Sail Area / Power

Discussion in 'Boat Design' started by dustman, Sep 2, 2020.

  1. fastsailing
    Joined: Sep 2017
    Posts: 83
    Likes: 8, Points: 8
    Location: Finland

    fastsailing Junior Member

    Wrong.
    However the force of a given sail area/trim will produce at a given apparent wind angle and speed is independent of other characteristics of the boat.
    The true wind needed to make it happen will depend on other characteristics of the boat quite a lot.

    Correct as long as all the sail is above water.
    But that result does not apply to power.
     
    Will Gilmore likes this.
  2. fastsailing
    Joined: Sep 2017
    Posts: 83
    Likes: 8, Points: 8
    Location: Finland

    fastsailing Junior Member

    Not always correct. If you increase the sail area for a given design, you can end up with a capsized boat and no power at all from the sails. Hence less power than with a smaller sail. Even heeling too much without capsizing can reduce power due to less righting moment. This is the most typical case for ballasted sailing monohulls.
     
  3. fastsailing
    Joined: Sep 2017
    Posts: 83
    Likes: 8, Points: 8
    Location: Finland

    fastsailing Junior Member

    The post you quoted did not make the claim you just wrote. Hence it's your own statement you do not comprehend.
    The original statemen was :"the net power per m2 appears independent at first order of the sails area, reaching", and in effect says power is linearly dependent on sail area when reaching at first order. Of course there are second order relations as well, which can indeed be very large. For example on foiling boats when the larger area allows foiling in given conditions and the smaller sail does not. It's also questonable if that is second order effect or rather the first order effect. Plenty of assumptions needed to make such simplifications even remotely valid.
     
  4. fastsailing
    Joined: Sep 2017
    Posts: 83
    Likes: 8, Points: 8
    Location: Finland

    fastsailing Junior Member

    Not so. Propulsive power by very definition is the product of boat speed and magnitude of the driving force.
     

  5. fastsailing
    Joined: Sep 2017
    Posts: 83
    Likes: 8, Points: 8
    Location: Finland

    fastsailing Junior Member

    I do. But first you have to define which frame of reference you want to use for the analyses. Anything goes, but the answer (numerical value for power) is not the same for all of them.
    Most common ones would include the frame where boat is stationary, and the one where water was initially stationary, before interacted by the hull and appendages, with significantly different results.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.