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Debs

Power in reverse

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Debs    9

We have not long bought a 45' narrowboat but we are finding that it doesn't have much power in reverse. This means that it's really hard to stop as well even when going at very low speeds. When we are at standstill, it will move backwards but very slowly. To resolve the issue, would we be looking at getting a bigger propeller or an Axiom one? The one we have at the moment is a 3 bladed, bronze right hand rotation on a PRM 80 2:1 gearbox. We don't know what diameter it is though.

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Machpoint005    575

There are blade (propeller) experts on here but you'll need to tell them the engine type as well as gearbox, and more information on the one you have at present.

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rusty69    279

I would get it looked at before going down the new prop route, particularly if all is well in forward. Perhaps some adjustment is required. 

I guess you checked the obvious, nothing round the prop, although that would probably also affect forward direction 

Edited by rusty69

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Machpoint005    575
1 minute ago, rusty69 said:

I guess you checked the obvious, nothing round the prop

Going down the weed hatch would also provide an opportunity to check the diameter (OK, the radius!).

Edited by Machpoint005
sp.

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Debs    9

It's an Isuzu 25 engine. (25hp). It seems fine in forward.

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mrsmelly Contributor    1,170
23 minutes ago, Debs said:

We have not long bought a 45' narrowboat but we are finding that it doesn't have much power in reverse. This means that it's really hard to stop as well even when going at very low speeds. When we are at standstill, it will move backwards but very slowly. To resolve the issue, would we be looking at getting a bigger propeller or an Axiom one? The one we have at the moment is a 3 bladed, bronze right hand rotation on a PRM 80 2:1 gearbox. We don't know what diameter it is though.

Hi Debs

Ask yourself why only " axiom " props are axiom prop shaped?

1 minute ago, Debs said:

It's an Isuzu 25 engine. (25hp). It seems fine in forward.

It will depend greatly on prop size and pitch also how long are the swims? on a blunt ended boat which a short one like that may well be then there is not as much water round the prop for the prop to " grip " as it where to bring the boat to a standstill.

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Athy Donate to Canal World    900

Could the clue be in the Isuzu 25 engine, perhaps under-powered for a boat of that size? So it will get the boat going forwards, but stopping it and then reversing may be straining those 25 wee horses.

 

(Caveat: I am not a technically-minded person and I am only assuming that the "25" refers to the brake horsepower, not for example 2.5 litres).

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mrsmelly Contributor    1,170
3 minutes ago, Athy said:

Could the clue be in the Isuzu 25 engine, perhaps under-powered for a boat of that size? So it will get the boat going forwards, but stopping it and then reversing may be straining those 25 wee horses.

 

(Caveat: I am not a technically-minded person and I am only assuming that the "25" refers to the brake horsepower, not for example 2.5 litres).

I don't think 25 gee gees for a boat that size is bad at all. Boats in general are having too many horses fitted for the canal system. My first boat was 56 foot and had a knackered 9 hp engine now that was a tad underpowered especialy when we did the tidal trent on it :mellow: but we managed......................

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OldGoat    142
2 minutes ago, Athy said:

Could the clue be in the Isuzu 25 engine, perhaps under-powered for a boat of that size? So it will get the boat going forwards, but stopping it and then reversing may be straining those 25 wee horses.

 

(Caveat: I am not a technically-minded person and I am only assuming that the "25" refers to the brake horsepower, not for example 2.5 litres).

As Athy above. It's a small engine

PLUS

Boats don't go fast in reverse -

It (can) take ages to stop any forward motion, then  to go backwards.

Even so it's the shape of the rear end of the boat that makes reverse performance poor. It's part of the learning curve, only resolved by 'anticipation' !!

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Paul C    323

We had a 45ft boat which wasn't brilliant in reverse. Basically, its not worth fiddling around with props, gear ratios etc if it compromises forwards performance. One boatyard engineer said it was due to the boat having a blunt swim, compared to a longer boat which might have a much more sweeping swim which makes reverse more effective.

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Debs    9
5 minutes ago, OldGoat said:

As Athy above. It's a small engine

PLUS

Boats don't go fast in reverse -

It (can) take ages to stop any forward motion, then  to go backwards.

