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Thread: reducing power with sail modification

  1. #1

    Default reducing power with sail modification

    hello

    i have a clamp on sailboat kit on an old town 158 with a 45sqft lateen-ish sail with a boom. i am mostly on large western us lakes (20 miles by 12 miles and hundreds of feet deep) and have no way (that i am aware of) to reduce sail area when winds and swells kick up.

    i have a second sail that i am haveing 'tailored' ( i am removing about 15 sqft) to reduce area and hopefully heeling. i am cutting out an arc that cuts inward from the top of the sail more than at the foot of the sail...sort of like slightly unbending a letter J .

    would tailoring the sail this way likely achieve depowering the best or should i have left the upper sail cut in a symetrical arc???


    thanks

  2. #2
    Join Date
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    Default

    You could try and mod your boom and fit some kind of system to wind it round your boom with crank.

    Also I remember my uncle doing something called reefing on his sailing dingy, dont know how it works but im sure if you google it youll get instructions on how to do it.
    Last edited by jimmyads; 4th-January-2016 at 01:54 PM.
    If in doubt, hit it with a hammer!!

  3. #3
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    The top of the sail is the most "powerful" part. Reducing that area will certainly reduce it's ability to tip the canoe - length of lever and all that.

    Simple reefing, as Jimmy mentions, involves a set of laces in a row parallel to the boom. These go through the sail and stick out either side - long enough so that you can pull the intervening sail down onto the boom and tie the laces around it. You can have more than one set of laces at different heights. You can only do this if the top of the sail is free to move on the mast - if you've a pocket sail over the mast you have a different problem.

  4. #4

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    thanks. i think this sail is the same as on sunfishes. it has a sleeve on the luff and foot that an aluminum spar and boom feed thru.

    i usually see reefing (area reduction) on the foot of sails so by cutting out more material at the top rather than the bottom i am not sure (other than definatley having less power) if that will produce any negative effects....steering, tacking, etc. the kit does allow me to adjust leeboard distance from the mast step.

  5. #5
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    One factor in how a boat handles is the relationship between the Center of Effort (CoE) of the sail and the Center of Balance (CoB) of the hull.

    CoE is effectively the geometric "middle" of the sail. You can find this if you make a scale card cutout of the sail. You suspend it from different points (typically the corners) and mark a line vertically down the sail from that point (ie with a plumb weight). Where these lines cross is the CoE.

    CoB is a little harder to find except by experimentation. It's basically the position along the hull where if you push sideways, the hull moves sideways without turning. EG if you push nearer the front the back will turn towards you and vice versa. Get the CoB and the hull will all move together.

    If you know where the current CoE of your sail is (front to back), you could alter the smaller one to match.

    Normally, CoE is slighty aft of the CoB. This gives you weather helm (boat turns upwind in gusts) which is considered a safety feature.

    Robert.

  6. #6
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    Lateen sails are notorious for their inability to be reefed - that's why they have largely fallen from favour in the UK, because being able to vary sail area is so important for our conditions. There were a fair few around in the early days of the OCSG but that was mostly following common practice in the USA, until we knew better for our conditions.

    I have seen some lateens reefed by bundling up a section of the sail to the lower spar (boom), so the sail sets lower. It makes for a long thin sail that neither sets nor points upwind very well.





    I just googled "reefing lateen sail" and came up with a load of stuff, much of it about Sunfish sails - I suggest that might be your best source of info.
    Last edited by windorpaddle; 5th-January-2016 at 02:54 PM. Reason: add another pic

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