Squaretop tuning

Discussion in 'Sailboats' started by mojounwin, Jan 5, 2010.

  1. mojounwin
    Joined: Dec 2004
    Posts: 77
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: Queensland, Australia

    mojounwin Junior Member

    Hi All,
    Just after any advice regarding tuning a square top main.

    I have a 26ft trailer sailer with a squaretop main. I'm having difficulties pointing well and also find that I become overpowered quickly. I'm still yet to spend much time in the boat, so haven't tried much yet to improve the situation. None the less any suggestions would be appriciated.

  2. kenJ
    Joined: Jul 2005
    Posts: 349
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Williamsburg, VA

    kenJ Senior Member


    Mast Rake and standing rigging tension affect pointing. Try checking with some other owners to see what they use. Or look on line for an owners assoc if there are none near you.

    The square top will overpower more quickly than a standard cut main. As you become overpowered, moving your traveller to leeward will help, as will decreasing vang or mainsheet tension to increase sail twist. There is an excellent sail trim forum at www.sailboatowners.com, select forums, then expert forums, then sail trim. Lots of knowledgeable folks there. There is also a trailer sailer forum at the same site.
  3. bistros

    bistros Previous Member

    Agreed on possible issues. I've got a square top main, and you've got two issues in play that are in conflict somewhat. Depowering a square top in gusty conditions is handled by the ability of the top mast to flex and let the excess area of the square top fall off and reduce effective sail area. This is why the original 49ers had a fibreglass mast top and and aluminum mast lower. Subsequently newer carbon masts are designed with different flex characteristics at different heights.

    Depowering a sail affects it's pointing ability. You have to accept that footing while depowered is better than pointing and being overpowered.

    Many square top implementations have uppers, normal shrouds with spreaders and lowers to allow fine tuning of the mast bend characteristics depending on wind conditions. This presupposes you are willing to play with mast tune on a regular basis. My dinghy has got the ability to tweak lower tension & rig tension on the water and mast rake at the dock. I currently use an aluminum mast (I'd love to be able to afford carbon) but it is stiff enough that uppers would have little effect.

    Reducing vang tension off the wind can allow more depowering of the square top, as can flattening the sail with increased cunningham and outhaul. Traveler position as well can be tweaked further outboard to allow the sail to blade out.

    Pointing ability has got many more possible sources of trouble and help than worth trying to explain. The best thing to do is to go out with a sailor that has great results in a similar boat and learn from their experience. You should also search out tuning guides from sailmakers to establish baseline measurements for all major issues like shroud tensions, sail positions, rake, depth etc.

    Getting a sailboat GPS that can measure and document results really helps so you can learn what works and what doesn't.

    Last edited: Jan 5, 2010
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