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Tiller/Rudder pressure


Richardcn

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Everyone's boat will steer to one side or the other to a certain extent even if the even if the steerer isn't aware of it. It happens as a result of the prop turning in one direction, so unless you have a twin engined boat with props counter-rotating your boat will steer to one side even if it's just a tiny bit. We tend to automatically compensate while steering and the only time we really notice is when we go into astern and have nothing to compensate with (i.e. no rudder).

 

But if the issue is really bad then perhaps there's a different problem. I tend to notice it on my boat because the length : width ratio is is about 4.75 : 1 compared to a narrowboat of the same length 8 : 1, so my boat tends to steer off course much more easily than a narrrowboat. The benefit of that is that I can turn it almost within its own length at idling speed, but the disadvantage is that if you take your eye off the river or canal for more than a few seconds you're in the bushes!

Edited by blackrose
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Everyone's boat will steer to one side or the other to a certain extent even if the even if the steerer isn't aware of it. It happens as a result of the prop turning in one direction, so unless you have a twin engined boat with props counter-rotating your boat will steer to one side even if it's just a tiny bit. We tend to automatically compensate while steering and the only time we really notice is when we go into astern and have nothing to compensate with (i.e. no rudder).

 

But if the issue is really bad then perhaps there's a different problem. I tend to notice it on my boat because the length : width ratio is is about 4.75 : 1 compared to a narrowboat of the same length 8 : 1, so my boat tends to steer off course much more easily than a narrrowboat. The benefit of that is that I can turn it almost within its own length at idling speed, but the disadvantage is that if you take your eye off the river or canal for more than a few seconds you're in the bushes!

Whilst the 'prop walk' is an issue at low speeds (and as you say, in reverse) the more forward momentum the boat gains the less noticeable is the effect, to the point where it becomes undetectable compared to other 'distractions'. My boat will steer to one side or the other dependent upon depth, if the canal become shallower on one side the prop will pull the stern of the boat towards that side, obviously pushing the bow in the opposite direction. I can't remember the name for the effect but it is what will draw two boats travelling in the same direction together if they get too close. Compared to these sort of effects, prop walk at higher momentum becomes ineffective.

 

I'm guessing from your description of your length/width ration that your boat is about 30 feet long so will also probably make it quite a bit shallower in the water which makes turning a lot more responsive (and going off course even easier!).

 

I still favour the theory that the boat has either cilled and bent the skeg and rudder or reversed into something to do the same. Prop walk can be useful if you work with it, for instance when winding, but what the OP describes is something that is a nuisance because you are constantly having to work against it.

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Just to follow up on this, I did contact the company who I am happy to name now. ABC wrote to me (yes an actual letter) in response to my email stating that they have examined the boat since my complaint. The skeg was not bent nor could they find any other damage, in fact they say that the rudder on 'Capped Heron' "... seemed quite smooth...". I will have to accept that they are happy with it as they have apparently checked everything but I am surprised that they could not replicate the problem that we had when cruising. I will just make a final clarification with them that the problem is not necessarily obvious unless at cruising speed and not necessarily a problem unless cruising for an extended period, unlike any 'test drive' I imagine they would do. I will leave it at though unless another hirer chances upon this thread and discovers the same issue of course! Just to balance my comments, the boat was, in all other respects, fantastic and the service from all the staff at Gayton nothing short of wonderful! They prepared the boat specially for our honeymoon at no extra cost and the handover (at both ends) was quick but professional, assistance by them along the was was also very good. I think we were extra lucky with my choice of boat as all the staff said that it was their favourite (and we could see why). They have also given us a £50 (additional) discount on any future hiring due to my complaint but my description above has not been biased by that fact, we are unlikely to hire again as we WILL have our own boat (he says, trying to nudge luck in our direction).

 

Many thanks for everyone's input.

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I posted about our how ourexperience removing 40mm from the leading edge of the rudder (off the balance blade) vastly improved the handling especially at higher power settings. I suspect it would have been even better to have put this section on the trailing edge as Mike did but the logistics for us were harder. From a sailing background I like big rudders! Going astern qiuckly you do have to be careful not to let the rudder snap over but rarely do we proceed that way and such a mode already needs full concentration.

