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Tiller judder


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A woman brought a very limp duck into a veterinary surgeon. As she laid her pet on the table, the vet pulled out his stethoscope and listened to the bird's chest.

After a moment or two, the vet shook his head sadly and said, "I'm so sorry, your pet has passed away."

The distressed owner wailed, "Are you sure?"

"Yes, I'm sure. The duck is dead," he replied.

"How can you be so sure", she protested. "I mean, you haven't done any testing on him or anything. He might just be in a coma or something."

The vet rolled his eyes, turned around and left the room. He returned a few moments later with a black Labrador.

As the duck's owner looked on in amazement, the dog stood on his hind legs, put his front paws on the examination table and sniffed the duck from top to bottom. He then looked at the vet with sad eyes and shook

his head. The vet patted the dog and took it out and returned a few moments later with a beautiful cat. The cat jumped up on the table and also sniffed the bird from its beak to it's tail and back again. The cat sat back on its haunches, shook its head, meowed softly, jumped down and strolled out of the room.

The vet looked at the woman and said, "I'm sorry, but as I said, this is most definitely, 100% certifiably, a dead duck."

Then the vet turned to his computer terminal, hit a few keys and produced a bill, which he handed to the woman. The duck's owner, still in shock, took the bill.

"£150!" she cried. "£150 just to tell me my duck is dead?!!"

The vet shrugged. "I'm sorry. If you'd taken my word for it, the bill would have been £20. But what with the Lab Report and the Cat Scan, it all adds up."

:cheers:

 

My old Liverpool boat had a good few inches more between the prop and rudder than this one.

I could do tricks with that one that amazed people (forward or reverse) I even frightened one bloke in Preston Dock

This new one, with much less distance, is a comparative camel of a thing, I am used to it now but I can still remember how good it could be.

I'm convinced that the prop wash has to be given time to form a 'slug' of water to push the rudder - not just splash itself aimlessly again the rudder.

This new one also needs a longer swim, its great on rivers where it can collect water from the depth but any thing less and its a slug.

I spent some months this year in the company of a Jonathan Wilson boat (with a14' swim) and it was definitely a better swimming boat than mine.

 

Alex

My boat is very similar to your previous boat, in that the rudder is a fair way from the prop. It might be as much as 12 inches, but can't be certain now. Either way,it steers without problems forward, and reasonably in reverse. Can't say I have noticed any problems (except rudder judder,but that is another issue.)

 

When you look at some sea going boats, 12 inches is extremely close to the rudder.

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:cheers:

 

 

My boat is very similar to your previous boat, in that the rudder is a fair way from the prop. It might be as much as 12 inches, but can't be certain now. Either way,it steers without problems forward, and reasonably in reverse. Can't say I have noticed any problems (except rudder judder,but that is another issue.)

 

When you look at some sea going boats, 12 inches is extremely close to the rudder.

 

I remember reading an article about a yacht owner who had replaced his engine/shaft drive with a "saildrive" unit, so the propellor ended up well forward of the rudder. Though it was done for reasons of space/economy/maintenence I seem to recall he found the boat handled much better under power after the conversion.

 

There's a popular yacht, I can't remember the name, that has the propeller astern of the rudder. No it's not made in Ireland and no, it doesn't go any better in reverse.

 

vegaprop.jpg

 

I tend to agree the rudder should be further back than they normally are, but then again most NB rudders (being constrained by draught) are undersized anyway.

Edited by Neil2
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  • 2 weeks later...

My narrowboat does exactly the same and it's the rudder bearing. One thing to check is, when you reverse hard does water come up onto the deck, if yes then it's the rudder bearing. The bearing costs £80 and one hour to fit it.....good luck!

 

My narrowboat does exactly the same and it's the rudder bearing. One thing to check is, when you reverse hard does water come up onto the deck, if yes then it's the rudder bearing. The bearing costs £80 and one hour to fit it.....good luck!

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  • 2 years later...

Our experience with removing 40mm off the balance arm of the rudder of Whio was that it significantly reduced the amount of tiller judder/shimmy especially at higher power settings.

I put this down to the increased distance from the prop to the rudder leading edge resulting this leading edge now encountering less prop induced turbulence then before. On a related note I believe that rudder balance is governed by, balance arm to trailing arm ratio, distance of the rudder to the prop, power setting and water depth so that no general rule on best balance arm ratio can be given. It is both boat and intended cruising ground (mainly river or canal) specific. Then there is the individual preference in the trade off between light steering and stable tracking.

