Propellors

[nb Innisfree]

On our original 33bhp engine we had a Crowther prop made for it, Keith who designed it said it would reach just under max revs (2000) and would absorb about 25bhp at those revs. He was spot on in both cases, if leisure batts were well down our large alternator would absorb the last 8 bhp and a little bit more, just noticeable when making an emergency stop in those circumstances.

[bargemast]

On our original 33bhp engine we had a Crowther prop made for it, Keith who designed it said it would reach just under max revs (2000) and would absorb about 25bhp at those revs. He was spot on in both cases, if leisure batts were well down our large alternator would absorb the last 8 bhp and a little bit more, just noticeable when making an emergency stop in those circumstances.

 

Wow, you really must have a huge alternator to use up 8 bhp, as that would be what's needed to produce about 5 Kva.

 

Peter.

[Tony Dunkley]

.The whole thing is something of a black art so if I can get acceptable fuel consumption, acceptable speed, acceptable acceleration (ahead and astern) I am happy and would not worry over a few hundred revs.

 

That's precisely the caveat that the eternally patient and long suffering Naval Architect retained by Manchester Dry Docks added to the conventional wisdom on propeller function and selection that he passed on to me as a persistently inquisitive young lad. I'm eternally grateful to him for having the time and patience to pass on some of his knowledge and experience on many different aspects of shipbuilding and marine engineering when his visits coincided with me picking up casual labouring work there when the Bridgewater Department barges were waiting for orders, and I think he would expect me to follow his example . . . . so here goes with some of it.

The selection and matching of engines and sterngear for slow displacement vessels begins with some well proven and long established principles, the first one being the selection of the largest diameter propeller than can be swung within the propeller aperture. This will ensure the highest possible propulsive efficiency that can be achieved for the subject vessel.

In the case of a cargo vessel the diameter is also governed by the need to ensure sufficient depth of immersion of the propeller blades in the light condition, and this in turn is dependent on the light, or in ballast draught. This, of course, is not applicable to pleasure craft.

Having determined the propeller diameter within the constraints of the hull design, the next step is to calculate the horsepower necessary to achieve the desired boat speed, and then select an engine and gearbox that will deliver that power at the lowest possible shaft rpm. For the size of pleasure craft we're considering here that means, in practical terms due to the range of suitably sized marine gearboxes available, a 3:1 Reduction ratio, and nothing less should be considered. As shaft rpm rises, propeller efficiency drops, and no amount of fiddling about with pitch can change that rather inconvenient fact.

Apart from blade area, number of blades and blade loading, which I won't go in to at this stage, the pitch is the next item to consider, and this where the 'black art' aspects start to creep in. In addition to the engines' ability (torque) to turn a propeller with any given pitch there are many other factors affecting the ideal pitch for any one vessel and installation, to name just three, hull design speed, the vessel's wake percentage and apparent propeller slip. All these things can be calculated, but the calculations involve the use of some 'constants' and the constants can either be lifted from tables of estimated and somewhat arbitrary figures, or arrived at by using generous helpings of experience and inspired guesswork, tempered with careful consideration of what has previously worked well on similar vessels.

Edited July 30, 2015 by Tony Dunkley

[Dalslandia]

 

Wow, you really must have a huge alternator to use up 8 bhp, as that would be what's needed to produce about 5 Kva.

 

Peter.

The alternator is probably 80-90% efficient, the belt and cooling take a lot of power too, so a belt driven alternator is probably 50% efficient

it means 8 HP produce about 3 kW maybe little more, ~210 Amp at nominal 12v (14v+)

[nb Innisfree]

The alternator is probably 80-90% efficient, the belt and cooling take a lot of power too, so a belt driven alternator is probably 50% efficient

it means 8 HP produce about 3 kW maybe little more, ~210 Amp at nominal 12v (14v+)

Alternator was 100 amp@24v, so about right, maybe prop absorbed a bit more than 25bhp.

