Vibrating rudder.

[CreakyDecks]

Last year I had a bit of a vibration in my rudder above a certain speed. I put it down to its loose bearings and made new ones. Unfortunately this hasn't solved the problem it has just moved it a bit. The tiller doesn't vibrate anything like as much but now the wooden blade vibrates in its housing and is much more noisy and annoying. At one particular speed it is louder than my outboard! Any suggested solutions would be welcome.

 

[aquaplane]

The bit that vibrates on my 20' boat when she starts going at a fair clip is the string that pulls the lifting rudder up.

What sort of boat? Transome hung rudder, I suspect not if you have bearings?

 

[CreakyDecks]

The bit that vibrates on my 20' boat when she starts going at a fair clip is the string that pulls the lifting rudder up.

What sort of boat? Transome hung rudder, I suspect not if you have bearings?

Jaguar 21, transom hung. When I said bearings I meant the plastic bushes that the pintles sit in. The wooden blade lifts vertically from an aluminium housing that the tiller is attached to.

 

[jimi]

I suspect sympathetic harmonic vibration with cavitation being one of the culprits. Perhaps smoothing and polishing may reduce cavitation and alter the harmonics?

 

[aquaplane]

Mine looks like this, the rudder is mounted in the stainles frame behind the outboard bracket:



I can put a bit of slack in the rope and the thrumming stops.

HTH

 

[ianat182]

If the vibration is at the higher speed when sailing the cause could be the trailing edge of the vertical rudder blade which although a good airfoil section needs a sharp breakway of the waterflow.This is usually achieved by planing a 3-5 mm rightangle flat at the trailing edge of the blade and stopps the humming sound and vibration; on a centreboarder the trailing edge of the keel would also benefit from this modification.


ianat182

 

[CreakyDecks]

If the vibration is at the higher speed when sailing the cause could be the trailing edge of the vertical rudder blade which although a good airfoil section needs a sharp breakway of the waterflow.This is usually achieved by planing a 3-5 mm rightangle flat at the trailing edge of the blade and stopps the humming sound and vibration; on a centreboarder the training edge of the keel would also benefit from this modification.


ianat182

So a sharp cut off is better than a rounded edge, which is what mine has?
I've not notice the lift keel vibrating, presumably because it is so much heavier and stiffer?

 

[ianat182]

Yep! The rudder may be being affected by the same conditions on the centreboard. Its a well known mod among dinghy racing fraternity!The relatively short chord width of the rudder being vertically mounted should work out . On the centreboard dinghies the part retraction of the board on reaches and near planing speeds alters both the chord ( and increases the length of the airfoil section, sometimes curing the humming which you can't replicate on your vertical blade.

ianat182

 

[William_H]

Rudder vibration

Almost anything you do to the rudder shape will change the nature of the vibration.
I would however reduce the slop in the rudder box. My rudder sits in a box but can swing back and up. I put a bolt through the back of the box and the rudder which has a big wing nut on it. I clamp this up until the rudder is tight in the box. This removes any free play. (this does make the rudder susceptible to damage from hitting things but with a keel a lot deeper than the rudder I have not had problems and no worse than drop rudder). I like a rudder that does not have free play but responds to nay movement not because of vibration. However this may fix your vibration. good luck olewill