Don NB Whio

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I posted about our how ourexperience removing 40mm from the leading edge of the rudder (off the balance blade) vastly improved the handling especially at higher power settings. I suspect it would have been even better to have put this section on the trailing edge as Mike did but the logistics for us were harder.

That's what I did

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Just to follow up on this, I did contact the company who I am happy to name now. ABC wrote to me (yes an actual letter) in response to my email stating that they have examined the boat since my complaint. The skeg was not bent nor could they find any other damage, in fact they say that the rudder on 'Capped Heron' "... seemed quite smooth...". I will have to accept that they are happy with it as they have apparently checked everything but I am surprised that they could not replicate the problem that we had when cruising. I will just make a final clarification with them that the problem is not necessarily obvious unless at cruising speed and not necessarily a problem unless cruising for an extended period, unlike any 'test drive' I imagine they would do. I will leave it at though unless another hirer chances upon this thread and discovers the same issue of course! Just to balance my comments, the boat was, in all other respects, fantastic and the service from all the staff at Gayton nothing short of wonderful! They prepared the boat specially for our honeymoon at no extra cost and the handover (at both ends) was quick but professional, assistance by them along the was was also very good. I think we were extra lucky with my choice of boat as all the staff said that it was their favourite (and we could see why). They have also given us a £50 (additional) discount on any future hiring due to my complaint but my description above has not been biased by that fact, we are unlikely to hire again as we WILL have our own boat (he says, trying to nudge luck in our direction).

Many thanks for everyone's input.

Sorry, rather late into this but two factors are relevant:

 

If the rudder is slightly bent at the back from reversing into the bank etc, this acts as a "trim tab" and tends to offset the natural position of the rudder, causing the boat to want to turn. Obviously the more power/speed the more force is required to overcome this effect.

 

If the rudder is well "balanced" ie has a fair bit of area in front of the pivot point so as to reduce tiller forces, the "trim tab" effect has more power in terms of tendency to turn. Maybe less effect in terms of force required to overcome.

 

All boats tend to turn away from a shallow bank with plenty of power on. The stern gets "sucked in" to the shallows presumably due to Bernoulli's effect (pressure reduces as flow speed increases). So a variable tendency to turn can be due to not being in the centre of the channel.

 

Ok 3 factors, but the Spanish Inquisition were not expected.

 

Oh and prop walk is mostly myth, presuming a properly submerged propellor.

 

Anyway, there is no reason to have a boat that turns on its own. The boat we used to borrow had light tiller forces but you couldn't let go for long -it would be off heading for the bank.

 

Our boat has heavy tiller forces when turning with power on, but it goes dead straight for a long time. I can literally go inside, put the kettle on and come back to the tiller without the heading having changed more than 10 degrees, although I do reduce to tickover as a precaution. If the boat turns, it will do it either way according to which side is shallower (Bernoulli).

 

Regarding their reaction, perhaps they are not keen to admit a fault lest you demand compensation, but hopefully they will have found it and fixed it for the next folk.

Edited by nicknorman
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Sorry, rather late into this but two factors are relevant:

If the rudder is slightly bent at the back from reversing into the bank etc, this acts as a "trim tab" and tends to offset the natural position of the rudder, causing the boat to want to turn. Obviously the more power/speed the more force is required to overcome this effect.

If the rudder is well "balanced" ie has a fair bit of area in front of the pivot point so as to reduce tiller forces, the "trim tab" effect has more power in terms of tendency to turn. Maybe less effect in terms of force required to overcome.

Okay this seems to make sense as the skeg is (apparently) not bent. Can you just confirm my thoughts though. Initially I believed, being from an aircraft background, that a bend (or indeed 'trim tabs') on the trailing edge of the rudder (such as the misalignment from the swan neck to PORT that I observed) would create a tendency to veer to PORT but now, taking into account the the balance blade, I believe that a rudder bent/trimmed on the trailing edge to PORT would deflect the rudder as a whole to STARBOARD thus creating a force in that direction on the tiller and sending the boat to STARBOARD if no counter-force was applied. Correct or incorrect?