[Dalslandia]

 

That's precisely the caveat that the eternally patient and long suffering Naval Architect retained by Manchester Dry Docks added to the conventional wisdom on propeller function and selection that he passed on to me as a persistently inquisitive young lad. I'm eternally grateful to him for having the time and patience to pass on some of his knowledge and experience on many different aspects of shipbuilding and marine engineering when his visits coincided with me picking up casual labouring work there when the Bridgewater Department barges were waiting for orders, and I think he would expect me to follow his example . . . . so here goes with some of it.

The selection and matching of engines and sterngear for slow displacement vessels begins with some well proven and long established principles, the first one being the selection of the largest diameter propeller than can be swung within the propeller aperture. This will ensure the highest possible propulsive efficiency that can be achieved for the subject vessel.

In the case of a cargo vessel the diameter is also governed by the need to ensure sufficient depth of immersion of the propeller blades in the light condition, and this in turn is dependent on the light, or in ballast draught. This, of course, is not applicable to pleasure craft.

Having determined the propeller diameter within the constraints of the hull design, the next step is to calculate the horsepower necessary to achieve the desired boat speed, and then select an engine and gearbox that will deliver that power at the lowest possible shaft rpm. For the size of pleasure craft we're considering here that means, in practical terms due to the range of suitably sized marine gearboxes available, a 3:1 Reduction ratio, and nothing less should be considered. As shaft rpm rises, propeller efficiency drops, and no amount of fiddling about with pitch can change that rather inconvenient fact.

Apart from blade area, number of blades and blade loading, which I won't go in to at this stage, the pitch is the next item to consider, and this where the 'black art' aspects start to creep in. In addition to the engines' ability (torque) to turn a propeller with any given pitch there are many other factors affecting the ideal pitch for any one vessel and installation, to name just three, hull design speed, the vessel's wake percentage and apparent propeller slip. All these things can be calculated, but the calculations involve the use of some 'constants' and the constants can either be lifted from tables of estimated and somewhat arbitrary figures, or arrived at by using generous helpings of experience and inspired guesswork, tempered with careful consideration of what has previously worked well on similar vessels.

As a black artist in a higher plane, but not under the surface, I know what it takes to calculate a propeller, and the same problem arise in airplanes as with boats, problem is several, drag? real power of engine? inflow? boats also have the problem called cavitating, that planes don't have, but have sometimes issues when approaching the speed of sound at propeller tips.

 

Then the question is what does the owner want out of it, and is it realistic?

Is a lower rpm/power compensated with a higher propeller efficiency? Boats have gearboxes (some airplane too) and the gear ratio can be chosen to fit the maximum propeller diameter possible to fit, just as Tony said. don't just go with standard 2:1 if a different ratio is better.

 

A bigger propeller can increase efficiency with 50%, that is not cat shit. when considering how low the efficiency is on a slow boat, at slow speed in a canal...

Edited July 30, 2015 by Dalslandia

[blackrose]

 

The overheating was caused as you say because of the skin tank not being adequete, that doesn't sound good to start with for a company had build quite a few boat before yours, and if people were prepared to pay a supplement with even more powerful engine, so even less adequate, not very serious if you ask me.

 

I'm glad the pilot was happy with the well matched engine, gearbox and prop, he was probably (I hope for him) a much better pilot than an engineer, if an engine can't reach it's maximum revs, it can't be a good match.

 

Peter.

 

The pilot was not aware what engine I had or what it's maximum revs were, he simply made his statement based on the boat's performance which is what we were talking about.

 

People who paid for a more powerful engine on a LB widebeam got an extra skin tank - at least my mate with the same boat with a 65hp engine did. So he didn't have any overheating problems.

 

I think I could probably take at least 50% of all canal boats made in the last 20 years (perhaps more) and get them on a river to find that they overheat and don't reach max revs because they are over-propped. Most people never find this out of course because they never venture from canals.

[blackrose]

 

You must consider the pilot's thoughts in the context and circumstances in which he expressed them.

Firstly, he would almost certainly have had only the performance of similar relatively modern canalboats with which to compare the performance of your boat, and there is no doubt that modern boats don't make efficient and effective use of the engine power they have in comparison with the commercial carrying boats of days gone by. Size for size, a fair comparison would be a Leeds and Liverpool Shortboat. Fully loaded a typical power/displacement ratio of around 0.4 bhp/ton, and light (empty) around 1.0 bhp/ton as against a modern widebeam canalboat, with a minimum of around 1.6 bhp/tonne, and usually much more. Overall performance and speed capability were very similar to that achieved by modern widebeams, and by any standards, that is something that todays so-called boatbuilders should be thoroughly ashamed of.

