Reversing and deadstick manoeuvring

[Minos]

Is there any way to improve this?

 

I'm pretty pleased with the way our little boat manoeuvres while the prop is turning forwards, although I am still learning. The waterway at our home mooring is as wide as the boat is long, and I can turn her round there without hitting anything, so I don't think I'm a complete muppet.

 

There is a time lag between starting the prop and the boat responding to the tiller position. I'm assuming that this is because it needs a fairly smooth flow of water across the rudder surfaces to have an effect, and the turbulence caused when the prop starts is too chaotic - hence the lag. It's a second or so, never more.

 

In reverse, the tiller is useless. And if I stop the prop altogether while moving forwards, I'm effectively a passenger while the boat makes up its mind what to do next.

 

The thing is, the hire boat I've just given back wasn't as responsive under power, but could be steered 'deadstick' into a lock or a mooring and even steered in reverse.

 

Is it me? Or would a bigger/better rudder help? Or is it a characteristic of hull shape?

[Robin2]

If you look at the rudder on a butty you will understand the problem. The normal rudder on a modern powered narrowboat is far too small to have any useful effect without the flow of water from the propeller. The rudder is useless when reversing because the water flow into the propeller is spread over a large area and is not focused on the rudder.

[dor]

Reversing a narrowboat is a dark art. Some respond better than others. A couple of things to be aware of:

 

"Prop walk" can work for you or against you; you need t oknow how how your craft responds to it as, in my experience, its effects are more noticable in reverse.

Reversing is usually a bit hit and miss - keep an eye on the bows and watch which way it is drifting. Then a quick burst in forward will hopefully redirtect you.

 

Learn to read your prop-wash. There is a known scientific principle that shows how a fluid in motion will tend to attach itself to a parallel surface. Often when you push the tiller right over ( well, 70 degrees - anything more you are wasting your time) the prop wash neatly splits and pushes as much one way as the other. Usually, wiggling the tiller and watching the wash, you will suddnely see the prop wash all coming out one way as the flow 'attaches' itself to the rudder. You can then probably turn the boat in its own length.

 

I find power helps - too timid and you are more likely to lose control in reverse.

 

Watch the wind - if it is blowing towards you, then the bows will rapidly swing away from you when reversing. You have to respond quickly to when the bows start drifting off.

 

Some boats seem to reverse really well. If you have such a boat you are very lucky; the rest of us have to try our best!

[nb Innisfree]

With our boat (60'nb) when using full rudder at slow speed more water and therefore thrust is directed if I momentarily use full rudder in the opposite direction before turning the way I want.

[nicknorman]

Is there any way to improve this?

 

I'm pretty pleased with the way our little boat manoeuvres while the prop is turning forwards, although I am still learning. The waterway at our home mooring is as wide as the boat is long, and I can turn her round there without hitting anything, so I don't think I'm a complete muppet.

 

There is a time lag between starting the prop and the boat responding to the tiller position. I'm assuming that this is because it needs a fairly smooth flow of water across the rudder surfaces to have an effect, and the turbulence caused when the prop starts is too chaotic - hence the lag. It's a second or so, never more.

 

In reverse, the tiller is useless. And if I stop the prop altogether while moving forwards, I'm effectively a passenger while the boat makes up its mind what to do next.

 

The thing is, the hire boat I've just given back wasn't as responsive under power, but could be steered 'deadstick' into a lock or a mooring and even steered in reverse.

 

Is it me? Or would a bigger/better rudder help? Or is it a characteristic of hull shape?

 

The deadstick response is partly down to rudder size but I suspect primarily down to the under water shape of the rear of the hull. Beneath the counter at the back, which probably looks fairly blunt, are the swims - the tapering of the hull to the propellor. Long swims will give a gentle convergence, so give good flow over the rudder even dead stick, but the compromise is reduced cabin space. If you have a shortish boat, chances are the swims are not long and you will never get good dead stick flow over the rudder, regardless of how big it is.

 

Reverse steering has similar issues, but one tip is to not use too much revs. Low revs reduces "prop walk" - the effect whereby the bottom swinging blades have more grip than the top swining blades and push the back of the boat sideways. Again hull shape is an issue and deeper draft with the top of the prop more submerged helps. But if you keep the revs low to minimise prop walk, once the boat starts to pick up speed backwards the rudder may start to have some effect if put at about 45 degrees. There is certainly no chance of the rudder working until the boat is moving backwards at moderate speed

Edited August 21, 2011 by nicknorman

[Minos]

Learn to read your prop-wash. There is a known scientific principle that shows how a fluid in motion will tend to attach itself to a parallel surface. Often when you push the tiller right over ( well, 70 degrees - anything more you are wasting your time) the prop wash neatly splits and pushes as much one way as the other. Usually, wiggling the tiller and watching the wash, you will suddnely see the prop wash all coming out one way as the flow 'attaches' itself to the rudder. You can then probably turn the boat in its own length.

