How do you determine the number and dimensions of staves in a Bird's Mouth Mast or Spar?

Birdsmouth is the word in the shop, lately. We have several orders for birdsmouth masts and spars that are in progress. I have been working hard at nailing down the process to be able to make them efficiently and to a very high standard and feel very excited about how it is all going. The Landing School of Boatbuilding has asked me to to give a talk/demo on making things birdsmouth style, so I've been pressed to improve our webpage on birdsmouth spars as well. On the page is my procedure for determining the number and dimensions of staves in a birdsmouth spar. Gaeten Jette, a featured contributer to Duckworks magazine on the topic of Bird's Mouth Spars, generously helped me customize the online calculator for my use and students' use. I hope you find it helpful, too.

We make two styles of Birdsmouth spar, using symmetrical staves (most common) and asymmetrical staves, which when done correctly will yield a perfect octagon and a spar that is slightly stronger and quicker to make. I decided to apply this type to making an ultralight kayak paddle shaft.

I am pleased with the results. The biggest hold up was fitting the plugs in the scoops that will take a ply-composite or a carbon fiber blade, which is already something we produce for our wood/composite, high performance oars.

With that part of the process ironed out it really is just a matter of setting up the operation to produce these paddles after some testing. This one will go to some paddler friends who will take the design on the seas and really test it out. Hopefully, sometime this summer the results will come in and production will begin. I'll leave you with the best part of making new things: breaking them with a hammer. We test most spars this way to make sure that things break the "right" way. That is, in a proper glued structure, the wood should always break before the glue joint does, otherwise there is a problem. Happily, all our spars have been breaking the "right way" in the shop so we know they won't break out on the water.