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

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

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

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

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.

MC wrote:
So now we agree.

Funny... do you realize what he's saying, MC? In any case, it does not "agree"
with your earlier statements.

Matt is exactly right, that lift comes at the cost of drag, and weather helm can
easily cost more in speed than it gains in reducing leeway. The usual figure
given as max desirable weather helm is 2 degrees, which ain't much.


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!

Really? You can state this from personal knowledge? How many races have you won,
MC? IIRC the last race you mentioned, you dropped out and ruined your dinghy
motor. Does dragging a dinghy upside down improve pointing?

DSK

DSK wrote:

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.

MC wrote:
So now we agree.


Funny... do you realize what he's saying, MC? In any case, it does not "agree"
with your earlier statements.


Yes he does, he now agrees that the rudder gives lift with weather helm.
Read it again carefully.


Matt is exactly right, that lift comes at the cost of drag, and weather helm can
easily cost more in speed than it gains in reducing leeway. The usual figure
given as max desirable weather helm is 2 degrees, which ain't much.


Of course, we all know lift always comes at the expense of drag! The
real issue is why might lift from the keel be more efficient than that
of the rudder?

Since the question was weatherliness and not speed, the increased drag
may be acceptable.

You probably don't know this but tests with a full size boat showed that
having two rudders and no fin keel per se. produced some real benefits
in windward work but it was at the expense of complexity and diffuclty
in control.




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!


Really? You can state this from personal knowledge? How many races have you won,
MC? IIRC the last race you mentioned, you dropped out and ruined your dinghy
motor. Does dragging a dinghy upside down improve pointing?


We weren't racing -when racing we don't tow a dinghy do you? Where do
you get your strange ideas?


Cheers

MC wrote:

Yes he does, he now agrees that the rudder gives lift with weather helm.
Read it again carefully.

*You* read it again carefully, stupid.

What Matt said was the the drag caused by the rudder angle was more of a penalty on
forward velocity than the lift was a gain in VMG. In his second statement, he said
that the geometry was such that the rudder's lift produced torque. Do you know what
*that* means?

DSK