Strangly,
That is not at quite what the towing tank data work here says.
For a conventional vessle sailing in moderate conditions with a slight
weather helm (Ra 3).
Yes, the rudder has a lift component to weather and it is most typically
below the center of bouyancy.
If the rudder provided significant hydrodynamic lift and the keel did
not: then the foil section for the keel would have no advangage and
vessles otherwise equal varying only in draft would be substantially
equal performers. I can demonstrate that this is not the case.
Also: the only attack angle control for the keel would be the slip angle
(leeway) and this is negative, so there would be no value in trying to
use boat speed to reduce the slip angle.
Matt Colie (see prior sigs)

MC wrote:
No, I'm afraid you are wrong. The turning moment which causes the boat
to heel has a component to windward. If the rudder is neutral it adds no
lift of couse and is simply feathered in the water flow. Perhaps you
might like to consider the rudder as a wing: the angle of attack to the
water flow causes lift (and drag)?

Cheers



Matt Colie wrote:

Close, but not quite the case. The rudder can not provide any
significant lift on its own.
Any rudder angle adds drag and any rudder angle effects heal. Rudder
to correct weather helm increases healing monemt.
What is really happening is that the weather helm introduces an attack
angle for the keel. What you actually want to do is set the boat up
to balance with a heading that is a little higher than desired course.
When the rudder brings the track back to course, you are left with the
foil (keel)at a small attack angle. This works on all hulls, but is
most apparent on fin keel boats.
Matt Colie -www.yachtek.com


Martin Baxter wrote:

MC wrote:

DSK wrote:



while most should know that the rake of the mast affects C of E and the
degree of weather helm, I'll guess that many do knot know that by
giving
the boat some weather helm she climbs to windward better as the rudder
adds lift.





I believe this to be true for full keels, but how does it work with a
fin keel?

Cheers
Marty