PolySail International

How to Build a Lightweight Box Mast

An 18' box mast can save over ten pounds of top end weight over a solid wood mast of the same dimensions. This weight difference translates into more speed and stability for your dinghy. The idea for this mast was proposed by William F. Crosby in an early issue of Rudder magazine. Crosby proposed making his box mast of 1/8" waterproof plywood. In our area 1/8" marine plywood is unavailable, but 5mm lauan is plentiful. While there would be less weight savings with the lauan plywood, it might be a possible substitute for Midwesterners and others who can't readily purchase the 1/8" plywood.

 The box mast has three spruce "fillers" at the head, base, and boom attachment positions. These are 12" to 18" solid spruce blocks with grooves to receive the 1/2" spruce strips shown in the corners of the mast in the diagram below. If you want to taper the head and/or base of the mast, the central filler can be made larger than the end fillers. Of course the outer plywood or lauan strips would also have to be tapered to fit.

The mast also includes two or three spruce "spacers" used to reinforce the mast at critical points. These spacers can be as little as 3/4" wide. If you feel that more reinforcement is needed, you can fill up the remaining spaces with Styrofoam strips. The diagrams below show how the box mast is constructed.

 

 This page last updated 1/14/03