Fuel Consumption Data

[Gunna Do]

My Beta 43 in 50ft Nb has averaged 1.12 ltrs/hr over the last 200 hours. Generally run at 1300/1400 revs so only using 20 BHP but sometimes give her a burst on the Trent.

[Robin2]

My Beta 43 in 50ft Nb has averaged 1.12 ltrs/hr over the last 200 hours. Generally run at 1300/1400 revs so only using 20 BHP but sometimes give her a burst on the Trent.

 

I'm interested to know how you calculate the 20hp?

[J R]

Mock ye not, the OP has a good point and full marks for the research. Don't have figures for a Suzi 35, but the 42 which to all intents and purposes is the same as a 35hp but is 2 litre, the HMI book says at 1400 rpm it uses a wopping 2.4 litres per hour. Someone did a study some years ago, a livaboard with an Isuzu 42, and found that over 18 months the average fuel consumption was 1.4 L/hr for what it is worth.

 

I work on 1.25 L/hr on average which seems about right from my rough calculations for us. (1100 rpm produces 4 mph on a 65 foot boat).

[nb Innisfree]

Mock ye not, the OP has a good point and full marks for the research. Don't have figures for a Suzi 35, but the 42 which to all intents and purposes is the same as a 35hp but is 2 litre, the HMI book says at 1400 rpm it uses a wopping 2.4 litres per hour. Someone did a study some years ago, a livaboard with an Isuzu 42, and found that over 18 months the average fuel consumption was 1.4 L/hr for what it is worth.

 

I work on 1.25 L/hr on average which seems about right from my rough calculations for us. (1100 rpm produces 4 mph on a 65 foot boat).

 

Perhaps that is at full load for those revs?

[RLWP]

Perhaps that is at full load for those revs?

 

That seems most probable.

 

Richard

[J R]

Perhaps that is at full load for those revs?

 

Thats got to be one hell of a load as the engine max RPM is 3000.

 

Had a bit more time to calculate out the OPs figures and reckon that he is not that far out, allowing for the fact that his engine is 35 hp as opposed to 42 hp. Down this way hire fleets seem to work on an average consumption of 1.5 L/hr accross the board for all engine sizes.

[Chalky]

I had a chat with one of my colleagues a few years ago who's a diesel combustion specialist. He said that since diesel is a slow burning fuel you don't get complete combustion above about 2000 rpm and you end up throwing unburned fuel out of the exhaust. In a car his advice was to run the engine as slow as possible and let the gearbox do the work.

[bargemast]

My Beta 43 in 50ft Nb has averaged 1.12 ltrs/hr over the last 200 hours. Generally run at 1300/1400 revs so only using 20 BHP but sometimes give her a burst on the Trent.

 

 

If you only use 1.12 ltrs/hr you're far from using 20 BHP, if you want your HP's you have to feed them, and 20 BHP that have to work will use closer to 3.5 ltrs/hr. You'll surely be able (if you're interested) to find a study that will show you the amount of gramm's of diesel needed per/Kw.

 

Peter.

[nb Innisfree]

Thats got to be one hell of a load as the engine max RPM is 3000.

 

At 1400 rpm that would probably be just under half max output i.e. about 16 bhp.

[ditchcrawler]

At 1400 rpm that would probably be just under half max output i.e. about 16 bhp.

Surly this is the possible output not the actual and an engine can run at anything up to maximum revs with no load and be producing very little horsepower, but if loaded could produce the rated horsepower.

[nicknorman]

Surly this is the possible output not the actual and an engine can run at anything up to maximum revs with no load and be producing very little horsepower, but if loaded could produce the rated horsepower.

Quite right - but don't call me Surly!

 

Well I think its a good idea

 

My experience has always been that peak MPG is always at peak torque on any engine. I would expect you will find that the highest efficiency will be at 1800 rpm with your Beta.

 

My maximum torque (Barrus 45) is between 1600 and 1800rpm my prop was chosen to allow me to cruise at these revs.

 

Alex

No, whilst you get the best ratio of fuel burn to bhp for a fully loaded engine at max torque rpm, when operating at a smaller load, the unnecessarily high rpm wastes a lot of energy through friction. Your boat would be much more economical with a larger /coarser prop. It would be like driving your car in low gear to get the revs up to max torque rpm at 30 mph -very uneconomical!

 

Nick

[nb Innisfree]

Surly this is the possible output not the actual and an engine can run at anything up to maximum revs with no load and be producing very little horsepower, but if loaded could produce the rated horsepower.

Yes possible, I think that is what the manufacturers are quoting, it would explain the apparent high consumption of 2.4 lts @ 1400 rpm.

