Going astern

[Jon]

FOR ORIGINAL THREAD SEE HERE

[Sam]

 

Do some of you people have promlemos while going astern?

Our boat is ok -

 

I think that to 'excell' at going backwards you need to keep an eye on your stern and your bow. This is because narrowboats "pivot" around the centre point of the boat. (if that makes any sense )

 

Also it helps not to put the boat into FULL reverse which I have seen first time hire boaters do many a-time.

 

All i can do when this is happens is shout " EVERYBODY DOWN" then the THUMP comes when the boat hits something whether it is the bank, boat or canoe !!

 

lol!

 

[howardang]

 

  Do some of you people have promlemos while going astern?

Our boat is ok -

 

I think that to 'excell'   at going backwards you need to keep an eye on your stern and your bow. This is because narrowboats "pivot" around the centre point of the boat. (if that makes any sense )

 

Also it helps not to put the boat into FULL reverse which I have seen first time hire boaters do many a-time.

 

All i can do when this is happens is shout " EVERYBODY DOWN" then the THUMP comes when the boat hits something whether it is the bank, boat or canoe !!

 

lol!

 

<{POST_SNAPBACK}>

 

Sam, You are repeating a myth that is often seen on canal forums about pivot points. A boat does not pivot around the centre point - it pivots around a point between 1/3rd and 1/2 its length from the bow when going ahead but this pivot point moves to about 1/3rd to 1/2 its length from the stern when going astern. The distance from bow or stern respectively depends to some extent on the speed through the water.

 

It is perfectly possible to make a narrow boat (or any other boat for that matter) steer when going astern but it is like a lot of things to do with boating - it takes practice and is not as easy as when going ahead. When the inevitable happens and you get off line, the easiest way to correct it is to give a kick ahead with the engine using the appropriate rudder input to swing the bow round before resuming the astern movement.

 

Regards

 

Howard Anguish

[David Schweizer]

The paddle action of the propeller automatically encourages a boat to move off line, and no boat is imune (unless you have two props rotating in opposite directions!) the degree to which this affect steering in reverse is governed by a number of other conditions, including depth of water, size of prop, distance of prop from the surface, hull shape, and speed. Although it is a broad generalization steering backwards is easier in a longer deep hulled boat with long rear swims with a large slow running prop which is at least four or five inches from the water surface. How many of us have all those conditions? so most of us do have problems.

[maffi mushkila]

 

  Do some of you people have promlemos while going astern?

 

Some have problemos with our keyboard!

[Blueantoo]

The paddle action of the propeller automatically encourages a boat to move off line, and no boat is imune (unless you have two props rotating in opposite directions!) the degree to which this affect steering in reverse is governed by a number of other conditions, including depth of water, size of prop, distance of prop from the surface, hull shape, and speed. Although it is a broad generalization steering backwards is easier in a longer deep hulled boat with long rear swims with a large slow running prop which is at least four or five inches from the water surface. How many of us have all those conditions? so most of us do have problems.

 

 

Another point to remember is that when going forward the prop pushes water against the rudder enabling you to steer. When going astern your rudder is in the wrong place e.g. the wrong side for steering. The prop is now sucking water past the rudder and it's hitting th hull. By moving the rudder you are reducing the amount of water available to one side of the prop, too much rudder and it all goes wrong. I try not to apply more than 1/3rd rudder.

 

Does any of this make sense?

[DHutch]

Another point to remember is that when going forward the prop pushes water against the rudder enabling you to steer. When going astern your rudder is in the wrong place e.g. the wrong side for steering. The prop is now sucking water past the rudder and it's hitting th hull.

Yes indeed, infact i'd say thats the main point!

- That why reversing is difficult, becuase the rudder has very little affect when the water isnt being directed at it.

- The "paddle wheel" affect is simply a general incovence/inperefection that is simply far more noticable when in reverse, for the above reason.

