Light Schooner Construction : Birdsmouth Masts


Birdsmouth test

I ripped down some 1x3 #2 pine to do a test section of birdsmouth mast. The staves are 1-3/8" wide and 3/4" thick. This gives a weight reduction vs a solid mast of about 30%, while maintaining 88% of the strength.

Mast material

I found some unusual wood to use for the mast -- Kauri Pine, also known by its botanical name, Agathis. It has similar properties to Douglas Fir, but was less expensive and was in stock at Curtis Lumber. I bought three pieces of 4/4 x 13", 14, 15, and 16' long, to be ripped down into staves for a hollow birdsmouth mast.

Birdsmouth jig

I made a jig for holding the staves tightly while they go through the tablesaw. I clamped a piece of scrap oak flooring to the fence, and then clamped top & bottom guides to it. This lets me get a perfect 45 degree slot in the staves.

Backyard Sawmill

I cut the staves for the mast on the back deck -- I made a LOT of sawdust -- 16 feet times 3 cuts (1 for width plus 2 for the notch) times 8 staves, plus 4 feet of taper per mast is over 400 feet of cuts. Times 2 masts!


Main mast dry-fitted as I'm losing light on Tuesday... Dry weight before gluing and rounding is 20 pounds -- 13 pounds under my estimate. Either my math is wrong, or my wood doesn't have a specific gravity of .56. As long as it holds together, though, I'm happy :-)

Mainmast planed

After gluing & shaping, the weight is 25 pounds, including a solid plug of spruce in the lower 4 feet.

Mainmast deflection

After shaping, it's a little bouncy, but still surprisingly stiff, with my 150 pounds. The deflection isn't as bad as it appears in the photo -- the perspective combined with the mast taper make an optical illusion.

Splicing rigging

I bought a splicing fid, so I can make custom lines for the rigging.

Boom Jaws

The plans show half-scale gaff jaws, and say "Boom Jaws similar". Well, similar is NOT identical, as I learned when my first attempt failed. The problem is that the gaff is 1.5" wide, while the boom is only 3/4". So, by making the jaws identical, I ended up with jaws that wer 3/4" undersized. This left too little material, and I had to start over. This is my second attempt, using 8/4 mahogany -- double the thickness specified in the plans. These are MUCH sturdier than the 3/4" doug fir from my first attempt.

Photo album generated by album from Dave's MarginalHacks on Fri Jun 10 09:24:55 2005