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You got that right, bend the trailing edge to port and the rudder want to go to starboard side, right!

but if the rudder blade isn't bent, but not in line with the tiller, it will not create any force it self, but the tiller will not be straight when rudder is,

I have a hydraulic steering with no servo, but valves that stop the feedback from rudder, except for when turning the wheel, and sure I can feel it goes easier to the port then starboard, the rudder is a schilling rudder with 23-24% balance area, propeller shaft isn't horizontal but angled some 10 degree or so, left hand propeller.

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but if the rudder blade isn't bent, but not in line with the tiller, it will not create any force it self, but the tiller will not be straight when rudder is,

 

Quite!

 

The force will be due to prop wash, not rudder geometry

 

Richard

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And that force can be trimmed out by a trim tab, take a look at big sailing boats, that use a trim tab to reduce fatigue of the helmsman, can often be seen that they have a smaller wheel in the bigger one, the smaller is connected to the tab

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Regarding their reaction, perhaps they are not keen to admit a fault lest you demand compensation, but hopefully they will have found it and fixed it for the next folk.

Indeed and that was my desired outcome, although if they don't fix anything that might be wrong and subsequently a forum user discovers the same fault and wishes to complain then they would have some explaining to do! Normally I would not be fobbed off if I felt that something was definitely not right but this occasion was far too important to allow me to be concerned enough to do any more than I have. I did respond to their 'no fault found' letter pointing out that we discovered and reported the 'fault' after our first full day of cruising and the 'fault' didn't go away nor alter in any way for the whole week so it was most unlikely that such a fault would just disappear. I suggested that maybe the 'road test' would need to be done at a faster speed and over a greater distance to reveal the issue as it affected us, just to make it clear that I wasn't convinced that there was nothing at all wrong and to give them an opportunity to recheck knowing that. Time will tell I suppose but I wouldn't be too surprised if they just deal with it when the boat is next out of the water and live with it until then. I did also suggest that if it is just a 'natural tendency' of that particular boat to drift to starboard then the very least they should do is to brief future hirers to be aware of that. Like you say though, any admission of such a defect would leave them open to a compensation claim so they are unlikely to tell me!

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You got that right, bend the trailing edge to port and the rudder want to go to starboard side, right!

but if the rudder blade isn't bent, but not in line with the tiller, it will not create any force it self, but the tiller will not be straight when rudder is,

Ok I'm glad I've got that straight now (I wish the rudder had been too ).

 

I understand about the tiller/rudder misalignment but, if I remember correctly, there was a curve to port to the part of the rudder that I could see. I expected that a rudder ought to be flat and straight and this particular one gave me the impression that it was bent which provided the misalignment with the swan neck. If ever I notice an mechanical problem (although I do a good line in emotional ones too ) and I can identify a mechanical issue then it will play on my mind until I resolve it. In this case the forum is providing a 'resolution' to a certain degree as I have no desire nor means ensure an actual resolution. I'd love to go down the marina and go through it with the resident engineer if it were at all possible though!

Maybe a tendency to turn one way had previously been reported, and some drongo mechanic thought it could be cured by repositioning the swan's neck relative to the rudder.

Lol

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... Oh and prop walk is mostly myth, presuming a properly submerged propellor. ...

Most canal boats have the prop' submerged only a few inches below the counter which is only a few inches below the surface.

 

Prop' walk is not a myth, I use it to my advantage and allow for it otherwise. e.g. on my small (33', 6 ton) boat with a high revving small prop' I can approach a LH mooring at an angle and a burst of reverse pulls the stern in; approaching a RH mooring I will steer left and counteract the rotation with a burst of reverse. Even in a lock I can stop parallel to and within <a foot of the side. If I need to stop in a straight line I apply full left rudder at the same time as full reverse.

 

70', 25 ton with a largish (22x15?) slow revving (180-800 rpm prop'), prop' walk is useful when reversing but anywhere near the bank or lockside the wash pushes the stern away from the bank.

