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

When will you remember the subject of the thread. Man are you dumb. the
discussion is about weatherliness (see the header). It's how close to
the wind can you sail anything that creates more lift helps. That's the
point.

Let me spell it out: We were not discussing VMG but weatherliness. Are
you finally admitting you don't understnad the difference?

Cheers



DSK wrote:


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.



When will you remember the subject of the thread.

Man are you dumb. The discussion is about weatherliness (see the header).
It's how close to the wind can you sail. Anything that creates more lift
at the tightest sheeting angle
helps. That's the point.

Let me spell it out: We were not discussing VMG but weatherliness.
Are you finally admitting you don't understand the difference?

Cheers

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.

It's not a racing question Doug.

In his second statement, he said
that the geometry was such that the rudder's lift produced torque. Do you know what
*that* means?

Are you saying that the keels lift does not?

Cheers

MC wrote:

... We were not discussing VMG but weatherliness.

Actually, we were discussing both.

Are
you finally admitting you don't understnad the difference?

Sure. I need a good laugh today, go ahead and explain.

DSK

DSK wrote:

MC wrote:


... We were not discussing VMG but weatherliness.


Actually, we were discussing both.


No WE weren't. Look at the thread title. I suggest the issue of VMG was
brought up to try to cover Matt's not knowing about rudder lift adding
to weatherliness.


Are
you finally admitting you don't understnad the difference?


Sure. I need a good laugh today, go ahead and explain.


At last! Go back and revise the thread. you'll get it eventually.