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Ask Sail: How Far to Ease Out?

It’s all about projecting more sail area dead downwind

It’s all about projecting more sail area dead downwind

Q: When sailing dead downwind (assume 22 knots of wind), if the main is eased out to 90 degrees relative to the wind (perpendicular to the wind) are roughly the same forces applied to the sail as to the sail if it isn’t quite out all the way, say, 75 degrees to the wind? My spreaders don’t allow me to let the main out all the way on a run, because they are swept. My friends said a 32-footer with a nearly identical sail plan and sail configuration walked right by us because my main couldn’t ease out to 90 degrees and his did. I disagree. I have a 140-percent genoa, and he had (maybe) a 150 percent headsail. Both were wing-and-wing. The only other difference was that his genoa was held open by a spin pole, mine wasn’t.

— Dana Paulson, Washington, DC

BRIAN HANCOCK REPLIES

If indeed, you are sailing dead downwind, in other words the wind direction is perpendicular to the transom of your boat, I’m afraid you are wrong. At that point of sail, it’s all about projected area, and the more area you can project, the better off you will be. Try this experiment. Sail dead downwind with your mainsail all the way out plastered up against the spreaders. Record your boatspeed. Now sheet it in so that it’s around 45 degrees and record your boatspeed. Now bring it onto the centerline and see what happens. Each degree of reduced projected sail area will reduce your boatspeed.

Note, this applies only to sailing dead downwind. As soon as you harden up onto a reach (or a beat) things change. When you are sailing dead downwind the wind is sucked around the edges of the sail and under the boom to the leeward side. However, as soon as you harden up, the wind starts to flow across your sail, in the process attaching not only to the windward side but the leeward side as well, thereby producing lift. As you start moving across the wind, you will also begin creating apparent wind, which will cause you to go faster still. With this in mind, with your swept-back spreaders you might want to consider heating the angle up a little, say, to a broad reach, which will increase your boatspeed sufficiently to more than compensate for the extra distance sailed. With any luck, when you gybe back in toward your original rhumb-line course, you’ll end up well ahead of where you would have been if you’d sailed the shorter, more direct heading.

One other thing: it’s possible that by flying their genoa on a spinnaker pole your “competition” was able to project more headsail area as well, which also contributed to them having some extra boatspeed.

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