Building the Rushton Catboat

Deck beams and deck

My friend Andrew Davis, naval architect for Tri-Coastal Marine, Inc. wrote a very good article on lofting deck beams for WoodenBoat magazine some years ago. In that article, he pointed out a common fallacy about deck beams being longer or shorter sections of the same curve. In fact each deck beam should be lofted individually. The starting point for this process requires that the deck center line be lofted in profile. This gives the height of the deck above the sheer at each station. On a plank I drew out a schematic showing the sheer width and deck beam height for each station. I made a jig that would allow me to draw a consistent, fair curve through those three points. [link opens in a new window. Ed.] The jig consists of two battens joined end to end with a small bolt. I drive nails into the board at the two sheer points for a given station. The legs of the batten rest on these nails, and then the battens are moved, forming a shallow angle, the apex of the joint lying on the point marking the deck height. I tighten the bolt to hold the battens at this angle and then, holding a pencil in the corner formed by the two battens, I slide the jig along the nails, first to one side and then the other. The resulting arc is my deck beam. I do this for all of the deck beams in the boat.

Like anything that has to do with lofting, if this is done correctly and with care it saves a great deal of work that would otherwise be spent with a hand plane and a batten, attempting to find high spots and unfair bumps in the deck beams and planing them off. All I had to do in this case was plane the band saw marks off my locust deck beams and install them. They were all perfectly fair and a batten laid down the beams lengthwise was a smooth, fair curve.

After installing the deck beams I screwed in blocking where the mast step and oarlocks would be. I also needed blocking for the foundation of the cockpit coaming. For the deck itself I used two layers of 1/4 inch marine plywood. I nailed both layers to the deck beams and blocking and also used 3M 5200 adhesive between the plywood. I cut the plywood to minimize the number of seams on the top layer. Over the plywood I applied one layer of Dynel cloth set in epoxy and painted. Dynel is a very nice material to work with and it looks very much like cotton canvas. It also has a great pebbly surface which makes a perfect non-skid surface.

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