Center of Effort of Aggressive Roach Main

I am trying to find out how to estimate the center of effort (CE) of a high roach main. With a triangular sail the roach is usually neglected when measuring the CE, but I am not sure this is the way to go with a high roach main, where the luff may take up 30% of sail area. Thank you very much for your help, Michiel

Hi Michiel, The center of effort of a high roached mainsail will be very close to the center of area of the mainsail, including the roach. The pressure distribution on the sail surface will change from light wind conditions to higher wind conditions because of the effect of the headsail. In wind less than 10 knots the headsail will have a small effect on the pressure on the mainsail. In 18 knots of wind the headsail will have a large effect on the mainsail. Where the flow from the headsail overlaps with the mainsail luff, there will be little pressure on the mainsail, so the center of effort of the mainsail will move slightly up and aft. However, as the breeze builds, the headsail develops a progressively greater percentage of the driving force of the entire sailplan. You really need to look at both sails together. When you look at both sails, the increased efficiency of the headsail relative to the mainsail will offset the aft movement of the center of pressure on the mainsail. So for all practical purposes, the center of effort of the sailplan is the center of area of the sailplan and the mainsail roach area should be treated the same as any other sail area. Regards, Dan Neri

Posted by admin  (November 30, 1999)

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