Secondly, you were paying him to get you and your boat to wherever you were going, and not to provide an assessment of the engine and sterngear installation. As a paying client, unless your boat was a floating deathtrap he would probably be hoping that you would engage him again should the need arise, so it's extremely unlikely that he would be inclined to be critical, or make adverse comments, about your pride and joy. Personally, I would say what I thought, but I've always had a talent for offending people by volunteering unsolicited opinions and saying things they may not want to hear.

 

I wonder why you assume I hadn't considered the pilot's comments in context and the circumstances in which he expressed them them? I was actually there after all (unlike yourself)...

 

You obviously don't know Bill Payne, who is very blunt when it comes to his opinions! A woman on a narrowboat who he brought into Portishead coming the other way warned me that she found him offesive. Apparently he made some sexist comments to her. Personally I'd go out of my way not to offend people who were engaging my services, but I guess he shares your self-professed talents!

 

She was correct. As soon as he stepped onto my boat at Portishead he was very critical and told me he didn't like widebeams and would rather take a narrowboat across because widebeams didn't handle and were usually underpowered. About 500 yards out of Portishead lock he told me we had plenty of power, and when we were about 2 miles out he said that mine was near the top of the range in terms of widebeams that he'd steered, but he obviously wasn't comparing it to a powerful commercial boat, he was comparing like for like. It only has a 55hp engine and that was my choice so it is a bit underpowered. I'm just trying to squeeze as much power out of it as I can. It does about 6.5mph which is the same as many narrowboats and faster than many others. It was built as a pleasure craft after all, so I don't really think comparison to powerful commercial craft is very valid.

 

Anyway, when we got into Sharpness he told me that I had a good boat. I don't think he said these things to because he wanted me to engage his services again. After all, the Gloucester Pilots pretty much have a monopoly when it comes to the Bristol Channel, so he knows that I don't have much choice but to engage their services if I want to make the crossing again.

Edited July 30, 2015 by blackrose

[peterboat]

Hi Mike,

 

I thought this thread had gone to bed As I have said before my boat was unpleasant to drive before the prop was repitched now its much more controllable I will find out next month when on the Trent if it has extra power but I am fairly confident that it has.

A gearbox and propeller change on my boat would have been an expensive change so a compromise had to be found, Woodwards did their magic and got it right for me. The real solution I suppose would be a variable pitch propeller but canal and river work does seem to damage normal props so a variable one wouldnt stand a chance.

If I had been that bothered I could have put a small turbo on this engine and boosted both the torque and horsepower up but I would have still been left with the low speed maneuverability issue with the original pitch.

I think we both did the right thing and the results are a good compromise at a reasonable cost so at least we both know we got it right

 

Peter

[bargemast]

The alternator is probably 80-90% efficient, the belt and cooling take a lot of power too, so a belt driven alternator is probably 50% efficient

it means 8 HP produce about 3 kW maybe little more, ~210 Amp at nominal 12v (14v+)

 

Hi Dalslandia, I was saying that because on one of my barges I had a genset with a Lister FR-1 that was driving a 4.5Kva alternator with no problems whatsoever, this genset was an factory made one, not something I put together myself.

 

Peter.

[bargemast]

 

The pilot was not aware what engine I had or what it's maximum revs were, he simply made his statement based on the boat's performance which is what we were talking about.

 

People who paid for a more powerful engine on a LB widebeam got an extra skin tank - at least my mate with the same boat with a 65hp engine did. So he didn't have any overheating problems.

 

I think I could probably take at least 50% of all canal boats made in the last 20 years (perhaps more) and get them on a river to find that they overheat and don't reach max revs because they are over-propped. Most people never find this out of course because they never venture from canals.

 

Hi Mike,

 

it doesn't matter what I and other people are saying about "Blackrose", she's your boat, and if you're happy with her and the way she performs, all is well.

