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Rudder judder


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Can anyone suggest how I might cure the annoying judder I feel through the tiller on my 19 year old NB.

 

Based on a then budget priced hull by Eastwood Engineering I fitted it out from a bare shell so know it's history inside out.

 

From new there was a discernible but tolerable judder that I accepted and lived with. Over the years this seemed to get a little more obvious but still acceptable. About 4/5 years ago I caught the skeg on a cill (he moves on quicklysick.gif ) after which the judder all but disappeared. Whilst there was no visible damage it was obvious that something had been bent slightly. About 2 years ago the top bearing, a taper roller in a casting broke up and was replaced. Obviously whilst the bearing was failing the judder returned. After replacement the judder remained. Last autumn the bottom cup was replaced. I also had the prop trued and balanced by Crouthers. At the time I measured the various clearances ie blades to uxtur plate, prop blades to rudder blade, boss to swim clearance and blades to skeg and confirmed with Crouthers that they were 'normal' I also confirmed that the prop 17"" x 12" was correct for my BMC 1.8 / PRM150 (2:1) set up. I don't know ratio of blade in front / behind the rudder shaft but it looks much the same as others I've seen. Also it is vertical not raked. None of last autumns work improved matters. If anything it is now worse.

 

 

Any opinions welcome

 

 

Frank

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I have had 12 years of rudder judder on our boat; did it from new. I am convinced that the rudder assembly is too light. I cable tied some weights to the swan neck as a test and it did have a damping effect and partly cure it. I intend to make a rudder out of much thicker plate but it is one of those "round to it" jobs. Another possibility once suggested by a member was to bolt a large anode to the rudder blade.

If it was a motorbike shaking its head I would stick a hydraulic steering damper on it.

Edited by Guest
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I just saw your problem about rudder judder. Have you tried relocating the bearing into a slightly different postion and then rebolting it back down again. Do not let the top bearing take the full weight of the tiller & rudder, it is only there to stop tiller waggling about and is not to aid powered steering. Sometimes as the rudder rotates and the prop is cavitating at a certain rev you will get a judder at a certain speed. Nobody will admit it but all boats have somesort of vibration somewhere.

 

Also pump some grease into the top tiller bearing sometimes helps.

 

It sounds like you have had some wear in the rudder for a while and catching the skeg has bent the alignment. Also when you had the bottom cup replaced was in the exact position as before. It maybe that the bottom cup being new will be tighter and all these little adjustments will affect it underway. I had a rudder pin replaced some years ago and it was fine out of the water but once back in the rudder jammed up and i could not move it and it had to be re-docked.

 

hope this helps

 

Regards

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When I had a new cup fitted last year the pin on the bottom of the rudder had worn quite oval even with a non-ferrous bust in the cup. As yours didn't do it from new something, like wear over the years must have caused it. if it was worn then cilling it may have moved the skeg and made it run tight for a bit so improving it.

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When I had a new cup fitted last year the pin on the bottom of the rudder had worn quite oval even with a non-ferrous bust in the cup. As yours didn't do it from new something, like wear over the years must have caused it. if it was worn then cilling it may have moved the skeg and made it run tight for a bit so improving it.

 

When I had a new cup fitted last year the pin on the bottom of the rudder had worn quite oval even with a non-ferrous bust in the cup. As yours didn't do it from new something, like wear over the years must have caused it. if it was worn then cilling it may have moved the skeg and made it run tight for a bit so improving it.

 

 

I have had 12 years of rudder judder on our boat; did it from new. I am convinced that the rudder assembly is too light. I cable tied some weights to the swan neck as a test and it did have a damping effect and partly cure it. I intend to make a rudder out of much thicker plate but it is one of those "round to it" jobs. Another possibility once suggested by a member was to bolt a large anode to the rudder blade.

If it was a motorbike shaking its head I would stick a hydraulic steering damper on it.

If I face the stern, grasp the swan neck firmly and pull this does reduce the juddering somewhat.

 

Sounds like you need to take an inch or more off the front edge of your rudder.

I thought of welding / bolting a strip on the trailing edge

 

I just saw your problem about rudder judder. Have you tried relocating the bearing into a slightly different postion and then rebolting it back down again. Do not let the top bearing take the full weight of the tiller & rudder, it is only there to stop tiller waggling about and is not to aid powered steering. Sometimes as the rudder rotates and the prop is cavitating at a certain rev you will get a judder at a certain speed. Nobody will admit it but all boats have somesort of vibration somewhere.

 

Also pump some grease into the top tiller bearing sometimes helps.

 

It sounds like you have had some wear in the rudder for a while and catching the skeg has bent the alignment. Also when you had the bottom cup replaced was in the exact position as before. It maybe that the bottom cup being new will be tighter and all these little adjustments will affect it underway. I had a rudder pin replaced some years ago and it was fine out of the water but once back in the rudder jammed up and i could not move it and it had to be re-docked.

