Converting from keel-stepped to deck-stepped mast

Discussion in 'Boat Design' started by Seafarer24, Feb 16, 2017.

  1. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    I might be helping a gentleman go this route after he lost his keel-stepped mast. I believe there is still a stub left, and there is a mast of approximately the correct proportions available, but it is deck-stepped.

    My proposition is this: Cut the keel-stepped stub even with the deck. Fabricate an aluminum plate with a bottom section that will slip into this stub and be welded to it, and a top section that will act as the step for the deck-stepped mast. The plate would protrude horizontally enough to support a ring of bolts through the deck to support it laterally. In this fashion, the original mast becomes a compression post for the new mast.

    Are there any flaws to this idea?
  2. gonzo
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    gonzo Senior Member

    That depends on the mast section. Keel stepped mast can be smaller section than keel stepped. If what is available was from a comparable boat, it is probably OK>
  3. TANSL
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    TANSL Senior Member

    "Comparable boat" as to what property of the boat. It can be very dangerous to choose an incorrect comparison item. You need to be careful with these simple solutions.
  4. latestarter
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    latestarter Senior Member

    please clarify
  5. Richard Woods
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    Richard Woods Woods Designs

    Obviously he meant keel stepped masts can be smaller section than deck stepped. That is because the deck stepped mast is pin jointed and Euler buckling means the inertia has to be double for the same stiffness

    Richard Woods of Woods Designs
  6. Rurudyne
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    Rurudyne Senior Member

    Now THAT's good to know!

    Is it similar for tabernacle stepped mast which mast steps are themselves anchored to the keel and not just pinned at the deck?
  7. TANSL
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    TANSL Senior Member

    Yes but what does "smaller section" mean because one section of larger dimensions than another may have less resistance to compression and bending (do not forget that a mast does not have to work only under compression). Buckling is not the only phenomenon to keep in mind.

  8. Ilan Voyager
    Joined: May 2004
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    Ilan Voyager Senior Member

    The simplest is the best. As TANSL and Richard said there are some engineering finesses.
    So you go for stepped mast after serious calculations by a NA, or more simple you go for the same or very similar profile, reuse all the hardware, and make a copy of the original mast, unless it was very badly designed.
    So maybe you can reuse the sails, gooseneck, spreaders, boom and other items. If possible that simplifies the task. Replacing a mast is already expensive, but redesigning and making a different mast is very expensive.
    If nothing is left like on a cheap boat bought dismasted, (very few people understand the true cost of a complete rigging until they have to make one) you can also maybe, very maybe, find a complete rig with the same mast profile and same style (head mast, 3/4 mast, 7/8 mast) with same sails dimensions. Very probably it has been designed for a boat of similar characteristics but you'll need to adapt every thing. A time consuming work but it can be done.
    Unhappily there are not cheap boats, there are only a bit less expensive boats.
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