 

Apart from that, I think that you did a very good job fitting her out into such a spacious and comfortable boat, which I think is her main purpose anyway, you don't need her for cargo transports on fast flowing rivers.

 

Peter.

[Tony Dunkley]

 

About 500 yards out of Portishead lock he told me we had plenty of power, and when we were about 2 miles out he said that mine was near the top of the range in terms of widebeams that he'd steered, but he obviously wasn't comparing it to a powerful commercial boat, he was comparing like for like. It only has a 55hp engine and that was my choice so it is a bit underpowered. I'm just trying to squeeze as much power out of it as I can. It does about 6.5mph which is the same as many narrowboats and faster than many others. It was built as a pleasure craft after all, so I don't really think comparison to powerful commercial craft is very valid.

 

 

If you want to "squeeze as much power" out of your boat as you can, then you have no option other than to change the gearbox for a model with the biggest reduction ratio available ( 3:1, unless you buy a gearbox designed for a bigger engine with a higher power output) and fit the largest diameter propeller the hull design will accommodate.

Your boat is by no means underpowered with an engine capable of producing 55 bhp, but at present it is very inefficient in the way it makes use of the available power, with only approximately one third of that 55 bhp being turned into useful thrust at the propeller.

I don't think you understand the basic principles behind getting the maximum efficiency from engines, gearboxes and propellers, and I can't imagine why you think there has been any comparison made between your boat and what you describe as "powerful commercial craft". The commercial carrying boats for which I gave some approximate power/displacement figures in comparison with those for modern widebeam pleasure craft were 62' in length by 14' beam, when loaded displaced well over twice the tonnage of your boat and typically had engines of no more than 30 bhp. These boats were not 'powerful' by any standards, but what they did do was to make the most efficient possible use of the relatively little power they did have.

Edited July 31, 2015 by Tony Dunkley

[peterboat]

They did Tony. Keith Smith 4 boats down from me from the age of 14 worked Sheffield size boats, however he is the first to say they could not push the tide if they overshot a lock on the trent they had to wait until slack to get back there.

Everything they did was based around tides and perfik timing. Keith told me he had lost count of the times he had spent on the mud because they were that underpowered. It was only when went to work at Arkers that he had a boat with an engine up to the job.

I suppose we have to remember that in those days labour was cheap and engines that were big enough were expensive so from owners point of view did it matter if crew were sat waiting.

Gardners were a revelation to old boatmen smooth quiet and powerful what more could you ask for

 

Peter

[Tony Dunkley]

They did Tony. Keith Smith 4 boats down from me from the age of 14 worked Sheffield size boats, however he is the first to say they could not push the tide if they overshot a lock on the trent they had to wait until slack to get back there.

Everything they did was based around tides and perfik timing. Keith told me he had lost count of the times he had spent on the mud because they were that underpowered. It was only when went to work at Arkers that he had a boat with an engine up to the job.

I suppose we have to remember that in those days labour was cheap and engines that were big enough were expensive so from owners point of view did it matter if crew were sat waiting.

Gardners were a revelation to old boatmen smooth quiet and powerful what more could you ask for

 

Peter

 

That's right Peter, the early model of 3 cylinder Listers that were in a lot of Sheffield boats were 27bhp, and the L&L Shortboats that I gave the Horsepower / ton figures for earlier would only carry half as much. The horsepower / ton for a Sheffield size with a 100 tons on and an early 3 cylinder Lister is 0.19 bhp / ton. The equivalent power / displacement ratio applied to a modern widebeam canalboat would leave you with an engine of about 6 bhp.

The performance and top speed of the L&L shortboats with around 30 bhp was comparable with what most modern widebeam pleasure craft can manage with around twice that much power, at the very least. It's all down to the majority of todays so-called boatbuilders being utterly clueless about marine engineering, and treating the engine and sterngear installation as sort of afterthought. They (the builders) get away with it because most of their customers know even less than they do about boat propulsion, and of course very few people want to believe that they've paid out good money for something that could, and should, perform much better than it does.

