I've got the shakes

[Guest]

 

 

Can anybody shed any light as to why I have got the shakes? The tiller on my boat has always had a slight shake from new when underway. Sorry the pics aren’t good, but maybe enough to form some opinions? I know little about rudders and suchlike.

 

Many thanks.

 

ps have searched but no results.

[Albion]

If the rudder stock bearings are OK then it might be a prop that hasn't got the same pitch on each blade. This can cause uneven thrust as each prop blade passes the rudder blade. Friends of mine have had this problem and had the prop re-pitched to correct it. Also, looking at your photos, the swim is very blunt ended. The bulk of the upper blade is masked by the blunt end of the swim. That will mean that two blades are relatively efficient (sitting in a clearer water flow) and one isn't. This will unbalance the thrust and could be a possible cause of your problem.

Roger

[blackrose]

If those bolts I can see in the pictures are the only thing holding the rudder onto the stock it could be that they've become loose or sheared.

I think the idea of that design is that you could take the rudder off the stock if you needed to while still in the water, but in practice I'm sure it would be impossible. When my boat was last out the water I put a bit of weld on the top and bottom of the stock where it meets the rudder to prevent the rudder from coming loose if those bolts ever sheared.

Edited September 11, 2009 by blackrose

[RobinJ]

Can anybody shed any light as to why I have got the shakes? The tiller on my boat has always had a slight shake from new when underway. Sorry the pics aren’t good, but maybe enough to form some opinions? I know little about rudders and suchlike.

How much play is there in the stock?

It could be the top bearing has gone, they tend to get a lot of water in and once they start to rust the 'balls' just wear away, leaving a gap between the two races! Unlikley if this has not changed from new!

Anything prop related will have an effect, chip, dent, plastic bag etc., introduces turbulance which will cause blade 'twitching', again unlikely if it was a new prop originally!

Finally there is very little leading edge on the blade, so any disturbance behind the stock will be amplified. Extending the leading edge increases the bight of the prop and helps prevent vibration.

I think the general concensus is no more than a third in front, two thirds behind?

[alan_fincher]

I'm not sure it has too much to do with "the shakes", but to my untrained eye...................

 

The rudder blade really does seem to have remarkably little leading edge. I would have thought that even hard over, a large amount of the prop remains "uncovered", so that an awful lot of the water thrusting backwards never get deflected by it. I'd there fore kind of expect it not to turn anything like as tightly as some boats.

 

Partly because of that very small leading edge, but not solely, the separation between prop and rudder looks very large to me. Not a lot you can do, other than increase the front bit, but even if it didn't solve the problem about which you are asking, I do think it would increase the effect of the tiller.

 

The tiller would almost certainly feel "lighter" with such a change, as at the moment when you swing it, you are trying to hold it against all the water it is deflecting on it's "big" side, but getting very little counter-balance by water pushing on the other.

 

But I speak only from opinion, not from any deep knowledge of such matters, so I'd not blame you if you ignored that lot!

[casper ghost]

I'm not sure it has too much to do with "the shakes", but to my untrained eye...................

 

The rudder blade really does seem to have remarkably little leading edge. I would have thought that even hard over, a large amount of the prop remains "uncovered", so that an awful lot of the water thrusting backwards never get deflected by it.

 

I agree. We work on a leading edge of a third the size of the rudder.

My friends boat had no leading edge and it was very hard to hold the tiller while going around tight bends.

Edited September 11, 2009 by casper ghost

[zenataomm]

I think the others are saying it but ...... you appear to have an amazing distance between the prop and the rudder. Plus there isn't much on the balance side of the rudder.

Kill two birds with one stone and bolt on a goodly length (technical term for an exact dimension) to the front of the rudder. If it doesn't work you can always unbolt it again.

[Guest]

Thanks everyone, will try an extension on leading edge when I drydock. There is little to lose

[Yoda]

Definitely put some leading edge on the rudder to make it more efficient but also check your prop blades for damage or distortion.

[WotEver]

... also check your prop blades for damage or distortion.

 

Good advice. When our boat was last out of the water for blacking and an insurance survey, the surveyor took one look at the prop and said "That's bent as a pig's ear; it needs replacing." I looked at it, the 'lad' who does the blacking looked at it, and the marina mechanic looked at it. We all said "Where?" Said surveyor pointed out one blade which, once my inexperienced eye looked closer, could be seen to be really very bent.

 

A couple of hundred quid later the boat was back in the water and it was transformed. Far less vibration, less 'wiggling' of the tiller, and less revs for the same speed as before. It must have been bent when we got her because she felt like a different boat with the new prop.

 

Tony

[ditchcrawler]

If the rudder stock bearings are OK then it might be a prop that hasn't got the same pitch on each blade. This can cause uneven thrust as each prop blade passes the rudder blade. Friends of mine have had this problem and had the prop re-pitched to correct it. Also, looking at your photos, the swim is very blunt ended. The bulk of the upper blade is masked by the blunt end of the swim. That will mean that two blades are relatively efficient (sitting in a clearer water flow) and one isn't. This will unbalance the thrust and could be a possible cause of your problem.

Roger

I think another friend of yours may have the same problem, I will measure the blade tips next year when I go in for blacking. Picked up a big bit of wood that wedged between blade tip and Uxter (spelling) plate, had to drive the prop round with the mooring hammer to free it.