 

hope this helps

 

Regards

Tried loosening the casting carrying the bearing but there's no play and I'm wary of elongating the holes at this stage. Loaded the bearing with grease before assembly and pumped grease in via the nipple using my trusty Wanner 315 grease gun. The lower cup was positioned so that there was the minimum of play between it and the lower pin

 

When I had a new cup fitted last year the pin on the bottom of the rudder had worn quite oval even with a non-ferrous bust in the cup. As yours didn't do it from new something, like wear over the years must have caused it. if it was worn then cilling it may have moved the skeg and made it run tight for a bit so improving it.

It did judder from new it's just that it seems worse since the lower cup was replaced.

Just to clarify. It's always juddered. It improved after the cilling. It got worse as the top bearing broke up. After the top bearing was replaced it juddered to the same extent as it did pre cilling. Since the bottom cup was replaced it still judders

 

Sorry if I've repeated ditchcrawlers comments several times

 

 

Frank

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I suspect the bottom pin is loose in the cup. As has been mentioned a new cup removes 'cup wear' but doesn't address 'pin wear'. Next time the boat is out of the water grab hold of the rudder and see if you can rattle the pin in the cup.

 

It fits all the symptoms you've described (including the cilling).

 

Tony

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I cannot see how you will ever get rid of tiller judder. Everytime the propellor vane comes inline with the rudder it will send a slightly stronger pulse of water past the rudder. Each time a gap between the prop vanes is inline with the rudder then the water pulse will weaken. Next prop vane will cause a stronger pulse and so on . I know all this happens quite quickly even so it must cause a little bit of judder. Your tiller cup and the tiller bearing/s will wear over time and this will exacerpate the judder. The OP says that there was always a smal amount of acceptable judder from new. Ways to reduce it, replace the tiller cup on the skeg. Renew the bearings at the top and bottom of the tiller tube if you have them and fit a prop with more vanes.

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If it 'rattles', i.e. metal on metal then you have play in the top or bottom cup/bearing.

If when you are tied up with engine off you give the tiller a good shaking you might feel or see what moves.

If that all seems ok then it might be water from the prop thumping the rudder in which case what Matty says could be worth a try, take a bit off the leading edge. I suppose making the rudder heavier would damp it a bit, narrowboat rudders are pretty crude affairs, you could run it in gear whilst tied and see if holding the rudder with the hook shaft stopped it shaking, one of those annoying things with no obvious cure I think.

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I cannot see how you will ever get rid of tiller judder. Everytime the propellor vane comes inline with the rudder it will send a slightly stronger pulse of water past the rudder. Each time a gap between the prop vanes is inline with the rudder then the water pulse will weaken. Next prop vane will cause a stronger pulse and so on . I know all this happens quite quickly even so it must cause a little bit of judder. Your tiller cup and the tiller bearing/s will wear over time and this will exacerpate the judder. The OP says that there was always a smal amount of acceptable judder from new. Ways to reduce it, replace the tiller cup on the skeg. Renew the bearings at the top and bottom of the tiller tube if you have them and fit a prop with more vanes.

Others have said that to me, but none at all on our first narrowboat.

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I suspect the bottom pin is loose in the cup. As has been mentioned a new cup removes 'cup wear' but doesn't address 'pin wear'. Next time the boat is out of the water grab hold of the rudder and see if you can rattle the pin in the cup.

 

It fits all the symptoms you've described (including the cilling).

 

Tony

Checked the cup against the pin at several points of the compass and there was very little free play with no apparent ovalling (is that a word?) Didn't think to check it with a vernier

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Checked the cup against the pin at several points of the compass and there was very little free play with no apparent ovalling (is that a word?) Didn't think to check it with a vernier

Yes that's a word :)

 

So... if it's not wear then I guess increasing the rudder mass is the simplest way forward.

 

Tony

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Thanks to everyone for their contributions and observations.

 

As soon as I get the engine re-assembled (currently in middle of cylinder head, injector pump / injectors overhaul) I intend to have the boat out of the water again. I'll cover all the suggestions repairing / replacing anything in the least suspect.

 

The only thing I'm not sure about is cutting a bit off the leading edge of the blade. Don't know if doing that or adding some on the trailing edge is the way to go. Have thought about bolting a strip on the trailing edge that I could unbolt again whilst in the water but doubt that I could reach

 

 

Thanks

 

 

Frank

 

.

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One other thought: after a change of gearbox to a different type which was a couple of inches longer, the prop ended up a couple of inches nearer to the rudder (and quite a long way back from the swim). We had a bit of judder for a while, then we had a couple of inches sawn off the inboard end of the shaft so we could slide it back in to its previous position and the judder disappeared.

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. Have thought about bolting a strip on the trailing edge that I could unbolt again whilst in the water but doubt that I could reach

 

 

Thanks

 

 

Frank

 

.