- You may notice that to go straight even when going forwards you have to hold the rudder slightly off center, to counter-act the paddling affect. And a right-hand prop'ed boat will always steer easyer to the left.

 

You are also right in the fact that for optimum steering in reverse a much smaller rudder angle is best. I usally aim for no more than 45degrees when reversing, and find that this just about counter-acts most of the paddle wheel affect (but not all, and certainly wont make the back end turn away from the direction the prop is paddling it.)

- Simularly, even when going forwards, flattening the rudder right over to 90degrees is equally counter productive, so depending where the rudder stops are placed holding it right over is not always best for maxamum steer.

 

 

Daniel

 

 

 

 

Although it is a broad generalization steering backwards is easier in a longer, deep hulled boat with long rear swims with a large slow running prop which is at least four or five inches from the water surface. How many of us have all those conditions? so most of us do have problems.

And even with most of the above features, to some degree or other (58ft long, 2'8" deep, 10ft swims, 26inch prop, spining at 1-200rpm) the affect is still very noticable.

- Admitadly we do have an underside (tho large) rudder, and the props only about 3inchs off the swim plate (and often no much futher off the bottom of the cut)

- But still, turning a junction "the wrong way" is much much harder, and she goes round left hand bends vastly more easly.

 

Every time we have her in dry dock we feel we should "do somthing" about the rudder situation, but as yet nothing has acutally materialised! Maybe onday ill knock up a schilling rudder for her?

 

 

Daniel (again)

Edited July 17, 2006 by dhutch

[John Orentas]

I am not sure there are any rules in all this, some boats steer a little better than others but that is probably all you can say, though I would dissagree with David, long swimmed boats are good at going efficiently in a straight line but not so good at low speed manovering.

 

I did once see a chap steer a very old blunt ended hire boat through a crowd of randomly moored boats in a marina with not a single correction but probably just luck.

Edited August 9, 2006 by John Orentas

[David Schweizer]

.....The "paddle wheel" affect is simply a general incovence/inperefection that is simply far more noticable when in reverse, for the above reason.....

That may be you experience Daniel, but Paddle action can be quite significant, particularly when going ahead. When I took my Board of Trade Boat Masters Licence examination one of the requirements was to be able to steer a boat, without a rudder, using Paddle action only. Believe me it takes some learning, but it is possible.

[Guest]

That may be you experience Daniel, but Paddle action can be quite significant, particularly when going ahead. When I took my Board of Trade Boat Masters Licence examination one of the requirements was to be able to steer a boat, without a rudder, using Paddle action only. Believe me it takes some learning, but it is possible.

I can't steer with a rudder.

[DHutch]

That may be you experience Daniel, but Paddle action can be quite significant...

I didnt say it was other than significant, i was just say that paddle action is not the reason that its harder to reverse than it is to go forwards. Rather that its just more noticable in reverse, becuase the rudders affect is greatly reduced. Sorry if that was not clear.

 

 

Daniel

[Alastair]

Paddle effect can be insignificant on some widebeam hulls. My barge doesn't exhibit any paddle effect at all, but will only go in a straightish line astern. As soon as any way astern is established, all rotation of the boat ceases. This can be handy - it is possible to make her 'skid' sideways - great for mooring in tight spaces. It is a pain when trying to do a 180 into the wind.

[mykaskin]

That may be you experience Daniel, but Paddle action can be quite significant, particularly when going ahead. When I took my Board of Trade Boat Masters Licence examination one of the requirements was to be able to steer a boat, without a rudder, using Paddle action only. Believe me it takes some learning, but it is possible.

 

OK - I give up - making the boat turn one way fine, but how do you make it go the other way without a rudder? Surely just putting it in reverse doesn't make it turn enough.

 

Also, how did they test this - did they have a boat without a rudder? I know that both my boats will head off in one direction even when the rudder is held in the middle out of gear.

 

Mike

[howardang]

OK - I give up - making the boat turn one way fine, but how do you make it go the other way without a rudder? Surely just putting it in reverse doesn't make it turn enough.

