Fitting an eliptical rudder to Fenn elite SL - new rudder vibrates

2 months 1 week ago #36544 by Lencioni
Hi,
wondering if anyone can help or has any experience here. I have attached the photos of my old sharkfin/surf rudder on my fenn elite sl. This rudder worked great but got a bit old so I ordered a new elliptical shaped rudder from our local fenn dealer. They said that this was the correct rudder for the fenn elite sl (2014 model approx. I dont think they built many of these).
The new rudder fitted fine and the shaft length was correct leaving only about 1-2mm of play once tightened up. However it vibrates like crazy! I can feel it on the foot pedals as soon as I get to 10km/h. I can even hear it.
From the pictures you can see that the interface of the rudder to the boat is quite different from my old rudder. The new rudder seems to have a large gap at the back. 
Anyone had any experience with this? 
Thanks in advance.
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2 months 1 week ago #36546 by Bill L
I am not sure why it would flutter, especially if the rudder is made for that ski. I kind of doubt the gap would cause it, but, anyway, you can fix that fairly easily.

Hold the rudder shaft in a vise with about 1/2" to 1" left out (between the blade and the vise). Grab the blade with two hands and GENTLY bend it a tiny bit in the direction to add/subtract gap. Do it very carefully, stopping and fitting the rudder back on the ski after each tiny bend attempt.

If you do it too hard or too much at one time, you could break the blade from the shaft; however, I have done it several times and have never had a problem.  Just go real slow and keep checking after each small bend.

I would be interested to hear if changing the gap stopped the flutter.

Bill L

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2 months 1 week ago #36547 by zachhandler
I don’t know if the gap causes the flutter or not. But if you want to close the gap another method I have used is to wrap masking tape around the top edge of the rudder. This creates a shallow pool that you can pour epoxy into. You can angle that wall as needed so that the fill will match the profile of the hull. Some times a little sanding is needed to fine tune it afterwards. I have never damaged the rudder using Bill’s method, but i have introduced slight bend in the shaft which then does not spin as freely in the rudder tube. 
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2 months 5 days ago #36556 by Lencioni
Thanks for the info. I will try the epoxy method first and see how it goes. 2 very helpful replies.

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2 months 5 days ago - 2 months 5 days ago #36557 by Jimi
Another option is to file the leading top edge of the rudder in front of the shaft down about 1.5 mm. then place a washer between the top of the rudder tube and yoke plate. You do want a bit of space between the back of the rudder and the bottom of the boat. this way if you hit something and bent the rudder you won't punch a hole in the boat.

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2 months 4 days ago #36560 by Ranga
Forget about the epoxy to fill the gap, the shaft is very soft and can be straightened on the ski. This is a very minor bend, it will take you a few seconds to rectify as opposed to trying to do an epoxy repair.  Just hold the ski down, even tied on the car will work well, rotate rudder about 30 deg from centre and apply a bit of force forwards and it will be sorted. Obviously if you have a vice available it will be a better option as mentioned before.
 

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