[Rhodes22-list] how straight does a rudder need to be?

[Roger Pihlaja]

Hi Mary Lou,

You didn't say which direction your rudder blade is tilted.  So, I assumed
the lower tip of the rudder blade was tilted towards the starboard side as
viewed from behind the boat.  Then, I analyzed the forces & resulting
torques that would be generated as a result of that rudder blade tilt and
compared them to the forces & resulting torques generated when the rudder
blade is not tilted.

Viewing the entire hull from above, the tilted rudder blade generates a
small net clockwise torque relative to the untilted rudder blade.  This will
cause the bow of the boat to have a tendency to turn towards starboard.   On
starboard tack, this would be weather helm.  On port tack, this would be lee
helm.  The boat will turn more easily to starboard than to port.

If the rudder blade is tilted in the other direction; then, all the above
comments would be reversed.

So, if the rudder blade is tilted to starboard as described above; then,
"fixing" the misalignment in the mounting gudgeons will reduce your problem.
If the rudder blade is tilted to port; then, realigning the mounting
gudgeons will probably make the problem worse.

Hope this helps, Mary Lou.

Good luck!

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Mary Lou Troy" <mltroy at verizon.net>
To: <rhodes22-list at rhodes22.org>
Sent: Sunday, January 02, 2005 8:45 PM
Subject: [Rhodes22-list] how straight does a rudder need to be?


> Happy New Year!
>
> Can you all stand to think about our starboard turning boat again? (There
> is a quick recap below if you don't remember the issue)
>
> We didn't get a chance to try any of the in-water tracking tests
previously
> suggested but we've done a fair amount of measuring of the boat on the
> trailer. We can't detect any asymmetries in the hull but did come up with
a
> slight asymmetry in the mounting of the gudgeons for the rudder. Our
> question is: is the variance enough and in the right direction to cause
the
> boat to consistently want to turn to starboard? We don't want to "fix" it
> and have the boat turn more strongly to starboard.
>
> The situation is that the upper gudgeon appears to be centered and the
> lower gudgeon is 5/16" off-center. This causes a slight slant to the
> rudder. The lower tip of the rudder is about 1" off of center. Is this
> enough to cause the observed turning to starboard?
>
> Thanks again
> Mary Lou
> 1991 R22  Fretless
> Ft. Washington, PA /  Swan Creek, MD
>
>
> Here's the summary of the posts from earlier this fall:
>
> We've had lee helm issues with Fretless since we got her. The learning
> curve learning to sail her and the fluky wind and current conditions on
the
> Chesapeake have slowed us down diagnosing the problem.
>
> She has always sailed better on starboard than on port. When we set her up
> this spring we lengthened the forestay and took up the backstays. In a
nice
> breeze with a full main and genoa this gave us a small amount of weather
> helm on starboard and less lee helm on port. It also made us really pay
> attention to the difference between her behavior on port and starboard.
>
> Roger mentioned looking at how she sits on her lines and indeed she does
> have a slight list to starboard sitting in the slip (in spite of the
> outboard, 7 gallons of gas and the battery all stored to port. Bill Effros
> said he thought that if the boat was too heavy to port it would turn to
> starboard. These two thoughts seem to contradict each other but we'll work
> a bit more on her trim.
>
> Bill & Slim mentioned heel as a contributor to weather helm but I think we
> heel about the same on port and starboard. Those fluky winds make it hard
> to tell.
>
> Jim Connolly mentioned a similar port/starboard problem but then mentioned
> that he thought he had a spreader problem that might be contributing. As
> near as I can tell, our mast is straight and centered. We tune the rig
with
> a Loos gauge and have measured with a halyard to the chainplates. We'll
> take a look at the spreaders though.
>
> Lastly, Steve and Slim mentioned that maybe something was out of whack
with
> the keel, the centerboard or the rudder. We've taken a look at those
> possibilities. There's nothing immediately visible with the keel or the
> rudder. The centerboard drops cleanly and does not bind or thump about
> significantly but we've never taken a really good look at it. Fretless has
> an unusual repair (?) to her centerboard trunk (there is a flat plate
> glassed over the forward part of the trunk - between the trunk and the
> centerboard cap) that prevents us from removing the centerboard in the
> usual fashion). Raising and lowering the centerboard has no effect on her
> tendency to want to turn to the right.
>
>
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