tiller/rudder vibration

[smeaks]

I have just taken on a new boat and during the shake down sail I notice a "chatter" vibration on the rudder. This can be severe and I only noticed at higher speeds, turning at full lock or with a lift off a following sea. I think it must be a resonant thing with the flow over the rudder, has ayone experience of this? and can it be sorted by adding a change of section across the rudder surface to move the resonance of the rudder ie screwing a flare to the rudders trailing edge?

 

[Sailfree]

What boat? had this once with a 38' Dufour but fixed under warantee with new bearings.

 

[Lakesailor]

Mine does that. Previous owner made a replacement blade and didn't shape the leading edge at all so I'm guessing that's the problem. I may do it one nice summer's day, but it doesn't worry me.

 

[smeaks]

this is a replacement also and is not shaped very much at all.. think your right... a job with the power plane next winter?

thanks

 

[Pye_End]

Met a boat in Calais last year which had developed this fault. Was very bad under power, and they had to go back home to come out and get it sorted, else they found steering in a marina near impossible. Wasn't loose engine or anything fouling the prop of sterngear. Didn't find out what it was, but guess it was a loose rudder bearing.

 

[Lakesailor]

I'm on gudgeons and pintles, so I know they're OK.
One thing I haven't checked is whether the offset outboard trailing in the water alongside the rudder has an effect.

 

[Birdseye]

I thought that all boats did it to a greater or lesser degree. certainly I've read of racing boats surfing down a wave vibrating, and my cruising boat does it a bit.

I always thought that it came about when speed reached the point that laminar flow left the rear quarters of the hull and you got turbulence over the rudder. Made worse by badly shaped rudders / hulls, and by turning sharply

Mind you, thats not based on any great knowledge of the subject so I'm probably not right /forums/images/graemlins/ooo.gif

 

[Lakesailor]

It may be. I'm a little cautious about re-shaping the leading edge of the rudder as it performs very well in other respects. It has little weather helm, which I know is a product of many other apsects of set-up, but is also a lot to do with balance, and it also grips the water for a long time, to acute angles of heel. I would be a bit annoyed if changing it's shape altered its splendid performance.

 

[smeaks]

I agree reshaping is a major change that is not easily reversed. I thought about cutting a half round out of a wooden rod and screwing it to the leading edge to make a smoother entry edge. If it worked - problem solved- if not it would be quick to take off

 

[savageseadog]

Could be the propeller if it's not a folding one. Other than that the bearings.

 

[wizard]

Could you state the type of boat, keel that you have and if the prop is fixed or folding and also if 2 or 3 bladed. This will help the general diagnoses.

 

[smeaks]

ok... she a 22 ft marcon striker, fin keel, two blade fixed prop - at last count!