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Date Posted: - Saturday - 03/24/07 - 6:36pm
Author: Randall, Murre, M31
Subject: Main Mast construction, measurements
In reply to: bryan 's message, "Building new mast' for a 31 ketch" on - Friday - 03/23/07 - 11:21pm

Bryan,

Steve's got it right.

The masts are hollow, "box" construction with solid plugs at key locations (mast head, spreaders, winch/gooseneck area, base, etc.).

They were made by Far East out of Sitka Spruce. Would Doug Fir be another alternative?

Measurements can be found in the archive section of the MOA web site. The guy who owned Bagpipe took measurements at 1" intervals. He's also given you the dimensions of the sides. The tricky part will be laying out the taper, which is entirley in the leading edge of the mast; i.e. the leading edge of the two fore and aft boards.

The overall length is listed on the line drawing for the M31 in the specifications section of the MOA site at 33' 4 1/2". I only mention because that's 1 1/2" inches longer than the Bagpipe measurement and 1/2" longer than mine. (Go figure!)


Two books to check out on the how-to are:

BOATBUILDING, Howard I. Chapelle, Norton, 1994, "Hollow Spars", p. 564.

The simple illustration here shows the placement of the plugs. This is a re-issue of the 1941 classic on wooden yacht construction.

HOW TO BUILD A WOODEN BOAT, David C. "Bud" McIntosh, WoodenBoat Publications, 1987, "the hollow spar" p. 204.

The illustrations for this section don't start until p. 211 but do a good job of showing how the four sides come together. There is also a discussion on the clamping-up, which, as Steve alluded to, can be kind of like trying to get a boa constrictor into a wedding dress. This is a fun book to read as McIntosh has a rye sense of humor and the drawings are great.

I took all the hardware off my main mast last year and measured most everything. If you need to have any of the hardware fabricated, i should be able to provide the details you need, etc.

Standing and running rigging measurements for the M31 are listed in the M31 specifications section of the MOA site.

Good Luck,

RR

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Replies:

[> [> Doug fir -- Steve M-32 Pyxis, - Saturday - 03/24/07 - 10:38pm

Since Douglas Fir is not technically a fir but is actually of the spruce family it would work. It's probably the second best wood to use for masts but it is a distant second to Sitka Spruce. If I'm building a mast to last another 35 years or so the cost difference is not that great.


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[> [> [> Sitka Spruce -- Bruce, - Wednesday - 03/28/07 - 6:37pm

Check out this link on Craig's list for Sitka Spruce. Looks like a great deal. $108 for 24' long 1x8's.
http://sfbay.craigslist.org/nby/boa/302120205.html


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