 

The previous owner of my boat had two inches removed from the forward edge of the rudder because beyond the 'ideal' 30° deflection it would be biased to full deflection. The rudder 'self centers' but this has no effect on the boat's ability to continue on a straight course. My rudder is a bit on the heavy side of 'well balanced' but it can easily be continuously biased by a small pressure from my hip/waist.

 

I prefer the heavier helm with good feedback to a light helm requiring constant attention. OTOH, I have no probem with hydraulic wheel steering with virtually no feedback. The OP (Richarcn) was fortunate to hire a boat that did not have a juddering rudder.

 

Alan

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Most canal boats have the prop' submerged only a few inches below the counter which is only a few inches below the surface.

 

Prop' walk is not a myth, I use it to my advantage and allow for it otherwise. e.g. on my small (33', 6 ton) boat with a high revving small prop' I can approach a LH mooring at an angle and a burst of reverse pulls the stern in; approaching a RH mooring I will steer left and counteract the rotation with a burst of reverse. Even in a lock I can stop parallel to and within <a foot of the side. If I need to stop in a straight line I apply full left rudder at the same time as full reverse.

 

70', 25 ton with a largish (22x15?) slow revving (180-800 rpm prop'), prop' walk is useful when reversing but anywhere near the bank or lockside the wash pushes the stern away from the bank.

 

The previous owner of my boat had two inches removed from the forward edge of the rudder because beyond the 'ideal' 30° deflection it would be biased to full deflection. The rudder 'self centers' but this has no effect on the boat's ability to continue on a straight course. My rudder is a bit on the heavy side of 'well balanced' but it can easily be continuously biased by a small pressure from my hip/waist.

 

I prefer the heavier helm with good feedback to a light helm requiring constant attention. OTOH, I have no probem with hydraulic wheel steering with virtually no feedback. The OP (Richarcn) was fortunate to hire a boat that did not have a juddering rudder.

 

Alan

Well all I can say is our boat shows no prop walk tendency. Stopping in deep water, it usually stays straight but if it decides not to, it will go either way. Reverse near the bank pushes the stern out regardless of the side. On the previous boat we used to borrow (much shallower drafted) I never noticed prop walk. I don't doubt some do it, but only because they are badly constructed.

 

We've had the discussion before but that time, no-one gave a convincing argument for the cause once ventilation was eliminated.

Edited by nicknorman
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Well all I can say is our boat shows no prop walk tendency. Stopping in deep water, it usually stays straight but if it decides not to, it will go either way. Reverse near the bank pushes the stern out regardless of the side. On the previous boat we used to borrow (much shallower drafted) I never noticed prop walk. I don't doubt some do it, but only because they are badly constructed.

 

We've had the discussion before but that time, no-one gave a convincing argument for the cause once ventilation was eliminated.

Probably the best way of seeing the effect of prop walk is if you had somewhere that you could turn the boat around in a single manoevre (a large turning circle!). What you will find is that in one direction (clockwise or anticlockwise) the diameter of the circle will be smaller than the other direction. Prop walk is clearly not a myth, the cause of it is the 'paddle-wheel' effect of the propeller going around. Whilst the majority of the drive will be in line with the length of the boat, a small percentage of the drive is at right angles thereby pushing the stern to starboard if the prop rotation is clockwise. As I said in an earlier posting I don't think that it has any connection with the OP's original problem since it is only relevant at low speed, as the forward momentum of the boat increases the effect becomes less noticeable. On Canals the prop walk effect can be easily overridden by other more powerful effects such as shallow water on the side of the channel which will tend to draw the stern towards it.

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Probably the best way of seeing the effect of prop walk is if you had somewhere that you could turn the boat around in a single manoevre (a large turning circle!). What you will find is that in one direction (clockwise or anticlockwise) the diameter of the circle will be smaller than the other direction. Prop walk is clearly not a myth, the cause of it is the 'paddle-wheel' effect of the propeller going around. Whilst the majority of the drive will be in line with the length of the boat, a small percentage of the drive is at right angles thereby pushing the stern to starboard if the prop rotation is clockwise. As I said in an earlier posting I don't think that it has any connection with the OP's original problem since it is only relevant at low speed, as the forward momentum of the boat increases the effect becomes less noticeable. On Canals the prop walk effect can be easily overridden by other more powerful effects such as shallow water on the side of the channel which will tend to draw the stern towards it.