That sounds interesting, dor - I'll look that up. Thanks.

 

Thanks for the other responses, everyone.

 

My boat is a 45' trad, and looking under the deck behind the engine it is obvious that the swims aren't very long at all; 4 feet, maybe a little bit longer. I'll try a few things while turning the boat around today.

[jelunga]

We are lucky with Lily Maud. With the ahead engaged at tick over and the tiller all the way across, then the thrust seems to act like a stern thruster. I do have to give the tiller a quick wiggle from straight to FSD now and again when I see the wash has split. Then it rejoins. I think watching ghost busters helped - "DONT CROSS THE (plasma) STREAMS

[Guest Quo Vadis]

Reversing a narrowboat is a dark art. Some respond better than others. A couple of things to be aware of:

 

"Prop walk" can work for you or against you; you need t oknow how how your craft responds to it as, in my experience, its effects are more noticable in reverse.

Reversing is usually a bit hit and miss - keep an eye on the bows and watch which way it is drifting. Then a quick burst in forward will hopefully redirtect you.

 

Learn to read your prop-wash. There is a known scientific principle that shows how a fluid in motion will tend to attach itself to a parallel surface. Often when you push the tiller right over ( well, 70 degrees - anything more you are wasting your time) the prop wash neatly splits and pushes as much one way as the other. Usually, wiggling the tiller and watching the wash, you will suddnely see the prop wash all coming out one way as the flow 'attaches' itself to the rudder. You can then probably turn the boat in its own length.

 

I find power helps - too timid and you are more likely to lose control in reverse.

 

Watch the wind - if it is blowing towards you, then the bows will rapidly swing away from you when reversing. You have to respond quickly to when the bows start drifting off.

 

Some boats seem to reverse really well. If you have such a boat you are very lucky; the rest of us have to try our best!

Aaaaah .... now I think I understand why sometimes my boat turns quickly and sometimes not. From now on I'll be giving the tiller a little wiggle and watching the prop-wash

Thanks.

[AlanH]

On our boat there is no such thing as prop walk. In reverse on a still day sometimes the bow swings right, other times it swings left.

Learn to read your prop-wash. There is a known scientific principle that shows how a fluid in motion will tend to attach itself to a parallel surface. Often when you push the tiller right over ( well, 70 degrees - anything more you are wasting your time) the prop wash neatly splits and pushes as much one way as the other. Usually, wiggling the tiller and watching the wash, you will suddnely see the prop wash all coming out one way as the flow 'attaches' itself to the rudder. You can then probably turn the boat in its own length.

 

The Coanda effect. Basis of fluidics logic.

Edited August 22, 2011 by AlanH

[Proper Job]

I'm lucky in that my boat reverses very well (for a NB) and in deep water can even be steered with high levels of sucess.

 

A large rudder blade helps

 

[nb Innisfree]

On our boat there is no such thing as prop walk. In reverse on a still day sometimes the bow swings right, other times it swings left.

 

 

The Coanda effect. Basis of fluidics logic.

 

I don't think prop walk is the main influence but something else is at work. My theory is an effect similar to power yaw on a single engined plane is responsible, the helix from a plane prop travels round the fuselage and on exit at the tail it passes under the fuselage but hits the tail plane above it so pushing it to one side resulting in a yaw.

 

A similar effect could be happening with a canal boat, the prop helix travels forward and on one side it passes underneath the swim but on the other side it strikes the swim and counter which provides an ideal surface to trap the helix and push boat to one side, this could explain why the effect can be reversed when near to the side of the canal as the helix instead of passing under the swim hits the piling and canal bed and bounces back to the swim.

 

Prop walk is still an influence but much less so.

 

 

ETA: I have depicted it with a left hand prop, should be the other way with a more common right handed prop.

Edited August 22, 2011 by nb Innisfree

[David Schweizer]

I guess that we are quite lucky, having a deep draughted boat with a massive rudder, very long swims. and a prop which is about six inches below the Uxter plate. Reversing still requires some carefull attention, and the wind can play havoc, but if we can get a shift on in reverse, she goes back in almost a straight line.

