|Topic Review (Newest First)|
|12-09-2009 08:06 AM|
I believe most boats are designed with the center of lateral resistance (Clr) forward of the center of effort, (Ce), so that they will have weather helm when they get over powered going to windward. I also believe the keels angle of attack will change as the boat is heeled over resulting in more lift to windward, up to the point it stalls and the boat rounds up. If you loose control of the boat temporarily, I think most would agree its better to do so with the bow to weather. I'd never thought of the differential of lwl between windward and leeward, but it might be an additive factor, though I still believe that most of the turning force is a result of the relationship of Clr and Ce.
Admittedly, my experince is pretty limited, but every boat (Tartan 37, Tartan 40, Oday 322, Catalina 36, Catalina 350, Beneteau 411) I've sailed has demonstrated weather helm when they get to the point of being over powered. This is with the crews paying attention to proper sail trim and focusing on pointing as well as they could.
I think if the boat is showing lee helm going to weather, there is probably a rigging issue that needs to be addressed or a poor design, but I stand ready to be edu-macated by the more erudite members of Sailnet.
|12-07-2009 11:09 PM|
Originally Posted by alman View Post
|12-07-2009 11:05 PM|
yes...many things...and we haven't mentioned proper tuning of the standing rigging, mast rake..etc
I think there's a lot more that goes into determining weather or lee helm than whether the boat is heeled over.
So my answer to the op's question would be.....it depends
|12-07-2009 10:50 PM|
Originally Posted by Faster View Post
|12-07-2009 10:45 PM|
|Garffin||Dang it I need pictures|
|12-07-2009 10:15 PM|
Originally Posted by jackdale View Post
|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.
|12-07-2009 10:02 PM|
|seabreeze_97||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.|
|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.
|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.
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