Fuel Consumption

[Alan de Enfield]

I have, in the past, asked questions about fuel consumption as the 'figure' in the owners / workshop manuals are frightening. I know that the consumption will be proportional to the HP developed but have never really appreciated the huge difference between 'tick-over' & WOT.

 

On our NB with a Lister LPWS4 (which gives us 3.5mph at 2000 rpm with a 3:1 gearbox) we are using a 'tad' over 2 litres per hour - or about 1.6 miles per litre.

 

On our new boat with twin (120hp) Ford engines we are achieving 5-6mph at 1500 rpm for a consumption of a tad over 2 litres per hour per engine (say a total of 1 gallon per hour) - or about 1.2 / 1.3 miles per litre.

 

Assuming my maths is correct, I was surprised at the similarity in consumption of the two very different set-ups.

 

I found this 'link' very interesting and note that other manufacturers data (ie Volvo) is also on the same website - I wonder if such data is readily available for the common narrowboat engines ?

 

http://www.boat-fuel-economy.com/cummins-mercruiser-diesel-1.7-2.8-4.2-7.3-fuel-consumption-imperial-gallons

[Alan de Enfield]

I have, in the past, asked questions about fuel consumption as the 'figure' in the owners / workshop manuals are frightening. I know that the consumption will be proportional to the HP developed but have never really appreciated the huge difference between 'tick-over' & WOT.

 

On our NB with a Lister LPWS4 (which gives us 3.5mph at 2000 rpm with a 3:1 gearbox) we are using a 'tad' over 2 litres per hour - or about 1.6 miles per litre.

 

On our new boat with twin (120hp) Ford engines we are achieving 5-6mph at 1500 rpm for a consumption of a tad over 2 litres per hour per engine (say a total of 1 gallon per hour) - or about 1.2 / 1.3 miles per litre.

 

Assuming my maths is correct, I was surprised at the similarity in consumption of the two very different set-ups.

 

I found this 'link' very interesting and note that other manufacturers data (ie Volvo) is also on the same website - I wonder if such data is readily available for the common narrowboat engines ?

 

http://www.boat-fuel-economy.com/cummins-mercruiser-diesel-1.7-2.8-4.2-7.3-fuel-consumption-imperial-gallons

[Machpoint005]

MIleage in terms of mpg or miles/litre is largely meaningless on a canal -- if you are in shallow water it takes a lot more effort to force the boat through the silt at the bottom of the cut.

 

If you have two engines you are using double the fuel, but each engine is only propelling half a boat! Presumably that's on really wet water though?

[KenK]

At the last Southampton boat show I was looking at the engine room on a large Sunseeker motor cruiser, I asked one of the sales reps who was in there how much fuel the boat carried given the size of the engines, 15000 litres was the answer. Next question, how far will the boat travel on that amount of fuel, answer 350-500 miles depending on speed and weather conditions. Apparently running one of those boats costs approximately 10% of the purchase price each year, that one was £6,500,000, so about £650,000 per year, makes running a Narrowboat seem very reasonable.

 

Ken

[spadefoot]

Surely it's hours per litre, or litres per hour on a boat on inland waterways? You just can't equate engine revs to mph on a boat, never mind all the time idling in locks etc.

[Paul's Nulife4-2]

Hi Gang,

My Fuel consumption has actually varied quite a bit on my Nanni 5.250 TDI.

Depends on SO many variables

Wind, Tide, Swell, Revs, Dirty Prop / Hull, Eng Service etc etc.

I guess it's around the 5-7 Lts an Hr at a comfortable 7ish kts mark as a guide.

Edited May 22, 2015 by Paul's Nulife4-2

[Naughty Cal]

Surely it's hours per litre, or litres per hour on a boat on inland waterways? You just can't equate engine revs to mph on a boat, never mind all the time idling in locks etc.

Even that can be meaningless.

 

For example we use between 3 and 30 litres per hour.

MIleage in terms of mpg or miles/litre is largely meaningless on a canal -- if you are in shallow water it takes a lot more effort to force the boat through the silt at the bottom of the cut.

 

If you have two engines you are using double the fuel, but each engine is only propelling half a boat! Presumably that's on really wet water though?

We travel a lot with a friend who has a boat with two of the same engine as ours. He doesnt use twice as much fuel as we use!

 

When we went to the Broads we used 160 litres in NC to get from Hull to Lowestoft. The twin engined boat used 240 litres.

[Machpoint005]

Even that can be meaningless.

 

For example we use between 3 and 30 litres per hour.

We travel a lot with a friend who has a boat with two of the same engine as ours. He doesnt use twice as much fuel as we use!

 

When we went to the Broads we used 160 litres in NC to get from Hull to Lowestoft. The twin engined boat used 240 litres.