 

I have demonstrated this many times at Braunston reversing back from UCC to the marina entrance and on more than one occassion elsewhere. Once when reversing back across Brentford Dock into the only vacant mooring space, when I got a round of applause from other boaters watching from the bank. The other memorable occassion was observed by no one except the Moorings Warden, when I had to move the boat backwards along the full length of the BW moorings at Thrupp and past all the club moorings to the bridge outside the pub. He stood on the front with a pole and was impressed that he did not have to use it once.

 

Of course hardly any of this is down to me, but rather Balliol Fowden who designed the boat, but it does not stop me from taking the credit when it goes well.

[nicknorman]

I don't think prop walk is the main influence but something else is at work. My theory is an effect similar to power yaw on a single engined plane is responsible, the helix from a plane prop travels round the fuselage and on exit at the tail it passes under the fuselage but hits the tail plane above it so pushing it to one side resulting in a yaw.

 

A similar effect could be happening with a canal boat, the prop helix travels forward and on one side it passes underneath the swim but on the other side it strikes the swim and counter which provides an ideal surface to trap the helix and push boat to one side, this could explain why the effect can be reversed when near to the side of the canal as the helix instead of passing under the swim hits the piling and canal bed and bounces back to the swim.

 

Prop walk is still an influence but much less so.

 

 

ETA: I have depicted it with a left hand prop, should be the other way with a more common right handed prop.

 

Well that is an interesting theory and I am sure it has some effect. However comparing our previous boat - relatively shallow at the back with relatively short swims, against our present one with 2' 7" draft and a well submerged counter, the new one stops about twice as quickly despite being a lot heavier for the same length, with barely detectable "prop walk" (or your effect?) compared to the old one which seemed to use most of the engine's power to move the back sideways! Therefore I still think that shallow props exhibit prop walk even if deep ones don't. The other thing I notice about the new boat is a much more pronounced tendency to move the back away from the bank when using reverse (even at tickover) to stop the boat when mooring.

 

I'm lucky in that my boat reverses very well (for a NB) and in deep water can even be steered with high levels of sucess.

 

A large rudder blade helps

 

Ah yes, that is because Steve built it!

[jelunga]

Oooh, Steve,

 

 

 

That's a big un!!

 

 

 

I'm lucky in that my boat reverses very well (for a NB) and in deep water can even be steered with high levels of sucess.

 

A large rudder blade helps

 

[Robin2]

The other thing I notice about the new boat is a much more pronounced tendency to move the back away from the bank when using reverse (even at tickover) to stop the boat when mooring.

 

 

Mine pulls in to the starboard bank and pushes out from the port bank.

[nicknorman]

Mine pulls in to the starboard bank and pushes out from the port bank.

Isn't that just prop walk?

[nb Innisfree]

Isn't that just prop walk?

 

Wrong way round unless he has a left handed prop.

[blackrose]

I don't think prop walk is the main influence but something else is at work. My theory is an effect similar to power yaw on a single engined plane is responsible, the helix from a plane prop travels round the fuselage and on exit at the tail it passes under the fuselage but hits the tail plane above it so pushing it to one side resulting in a yaw.

 

A similar effect could be happening with a canal boat, the prop helix travels forward and on one side it passes underneath the swim but on the other side it strikes the swim and counter which provides an ideal surface to trap the helix and push boat to one side, this could explain why the effect can be reversed when near to the side of the canal as the helix instead of passing under the swim hits the piling and canal bed and bounces back to the swim.

 

The helix wouldn't be straight even if it didn't hit the swim, and it would always skew off to one side. It does the same in forward and we'd all see the effect very clearly if we didn't have rudders.

Edited August 28, 2011 by blackrose

[nb Innisfree]

The helix wouldn't be straight even if it didn't hit the swim, and it would always skew off to one side. It does the same in forward and we'd all see the effect very clearly if we didn't have rudders.

 

Yes the rudder does reduce the helix veering off to one side when in forward, but as the swim is very close to the prop I would think when in reverse the same thing applies but even more so, dividing the helix in half before it has a chance to veer.

 

I just get the impression that propwalk is too subtle an effect to be totally responsible for the apparent readiness of a heavy narrowboat to veer off in reverse but less so in forward, ok I know we automatically correct it with rudder but it still seems to me to be more subtle an efect in forward.