That is exactly what I did, but it has to be inline, if you bolt it on one side it will make it pull one way

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I cannot see how you will ever get rid of tiller judder. Everytime the propellor vane comes inline with the rudder it will send a slightly stronger pulse of water past the rudder. Each time a gap between the prop vanes is inline with the rudder then the water pulse will weaken. Next prop vane will cause a stronger pulse and so on . I know all this happens quite quickly even so it must cause a little bit of judder. Your tiller cup and the tiller bearing/s will wear over time and this will exacerpate the judder. The OP says that there was always a smal amount of acceptable judder from new. Ways to reduce it, replace the tiller cup on the skeg. Renew the bearings at the top and bottom of the tiller tube if you have them and fit a prop with more vanes.

Make the rudder as an airfoil, for slow canal boats the turning is the most important, so a thick schilling type rudder work the best. can be up to 25% thick, at 20% of the chord (length)

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Make the rudder as an airfoil, for slow canal boats the turning is the most important, so a thick schilling type rudder work the best. can be up to 25% thick, at 20% of the chord (length)

When we were on holiday in Norway I spotted this on a Lifeboat rudder, just a piece of angle welded on the trailing edge of a plate rudder

post-261-0-46139000-1460814558_thumb.jpg

post-261-0-21248500-1460814569_thumb.jpg

Edited by ditchcrawler
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That piece of angle iron on the back of the rudder is intended to give the boat a bit more ability to turn, as it starts to turn it deflects the water a few degrees more than the main part of the rudder, its not an airfoil like Daslandias Schilling rudder but its probably a bit of an improvement on a flat slab of steel, dunno how effective it is, probably wouldn't make any difference to rudder vibration. Theres lots of lovely equations and theory on this sort of thing of which I understand not a jot.

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That piece of angle iron on the back of the rudder is intended to give the boat a bit more ability to turn, as it starts to turn it deflects the water a few degrees more than the main part of the rudder, its not an airfoil like Daslandias Schilling rudder but its probably a bit of an improvement on a flat slab of steel, dunno how effective it is, probably wouldn't make any difference to rudder vibration. Theres lots of lovely equations and theory on this sort of thing of which I understand not a jot.

Same here,as its so simple I was going to give it a try

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  • 5 years later...

I don't have to much experience of narrowboat rudders but I have built wooden boats in the past. The rudder alignment is very important. Make sure the hull is as level as possible. Then hang a plumb Bob (weight attached to a bit of string) and it will show you how far out the rudder is. Adjust so it is perpendicular to the hull and there should be less vibration. Creating a rounded leading edge and tapered trailing edge might help as well. Also weed and build up of blacking won't help. Rudder rake fore and aft controls feel. A vertical rudder will be a light feel. Rake it aft for more if a weighted feel. Also the rudder position relative to the prop wash turbulence will affect things. Cheers

 

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48 minutes ago, Paul Lester said:

I don't have to much experience of narrowboat rudders but I have built wooden boats in the past. The rudder alignment is very important. Make sure the hull is as level as possible. Then hang a plumb Bob (weight attached to a bit of string) and it will show you how far out the rudder is. Adjust so it is perpendicular to the hull and there should be less vibration. Creating a rounded leading edge and tapered trailing edge might help as well. Also weed and build up of blacking won't help. Rudder rake fore and aft controls feel. A vertical rudder will be a light feel. Rake it aft for more if a weighted feel. Also the rudder position relative to the prop wash turbulence will affect things. Cheers

 

 

Thank's for your input, but one's ability to round the leading edge and chamfer the trailing edge on a bit of 6mm steel plate is somewhat limited. It is also likely that to later rake will require a fair bit of engineering on an existing boat.

 

Although less likely, in the case of the OP all too often complaints of rudder judder on narrowboats turn out to be caused by new boaters trying to drive the boat too fast for the waterway.

  • Greenie 1
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If you do find there is some play between the rudder pin and bottom cup, I found trapping a bronze ball bearing in the cup was a decent (and DIY) alternative to getting either replaced. My bearing was around 15mm dia from memory, and I drilled a 45 degree countersunk hole dead-center in the both the bottom of the cup and the end of the pin. Deep enough to leave a few mm gap when assembled with the bearing in place. It now centres on the countersunk holes rather than the outside of the pin / inside of the cup. 

Edited by Thames Bhaji
  • Greenie 2
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9 minutes ago, Thames Bhaji said:

If you do find there is some play between the rudder pin and bottom cup, I found trapping a bronze ball bearing in the cup was a decent (and DIY) alternative to getting either replaced. My bearing was around 15mm dia from memory, and I drilled a 45 degree countersunk hole dead-center in the both the bottom of the cup and the end of the pin. Deep enough to leave a few mm gap when assembled with the bearing in place. It now centres on the countersunk holes rather than the outside of the pin / inside of the cup. 

 

Now that is ingenious.

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