How big does a sail need to be?

Discussion in 'Boat Design' started by stonedpirate, Aug 19, 2011.

  1. stonedpirate
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    stonedpirate Senior Member


    Does anyone know if there is math available for calculating how much sail you need?

    Lets say you have a finished hull, you know its weight when fully loaded and its max hull speed.

    Is there a way to know how much sail area generates the required force to bring it to hull speed?

    Also, what wind speed should you design for?

    For example, full sail out in 20 knots brings you to hull speed then start reefing above 20 knots?

    What wind speed should be targeted for full sail out for hull speed?

    Sorry if that doesnt make much sense, hard to explain :p

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    BATAAN Senior Member

    I don't know a lot about modern yachts but a great deal about the traditional craft of the past that had to make a living without an engine.
    The usual work boat had to reef in 10-15 knots, so had a large rig with few or no light sails.
    Most sailing is done in light winds, unless you live in an area that has unusually high wind speeds as the usual thing.
    Reefing or reducing sail in any way isn't done just because you have reached hull speed, but because the boat gets hard to steer, rounding up and overpowering the helm.
    A working rig designed for 20 knot winds will give slow and poky performance in winds much below that.
    Work boats had sails that were easy to reef or take down. Some modern rigs have discarded this simplicity for roller furling which is great until the furling line breaks or a swivel fails, both of which happen occasionally on boats that are sailed hard.

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  3. PAR
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    PAR Yacht Designer/Builder

    There are many books available on the subject, you'd be best advised to avail yourself of one or more. "Principles of Yacht Design" is typically the first recommendation, though it's a little "thick" for the average guy. "Understanding Boat Design" by Ted Brewer is a more basic approach, though you will not get all the information you need, you will discover the issues you need help with.
  4. michael pierzga
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    michael pierzga Senior Member

  5. DCockey
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    DCockey Senior Member

    Stability is another factor to consider when deciding on sail area.
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