Survival load on mast or antenna

Discussion in 'Boat Design' started by floating, Apr 25, 2011.

  1. floating
    Joined: Jun 2009
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    floating Junior Member

    I have a question related to the survival of a slender tall structure mounted on a 'vessel' which is compliant with the waves, i.e. pitching and moving a lot. You can think of the structure as a mast on a small ship but actually is is a large antenna on top of a buoy. Waves are very high and steep (survival conditions). I believe the worst-case scenario is a breaking wave hitting the mast from the side, producing high pressure along the mast. Here's my question: Does this peak pressure move vertically along the mast, resulting in a time delay similar to the delay of a pressure pulse along the deck of a ship when it slams into the sea surface? Or is the pulse applied simultaneously along the whole length of the mast?

    Also is there a 'bible' text that covers mast design for small ships? It's not my area (as this question makes clear), so I'd like to get oriented.
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    I think it is the momentum of the buoy when it suddenly changes angle and position while hit by a wave. With a rigidly mounted antenna the base is loaded twice with every wave, first when the buoy heels, then when the antenna decelerates to a new position.

    An antenna mast is normally a small surface compared to the buoy body and when hit by a breaking wave, the load is in the direction of movement.

    I would make the base either very sturdy or mount the antenna on a spring or rubber element to soften the blows.
  3. Ad Hoc
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    Ad Hoc Naval Architect

  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The math for a dynamic situation like that is fairly complicated. If you need an antenna for those conditions, you can call the manufacturers with the specifications. They can tell you if their product is designed for it.
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