Ask SAIL: Powering Up a Main

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Q: My friends tell me that I need to “power up” my mainsail in light winds, but I am not really sure what that means. Can you explain? I race a Pearson 37, mostly beer-can races.

Joseph O’Brian, sailmail@sailmagazine.com

BRIAN HANCOCK REPLIES

Powering up your main is very important in light winds. Equally important is being able to “depower” the sail when the wind comes up. Powering up your main means adding depth to the sail. Mainsails are designed with a specific chord depth (draft, or curvature depth) for general sailing purposes. In light winds you want to increase the chord depth, and there are a number of ways you can accomplish this. The first and easiest thing you should do is ease the outhaul. This immediately adds depth to the sail because you are effectively bringing the leech closer to the luff. Also, ease the halyard or cunningham. This, in turn, relaxes the fabric along the luff allowing the draft to increase. Another important thing you can do is to ease the backstay, effectively straightening the mast. The reason for this is that part of the sail’s overall shape is induced by the amount of luff curve the sail designer has specified for the sail. When the mast is bent, the luff curve matches the mast and the sail has a flatter shape. When the mast is straightened (by loosening the backstay) that luff curve shape is pushed into the body of the sail and increases overall depth. To depower a sail, simply do the reverse to reduce the amount of draft, or curvature, thereby producing a flatter sail.

Got a question for our experts? Send it to sailmail@sailmagazine.com

April 2017

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