[peterboat]

 

That's right Peter, the early model of 3 cylinder Listers that were in a lot of Sheffield boats were 27bhp, and the L&L Shortboats that I gave the Horsepower / ton figures for earlier would only carry half as much. The horsepower / ton for a Sheffield size with a 100 tons on and an early 3 cylinder Lister is 0.19 bhp / ton. The equivalent power / displacement ratio applied to a modern widebeam canalboat would leave you with an engine of about 6 bhp.

The performance and top speed of the L&L shortboats with around 30 bhp was comparable with what most modern widebeam pleasure craft can manage with around twice that much power, at the very least. It's all down to the majority of todays so-called boatbuilders being utterly clueless about marine engineering, and treating the engine and sterngear installation as sort of afterthought. They (the builders) get away with it because most of their customers know even less than they do about boat propulsion, and of course very few people want to believe that they've paid out good money for something that could, and should, perform much better than it does.

Sheffield boats do look nice out of water, nice shape good flow to swim If I had found one before I bought this boat I suspect with a good survey I would have preferred the the sheffield size, I would have had to put a Gardner in it though not a big one but something nice and smoth with 6 cylinders

 

Peter

[blackrose]

 

Hi Mike,

 

it doesn't matter what I and other people are saying about "Blackrose", she's your boat, and if you're happy with her and the way she performs, all is well.

 

Apart from that, I think that you did a very good job fitting her out into such a spacious and comfortable boat, which I think is her main purpose anyway, you don't need her for cargo transports on fast flowing rivers.

 

Peter.

 

Thanks Peter. I don't give too much credibility to the firm convictions of people who claim to know-it-all but have never been on my boat so don't actually know how it performs.

Edited July 31, 2015 by blackrose

[bargemast]

I have 3 very interesting books here that are written by Mike Taylor :

 

1/ Richard Dunston Ltd.

2/Dry Cargo Barges on the Humber Waterways.

3/The Canal & River Sections of the Aire & Calder Navigation.

 

In these books they show lots of the localy built barges and tell about the and their history, many started with Lister JP-2 22 Hp engines that seems to have been the most popular at the time, later many JP-3's, but alsp some single and twin cylinder Widdop engines.

 

Later more powerful engines were installed, but they did pretty well for many years with their low powered barges, and they knew how to make the best use of the few horses (Hp's) that were available to work with.

 

Peter.

[blackrose]

 

If you want to "squeeze as much power" out of your boat as you can, then you have no option other than to change the gearbox for a model with the biggest reduction ratio available ( 3:1, unless you buy a gearbox designed for a bigger engine with a higher power output) and fit the largest diameter propeller the hull design will accommodate.

Your boat is by no means underpowered with an engine capable of producing 55 bhp, but at present it is very inefficient in the way it makes use of the available power, with only approximately one third of that 55 bhp being turned into useful thrust at the propeller.

I don't think you understand the basic principles behind getting the maximum efficiency from engines, gearboxes and propellers,

 

You misunderstood me - perhaps I didn't explain properly. I want to squeeze as much power as I can out of the current setup, so I certainly don't want to spend money on a new gearbox.

 

I'm not sure where you're getting your figures from, but according to the engine specs, at 2200rpm I'm getting about 44bhp from the engine which is not great, but it's certainly a lot more than one third (18bhp) that you state. Perhaps it's you who doesn't understand the basic principals.

 

Isuzu 55 power output and torque curves:

Propcalc seems to think the boat has a lot more but this seems to be an overestimate:

 

Data Input Waterline length in feet: 54 feet Beam at the waterline in feet: 12 feet Hull draft in feet (excluding keel): 2 feet Vessel weight in pounds: 70500 lbs Engine Horsepower: 55 HP Number of engines: 1 Total Engine Horsepower: 55 HP Engine R.P.M. (max): 2200 RPM Gear Ratio: 2.09:1 Shaft R.P.M. (max): 1053 RPM Number of shaft bearings (per shaft): 1 Desired speed in Knots: 6 knots Horsepower Calculations This will calculate the maximum horsepower and torque available at the prop(s). Total available horsepower at the engine(s): 55 HP Total available torque ft/lbs at the engine(s): 131 ft/lbs Horsepower loss of 3% per gearbox: - 1.6 HP Horsepower loss of 1.5% per shaft bearing: - 0.8 HP Total horsepower available at the propeller(s): 52.5 HP

Edited July 31, 2015 by blackrose

[Tony Dunkley]

 

You misunderstood me - perhaps I didn't explain properly. I want to squeeze as much power as I can out of the current setup, so I certainly don't want to spend money on a new gearbox.

