Building the Rushton Catboat

Spar making

For the catboat's spars I bought material from a mill in the remote part of Vermont known as the Northeast Kingdom. The mill cuts local spruce and had far and away the best selection of clear material in lengths up to 18-20". They mill the very best spruce in to 1" thick material for trim, so I had to laminate all the spars as well as the oars. The mast, which has a maximum diameter of 4", is composed of five layers, the boom, three and the gaff two.

In traditional spar making the first step is to square the basic blank, and then cut the taper on the four sides. It is important to work accurately from the beginning, as any mistakes early in the process will just magnify as the project goes on. With a cleanly tapered square spar the next step is to make a spar gauge. This jig allows you to mark lines the length of the spar on all four faces that delineate a perfect octagon. The photograph how to derive a perfect octagon from a square: an arc the equal of the distance from the corner of the square to the center is swung from each corner. Where those arcs intersect the sides represent the corners of a perfect octagon. I make the spar gauge a little bit larger than the actual spar so that I can slide it easily. In this case I use the same geometry to derive the octagon points for a 4.5" square. At those points I drill holes and insert pencils. The outer edges I make of scrap wood with points, because the spar gauge is turned as I slide it down the tapered spar. The outer points are always in contact with the side of the spar and the pencils retain the proper ratio from the thickest end to the thinnest. My mainmast tapers from 4 inches maximum diameter to 1.5 inches at the top. It also tapers from the deck to 2 inches in diameter at the heel, or mast step.

For the oars I rough cut the octagon for the looms on my table saw, the blade set to 45 degrees. I glued material for the blade later. For the spars I used a portable power plane to remove most of the material, finishing things up with a long hand plane. Again, attention to detail and working on the whole length of the spar is what yields a nice, even tapered piece. Once the spar is a tapered octagon, I took two passes down each of the corners with the power plane. It's amazing how quickly one can go from square stock to a circle with this method.

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