Twister_Ken
Well-known member
Hoo sed?
cruising range fuel/consumption
- Thread starter benlui
- Start date
Hoo sed?
ChrisE
Active member
Go on, you know you can do it.
Mudisox
Well-known member
Commanche Cat
2x 12.5 Betas
0.95l/hr average over season at a guestimate 5 kts on one engine.
2x 65l tanks and 40l in cans carried so 8-900 odd miles.
2x 12.5 Betas
0.95l/hr average over season at a guestimate 5 kts on one engine.
2x 65l tanks and 40l in cans carried so 8-900 odd miles.
ChrisE
Active member
As you're not here's the figures:
Average tankage: 260l
Average range: 446m
However, these figures are skewed by some of the bigger vessels, so taking 200l as a cut off point and this takes in 22 boats
Average tankage: 113l
Average range: 303m
ITH
Member
Cruising range/fuel consumption
Nauticat 35
Volvo Penta 2003T diesel, 3-cylinder turbo diesel, circa 1989:
3-blade, fixed prop
Standard specifications (Nauticat 35 manual):
Fuel capacity 350l in two tanks, and cruising range 600Nm. So the theoretical consumption is 1.70 l/Nm
In practice however, there is probably only 315l 'available' fuel in the two tanks.
Based on two years of practical measurements: litres used/engine hour run - generally on longer passages (50 to 350Nm) - our actual consumption across a range of weather conditions and sea states is from 1.6 to 2.4 l/hr. On that basis we have an engine running time of from 130 to 194 hours on full tanks.
Nauticat 35
Volvo Penta 2003T diesel, 3-cylinder turbo diesel, circa 1989:
3-blade, fixed prop
Standard specifications (Nauticat 35 manual):
Fuel capacity 350l in two tanks, and cruising range 600Nm. So the theoretical consumption is 1.70 l/Nm
In practice however, there is probably only 315l 'available' fuel in the two tanks.
Based on two years of practical measurements: litres used/engine hour run - generally on longer passages (50 to 350Nm) - our actual consumption across a range of weather conditions and sea states is from 1.6 to 2.4 l/hr. On that basis we have an engine running time of from 130 to 194 hours on full tanks.
Twister_Ken
Well-known member
You're awful, but I do like you.
GAJ
Member
Still have not had the chance to confirm most economical cruising revs as we not done enough miles, did ask on the forum but it appears no one has a power output/fuel consumption chart to hand that might give me a clue. I was told that the motor is 50hp though......... but the story so far is:
Amel Sharki 40ft
Perkins Prima M50
350 lt. fuel. I like to leave around 30 lt in reserve for unforseen stuff.
My experience so far is that we use about 2.25 lts an hour at 2400 rpm which gives 6.2 kn in flat water, so leaving 30 lt in reserve range somewhere around 900 Nm not allowing for sea state and weather conditions.
Amel say the range is 550 Nm at 7.7 kn and 750Nm at 6.7 kn. which sounds realistic.
Amel Sharki 40ft
Perkins Prima M50
350 lt. fuel. I like to leave around 30 lt in reserve for unforseen stuff.
My experience so far is that we use about 2.25 lts an hour at 2400 rpm which gives 6.2 kn in flat water, so leaving 30 lt in reserve range somewhere around 900 Nm not allowing for sea state and weather conditions.
Amel say the range is 550 Nm at 7.7 kn and 750Nm at 6.7 kn. which sounds realistic.
benlui
Member
Some really surprising and interesting results there. I like the avg calculations carried out too, that's great thanks. However, as some people have included fuel on deck, has this been taken into account? I guess the cruisingrange should includethisunlike stated in my original post. I carry 44ltrs spare when cruising almost giving me 40% more cruising range but,i didn't include this in my original post as i say.
I was quiet surprised at the consumption on the larger boats, being higher than I would have anticipated. Thank god for sails
G12, we did some rough calculations previously with my engine supplier and we came to the conclusion that given the LOA at water line of the Shipman 28, an 18hp engine would be quiet sufficient.
Anything above that would not make much difference giving her maximum hull speed. My 21hp with 3 blade fixed prop, gets me out of almost anything.
I opted for the 21hp mainly due to the fact that I felt the engine would have to work less over its life, and it was only 200euro more expensive given the deal i got at the time.
I was also surprised to see how many people actually know their consumption figures for their boats too, lots of you have it worked out to the bone. In the past when I have asked people down the marina or where ever, they just have no idea which was again surprising.
Very interesting results thanks........
I was quiet surprised at the consumption on the larger boats, being higher than I would have anticipated. Thank god for sails
G12, we did some rough calculations previously with my engine supplier and we came to the conclusion that given the LOA at water line of the Shipman 28, an 18hp engine would be quiet sufficient.