 

I'm not sure where you're getting your figures from, but according to the engine specs, at 2200rpm I'm getting about 44bhp from the engine which is not great, but it's certainly a lot more than one third (18bhp) that you state. Perhaps it's you who doesn't understand the basic principals.

 

Isuzu 55 power output and torque curves:

 

The 43-44 bhp that power curve shows at 2200 is at the engine flywheel, and may or may not include an allowance for ancillaries.

After deducting the usual (nominal) percentage figure of 5-10% losses in the gearbox and shaft bearings, and then applying an appropriate percentage efficiency figure (45%, and that may be optimistic) for the high revving small diameter propeller you have, you're left with about 18 bhp worth of thrust actually being produced at the propeller.

 

In the light of this latest post from you, I no longer think that you don't understand the basic principles, . . . . I'm absolutely certain that you don't.

Edited July 31, 2015 by Tony Dunkley

[Dalslandia]

But at 2200 you had 43-44 HP

[Tony Dunkley]

 

Propcalc seems to think the boat has a lot more but this seems to be an overestimate:

 

Data Input Waterline length in feet: 54 feet Beam at the waterline in feet: 12 feet Hull draft in feet (excluding keel): 2 feet Vessel weight in pounds: 70500 lbs Engine Horsepower: 55 HP Number of engines: 1 Total Engine Horsepower: 55 HP Engine R.P.M. (max): 2200 RPM Gear Ratio: 2.09:1 Shaft R.P.M. (max): 1053 RPM Number of shaft bearings (per shaft): 1 Desired speed in Knots: 6 knots Horsepower Calculations This will calculate the maximum horsepower and torque available at the prop(s). Total available horsepower at the engine(s): 55 HP Total available torque ft/lbs at the engine(s): 131 ft/lbs Horsepower loss of 3% per gearbox: - 1.6 HP Horsepower loss of 1.5% per shaft bearing: - 0.8 HP Total horsepower available at the propeller(s): 52.5 HP

 

That entire calculation is completely meaningless and wrong because it uses an incorrect engine horsepower figure (55 bhp) for the stated maximum rpm of 2200.

 

It should also be noted that they give the horsepower available at the propeller and make no deduction to take into account the likely propeller efficiency, or in other words, how well the propeller turns that horsepower into useful thrust.

Edited July 31, 2015 by Tony Dunkley

[Dalslandia]

As a figure in a park of balls, if engine is rated according British BHP, or SAE using 85% of the rated is a good idea, the rest is used up for cooling pumps, generator, exhaust system, air filter.

 

And that do not include an extra alternator.

 

DIN or newer have those items included in the stated power figures.

 

Blackrose, try 43 hp at 2200, if you have an extra alternator, take off a couple more for the un-loaded situation. (belts and cooling drag)

Edited July 31, 2015 by Dalslandia

[David Mack]

Probcalc is saying that the engine and power train delivers (a maximum of) 52.5 hp to the prop. Tony is saying that the efficiency of the prop is such that the amount of power pushing the boat forwards is about 18hp. Those 2 statements don't seem to me to be too far apart.

[Tony Dunkley]

Probcalc is saying that the engine and power train delivers (a maximum of) 52.5 hp to the prop. Tony is saying that the efficiency of the prop is such that the amount of power pushing the boat forwards is about 18hp. Those 2 statements don't seem to me to be too far apart.

 

Propcalc, whoever they are, are not using the correct horsepower figure for that engine at 2200 rpm. Allowing for ancillaries it's only a little over 40 bhp at the flywheel at those revs.

[RLWP]

But at 2200 you had 43-44 HP

 

Up to 43-44 HP. The engine will only produce enough power to maintain the speed demand

 

Richard