 

Yes, I understand that, but since the OP has two engines, his fuel consumption is double the fuel consumption per engine he was quoting.

[bottle]

 

I wonder if such data is readily available for the common narrowboat engines ?

 

Yes it is for Beta Marine engines, just look on their website.

[churchward]

Fuel consumption can seem a mysterious subject but in fact is quite straight forward and much more so than many manufacturers would like you to think as most engines only deviate from the norm by very small amounts of different efficiencies.

 

This link has a good summary of how to get a rough guide to consumption.

 

http://ltsc.co.uk/index.php/yacht-articles/564-diesel-engine-fuel-consumption-quicl-calculation

[Tony Brooks]

However that makes no comparisons between different lengths, beams, and hull shapes for boats which will also have an effect on fuel consumption. I suspect the boat with the twin 120 bhp engines has a more efficient hull shape at displacement speed and is probably lights and easier to push through the water where as the Lister is trying for push water down a canal in front of it because it is hard for canal water to pass down the sides and underneath. I suspect the two effects more or less cancel each other out. Now, if the twin engine boat was driven at above displacement speed but below planing speed the wave making would make fuel consumption far higher. The consumption may or may not then drop as the boat climbed out onto the plane.

 

Wave making and dropping the stern into the tough of the bow wave requires more power. Shorter boats have a lower speed at which wave making becomes significant and it is doubtful that many narrowboats of "typical" length can actually reach that speed. Just compare the wash from a GRP job on the Thames and a narrowboat at the same speed.

[Alan de Enfield]

 

Yes, I understand that, but since the OP has two engines, his fuel consumption is double the fuel consumption per engine he was quoting.

 

I actually said :

 

On our new boat with twin (120hp) Ford engines we are achieving 5-6mph at 1500 rpm for a consumption of a tad over 2 litres per hour per engine (say a total of 1 gallon per hour) - or about 1.2 / 1.3 miles per litre.

 

Having two engines does not use twice the fuel - maybe 1.5 times the consumption of one engine. Each engine is working less hard than a single engine would be.

 

Just as a matter of interest we have a 3 fuel tanks ( keel tank at 1000 litres and two 'wing' tanks each of 900 litres) Theoretical range of over 2000 miles

[churchward]

However that makes no comparisons between different lengths, beams, and hull shapes for boats which will also have an effect on fuel consumption. I suspect the boat with the twin 120 bhp engines has a more efficient hull shape at displacement speed and is probably lights and easier to push through the water where as the Lister is trying for push water down a canal in front of it because it is hard for canal water to pass down the sides and underneath. I suspect the two effects more or less cancel each other out. Now, if the twin engine boat was driven at above displacement speed but below planing speed the wave making would make fuel consumption far higher. The consumption may or may not then drop as the boat climbed out onto the plane.

 

Wave making and dropping the stern into the tough of the bow wave requires more power. Shorter boats have a lower speed at which wave making becomes significant and it is doubtful that many narrowboats of "typical" length can actually reach that speed. Just compare the wash from a GRP job on the Thames and a narrowboat at the same speed.

Quite so but you are thinking of load upon the engine when the numbers quoted in the link are an approximate of what the engine produces power for a given amount of fuel. This is reasonably standard as the fuel has a fixed energy potential and the engines will be within a narrow band of efficiency in extracting the maximum potential from the fuel.

[Wanderer Vagabond]

I have, in the past, asked questions about fuel consumption as the 'figure' in the owners / workshop manuals are frightening. I know that the consumption will be proportional to the HP developed but have never really appreciated the huge difference between 'tick-over' & WOT.

 

On our NB with a Lister LPWS4 (which gives us 3.5mph at 2000 rpm with a 3:1 gearbox) we are using a 'tad' over 2 litres per hour - or about 1.6 miles per litre.

 

On our new boat with twin (120hp) Ford engines we are achieving 5-6mph at 1500 rpm for a consumption of a tad over 2 litres per hour per engine (say a total of 1 gallon per hour) - or about 1.2 / 1.3 miles per litre.

 

Assuming my maths is correct, I was surprised at the similarity in consumption of the two very different set-ups.

 

I found this 'link' very interesting and note that other manufacturers data (ie Volvo) is also on the same website - I wonder if such data is readily available for the common narrowboat engines ?

 

http://www.boat-fuel-economy.com/cummins-mercruiser-diesel-1.7-2.8-4.2-7.3-fuel-consumption-imperial-gallons

I'm interested in your fuel consumption with your Lister LPWS4. We have the LPW4 on a 60 foot nb and running at about 1600rpm (roughly 3mph) we are using between 0.8 and 1 litre per hour, you're not pulling a trawl net are you?