 

I suppose the one way to prove it would be to make a working model with the bottom plate extended to match the counter so stopping the helix escaping underneath.

[blackrose]

Yes the rudder does reduce the helix veering off to one side when in forward, but as the swim is very close to the prop I would think when in reverse the same thing applies but even more so, dividing the helix in half before it has a chance to veer.

 

I just get the impression that propwalk is too subtle an effect to be totally responsible for the apparent readiness of a heavy narrowboat to veer off in reverse but less so in forward, ok I know we automatically correct it with rudder but it still seems to me to be more subtle an efect in forward.

 

I suppose the one way to prove it would be to make a working model with the bottom plate extended to match the counter so stopping the helix escaping underneath.

 

Yes, the swim sends the helix of water all over the place in reverse and all you can really do is use the rudder as a deflector, go into forward to correct the boat if it goes off course and carry on like that. I've never tried to steer a narrowboat in forward in a straight line without a rudder, but I imagine it would be equally difficult and the stern would go off course fairly quickly.

[Minos]

There is a time lag between starting the prop and the boat responding to the tiller position. I'm assuming that this is because it needs a fairly smooth flow of water across the rudder surfaces to have an effect, and the turbulence caused when the prop starts is too chaotic - hence the lag. It's a second or so, never more.

After a consultation with someone who knows, my engine's tickover speed has been increased and this 'lag' has been eradicated. The engine is running a lot smoother, quieter (apart from one sodding panel which resonates at tickover and I need to remove three others to get at the little ****) and cleaner. This means that throttle responses are a lot sharper and other bonuses included less smoke, easier starting...

 

There were obviously reasons why the previous owner reduced the tickover speed from the manufacturer's recommendation, but it came at a cost. Increasing it to the recommended speed has helped.

 

Meanwhile, I've been practising a lot, and last weekend managed to reverse round a corner in Lemonroyd Marina, swinging the bow round to line up with the marina exit. (And did any of you buggers see my expert manoeuvring? No! I bet you'll be there with cameras when I cock it up, though.)

 

Anyway, steering while reversing: 'prop wash' is incredible! If I get all the wash down one side of the boat then it turns on its own arse. The trick is getting it down the side I want it... Anyway, thanks for the tip, Dor.

 

And with deadstick steering: the trick seems to be in timing it just right, and then pushing the tiller hard, all the way, at just the right moment. It's easy in the still waters of a canal, much harder in the livelier waters of a river.

 

Mind you, I also fly model helicopters. They are far harder to manoeuvre, and when you get it wrong with one of those you generally lose a finger and have a four figure repair bill. There's less to go wrong when manoeuvring a boat, and it's not so catastrophic when you get it wrong.

 

Thanks again for all the comments and suggestions - you've been very helpful.

[Neil2]

Well there's one thing for certain the boat will do exactly as you want so long as no-one is watching and vice versa.

 

The point about the butty is right - and look at the size of yacht rudders.

 

I read a book recently written by an american wooden boat designer/builder who has sailed all over the world and built yachts and motor boats all shapes and sizes. Interestingly he insists his rudders are not faired, so they are all 2" wide with sharp corners. His theory is the passage of the angular shape throught the water sets off a different flow pattern to an "aerodynamic" rudder which sort of makes the rudder have the effect of a bigger rudder, if that makes sense. Our NB rudders are pretty thin of course so maybe a thicker, "squarer" rudder might work better..? Like a heavy wooden cruiser our narrowboats are not built for speed so the notion that a rudder has to slip through the water is maybe at odds with the general design.

 

Maybe someone already has a boat with a "thick" rudder?

[Chertsey]

I have not heard the term 'deadstick' before. I think I get the general gist, but what exactly does it mean, and where does it come from?

[mike31]

I have not heard the term 'deadstick' before. I think I get the general gist, but what exactly does it mean, and where does it come from?

 

dead stick is more a plane term, but means coming in without power. or on a boat in neutral, or with a dead engine

[Bob18]

Both reversing and deadstick (a term borrowed from aviation I think) manoeuvres are subject to one of the great laws of the universe.

This law states that you can do something very difficult perfectly without an audience, however the presence of an audience will increase the probability of getting it wrong.

 

 

 

Crudely the rudder on a narrowboat works best when there is water being forced over it by the propeller, not when the water is being sucked over it. It does so by bending the wake to one side or the other, obviously when going astern the wake is going forward, and can't be bent properly because it hits the swim which does its best to make it go straight again...

Edited September 27, 2011 by Bob18