Edited September 11, 2009 by ditchcrawler

[Guest]

Would the house agree that this rudder looks balanced?

 

Edited September 11, 2009 by Guest

[MtB]

Thanks everyone, will try an extension on leading edge when I drydock. There is little to lose

 

 

Don't add too much or you'll get the same problem we had, as discussed in this thread.

 

http://www.canalworld.net/forums/index.php...c=21994&hl=

 

Too much on the leading really messes up the behaviour of the tiller, and we had some metal taken off the leading edge of ours. The before and after photos at the end of the thread give a good idea of the proportions that worked and that didn't work (on our boat at least).

 

Cheers, Mike

[Guest]

Don't add too much or you'll get the same problem we had, as discussed in this thread.

 

http://www.canalworld.net/forums/index.php...c=21994&hl=

 

Too much on the leading really messes up the behaviour of the tiller, and we had some metal taken off the leading edge of ours. The before and after photos at the end of the thread give a good idea of the proportions that worked and that didn't work (on our boat at least).

 

Cheers, Mike

thanks for the useful link.

[zenataomm]

Would the house agree that this rudder looks balanced?

 

 

That anode needs a lot more bitumen on it or it'll just melt away!!!!

[alan_fincher]

Would the house agree that this rudder looks balanced?

 

Other than it appears to have a wooden notice fixed to it with a bungee strap that probably will not stay attached too long.

 

On the other hand, (even allowing for the angle of the shot) I'd say the prop-shaft is too long, resulting in the weight of the prop being on more unsupported shaft than is sensible.

 

I think previous threads concluded that the shaft showing between stern tube bearing and prop should not be more than about 1.5 times shaft diameter. I may have got that wrong, but I think that was consensus).

[ditchcrawler]

Don't add too much or you'll get the same problem we had, as discussed in this thread.

 

http://www.canalworld.net/forums/index.php...c=21994&hl=

 

Too much on the leading really messes up the behaviour of the tiller, and we had some metal taken off the leading edge of ours. The before and after photos at the end of the thread give a good idea of the proportions that worked and that didn't work (on our boat at least).

 

Cheers, Mike

We had the same problem.

[blackrose]

You say the tiller has always had a slight shake Catweasel, and most do simply because as the blades of a prop pass the rudder it exerts more force on it. Has the shake got worse recently? Presumably his rudder hasn't just lost 2 inches off its leading edge?

The first thing I would check is that those bolts are holding the rudder onto the stock securely.

Edited September 16, 2009 by blackrose

[Chris Pink]

Thanks everyone, will try an extension on leading edge when I drydock. There is little to lose

 

there is also a huge gap between rudder and propellor - i don't know what influence this would have but it don't look right - don't know what you could do about it though.

[robkg]

That anode needs a lot more bitumen on it or it'll just melt away!!!!

Have I missed a joke or are you genuinely suggesting the anode should be painted?

 

If you are then you are incorrect, once painted it will not work.

[Guest]

You say the tiller has always had a slight shake Catweasel, and most do simply because as the blades of a prop pass the rudder it exerts more force on it. Has the shake got worse recently? Presumably his rudder hasn't just lost 2 inches off its leading edge?

The first thing I would check is that those bolts are holding the rudder onto the stock securely.

Thanks I will try the welding thing when in drydock that you mentioned earlier, as it isn't brilliant just bolted. It has always had a slight shake to it,and I haven't noticed any worsening, it is just one of those jobs that I haven't got around to yet

[casper ghost]

Thanks I will try the welding thing when in drydock that you mentioned earlier, as it isn't brilliant just bolted. It has always had a slight shake to it,and I haven't noticed any worsening, it is just one of those jobs that I haven't got around to yet

 

They've a novel way of removing tiller shake up here in Ellesmere

[robkg]

Would the house agree that this rudder looks balanced?

 

 

My boat has a smaller leading edge and functions fine, although I guess there is a range rather than an exact dimension that will work.

 

 

[Guest]

there is also a huge gap between rudder and propellor - i don't know what influence this would have but it don't look right - don't know what you could do about it though.

I agree the gap is larger than normal. The fuel tank is deep which pushes the weedhatch well forward from the rudder tube. This in turn makes the swim to rudder stock quite long. Can't really lengthen the shaft cause that is not good I am told. Instinct tells me that the gap will reduce thrust on the rudder and that a larger rudder area will be required. I should add that my instinct is often wrong. Funny thing is that the boat handles quite well and reverses reasonably in NB terms. Will definitely increase the area especially the balance, and weld the stock to the blade as Blackrose suggests. Can't see it doing any harm.

[Yoda]

I agree the gap is larger than normal. The fuel tank is deep which pushes the weedhatch well forward from the rudder tube. This in turn makes the swim to rudder stock quite long. Can't really lengthen the shaft cause that is not good I am told. Instinct tells me that the gap will reduce thrust on the rudder and that a larger rudder area will be required. I should add that my instinct is often wrong. Funny thing is that the boat handles quite well and reverses reasonably in NB terms. Will definitely increase the area especially the balance, and weld the stock to the blade as Blackrose suggests. Can't see it doing any harm.

 

Increase the area of the rudder forward and then run it just in case its worse. Don't weld something that might have to be dismantled.