Mast Building Details

[BillyBudd]

Since I'm putting on the cuddy roof, have the seat framing in --Wow--I'm starting to think about the main and the mizzen mast for the Chebacco (20'x7.5'). Bolger has them both set in steps and partners, both in square form. Its fair to say that a) they aren't to rotate, and b) he probably considered that they'd be shaped from solid material. Above the partners they transition to round. Main mast = 19' (gaff goes higher), mizzen = 13.5'.

Because I think there is a saving in weight aloft, I'm thinking about doing the bird-mouth hollow mast bit that has been shown in a WB mag issue, talked about on the forum. BUT! Since the hollow form starts out octagonal...what to do? Should I add appendages with epoxy that square up the step-to-partner lengths? Will these add-ons resist the twisting? Thoughts, suggestions, comments?

[Ian McColgin]

It's very common to have spars taper from the partners down to the heel and to have the very heel a square section to keep the mast from twisting and to facilitate various wedging patters. The slot in the mast step will be longer than the corrosponding tounge of mast that sticks into it. The side to side fit is close enough to set in without either jaming or shaking and have the very bottom relieved a bit so you can get it started down. The heel of the mast can be wedged a bit forward if you need to rake the mast aft and visaversa.

Now, what Bolger did. It's square through the partners most likely to make construction of the partners that much easier. Bolger tends to be ruthlessly practical and he'd call for a box construction all the way up if it were not a gaff sail. Easier to set up a gaff with jaws and cheaper to run the sail on a lashing and for those you need a round spar.

You definatly can make a bird's mouth spar and it will be lighter. Will that be good? I think you should ask Bolger. The lighter spar may make the boat a bit more whippy in her roll, maybe even uncomfortable. That little extra weight aloft might dampen the motion nicely. Or it might not matter. Bolger is a friendly sort who will point you right for the price of a phone call.

G'luck

[Keith Wilson]

Birdsmouth spars are surprisingly easy and fun to build; watching that nest of writhing epoxy-covered snakes magically form themselves into a tube is very very satisfying. They can be made out of inexpensive construction lumber (throw away the parts with knots or bad grain) and the light weight makes them very pleasant to use. I love stepping the mast on my Cartopper variant with one hand. Increasing the diameter slightly will more than make up for any loss of strength or rigidity from the hole in the center. You probably want a solid plug in the hole at the partners, and where the gaff jaws sit. I would add appendages to make it rectangular where it sits between the partners for more bearing area to hold it in place; you could even make the appendages out of harder wood with essentially no weight penalty. IMHO changing the weight of the Chebacco's mast won't have any appreciable affect on her motion in, but asking Bolger can't hurt. He doesn't have a listed phone number, but apparently responds quickly to faxes.

[ 07-08-2004, 10:39 AM: Message edited by: Keith Wilson ]

[DerekW]

Yup, adding on four triangular-section strips with epoxy to square the octagon will work fine. We have a 20 foot birdsmouth mast built that way, and it gives no concern.Be sure and arrange for a good internally tapered plug inside the spar where it passes through the partners.

cheers
Derek