Steve’s Boat Building An amateur’s attempt to build a strip plank dinghy

The Mast

Having a penchant for making life difficult for myself, I decided to make a strip-plank mast. I could find very little information on the Internet, other than for round masts, which was going to be way too easy! Fortunately, Hamish, the technical adviser at West System (the epoxy manufacturers) dug out a very comprehensive document which set me on my way.

My initial reason for making the mast this way was to save weight. The core of a mast adds very little strength to it, as the windward side is in tension, and the leeward side is in compression - the core is in ‘neutral’. Hamish’s document suggested a wing profile, with a sheer web of plywood running from side to side. I set about making a small mock-up to assess the problems, and look at the likely shape. In the photo of this small section below, the darker strips are of Western Red Cedar, and the lighter sections of Oak. The shear web is clearly visible, and in the final mast would give lateral strength. The wing shape lends for and aft strength.

Constructing the full size mast proved to be much more challenging. I decided right at the start of the process that I would use the traditional spar making material, Sitca Spruce. This timber is very long grained, and exceptionally strong. I am fortunate to have a very good marine timber supplier locally, and I sourced a piece of clear 100 X 150 Spruce 7.5 metres long from Stones Marine Timber. This was far to big for me to cut into the required 8 X 20 mm strips, and so I had to have it cut before delivery.

Being a complete idiot, I decided to taper the mast above the hounds both laterally and towards the aft. Unfortunately, it is very poor practice to just use a straight taper, as this introduces a single sharp bend in the timber a the start of the taper, and among other considerations, looks horrible. I therefore designed a parabolic curve from the hounds to the top of the mast.

This sounds complicated, but it is fairly simple using the following method. (Thank you, Euclid!)