Don Robertson

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My old Liverpool boat had a good few inches more between the prop and rudder than this one.

 

I'm convinced that the prop wash has to be given time to form a 'slug' of water to push the rudder - not just splash itself aimlessly again the rudder.

 

 

Alex

 

it takes up to a turn for the water to settle in a helical (cleanish) form, so about as long as the pitch of the propeller.

 

The distance from trailing edge of propeller blade to leading edge of rudder should be minimum 10% of propeller diameter, and 20% from the leading edge of propeller to the swim.

and 10% minimum or minimum 2" from prop tip to hull, or 6% to skegg.

see http://sleipnerab.se/kategori/1842/radice-propeller-2-blad/

Under the picture of the propeller click on the tag PLACERING & INSTALLATION

 

I see the rudder as an wing, not one forward and one rear part. the stock is just the pivot point.

an airfoils AC aerodynamic centre, is close to 25%, at this point the moment is constant with change in angle (alpha) an symmetrical airfoil don't have any moment at zero alpha.

 

The centre of lift is something ells, it moves around with alpha, when the airfoil is stalled it often moves forward and can be forward of the 25% making a positive moment

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When I had my engine changed this year I took the opportunity to move everything forward by an inch, which put the prop closer to the boat but further from the rudder. The improvement (ie reduction) in the amount of tiller judder was wonderful.

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  • 1 month later...

First post on here, so forgive me if I've missed the point, but does the rudder shaft have a camber angle? with a car it helps the wheels "self centre" and wonder if this was a consideration along with leading and trailing edges of the rudder itself ?

Edited by sniffy
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Yes out boat has a tilted rudder shaft so tends to self-centre, but plenty of boats seem to have a vertical shaft so they don't. That said I think the self-centring action is mostly only relevant when the boat is stopped, but it does for example ensure that the tiller remains straight in locks. The forces on the rudder from water flow etc are greater than the mass balancing action. If you have a rudder that doesn't like to stay in the middle whikst you are cruising, it may be that it has too much blade area in front of the pivot. Reducing this area will improve the self-centring effect under way, but increase the forces required to deflect the rudder.

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First post on here, so forgive me if I've missed the point, but does the rudder shaft have a camber angle? with a car it helps the wheels "self centre" and wonder if this was a consideration along with leading and trailing edges of the rudder itself ?

By the way, Welcome to this world.

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  • 4 weeks later...

rudder and tiller

A rudder on a boat is a flat piece of wood or other material attached to the boat’s stern (back end). It is positioned vertically in the water and is moved to the left or right in order to steer the boat through the water.

A tiller is used instead of a steering wheel on small boats; the tiller is a stick or pole attached directly to the top of the rudder so that the helmsman can turn the rudder easily.

So, the tiller is the stick that controls the rudder.

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My boat has a tiller, does that make it small? (60ft)

Phil

 

 

My boat has a wheel does that make it big? (23ft)

 

Now that poster took an interest from a very long way away and made a post that could have cleared up a lot of confusion, and you two just go and cause more confusion. Have a word with yourselves! wink.png

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I've just read the whole of this thread from the beginning.

I'm glad the OP was given good advice and seemed to resolve his problem ..... to me the relevant points were, he'd only had it 6 months and was told by the previous owner there was "rudder judder" (sounds like a 50s rock and roll song) and he still bought it with no mention of a survey.

 

And then we still see similar posts every month asking why they should bother with a survey.

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I've just read the whole of this thread from the beginning.

I'm glad the OP was given good advice and seemed to resolve his problem ..... to me the relevant points were, he'd only had it 6 months and was told by the previous owner there was "rudder judder" (sounds like a 50s rock and roll song) and he still bought it with no mention of a survey.

 

And then we still see similar posts every month asking why they should bother with a survey.

A survey probbly wouldn't have revealed that problem.

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A survey probbly wouldn't have revealed that problem.

 

Really? I have to disagree.

 

I've used surveyors three times and two of them finished the survey by checking how it handled once back in the water.

 

The third didn't because it was a butty and the only moving parts were an elum, two doors into the cabin and one into the hold.

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