 

Also, how did they test this - did they have a boat without a rudder? I know that both my boats will head off in one direction even when the rudder is held in the middle out of gear.

 

Mike

It does seem a rather pointless exercise - if you had lost your rudder the best place to be is on the bank, and if you hadn't lost your rudder then why not use it. It certainly wouldn't be practical to try and proceed for any distance by trying to steer using transverse thrust alone and I am surprised that David had to learn it for his BM exam. It might make a nice party trick given a boat with specific handling characteristics but no more than that!

 

Regards

 

Howard Anguish

[enigma]

A narowboat steers better forwards than backwards.

 

When going forwards the propeller pushes water towards the back of the boat across the rudder. This makes the rudder effective because of all the water from the propeller flowing across it.

 

When going astern the propeller pushes water towards the front of the boat away from the rudder. The rudder has little water flowing across it, just the speed of the boat in reverse, and is just about ineffective.

 

When going forward, the water from the propeller because of the cork-screw movement of the water, tends to hit one side of the rudder more than the other. That is why the tiller tends not to be on the centre line of the boat and why it seems easier for the boat to turn one way rather than the other.

 

What has been described in this thread as paddle wheel effect is formally known as prop effect. For a boat to feel prop effect the prop-shaft has to be at an angle to the water surface. It does not affect narrowboats with a horizontal prop-shaft, (I assume the vast majority have a horizontal prop-shaft and the slight bow up attitude that a narrowboat has is less than ½ degree and has no effect). For a full description of this effect have a look at this web page: http://www.cruisingschool.co.uk/home/icc/prop%20walk.pdf

 

enigma

Edited August 10, 2006 by enigma

[howardang]

A narowboat steers better forwards than backwards.

 

When going forwards the propeller pushes water towards the back of the boat across the rudder. This makes the rudder effective because of all the water from the propeller flowing across it.

 

When going astern the propeller pushes water towards the front of the boat away from the rudder. The rudder has little water flowing across it, just the speed of the boat in reverse, and is just about ineffective.

 

When going forward, the water from the propeller because of the cork-screw movement of the water, tends to hit one side of the rudder more than the other. That is why the tiller tends not to be on the centre line of the boat and why it seems easier for the boat to turn one way rather than the other.

 

What has been described in this thread as paddle wheel effect is formally known as prop effect. For a boat to feel prop effect the prop-shaft has to be at an angle to the water surface. It does not affect narrowboats with a horizontal prop-shaft, (I assume the vast majority have a horizontal prop-shaft and the slight bow up attitude that a narrowboat has is less than ½ degree and has no effect). For a full description of this effect have a look at this web page: http://www.cruisingschool.co.uk/home/icc/prop%20walk.pdf

 

enigma

If you want to be technically correct the formal description of paddle wheel effect, prop walk or prop effect is actually Transverse Thrust. I would disagree that the shaft has to be at an angle - this effect is present with all propellers to a greater or lesser extent.

 

Regards

 

Howard Anguish

[dor]

As I understood it, the reason you get the paddle wheel effect on a narrowboat is because of the proximity of a relatively large flat area just above the prop. This means that the prop has more effect at the bottom where it is in clear water rather than at the top where it is restricted. This give rise to more sideways thrust at the bottom of the prop than at the top.

 

the diagram in the link above which claims that there is no prop effect on a horizontal prop would be right if the whole prop was in clear water. This is not the case in a narrowboat wher ethe effect can be quite significant even with a horizontal propshaft.

[enigma]

howardang and dor

 

My statements are correct.

 

enigma

[DHutch]

A narowboat steers better forwards than backwards.

Correct.

 

 

When going forwards the propeller pushes water towards the back of the boat across the rudder. This makes the rudder effective because of all the water from the propeller flowing across it.

Correct.

 

 

When going astern the propeller pushes water towards the front of the boat away from the rudder. The rudder has little water flowing across it, just the speed of the boat in reverse, and is just about ineffective.

