sail chord length/aspect ratios

  • 13 Dec 2014 15:59
    Reply # 3169713 on 3169483

    I think it's the highly manoeuvrable, aerobatic birds (eg lapwings) that have short, broad wings. This doesn't have any counterpart in sailing. However, Marchaj showed a long time ago that a low aspect ratio sail (eg gaff mainsail, viking square sail) is more efficient downwind than high aspect ratio.

    On the other hand, high aspect ratio is more efficient for soaring and gliding (eg albatross) and for sailing upwind (eg America's Cup hard wing).

    So since junk sails are pretty good downwind anyway, spreading all their area to the wind, I'm moving over towards the high AR camp, having found that even a boat like Tystie, with limited stability and hence sail carrying ability, can carry quite a high sail. Too, a higher AR means shorter, lighter battens and yard, easier gybing and no need to swing the sail across the mast for downwind helm balance.

    But, moderation in all things *

    A high junk sail is more difficult to sheet effectively. My current sail has an AR of about 2:1, and that's about as high as I care to go. 

    In two masted junk rigs, it gets simpler. It's hard to make the sails wide. Allowing enough drift for a sheet, between the foresail and the mainmast, and between the mainsail and the stern, strictly limits the width, and on most boats, to get sufficient area, the only way is upwards. Schooner's sails commonly have an AR of 2:1 or more.

    * "including moderation", said Oscar Wilde.

  • 13 Dec 2014 00:19
    Message # 3169483
    Deleted user

    Opinions please, on high aspect/taller mast, shorter chord length sails vs. low aspect/shorter mast, long chord length sail.

    In nature, it appears the soaring birds all have high aspect, very short chord wings. The power birds have the long chord low aspect wing shape.....or so it seems to me anyway.

    What do you think is better for offshore cruising?

    Is there an ideal ratio of chord depth to length of wing/sail?

    I ask because in my drawings, two masted schooner, you can pack on the sail area with a low aspect rig with long chord length, but maybe less overall sail area is more efficient in a higher aspect shorter chord design.

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