Even so it's the shape of the rear end of the boat that makes reverse performance poor. It's part of the learning curve, only resolved by 'anticipation' !!

We have hired boats though and had no trouble at all with stopping and reversing

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Athy Donate to Canal World    900
5 minutes ago, Debs said:

We have hired boats though and had no trouble at all with stopping and reversing

Probably because they had bigger engines. Our 30' widebeam hire boat in France last month would virtually stop on a sixpence (well, a centime) but then it had a 42 h.p. mill.

The Isuzu 25 is only an 1100 c.c. unit.

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When it comes to stopping power, propeller diameter is everything in my experience. The bigger the blade, the better the stopping performance.

My second narrowboat was the same as you describe. It would take approximately the length of the Oxford Canal to stop unless I absolutely revved the nuts off it in astern. So much so that people 100 yards away would look up to see what was happening. 16" blade on it, see?

Actually on reflection, it was probably 15".

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Athy Donate to Canal World    900
2 minutes ago, Mike the Boilerman said:

When it comes to stopping power, propeller diameter is everything in my experience. The bigger the blade, the better the stopping performance.

My second narrowboat was the same as you describe. It would take approximately the length of the Oxford Canal to stop unless I absolutely revved the nuts off it in astern. So much so that people 100 yards away would look up to see what was happening. 16" blade on it, see?

Actually on reflection, it was probably 15".

Good point. But isn't it the case (although I'm sure there are exceptions which prove the rule) that the bigger the engine, the bigger the propeller which is fitted to the boat?

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mross    269

It might be worth checking that the gearbox is not slipping when is astern (reverse).  I would try disconnecting the cable at the gearbox end and engaging locally.

  • Greenie 2

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mross    269

My 60' NB has an 18hp engine and does fine.  But it is a trad engine, so quite torquey.

Edited by mross

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20 minutes ago, Athy said:

Good point. But isn't it the case (although I'm sure there are exceptions which prove the rule) that the bigger the engine, the bigger the propeller which is fitted to the boat?

No.

My 15" blade was on a 35hp Beta. What diameter blade do you have on your 22hp Gardner?

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OldGoat    142
2 minutes ago, mross said:

My 60' NB has an 18hp engine and does fine.  But it is a trad engine, so quite torquey.

That's a point that is never discussed. It's not the rated power of an engine that matters per se. It's how much power you can get to the propeller before it starts cavitating.

With a 'proper' engine and ditto draft you can do magic.

I've got a 50HP engine but that's at 3000 rpm - so all I can do at those revolutions is to make bubbles...

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Athy Donate to Canal World    900
6 minutes ago, Mike the Boilerman said:

No.

My 15" blade was on a 35hp Beta. What diameter blade do you have on your 22hp Gardner?

22", on a 28 h.p. Gardner by the way.

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mross    269
2 minutes ago, OldGoat said:

I've got a 50HP engine but that's at 3000 rpm - so all I can do at those revolutions is to make bubbles...

You need a gearbox! :)

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Athy Donate to Canal World    900
2 minutes ago, Mike the Boilerman said:

 

With a direct drive transmission then I imagine. Otherwise the engine will be woefully under-loaded. 

Imagine away lad, I have no idea! It has a PRM 260 gearbox, if that is any sort of clue.

Mel Davis sent the boat spec. to Crowther's who supplied the prop - he said "I've never known them get one wrong yet".

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22 minutes ago, Athy said:

Imagine away lad, I have no idea! It has a PRM 260 gearbox, if that is any sort of clue.

Mel Davis sent the boat spec. to Crowther's who supplied the prop - he said "I've never known them get one wrong yet".

 

In which case it must be 2:1 reduction or 3:1 reduction (approx).

Mel's faith in Crowthers is very sweet, and misplaced in my personal experience of one of their cock-ups.

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Athy Donate to Canal World    900

Well there we are then.

If Crowther's props have always performed well on Mel's shells, it is reasonable that he has faith in them.

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OldGoat    142
43 minutes ago, mross said:

You need a gearbox! :)

I do - but 2 : 1 (they wouldn't sell me a 3:1, anyway it's not sensible in a 2'3" draft hull) and a Crowther prop - in their day (?) they were the bees knees

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