Correct

 

 

When going forward, the water from the propeller because of the cork-screw movement of the water, tends to hit one side of the rudder more than the other. That is why the tiller tends not to be on the centre line of the boat and why it seems easier for the boat to turn one way rather than the other.

Cant see that being the case tho.

- Ok, so the prop causes the water to turn with it to a degree.

- Hoever, while it might hit the top of the rudder more on one side, surely it will hit the bottom of the rudder equaly on the other side. NO?

 

 

What has been described in this thread as paddle wheel effect is formally known as prop effect.

I have indeed also called it that.

- Although in narrowboating circles, i find "paddle wheel affect" far more commanly used.

- My grandad also used this term, and is an exprenced helmsman with many years at sea.

 

 

For a boat to feel prop effect the prop-shaft has to be at an angle to the water surface.

I dont beleave so, no.

 

 

It does not affect narrowboats with a horizontal prop-shaft, (I assume the vast majority have a horizontal prop-shaft....)

Simply rubbish.

- I chalenge you to find a single narrowboat that does not suffer from the dissued affect, regardless of what you call it. (paddlewheel affect, prop affect, pain in the arse affect, whatever)

- Further more i invite you aboard emilyanne to inspect our prop-shaft arrangment. I think you will find the it is perfectly paraplell with the base plate along all its 20ft of lenght, and that the baseplate, and therefore propshaft, are perfectly horizontal within your own definition of a suitable tollerence or error-bound.

 

For a full description of this effect have a look at this web page: http://www.cruisingschool.co.uk/home/icc/prop%20walk.pdf

I have read the above pdf file.

- It seams to talk aproxxamant sence, however, it is talking about a completly diffrent affect.

 

 

 

We are talking about the affect of the top of the propeller being closer to the boat, and bottom "paddle wheeling" (for what of a better term) though that water.

- Hence causing a degree of corrective helm to be applided when in forwards motion.

- Hence causing the affect of one direction being easyer to turn in (when going forwards)

- Hence causing reversing, when the rudder has a greatly reduced affect, to be diffcult, and possably impossable, to fully control to a stright path.

 

 

 

Daniel

Edited August 12, 2006 by dhutch

[David Schweizer]

It does seem a rather pointless exercise - if you had lost your rudder the best place to be is on the bank, and if you hadn't lost your rudder then why not use it. It certainly wouldn't be practical to try and proceed for any distance by trying to steer using transverse thrust alone and I am surprised that David had to learn it for his BM exam. It might make a nice party trick given a boat with specific handling characteristics but no more than that!

 

Regards

 

Howard Anguish

Sometimes I loose the will to live. The reason we had to learn how to do it was precisely in order that we could manouver the boat to the side, in order to minimise any risk to the passengers by floating around in the middle of the watercourse.

 

If you want to see the evidence of how it works get on a boat and get it moving forwards at normal speed. Let go of the tiller and open up the throttle, depending on whether you have a right hand or a left hand prop the front of the boat will slew across to port or starboard, now drop the revs put the boat into reverse and open up the throttle, the front of the boat will slew across in the opposite direction, whilst it is still moving forwards.

 

My boat moves to port in forward and starboard in reverse. And as for it being a party trick, wherever possible, I use paddle action to advantage when bringing the boat alongside for mooring. The working boatmen knew how to do this and always used it to bring their boats alongside.

[enigma]

Daniel

 

I do not write rubbish.

 

enigma

Edited August 13, 2006 by enigma

[John Orentas]

Enigma.

 

I have found in this forum that if you write something that is original and perhaps controversial you are likely to get strongly contradicted.

 

Let me have my last go. Whether it is going forward or back-wards a boat propeller will exert a minor thrust in several directions, most notably you will get measurably more side thrust from the area of the bottom of the prop than you will get from the top part, because the deeper water will offer more resistance and there will be no air mixed up with it.