So, explain to me the paddle wheel effect if you would please. All the paddle steamers I have seen have the paddle 1/2 submerged or less, and it's easy to see how they work - bottom half pushing against water, top half pushing against air -the latter being much harder to push against of course. But fit a paddle wheel to a submarine and now tell me how well it works ( hint - it doesn't!)

 

I certainly agree that shallows etc can pull a stern sideways, that's why I specified "in deep water" when I said our boat either stops straight, or randomly turns left or right a bit.

Edited by nicknorman
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The OP (Richarcn) was fortunate to hire a boat that did not have a juddering rudder.

Er actually it did have a juddering rudder, I didn't mention it previously as it just felt like prop wash and increased with rpm. I took it either to be the norm or to be a symptom of the larger problem. Sorry I probably should have said at the outset. On reflection it was probably a combination of the two effects that made steering so tiring as there were constant small pressure changes within the correcting pressure being applied. The juddering was most noticeable though when accelerating the boat, during burst throttle movements and/or in shallow water.

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So, explain to me the paddle wheel effect if you would please. All the paddle steamers I have seen have the paddle 1/2 submerged or less, and it's easy to see how they work - bottom half pushing against water, top half pushing against air -the latter being much harder to push against of course. But fit a paddle wheel to a submarine and now tell me how well it works ( hint - it doesn't!)

 

I certainly agree that shallows etc can pull a stern sideways, that's why I specified "in deep water" when I said our boat either stops straight, or randomly turns left or right a bit.

Rather than try to explain the principle, read this which gives a precis of the effect

 

http://en.wikipedia.org/wiki/Propeller_walk

 

Alternatively explain to me why, when turning my friend's seagoing boat around in a full circle under power the anticlockwise circle is smaller that the clockwise circle? Does the boat become shorter when turning anticlockwise???unsure.png

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Rather than try to explain the principle, read this which gives a precis of the effect

 

http://en.wikipedia.org/wiki/Propeller_walk

 

Alternatively explain to me why, when turning my friend's seagoing boat around in a full circle under power the anticlockwise circle is smaller that the clockwise circle? Does the boat become shorter when turning anticlockwise???:unsure:

Quite a lot of seagoing boats have an offset (either laterally or angularly) propellor but without seeing it (out of the water) it's hard to know.

 

The wiki article isn't very scientific but it says that at low speed the primary cause is unbalanced amounts of left and right flow impinging on the rudder. But the extent or even direction of that effect will depend on the relationship between the rudder and the prop. Narrowboats typically have large square-shaped rudders which is maybe why they don't seem to exhibit prop walk (except when ventilation is the cause).

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Quite a lot of seagoing boats have an offset (either laterally or angularly) propellor but without seeing it (out of the water) it's hard to know.

 

The wiki article isn't very scientific but it says that at low speed the primary cause is unbalanced amounts of left and right flow impinging on the rudder. But the extent or even direction of that effect will depend on the relationship between the rudder and the prop. Narrowboats typically have large square-shaped rudders which is maybe why they don't seem to exhibit prop walk (except when ventilation is the cause).

Surely with an offset propeller steering in a straight line is going to be a problem? Steering my friend's boat in a straight line is no problem.

 

Can you explain what you mean by the highlighted text? How do you 'ventilate' a propeller? Do you mean cavitation?

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Ventilation occurs when the tips of the prop clears the water (if bow heavy for example) causing circulation of air and water instead of just water, the prop then has a much less dense surface to push against.

 

Lee.

Having tried some research into it on the RYA site it seems that it most commonly occurs when you get the boat up on the plane (haven't managed to do that yet with my narrow boat cool.png ). I would suggest that if your stern is far enough out of the water to expose your propeller you have far more to worry about than a bit of 'ventilation'!

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