epoxy is set, the blocks are easily removed with a blow from a hammer. In the photo below, the blocks are being glued to the large top stringer of one of the beams. Glue is applied to the block, and the accelerator is sprayed on the beam surface. A few seconds of pressing it in position by hand and it is secure.

Below you can see a vertical web (left) which has already been sandwiched between the two stringers that are laminated to the bottom edge, where it joins the floor web. The angled top stringer with temporary clamping blocks glued to it is shown just to the right of it. On the far right is another crossbeam assembly already clamped up and glued with epoxy.

Below are two beam assemblies in the clamps while the epoxy sets. We use lots of clamps on assemblies like this to insure even pressure while laminating. The use of clamps eliminates the need for making a lot of extra holes in such assemblies as you would have to do using temporary screws.

Below are the three beams: mast, aft, and forward. The next step will be to glue in the small ply triangles that support the front fairings.

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