Anything above that would not make much difference giving her maximum hull speed. My 21hp with 3 blade fixed prop, gets me out of almost anything.
I opted for the 21hp mainly due to the fact that I felt the engine would have to work less over its life, and it was only 200euro more expensive given the deal i got at the time.
I was also surprised to see how many people actually know their consumption figures for their boats too, lots of you have it worked out to the bone. In the past when I have asked people down the marina or where ever, they just have no idea which was again surprising.
Very interesting results thanks........
Phoenix of Hamble
Active member
I've got the data here for an M50, which i'll try to scan for you later.... the optimum power/consumption is at 1900rpm...
The engine is rated for 3000rpm max, so 2400 is possibly just a tad high for long range running... we run ours at 2200rpm when needed for extended periods
The engine is rated for 3000rpm max, so 2400 is possibly just a tad high for long range running... we run ours at 2200rpm when needed for extended periods
jdc
Well-known member
graphs (groan;-)
I'd not thought about this before in any quantitative way and so thought it would be interesting to work out what one would expect assuming the absolute minimum a-priori, and using only very simple physics. The predictions from this rather trivial exercise turn out very close to what I find in practice , so, in case it's of interest to anyone else, I reproduce the thinking and results here. SolentBoy I think made the point that range increases as you go slower - this certainly backs that up.
If anyone can suggest improvements to this simplistic theory so much the better. I'm particularly interested in numbers for propeller efficiency for a large 3 bladed fixed pitch prop (I have a Gori, which is not spectacularly efficient I think).
1. Start with the consumption expressed in litres (or kg) / kWhr. This is close to 0.3 litres / kWhr, and pretty much independent of speed, as can be seen from this graph, (c)kubota, from their data sheet for the V2203-M. It's pretty much independent of engine size or make, but I chose to illustrate the v2203-M as it's the base engine for the Beta 50HP which is what I have. it's 0.245kg / kWhr, so divide by density of diesel (0.83) to get 0.295 litres / kWhr.
2. Know the thrust required to move the boat at a given speed.
I estimate it (and measured it, albeit at lower speeds) as 3.4kN at 6 knots. The boat is 14 tonnes, 42' LOA and fairly high wetted area for a modern boat. I expect it to scale for different boats approximately as WLL squared since drag is proportional to wetted area.
3. Calculate thrust, R, as a function of engine rpm
I assume it is directly proportional to shaft rotational speed, which is maybe slightly dubious but not too awful for a fixed-pitch prop. I know the engine rpm required to get 6 kts is 1850 rpm on my boat, so
R = rpm / 1850 * 3.4kN
4. Calculate the velocity as a function of thrust using Froude's equation:
R = f.A.v1.82
where:
R = thrust
f = a factor dependant on units, water viscosity and many other factors which make no odds here
A = Wetted Surface Area
v is velocity.
So v = 6kts * (R / 3.4kN) ^ (1/1.82)
5. Calculate motive power as force x velocity, ie P = R x v (in kW).
6. Convert to shaft horsepower by allowing for the efficiency of a propeller (ie not all power put into a shaft drives the boat forwards, some just whisks the water). I assume 75% of shaft horsepower is converted (this figure could do with better justification).
7. Calculate consumption in litres per hour as a function of rpm; consumption = P * 0.295
8. Calculate miles per litre as: mpl = v / consumption, and range is thus mpl x tank capacity (300 litres in my case).
And that's it. I plot here the speed, consumption per hour and per mile, HP and range all as a function of rpm. As far as I can tell these are all spot on what I have measured, which is reassuring.
It's maybe worth recapping the few parameters which vary with boat:
(i) Drag for a certain speed. This can be expected to vary with LWL squared, and slightly with hull form (NB assumes non-planing hull).
(ii) rpm required to get a certain speed. This is only used if one wants to calibrate the rpm scale. It doesn't actually affect the range as a function of speed, so if you've no rpm meter, don't bother with this parameter.
(iii) Propeller efficiency, which hardly varies from boat to boat assuming all have an appropriately chosen prop.
Warning: it's an approximation for the purpose of better understanding, not an exact predictor - that it doesn't take into account tidal stream, windage, admixture of bio-fuels, skipper's halitosis etc etc is understood.
I'd not thought about this before in any quantitative way and so thought it would be interesting to work out what one would expect assuming the absolute minimum a-priori, and using only very simple physics. The predictions from this rather trivial exercise turn out very close to what I find in practice , so, in case it's of interest to anyone else, I reproduce the thinking and results here. SolentBoy I think made the point that range increases as you go slower - this certainly backs that up.
If anyone can suggest improvements to this simplistic theory so much the better. I'm particularly interested in numbers for propeller efficiency for a large 3 bladed fixed pitch prop (I have a Gori, which is not spectacularly efficient I think).
