Building the Rushton Catboat

Spiling the Planks

In lapstrake boat building spiling is easy. Planking stock is laid in place and the bottom edge (the edge closest to the keel) is traced off the previous plank. The top edge is marked from the points on the moulds where the planks were lined off (in my case the ribbands). One has to just make sure to ADD the width of the lap to the bottom edge (because you traced off the bottom edge of the adjacent plank, but the plank you marked needs to overhang the previous plank by the width of the lap). Before I made up my planking material I used a special spiling batten to determine the most efficient way to use my material. My batten consists of two eight foot strips of 1/4" plywood, five inches wide. I fasten the two together end-to-end, at one corner, with a small bolt that allows the two pieces to swivel. I then carefully clamp this on my moulds so it lies where my next plank will be. I am very careful not to edge set my batten, making sure that it lies down naturally across the moulds.

I can look at the batten fore and aft and determine how wide a piece of plywood I need for my plank. At the hinge in the middle I measure the angle between the two pieces. The planking on this catboat required material between six inches and eight inches wide, scarfed together at an angle of between zero (the garboard) and eight degrees. This method results in a huge savings over the course of the boat. Two six inch wide, eight foot strips scarfed together at a seven degree angle, for instance, is equivalent to two eleven inch wide strips scarfed together in a straight line. The savings are obvious, as I am using almost half as much material. Of course this particular boat is in some ways extreme and her planks had quite a lot of shape. If I had built her with lumber instead of plywood, I would have certainly added one more plank per side. Planking her with nine planks per side instead of eight would let me use narrower plank stock.

My spiling batten hung in place on the boat. I can look at where my plank needs to go and determine just how wide my material needs to be.

The hinge at the middle of my spiling batten. I can measure this angle and determine what angle to scarf my plywood together, resulting in much less wasted material.

The scarfed plank being hung on the boat. Once in place I can trace off its shape.

My scrap pile after planking. All in all very little wasted material.

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