Birsmouth mast & carbon fiber tape

Discussion in 'Wooden Boat Building and Restoration' started by Robert Miller, May 23, 2005.

  1. Robert Miller
    Joined: Dec 2003
    Posts: 95
    Likes: 1, Points: 0, Legacy Rep: 12
    Location: Rhode Island

    Robert Miller Junior Member

    Thinking of using the "birdsmouth method" to build mast for my son's CLC Skerry. We are going with a balanced lug of about 64^2 ft.

    The mast will be about 3 inches maximum diameter at the partners, and slowly taper to head, and taper to lesser degree to the heel. Total length under 14 feet.

    We were going to use the dimensions suggested in WoodenBoat #148, and total 8 staves.

    My question is... could the thickness of the spruce staves be reduced, if prior to assembly, a layer of carbon fiber tape were epoxied to inside surface of each stave?

    For example, 3/4 inch wide unidirectional tape epoxied to entire internal length of each (now less thick) stave on its internal aspect only, followed by assembly of birdsmouth joints in usual manner?

    The goal is, obviously, to further lighten the mast without losing strength.

    I have read about introducing some carbon fiber strands into the birdsmouth joints themselves. It seems to me that a layer of carbon fiber tape laminated to the internal surface of each stave would be easier to do.

    Would this result in a structure strong enough to permit reducing stave thickness, and therfore overall weight?

    Thanks very much.

  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    My rough math makes little gain over all on your stick. Three inches at the partners seems quite thick for a pole holding such a small area of sail, in any case a hollow eastern white or silver spruce birdsmouth built mast will weigh in around a fat ten pounds, with a 20% stave thickness (typical) or a few pounds less using a lighter stave like 15%. At 15% the stave would be just barely a 1/2" thick and at 20% it would be .67" thick, neither of these dimensions is very heavy and I'd not want to work them down any thinner. My math showed you only need just over 2" at the partners for a bed sheet like 64 sq. to fly with sufficient strength in protected waters. How much weight do you really need/want to save? At around 10 pounds, you don't have a lot to play with, both in strength and bonding surfaces. You may half the weight of this stick with an all carbon affair, but really . . . for 5 pounds?
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.