Matt Colie wrote:

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.

So now we agree.

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 think you've evaded the point. Of course the keel provides most of the
lift but the rudder dfoes add some -right? Remember even a small gain
wins races to windward!

Cheers MC

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