What we do have in very plentiful supply are Jarrah and Tasmanian Oak. Jarrah is an incredibly dense, strong, durable timber. Great for railway sleepers (all the railway sleepers in the London underground were made from Western Australian Jarrah), but challenging to build a boat with. Tasmanian Oak is slightly less dense than Jarrah, but still isn't exactly a lightweight timber. So I'm wanting to build a wooden mast. You can see my dilemma. There's no way I'm going to build it out of Pine or Western Red Cedar, because both are much too soft. I'm interested in the birdsmouth construction, but I want a sailtrack, and I can't think of a straightforward way to do that with normal birdsmouth.
Well if a simple method won't suffice, surely a complicated method will. If I build a sailtrack piece out of Jarrah, then use that to replace the back three birdsmouth staves in an eight sided spar, then mirror everything so the left and right sides are the same, I end up with something that will do what I want.
So I designed my mast in sketchup. The birdsmouth bits are 30mm x 12mm Tassie oak. The sailtrack bit is made from two pieces of 30mm x 12mm Jarrah, cunningly joined after cutting the track with biscuits. Then a pair of 18mm x 30mm tassie oak bits get laminated on, and more cutting happens to make the back of the mast. After assembly the whole lot is planed to an oval shape 63mm wide x 76mm long.
I started by cutting the birdsmouths into my 30mm x 12mm tassie oak. I used a 12mm dia 90 degree V bit in my trim router, with some guides screwed into the base.
Once my lamination had set up I cut rebates into the tassie oak part to locate the front five staves.
This is what my prototype looks like now. I still need to bevel the back sides and cut open the sailtrack slot, glue the whole shebang together, then plane it to an oval. I weighed this 300mm section this morning at 649g. That's with a fair bit of material still to be removed. That means a 6.1m mast built like this should weigh around 13kg, and hopefully be as strong as they come...
The result looked really awful. The tabernacle looked very heavy and the spine rather light. It looked kinda perched there.
The tabernacle is made from Jarrah, with 16mm thick side plates and a solid wedge shaped piece between them. I bored an 18mm dia hole for the mast pivot bushings. I'll turn up some bushings to go in there and use a 12mm bronze shaft for the mast pivot. I'm waiting on some 12ga bronze screws to screw the base of the tabernacle down to the bridge piece. I'll attach the centerboard lifting block to the back of the tabernacle once it's installed.