Edited May 22, 2015 by Wanderer Vagabond

[Alan de Enfield]

I'm interested in your fuel consumption with your Lister LPWS4. We have the LPW4 on a 60 foot nb and running at about 1600rpm (roughly 3mph) we are using between 0.8 and 1 litre per hour, you're not pulling a trawl net are you?

 

No (ha-ha) but we have a 3:1 gearbox so to achieve the same speed as a 2:1 gearbox the engine is 'reving' much higher and thus using more fuel.

 

Do you have a 2:1 gearbox ?

 

With a 2:1 gearbox at 1600 rpm the prop is achieving 800 rpm - to achieve 800 rpm with a 3:1 gearbox the engine needs to be running at 2400 rpm.

[Timleech]

 

No (ha-ha) but we have a 3:1 gearbox so to achieve the same speed as a 2:1 gearbox the engine is 'reving' much higher and thus using more fuel.

 

Do you have a 2:1 gearbox ?

 

With a 2:1 gearbox at 1600 rpm the prop is achieving 800 rpm - to achieve 800 rpm with a 3:1 gearbox the engine needs to be running at 2400 rpm.

 

That only applies if both engines have the same prop.

If the prop is properly matched with your 3:1 box, it ought to be slightly more efficient and use less fuel.

 

Tim

[nb Innisfree]

Our LPWS4 in a 60' nb uses 1-1.8 ish lph, the main variation is down to our large alternator which under max load at 1200 rpm absorbs the same power as the prop (I checked that by noting the rev drop when engaging the prop as opposed to switching in the alternator) When batts are full and alt is producing a few amps I reckon we are using approx 1 lph at 2-3mph, handy for calculating fuel split for HMRC.

Mind you when blasting up the Thames on a tight schedule we used double the amount.

[Rose Narrowboats]

Our hire boats average out over the year at around 1 ltr/hr - that's Lister SR/TS/Alpha (until last week) and Isuzu 42/Canaline 42.

 

This is considerably lower than other hire companies whose usage I know, and I put it down to decent hull shape and careful prop choice. They are fitted with 3:1 boxes where possible which, as Tim Leech has already pointed out is slightly more efficient, and better at holding back too.

[ditchcrawler]

Our hire boats average out over the year at around 1 ltr/hr - that's Lister SR/TS/Alpha (until last week) and Isuzu 42/Canaline 42.

 

This is considerably lower than other hire companies whose usage I know, and I put it down to decent hull shape and careful prop choice. They are fitted with 3:1 boxes where possible which, as Tim Leech has already pointed out is slightly more efficient, and better at holding back too.

Interesting observation

[DHutch]

Next test, what's the new boats fuel usage with only one engine running....

 

Also; photos of the new boat required!

 

 

Daniel

[Alan de Enfield]

 

Also; photos of the new boat required!

 

 

Daniel

 

Taster pics :

 

Inside Helm station and Chart table

 

 

Lounge

 

 

Engine Room (Engine 1 & Engine 2)

 

 

Rear Cabin

 

[cuthound]

When I had a share in Honeystreet the co-owners were concerned about a perceived increase in fuel consumption from the then 10 year old BMC 1.8 engine.

 

I ran a spreadsheet for a year, asking co-owners to tell me how many hours the engine ran per holiday, and how many lock-miles they covered.

 

Consumption varied from 1.4 to 2.1 litres per hour. Unsurprisingly routes with more locks used less fuel than those with relatively few locks.

 

Edited to replace more with less as I was confused.

Edited May 25, 2015 by cuthound

[Jim Riley]

Why not turn off engine in locks? I did it with my Dawn craft, a pull start Honda 10.simple to start on boarding boat after doing lock. Would there be too much drain on battery, given that engine will be hot. It would also save lungs from diesel fumes/particulates.

[Giant]

To throw in another data point -

 

Lister JP3M, 35hp @ 1200rpm with 2:1 box and 29" prop, pushing a Sheffield size keel (61'5" x 15'6", 3'10" draft, about 65 tons).

 

On open water, cruising at 4.5kts, we made about 7 miles per gallon on the last trip - or 1.54 miles per litre.

 

That's almost the same as what you have for your NB on the canals, which I think mostly goes to show how much more power is required to make progress in a shallow, narrow channel.

[ditchcrawler]

To throw in another data point -

 

Lister JP3M, 35hp @ 1200rpm with 2:1 box and 29" prop, pushing a Sheffield size keel (61'5" x 15'6", 3'10" draft, about 65 tons).

 

On open water, cruising at 4.5kts, we made about 7 miles per gallon on the last trip - or 1.54 miles per litre.

 

That's almost the same as what you have for your NB on the canals, which I think mostly goes to show how much more power is required to make progress in a shallow, narrow channel.

That is why I always wonder who have overheating problems on rivers. I was on the Weaver last week doing 4½ mph and the engine was on a fast tickover, probably less than when I was doing 3mph on the T&M