 

When going forward with water rushing past the rudder you are not aware of this because you compensate for that small effect on the tiller, there is an equal and opposite up and down effect too, one side lifting the boat and the other side pushing it down, but of course you will never be aware of these.

 

Oh, and remember too that for every bit of torque your engine exerts on the prop-shaft there is an equal force trying to rotate the boat along it's length.

[blackrose]

I've heard that there should be no prop walk (just to add some more terminology) on boats with a horizontal or flat propshafts from other sources too, but this is contradicted by the evidence from the majority of canal boat owners whose boats skew off course in astern.

 

Edward Burrel (Motor Barge Handling), recommends counteracting prop walk by holding the rudder at a 45 degree angle opposite to the direction that the stern moves towards (prop walk can move the stern to port or starboard depending on the prop direction of the particular boat). The rudder is then acting as a deflector rather than a rudder and has to be balanced with the correct amount of engine revs to keep it in a straight line. This may apply more to barges with large rudders but it's worth a try.

 

If you do manage to achieve this balance resist the temptation to increase engine revs or you will soon be offline again.

 

It's essential to know which way your boat moves in astern - in certain situations the effects of prop walk can be used to your advantage to get the boat into/out of moorings and when using astern to turn around for example. (If you know which way prop walk will take your stern in reverse you can use this to decide which way you steer the bow to start the turn in forward so that you keep the stern moving in the same direction when you put it into astern). In this way prop walk can actually assist handling and can be seen as an aid rather than an obstacle.

Edited August 13, 2006 by blackrose

[mykaskin]

Sometimes I loose the will to live. The reason we had to learn how to do it was precisely in order that we could manouver the boat to the side, in order to minimise any risk to the passengers by floating around in the middle of the watercourse.

 

Seems sensible to me, but unless your rudder falls off completely, it is more likely to get stuck at an angle, and therefore you could end up going around in circles! This is what happened to us on the River Humber when we caught a large barge sized rope around the prop, which not only stopped the engine dead, but locked the rudder solid as well!

 

I also find that most boats will have a tendency to driff off to the side anyway, even out of gear! On a canal I don't suppose it's really a problem, but a useful trick on a wide river I guess.

 

 

If you want to see the evidence of how it works get on a boat and get it moving forwards at normal speed. Let go of the tiller and open up the throttle, depending on whether you have a right hand or a left hand prop the front of the boat will slew across to port or starboard, now drop the revs put the boat into reverse and open up the throttle, the front of the boat will slew across in the opposite direction, whilst it is still moving forwards.

 

My boat moves to port in forward and starboard in reverse. And as for it being a party trick, wherever possible, I use paddle action to advantage when bringing the boat alongside for mooring. The working boatmen knew how to do this and always used it to bring their boats alongside.

 

 

If I let go of my tiller on Shoestring, she always turns to the left. My other boat is a little better behaved, but underpower will usually eventually pull either to the left, or the right depending on how close the tiller is to centre. I suspect the rudder balance is wrong, or perhaps the rake on the shaft.

 

In reverse Shoestring's stern pulls to the left, so I try to get on the left side of wide locks where possible. I'll have to give it go when actually travelling forwards, and see if it will pull the rest of the boat round.

 

GU Boats like the Narrow Boat Trust's Nuneaton (a large Northwich) were designed to pull to the left in reverse, so that they could put the butty on the starboard (right) side of the motor. This gave the motor the deepest part of the canal when passing other boats when brested up. Unfortunately, since they replaced the original engine, it now pulls to the right causing allsorts of annoyance!

[Silkhay]

depending on whether you have a right hand or a left hand prop

 

A vaguely related question. Whenever this topic is discussed reference is made to "Right Hand" or "Left Hand" props.

 

I can never really make up my mind just what is meant by these terms. My guess would be that right hand means turning clockwise and that this is when facing forward!!!

 

Have I got it right (sic) ?

 

Have a great weekend it'll soon be time to crack open and beer or three

 

Martin