Stupid Idea or ? Building a Mast Step Beam

Discussion in 'Sailboats' started by wesley Sherman, Aug 21, 2020.

  1. wesley Sherman
    Joined: Jan 2020
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    Location: New York

    wesley Sherman Junior Member

    I've decided to pull my posts.
     
    Last edited: Aug 23, 2020
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Hi Wesley,

    Im not sure what comments you are seeking?...it is not clear. Other than:-

    I would avoid placing wood in contact with aluminium like the plague.

    No where on a boat escapes moisture/condensation/leaks etc... ergo, you can never guarantee there will be no moisture during its life.
    The aluminium will corrode away slowly and you wont know it.
     
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  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I would agree with Ad Hoc - even though it is marine grade and has "very good corrosion resistance, especially in marine atmospheres", it can still suffer from nasty things like poultice (?) corrosion where it is in contact with damp wood.
    I know that you have bonded the ally to the wood with epoxy, but even so, you won't know what is happening inside the sandwich, if anything is happening.

    I presume that the original beam was all laminated timber - and they didn't have epoxies for laminating with in the 60's I don't think, so it should be possible to build a timber beam that is strong enough?
    Is the forward side of the beam in contact with the bulkhead shown in the photo?
    If so, then you could laminate the beam to the bulkhead as well, which would give it extra strength?
    And run pillars down each side of the entrance to the forecabin, and it should then be massively strong.
     
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  4. Rumars
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    Rumars Senior Member

    Sometimes the funniest things happen. You trust your life to some 50 years old polyester that is more brittle now than is was when new, but you don't trust modern epoxies and have to use bolts?
    You know why that delaminated beam did not just fall out of there? Because it just serves to transfer the compression loads of the mast onto the uprights in your picture, the two timbers flanking the door that go down to the keel. Basicly it is a lintel and the bulkhead serves as a knee between it and the posts and boatskin.
    Stop worrying and trying to "improve" the structure, just laminate a beam out of new wood and glue it with thickened epoxy to the cabin top, bulkhead and uprights.
    The aluminium is just needless complication and in your configuration not even structurally efficient.
     
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  5. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    I agree with Rumars about the structural effeciency.
    If you want a really stiff beam, put the aluminum on the top and bottom of the beam.
    The center plate does nothing but add weight.

    Comments about corrosion I would direct to Gougeon brothers technical help line. They have lots of testing to back up their opinion.

    But, I once glued an aluminum tube to a wooden supporting structure.
    When I set it out in the sun, it soon separated due to the aluminum expanding far beyond the ability of the epoxy to restrain it.
    No other load at the time.
     

  6. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    Your writings are not really making sense to me.

    First the mast step. What are you talking about? Some piece of wood on the deck, in the deck or under the deck? Can you provide a picture?

    Second the pictured beam, wich is the main (and only) deckbeam. It should be glued to the bulkhead, deck, compression posts, and cabinsides with thickened epoxy. The bolts are not necessary, if the epoxy fails it will also fail in between the laminations and your bolts will not hold anything to the bulkhead. Once glued you wipe of the excess epoxy and varnish or paint the whole thing.
    Yes the pictured beam will work. It is heavier then necessary, was complicated to build and may be trouble sometimes in the future, but it is ok to install and use.
    Your doubling the top of the bulkhead was unnecessary, but since it's done you live with it. Just make sure you bond the bulkhead in with fiberglass tape and epoxy all around.

    If you have problems with glue holding things together you should not own a fiberglass boat (glue holding the glass) with plywood bulkheads (glue holding the veneers).
     
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