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alman 12-07-2009 07:32 PM

Settle the argument....
When you are heeled hard over, does it produce lee helm or weather helm?

bubb2 12-07-2009 07:43 PM

On a good boat weather helm and on a bad boat lee helm. I am glad I could help settle that!:D

jackdale 12-07-2009 08:44 PM

Usually weather helm. I have seldom been on a boat with lee helm.

I also have theory that says that weather helm is induced by heeling. The leeward side is longer that the windward side. Hull speed is a factor of LWL. The leeward side wants to go faster than the windward side, inducing a tendency to round up, thereby inducing weather helm.

When racers want to reduce heeling they change down the foresail. I have also done this. Result - less heel and less weather helm.

alman 12-07-2009 09:18 PM

Thanks for the answer, Jackdale.
From your experience, I believe your theory is correct. I was on the other side of the argument because I thought that the lee side would have the big drag through the water and that there would be very little, if any, drag on the weather side, hence lee helm. Obviously my reasoning was not correct.

klem 12-07-2009 09:47 PM

When the boat heels over, the center of effort of the sails moves to leeward much more than the center of lateral resistance. When the boat is not heeling, these are essentially directly in line so there is no torque about the vertical axis. However, when the boat heels, since the CE is more to leeward, you get a torque about the vertical axis.

There are additional effects from drag and the change of the water flow on the rudder but in a well designed boat, those should be really small.

If you have the chance to sail a small light boat (10-20ft) with the tiller lashed, it will be really instructive. Heeling the boat more will cause you to head up, heeling less will cause you to fall off. Moving weight forward will cause you to head up and moving weight aft will cause you to fall off. Then you can start messing with sail trim.

jackdale 12-07-2009 09:52 PM


I like that explanation.

The C of LR (usually somewhere around the keel) may actually move to leeward as the boat heels, increasing the distance between it and the C of E.

seabreeze_97 12-07-2009 10:02 PM

Nice theory, but I'm not buying it. Case in point. Catalina 310. Reasonably stiff boat. Anyway, it doesn't heel enough to make any appreciable difference in hull lengths in 10 knots that suddenly becomes 15 knots. The wind gusts, and there's an immediate strong weather helm as if the wind grabbed the boat by the nose and snarled, "Get over here!" The wheel was a solid stone in my hands. That's the hull being yanked around by the rig, not the hull dictating the course. This happened in a fraction of a second....far too quickly for it to be a response to differential hull waterlines. Flattening the main solved the issue. It's your idea, but it applies to air over the sail, not water over the hull. Flattening the sail reduces the differential between both sides of the sail, thus easing the weather helm forces that had been present. Try this. Get a tender boat and put everyone on one rail. The boat (sails down, engine putting along) will most likely need corrective steering to weather to compensate as it will favor the low rail. Now, raise the main and watch the boat go to weather as it fills. Trim it flat and watch it ease off. Even with all the people on the windward rail and the boat sailing flat, it'll have weather helm if overpowered. At least, that's where I am on things.

jackdale 12-07-2009 10:10 PM

The question was about heel, not about sail trim.

I agree that flattening mainsail will depower it and reduce weather helm.

Balancing sails is also essential in adjusting "helm."

On race boats moving the crew around has an effect on helm.

There are many factors involved.

Faster 12-07-2009 10:15 PM


Originally Posted by jackdale (Post 548839)
...There are many factors involved.


Garffin 12-07-2009 10:45 PM

Dang it I need pictures:)

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