Ok -- I can verify this theory as well. It's been blowing 25kts+ the last few days, so I've just been running a fores'l and stays'l -- CoE has got to be forward of the centerboard -- and low and behold, I still experience slight weather helm at least when gusting. So, who knows weather helm and The CoE/CLR relationship might be unrelated after all...

A pic of Valora under fore and stay only:

[sphotos.ak.fbcdn.net]

--
Ben Eriksen
BCC #91 Elizabeth

Web Design | BCC Elizabeth

Boat designer build in CE lead in relationship to the CLR to counteract turning moment caused by the CE being outside the center line of the boat when the boat is heeled. Suggest you read Helm Balance, p92 in Ted Brewer's book Understanding Boat Design.

If a boat has too much lead, it will have lee helm. The amount of CE lead in relationship to the CLR is very much dependent on the boat design and the experience of the designer. As a boat heels the CE moves outside the boat causing it to turn into the wind. As an example, with one finger on the point of a pencil hold the pencil vertical with the eraser on a flat surface. Assume the lettering is forward. Move the tip of the pencil forward. If this were a mast, the bow would dig into the water - downwind spinnaker runs. Now heel the pencil and ensure the eraser end can not slide on the surface with your free hand. Now push the pencil forward at the tip. The pencil tip will move in a circle toward the weather side of the boat. This assumes the pencil is directly above the CLR. To counter this turning moment, designers build in lead (lee helm) by place the CE forward of the CLR. Normally, This would cause lee helm. By placing the CE forward of the CLR, the boat has neutral helm until the heel angle increases to the point where induced lee helm caused by the lead can no longer counter the turning moment caused by the centered CE being outside the boat. If boat does not have enough lead, it will develop weather helm early and if it has too much lead, it will develop lee helm.

In the late 40's and early 50's, one yacht designer, designed custom cruising boats with two centerboard keels - one aft and one forward the CE. By raising and lowering the boards, one could move the CLR in relationship to the CE, thus balancing the boat in all wind conditions and angles of heel.

This is all I will write about the subject. This subject is covered extensively in Brewer's book and Greene's book Cruising Sailboat Kinetics.

Cheers,

BCC IDUNA

I think your sail plan image might provide the answer.

The CoE of the new jib is lower, and the foot of the new sail is considerably lower, therefore, the CoE on the new sail seems to be forward and lower.

A line drawn between the clew and the midpoint on the forestay will indicate the CoE.

In a wind, and assuming a 15 degree list, the jib will "throw away" effort from the top of the sail, so the lower the foot, the more power the jib will retain.

The attached image is extremely rough,I didn't take exact measurements,

John Cole
[www.coledata.com]

Thanks John, what you say is the direction I am leaning. But it does seem like a lot of change for the difference in CoE. The compariosn sail will tell the tail.

Gary Felton
S/V Shanti
US Virgin Islands
[www.yacht-photography.net]

Thanks Rod,
I think what may be happening is the new sail has moved the CoE to far forward, as John mentioned. I must have reached a breaking point between lee and weather helm. the result was way to obvious. My first thoughts were the obvious, which was the trim point. But that seems to be only a by product of the new sail and not the cause.

I will purchase the books you recommened.

Thanks,
Gary

Great thread and discussion! I may be on the verge of discovering why my boat moves.

Tom
"Terrier" #31

Tom:

Boat are propelled by "The Force" and we only hoist sail to look good :-)

On Fri, Aug 6, 2010 at 6:25 PM, BCC Forums <bccforums@samlmorse.com> wrote: