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AuthorMessage
treasure
treasure

Posted: Thu Aug 27, 2015 10:45am

Post Subject: Rudder Vibration

For the last 3 years I have tolerated varying degrees of vibration on the tiller of my 64ft boat. I did have the bottom skeg bush replaced and the top rudder bearing (nylon) replaced and it improved somewhat but didn't go away and it has now come back and the top nylon bearing is worn again. Next time I have the boat out of the water I want to investigate/eliminate the problem. Can you advise what the cause may be? I do wonder if the rudder stock is bent or the rudder design needs improving as when I look at other boats there seems to be no standard on how close the rudder gets to the propeller or what proportion of the rudder is in front and behind the rudder stock. I also recall some mention of tapering the front edge of the rudder.

Rudder Vibration
Tony-B
Tony-B

Posted: Thu Aug 27, 2015 7:49pm

Post Subject: Rudder Vibration

First of all we need to make sure the problem is not caused by trying to drive the boat too fast on shallow canals. If you do the prop wash can bounce back up from the canal bed and hit the rudder. Typically the balance (the part of the blade in front of the rudder stock) would be about 1/3 the area of the rear portion. On your boat it seem rather less than this. I suspect the back of the blade may be too long rather the the balance being too short. I also not the you seem to have a vertical blade between the prop and rudder. I have no idea it purpose but it moves the rudder rather further from the prop when compared with most boats. I think that you need to discuss and inspect this with the boatyard who take it out of the water, solving the vibration may turn out to be a very hit and miss affair. The only thing I can associate with tapering edges is on props to cure singing. However fitting a completely rudder design like a Schilling rudder would produce tapered leading and trailing edges but the the body of the rudder is much thicker than a simple plate rudder. This may or may not reduce the vibrations but would almost certainly be expensive to commission.

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