[Timleech]

I'm interested to know how you calculate the 20hp?

 

I think he's taken it from the Beta power curve, but that's what the engine can develop.

Propeller power follows roughly the cube of the rpm, so if you ignore ancillary loads, at 1400 rpm it will be using about 5 bhp - enough to push a narrowboat along very nicely

 

Tim

[nb Innisfree]

I think he's taken it from the Beta power curve, but that's what the engine can develop.

Propeller power follows roughly the cube of the rpm, so if you ignore ancillary loads, at 1400 rpm it will be using about 5 bhp - enough to push a narrowboat along very nicely

 

Tim

 

Yes, at 16 bhp @ 1400rpm I was meaning the Isuzu 35, didn't read the post properly, 20 bhp sounds about right for the Beta 42 at full load @ 1400rpm.pm

 

When I put our engine in gear at our tickover of 1200 rpm it drops nearly the same number of revs as if I just excite our alternator which absorbs about 6-7 bhp according to it's graph. on that basis I would say our prop absorbs about 6-7 bhp @ 1400rpm, pretty much in the same region of your estimate.

Edited July 6, 2011 by nb Innisfree

[NB Alnwick]

The comparison between big and small engines is interesting. Over the last five years or so the average fuel consumption of our Kelvin K3 has worked out at 1.8 litres an hour. That average does include a fair proportion of River cruising and two trips in the Severn Estuary at near maximum rpm. Having said that recent experience indicates that fuel consumption during canal cruising at around 275 rpm (which gives about three miles an hour) produces a fuel consumption rate as low as a Litre an hour. I think this says quite a lot about the efficient combustion achieved with the Ricardo 'Comet' design at low revolutions. On the other hand we have also found that a variety of factors can make a huge difference overall - some example are listed below:

 

Weed growth on the hull - we found that after the boat had been freshly blacked we could travel along the same length of canal at the same speed with the propeller turning nearly 10% slower! 275 rpm after blacking compared to over 300 rpm beforehand!

 

Stuff caught on the propeller - in 2006 when we went up the River Lee we were using almost four times as much fuel as normal (over a gallon an hour) - the cause turned out to be a large silk dress and various other items wrapped round the prop and prop shaft.

 

Shallow or narrow water - the boat slows considerably when the bottom of the canal is too close to the top or when it is very narrow as in the now opened-up Fenny Compton Tunnel section. In these circumstances, it is tempting to open the regulator and have the engine run fast but this uses a lot more fuel.

[nb Innisfree]

On the cut it seems all engines big or small seem to use similar amounts of fuel (providing engines are not overly large or small and are in good tune) supporting the logic that it takes a certain amount of energy and therefore fuel to propel a boat at a certain speed.

[RLWP]

<snip>

 

I think this says quite a lot about the efficient combustion achieved with the Ricardo 'Comet' design at low revolutions.

 

<snip>

 

Does it say that it's about as efficient as something thrown together by a bunch of Brummies at Longbridge?

 

Tawny Owl's BMC 1.8 also does about 1 litre per hour on canals

 

Richard

Edited July 7, 2011 by RLWP

[dor]

Just to add some figures for comparison:

 

My 57ft / 24" max draft NB with 42 HP Vetus M4.17, 2:1 gearbox & 17x11 prop has used about 1.35 litres per hour over the last 400 hours. Over 95% of that is cruising rather than running out of gear.

 

You may also be interested in some speed figures:

 

RPM............................Shroppie....................................Weaver

850(tickover)..................2.4

1000................................2.8

1200................................3.3............................................3.5

1400................................3.9............................................4.1

1600................................4.2............................................4.6

1800..................................................................................5.0

2000..................................................................................5.5

 

Obviously the Weaver is deep water, the Shroppie typical but not overly shallow canal. 2000rpm is close to maximum - it will just about reach 2300 in gear (3400 in neutral).

[Ex- Member]

On the cut it seems all engines big or small seem to use similar amounts of fuel (providing engines are not overly large or small and are in good tune) supporting the logic that it takes a certain amount of energy and therefore fuel to propel a boat at a certain speed.

 

Excellent observation of course with the odd exception but something around 1.3 litres per hour looks to be about average without actually adding up every post. I'm wondering weather some clever person could set up a poll. Any members who can input figures they believe are accurate stating engine size + HP The more data the better the result and similar engine sizes can compare data.

 

The only useful consumption data IMO is that spread over some time with a mixture of cruising and generating. Although the posters data and the way it's been gleaned is as valuable and the figures he's quoted thus far are well within what's been quoted by other members.

