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  1. #1
    Join Date
    Jan 2014
    Location
    Manitoba, Canada
    Posts
    7

    Question 14ft Birdsmouth Mast for 85sqft Balanced Lug?

    Hello all!

    I'm upgrading my 12ft Summer Breeze skiff to an 85sqft balanced lug sail (similar to the one used on the PDRs), and it needs a longer mast of 14ft.


    I plan on building an 8-stave birdsmouth mast, using .75'' x 1.5'' Sitka spruce (could go to fir?), which ends up giving a 3.75in OD mast with ~0.7in wall thickness. Good epoxy is sadly not availiable in my area and costs too much to ship in, so I want to use Titebond 3 glue (ofc making sure to clamp properly).


    2 Questions:
    1- Will this 14ft mast (3.75in OD, 0.7in wall thickness) be able to support an 85sqft standing lug?
    2- Will the Titebond 3 work until I can get my hands on good epoxy and build another mast?


    Thank you for all your input!


    Note: I know the 85sqft is overpowered, but my area usually has low winds, and a balanced lug is so easy to reef that it's worth having the extra area.

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  3. #2
    Join Date
    Feb 2008
    Location
    Eustis, FL, USA
    Posts
    2,270

    Default

    A 1.5" x .75" stave will yield a 3.5" mast with a .75" wall (min. wall will be .7"). This is a huge mast for only 85 sq. ft. At these dimentions (3.5" tapering to about 3" at the head) a Douglas fir mast with a 20% wall will weigh about 17 pounds, which is a lot for a 14' long mast. A sitka mast will be 14 pounds. I just built a 15' 5" mast that carries 116 sq. ft. (free standing) and it's not this large.

    There are a number of things to consider for mast dimension calculations, besides the total area. I wouldn't use TiteBond III for this application, because of joint creep, which will be extensive on a free standing mast.

    Epoxy can be had through one of several online stores. I'd recommend you look at Marinepoxy from bateau.com and the products at epoxyproducts.com. I'm not sure what you mean by "good epoxy", but all the major players formulate epoxy within a fairly close set of physical properties. Simply put they're all quite similar to each other.

    You can try a PVA (like TiteBond), but you'll have issue with working time, while trying to coat the staves. This is one of the draw backs to PVA's. You can cut the glue with water, but no more than 10%, which will extend the working time a bit, though it also weakens the glue line too.

  4. #3
    Join Date
    Feb 2008
    Location
    Eustis, FL, USA
    Posts
    2,270

    Default

    To further this discussion, some quick math (incomplete without boat spec's) suggest a 3" base diameter, tapering to 1.75" at the head will do for this amount of area, though may be too "bendy" for a lug, so possibly 2" at the masthead. This mast, if sitka will be about 8 pounds, with a 20% wall thickness.

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