1. Start with the consumption expressed in litres (or kg) / kWhr. This is close to 0.3 litres / kWhr, and pretty much independent of speed, as can be seen from this graph, (c)kubota, from their data sheet for the V2203-M. It's pretty much independent of engine size or make, but I chose to illustrate the v2203-M as it's the base engine for the Beta 50HP which is what I have. it's 0.245kg / kWhr, so divide by density of diesel (0.83) to get 0.295 litres / kWhr.
2. Know the thrust required to move the boat at a given speed.
I estimate it (and measured it, albeit at lower speeds) as 3.4kN at 6 knots. The boat is 14 tonnes, 42' LOA and fairly high wetted area for a modern boat. I expect it to scale for different boats approximately as WLL squared since drag is proportional to wetted area.
3. Calculate thrust, R, as a function of engine rpm
I assume it is directly proportional to shaft rotational speed, which is maybe slightly dubious but not too awful for a fixed-pitch prop. I know the engine rpm required to get 6 kts is 1850 rpm on my boat, so
R = rpm / 1850 * 3.4kN
4. Calculate the velocity as a function of thrust using Froude's equation:
R = f.A.v1.82
where:
R = thrust
f = a factor dependant on units, water viscosity and many other factors which make no odds here
A = Wetted Surface Area
v is velocity.
So v = 6kts * (R / 3.4kN) ^ (1/1.82)
5. Calculate motive power as force x velocity, ie P = R x v (in kW).
6. Convert to shaft horsepower by allowing for the efficiency of a propeller (ie not all power put into a shaft drives the boat forwards, some just whisks the water). I assume 75% of shaft horsepower is converted (this figure could do with better justification).
7. Calculate consumption in litres per hour as a function of rpm; consumption = P * 0.295
8. Calculate miles per litre as: mpl = v / consumption, and range is thus mpl x tank capacity (300 litres in my case).
And that's it. I plot here the speed, consumption per hour and per mile, HP and range all as a function of rpm. As far as I can tell these are all spot on what I have measured, which is reassuring.
It's maybe worth recapping the few parameters which vary with boat:
(i) Drag for a certain speed. This can be expected to vary with LWL squared, and slightly with hull form (NB assumes non-planing hull).
(ii) rpm required to get a certain speed. This is only used if one wants to calibrate the rpm scale. It doesn't actually affect the range as a function of speed, so if you've no rpm meter, don't bother with this parameter.
(iii) Propeller efficiency, which hardly varies from boat to boat assuming all have an appropriately chosen prop.
Warning: it's an approximation for the purpose of better understanding, not an exact predictor - that it doesn't take into account tidal stream, windage, admixture of bio-fuels, skipper's halitosis etc etc is understood.
Billjratt
Active member
I was going to add that my perkins 4108 running at 1500 revs in a 6.5-ton 30ft squattish m/s with a 3-blade prop and 50 gallions in the old tank, 40 litres in the new cans,(see how I've adapted?), uses 1.4 lit calm and 2 lit headwind/seas, so would give about 175 hours on average, at 5.5kn-ish.
But it would cock-up all the calculations you've already done, so I won't.
But it would cock-up all the calculations you've already done, so I won't.
pagoda
Active member
Having read my way through the responses, some people must be looking forward to eye-watering tanking up coats this year?
I don't mind sailing slowly now and again, but can usually sail faster than motoring in over 8-10Kts of wind. And I hate the noise motoring anyway...
Jeanneau 35, 3gm30 70l (some in in jerrycans) - about 200 miles range perhaps. Maybe more if 2200 rather than 2400 RPM.
Graeme
cliff
Active member
Sadler 34
Bukh DV24
100 Litres main tank & 100 Litres reserve
1.5 L/hr @ 2400rpm giving 6knts (18nm/gal) - 360nm range
I mean wind is not taxed (at the moment). Now I don't know about others here but I can nip along nicely in 8-10 knts of (free) wind without lining the pockets of HMRC.
Bukh DV24
100 Litres main tank & 100 Litres reserve
1.5 L/hr @ 2400rpm giving 6knts (18nm/gal) - 360nm range
Why? the figures are for motoring not sailing
I mean wind is not taxed (at the moment). Now I don't know about others here but I can nip along nicely in 8-10 knts of (free) wind without lining the pockets of HMRC.
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whisper
New member
Botnia Targa 25
Fuel Cap. 80 gals
Avge Fuel Consumption over 4 yrs = 3.2mpg
Normal Cruising Speed 20-22kts
Theoretical Range Approx. 250 N.Miles.
Cost of a fill-up now looking daunting!!
Fuel Cap. 80 gals
Avge Fuel Consumption over 4 yrs = 3.2mpg
Normal Cruising Speed 20-22kts
Theoretical Range Approx. 250 N.Miles.
Cost of a fill-up now looking daunting!!
