Best shape for bridgedeck?

Discussion in 'Multihulls' started by Alex.A, Mar 19, 2010.

  1. Alex.A
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    Alex.A Senior Member

    Aerodynamically thinking? Could it be used to influence the mainsail as part of aero package? to either stall airflow or funnel it away completely? Thinking racing / cruiser racer? Add to the this the hullsides....?
     
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  2. gonzo
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    gonzo Senior Member

    Why do you want to stall airflow? The goal is to streamline it to prevent as much turbulence as possible.
     
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  3. Fanie
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    Fanie Fanie

    That is true, the wind mustn't know there is anything. Some parts of the boat could probably be shaped to dump wind on the sails instead of blocking it, but it's not so easy. There are a lot of compromises and mostly if you weigh them you end up where you started from.

    Angling the hull sides could make a difference, but you would also allow waves to rinse onto the boat more easily. What would the negatives of this be... extra weight of the water half the time, and where will you pilot from etc so there is a lot to consider.
     
  4. Fanie
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    Fanie Fanie

    Remember all hull's dump wind on the sails at a certain angle of heel to a more or lesser degree. At this stage that is actually where you want less wind on the sails ;)

    Only the mono hullers like heel, at least it makes it feel faster :D :rolleyes: (Sorry, couldn't help myself)

    I have often wondered why nobody ever applied the hydofoil to keep the hull from flying, ie swim the windward hull down. If you can keep the hulls level in theory you can apply unlimited power and the boat won't capsize with speed as the result.
     
  5. tspeer
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    tspeer Senior Member


    Many have. One type is called a Bruce foil, for its inventor, Edmund Bruce.
     
  6. Fanie
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    Fanie Fanie

    Thanks Tom.

    This brings us to the next question, why use the guy's surname and not the name - why isn't it the Edmund foil :D
     
  7. Autodafe
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    Autodafe Senior Member

    Aerodynamically, best bridgedeck is no bridgedeck.

    The only use I know of for bridgedeck sail interaction is having a low boom and using the cabin-top as an endplate, but this applies equally to decks on open bridgedeck designs.

    Curving hull edges can help significantly, but it costs a fair bit of deck area, and adding a useful toe-rail (as required in some races) may off-set much of the benefit.

    The best you can do is try to minimise drag for all wind directions forward of the beam, so streamlined and minimise frontal area, particularly for apparent wind at ~30deg.

    I think it's a moot point for most cruisers as the tenders, canoes, surfboards, liferafts, stanchions, grab-rails, lifelines, jerrycans, sunshades, hardtops, bimini's, etc, etc, invariably spoil the designers perfect flow anyway.
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

    Which leads to the obvious conclusion of having a proper, preferably more aerodynamical superstructure instead.. anyway for cruisers...
     

  9. Alex.A
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    Alex.A Senior Member

    Angle the toe rail.... i think i've been watching too much Formula1 - and aero isn't helping there.
     
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