 

Maybe a list of engines and members enter their consumption against their respective engine.

 

 

 

[Tiny]

Our Beta 38 does roughly an hour a litre at 1100 revs which gives a good forward speed with our john white hull.

[alan_fincher]

I think perhaps the biggest pitfall in comparing what people believe their cruising usage to be will be down to the waterways people travel on, and the unencumbered cruising speed they think is "normal".

 

It is obvious to me that as you regularly get queues of people on busy canals lined up behind a boat who's steerer thinks their speed is appropriate, that not all people expect to make the same progress.

 

I suspect how fast you consider "normal" has more to do with it a lot of the time than on exact engine type, horsepower, reduction or prop size.

 

It is a simple fact that to push a boat through the water faster requires more fuel.

 

Therefore if two people have near identical set-ups, and one routinely travels at 2.5 mph and another at 3.5 mph, you would undoubtedly record a greater fuel consumption by the latter, (very noticeably so, I'd say).

 

We would struggle to get 1 litre per hour, because we are not in the habit of hanging about where the canal and other users permit it. However I suspect there are some on here who could take Chalice and get much closer to that figure! (They would take longer to get places, of course!).

 

So unless people can measure speed accurately, (and I doubt many can really estimate it accurately!), I think comparisons have little legitimacy.

[Robin2]

The only useful consumption data IMO is that spread over some time with a mixture of cruising and generating. Although the posters data and the way it's been gleaned is as valuable and the figures he's quoted thus far are well within what's been quoted by other members.

 

So unless people can measure speed accurately, (and I doubt many can really estimate it accurately!), I think comparisons have little legitimacy.

 

The main reason I made the measurements was to get a reasonably accurate idea of how much it costs to run the engine to generate electricity.

 

For all the reasons that people mention the fuel usage when cruising will be difficult to compare - including, for example, whether you shut off your engine while working a lock.

 

I forgot to mention in my original post that for most of the tests there was about 30A going into the battery and maybe another 8 into the fridge some of the time. I had intended to try to isolate the fuel usage due to the alternator load but, as I said, I ran out of time. I have kept my apparatus intact and I will probably do another series of tests in the next week or 2. To be honest I was surprised that my apparatus worked as easily as it did and I was not really expecting to get results straight off. Next time I will be able to devote more time to testing and less to setting up.

 

It would be interesting to see if it makes any difference to remove the alternator drive belts to remove both the electrical and mechanical load, but I am not sure if I am that enthusiastic.

[RLWP]

It would be advantageous to measure a greater volume of fuel, perhaps 100cc, otherwise your equipment is fine

 

Being me, I would have teed the injector spill into the system between the engine and your calibrated feed pipe so it wasn't dribbling into the thing you were reading. Instinctively this would make it easier to read

 

Richard

[Ex- Member]

In reality there's no accurate figure, the best you could hope for would be an average figure with an error factor of possibly 10% either way, there's simply too many variables.

 

But if 10 people put figures in for consumption for the same engine measured over a reasonable period of time then there's an average to be had, it's likely that out of the ten 5 might cruise faster 5 might not who knows, then as to all the other variables Alan has mentioned and they will possibly even out as well, the more info put in the more accurate the average will be. But it would be interesting if a trend emerged that showed if certian engines were thirstier than others.

 

 

 

Of course Robins set up could measure in set different circumstances like measuring consumption whilst just charging in neutral.

 

 

These could be really useful figures now and in the future as the price of diesel will most likely continue to rise and alternative energies become cheaper, the only people who can actually collate this figures are boaters themselves, as manufacturers consumption figures mean little in the real world of boating.

[Robin2]

It would be advantageous to measure a greater volume of fuel, perhaps 100cc, otherwise your equipment is fine

 

Being me, I would have teed the injector spill into the system between the engine and your calibrated feed pipe so it wasn't dribbling into the thing you were reading. Instinctively this would make it easier to read

 

Richard

 

I partially agree about the larger volume. Two factors go against it - lack of patience, and the fact that the fuel level dropping quickly in the narrow tube makes it easier to detect when the marker line is passed.

 

I understand what you are saying about the injector spill but I wonder if it would need to be more complex. As far as I could see there are occasional air bubbles in it and my system allows them to escape. I think you would need a second riser for the overspill - but it could be arranged. It would also avoid the minor problem that the fuel level dropped momentarily when the key was turned and the electric fuel pump started. I discovered I had to wait a few moments before starting the engine.

 

It's got me wondering again about some solar cells ....

Edited July 7, 2011 by Robin2