I have a bit of a problem with vibration in my rudder largely created by the prop wash I believe. It hits the trim tab and causes it to vibrate and I get a bit of an annoying rattle when the boat gets up to speed. I usually will have the trim tab in the locked position.
When the boat is under the wind vane sail I don’t get the same effect, and also when it is controlled by the tiller pilot. Does anyone else have this problem and a solution.
I think Rod’s trailing email (circa 2002) which includes .input from Roger Olson reflects my experience perfectly!
Re: Xiphias Style Windvane
Posted by: tibetanmoon (IP Logged)
Date: August 23, 2002 07:25PM
Category: Autopilots and windvanes
I should have done a seach on the discussion forum before I posted by
question about the windvane. Roger Olson wrote the following
sometime ago:
"
First, I added about 10 % to 15% of the trim tabs surface area to the
leading edge to help balance it. Mike Anderson of Freehand Steering
and I have worked this out pretty good. The older or original trim
tabs had the leading edge go the full length of the trim tab. This
caused severe vibration under power because of the erratic prop
wash. If the additional area is added as low as possible will help
reduce this problem…I don’t know the actual numbers in my head but I
guess it is about 1-1/2 to 2" deep and about 8" to 10’’ long. First,
I removed any leading edge that now exists. Then add the piece at
the bottom by drilling and tapping into the shaft. If you do this
make out of teak and a little more that 20% so if it is over balanced
(oversteers) some can be planed off until you get exactly what you
want. For more details on actual size email Mike at Freehand
Steering. I just discovered I don’t have the address but I think he
subscribes to this group.
You used the term vertical shaft, I presume that you did not mean
vertical because it has to go at quite an angle to the aft end of the
rudder. The shaft axis must meet the rudder’s pintle axis where the
adjusting arm is located. I don’t think this is an issue but if it
is let me know and I will give you more detail.
To reduce friction on the trim tab I discovered that by making the
bottom gudgeon a blind hole instead of a through hole really helps.
Let me explain. I had the bottom gudgeon counterbored for a blind 1"
hole. Inside the hole I place a 1/8" to 1/4" flat delrin or teflon
disc followed by a 1" OD x 3/4" ID bushing. I cannot remember the
type of bushing but if you have access to a McMaster-Carr catalogue
you will find the ones with the minimum friction that is not effected
by emersion in water . Delrin will work but not as well as this
bushing… I can’t remember. I use the same bushing inside the
middle and upper trim tab gudgeon. Now the problem is that the trim
tab can come out of this bottom bushing when you don’t want it to.
Also at McMaster-Carr they have a 3/4" stainless steel split collar.
I place this collar directly under the upper gudgeon so the shaft
cannot be raised without removing this collar. It also makes it
possible to remove the trim tab without getting wet. Just remove the
collar, lift the trim tab shaft until it clears the bottom gudgeon
then shove the shaft down until it slips out of the middle gudgeon.
It does take a little effort to miss the bottom gudgeon but not a
problem
The major problem with the windvane on a pedestal is to reduce
friction and the ease of making adjustments. I don’t feel it is
necessary to discuss how to reduce friction but it must be free.
Unlike what some people believe, a loose fit does not create less
friction than a good fit. Personally, I like a clearance of about 2
to 5 thousands between shaft and bushing. However the bushing should
not swell as delrin will. So if using delrin use .005 clearance.
I found the vane really worked well in most all conditions…if the
sails are properly balanced and the friction is reduced. After I
worked extensively to reduce friction and took out the major weather
helm the vane would steer downwind in 5 knots of wind. Also, the
friction in the trim tab is only as good as the friction on the
rudder gudgeons and pintles. The trim tab steers the rudder so if it
is not really free it will not work as well. Again I want to
emphasize that a loose fit is not as good as a close fit.
I also found that there has to be some kind of locking device for the
trim tab when motoring or backing. I also did not like the original
clamping design because: It would slip in rough conditions and it had
to be adjusted by climbing out on the boomkin. I designed a
different method that I could adjust from the cockpit. I have
drawings of it at work but it is a little complex unless you have
access to silver solder or oxyacetylene. If you want me to try to
explain it in writing let me know and I will try. Perhaps you are
happy with what you have or may even have a better design.
Lastly, and again I am sure I am saying something you already
know…I found that by using the cheapest autopilot on the trim tab
works perfectly with the minimum of current draw. On my new boat, I
hardly ever use the vane anymore because the autopilot is so
effective and efficient.
The only limitations I found with this vane is:
It creates more of a load on the tiller when hand steering because of
the additional surface area aft of the rudder. However it is this
distance and surface area that gives the vane soooo much power to
drive the rudder…
There is a real heavy load in reverse unless the trim tab can rotate
360 degrees freely. Something I cannot not do now so I have a lock
There will always be some vibrations when motoring at higher RPMs
It is susceptible to damage when going aground.
Don’t hesitate to ask anymore questions, I have nothing but time
right now."
I will discuss an improved clutch design with Roger, as I believe
this style windvane is in limited use.
Sorry about my earlier message.
Rod