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 Lee Helm		  New Topic  Topic Locked
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sanibelle
Deckhand

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USA
22 Posts
Initially Posted - 09/02/2007 :  14:23:39  Show Profile
What's the proper way to avoid lee helm when sailing with only the head sail? I was out yesterday in about a 12 knot wind and had some trouble. I seemed to have less trouble with the 150 head sail completely unfurled. In fact, at times I could let go of the tiller with no change in direction. What physics is involved here?

Joe Russo, Sanibelle, 1980 TR/FK
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JimB517
Past Commodore

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USA
3285 Posts
Response Posted - 09/02/2007 :  15:13:31  Show Profile  Visit JimB517's Homepage
With the jib only you are going to have lee helm as the wind tries to blow the bow down wind (bow heading upwind is weather helm).

Probably with just the 150 the center of effort is moved farther back decreasing lee helm (more load on your sheets/winches, less on the forestay).

With both main and jib up if you have lee helm you tilt the mast backward to relieve it.
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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts
Response Posted - 09/02/2007 :  16:00:58  Show Profile
I found that moving the car forward and easing the sheet a little more than normal helped. It moves the draft, and therefore the center of effort back and reduces the leeward pressure of the sail. I didn't find that it slowed me down appreciably--possibly the opposite. (That also implies falling off a little from your normal beating angle.)
Edited by - Dave Bristle on 09/02/2007 16:02:09
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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts
Response Posted - 09/02/2007 :  16:31:27  Show Profile
Oh... the second part of your question... The physics has to do with the fore-to-aft locations of the Center of Effort (COE) and the Center of Lateral Resistance (CLR). The COE is roughly at the "center" of all the sail area you have up, and the CLR is roughly at the center of the keel, although the rest of the hull form and the rudder have something to do with it. If the CE is forward of the CLR, you'll have lee helm. If the reverse, weather helm. Slight weather helm is generally preferred, both for safety (let go and the boat stops) and speed (somewhat greater lift from the keel). As Jim said, your 155 alone will have a CE further aft than a 110 alone. Your experience with the 155 suggests it's directly above the CLR.

Does that 'splain it?
Edited by - Dave Bristle on 09/02/2007 16:35:22
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glivs
Admiral

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USA
836 Posts
Response Posted - 09/05/2007 :  19:44:01  Show Profile
Joe,
FWIW....I explored various sail configurations a bit this summer to demonstrate to the admiral that we can sail in winds over 10Kts without heel. Like you I was not happy with the lee helm when sailing with only a headsail, particularly when trying to leave an anchorage. Because of the relative positions of the CE and CLR as Dave described I found the storm jib (hank on) the most adverse. To my surprise, however, I found that with 20Kt winds, sailing with the storm jib and a single reefed main we could sail upwind and on broad reach at or near hull speed (5.5 - 6Kts GPS, no current) with almost no heel and still keep a bit of weather helm by relaxing the adjustable backstay. Great fun!
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.