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Old 03 November 2005, 06:52   #1
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Formula for Fuel

Hi

Is there a formula to work out how many litres of fuel an engine will burn at a given speed...... don't know if that makes sense but was told there could be a way of working out a max fuel flow.....
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Old 03 November 2005, 07:13   #2
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Fuel Burn

For a diesel engine 5 gallons per hour per 100 horsepower used.

For a petrol engine about 10 gallons per hour per 100 horsepower used. (My 150hp optimax uses about 56 litres per hour flat out).

If you are thinking about your boat I would guess 1.1 litres per mile at 28 knot cuising speed.
50+ litres per hour flat out1
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Old 03 November 2005, 07:16   #3
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Quote:
Originally Posted by Searider
If you are thinking about your boat I would guess 1.1 litres per mile at 28 knot cuising speed.
50+ litres per hour flat out1
hmmm the engine I had in mind was a

Volvo GXi 5.7 V8 320hp with a Volvo Duo Prop
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Old 03 November 2005, 07:53   #4
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Quote:
Originally Posted by Searider
For a diesel engine 5 gallons per hour per 100 horsepower used.

For a petrol engine about 10 gallons per hour per 100 horsepower used. (My 150hp optimax uses about 56 litres per hour flat out).

If you are thinking about your boat I would guess 1.1 litres per mile at 28 knot cuising speed.
50+ litres per hour flat out1
If only it was that simple!
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Old 03 November 2005, 08:43   #5
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No it really easy that simple for an outboard;

2.5 x V6 + 4m = 100 / day

This can be broken down into "simpleton" terms as follows;

Big lump x V6 + big ass waves = big hole in pocket!

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Old 16 November 2005, 09:45   #6
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at max chat with throttles wide open then aound 22 -24 us gals per hour

pull the throttle back to around 75% and you should be down to 13-15 us gals per hour

its the last 25 % that is the buckets down the pots syndrome

pure estimation on what i have read up on

but check your fuel pipes and pump from the tank, if the pipe is 3 inchs in diameter with a huge petrol pump then worry

if its is less than 3/4 inch then should be ok with above

does that help any?

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Old 16 November 2005, 10:45   #7
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Quote:
Originally Posted by Hugh Jardon
but check your fuel pipes and pump from the tank, if the pipe is 3 inchs in diameter with a huge petrol pump then worry
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Old 16 November 2005, 11:44   #8
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Also the following site might be good for getting test reports on american boats etc....

http://www.boattest.com/index.aspx
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Old 16 November 2005, 12:50   #9
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Fuel Consumption - Planing Boats

Quote:
Originally Posted by Nauti Buoy
Hi

Is there a formula to work out how many litres of fuel an engine will burn at a given speed...... don't know if that makes sense but was told there could be a way of working out a max fuel flow.....
This is taken from RYA Navigation Handbook, I take no credit nor blame for accuracy;

Power = (K x engine speed^4) / boat speed

^ means 'raised to the power of'

eg A RIB has a 120hp 4-stroke engine capable of 6000rpm and 40knots. Cruising speed is 30knots at 4200rpm.


1. Find 'K' by putting real numbers into the formula:
120 = (K x 6^4) / 40

120 = (K x 1296) / 40

so, K = 3.7

2. Use K to find out how much power is being developed at crusing rpm:
Power = (3.7 x 4.2^4) / 30

Power = (3.7 x 311) / 30

Power = 38hp
3. A 4-stroke petrol engine developes about 12 - 14hp.hr per gallon, so 38hp divided by 12 gives about 3 gallons per hour. For reference, a 2-stroke petrol engine developes about 8 - 10hp.hr per gallon, diesels produce about 20hp.hr per gallon.


Enjoy!

Andy Beach
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Old 16 November 2005, 13:12   #10
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Quote:
Originally Posted by AndyB007
3. A 4-stroke petrol engine developes about 12 - 14hp.hr per gallon, so 38hp divided by 12 gives about 3 gallons per hour. For reference, a 2-stroke petrol engine developes about 8 - 10hp.hr per gallon, diesels produce about 20hp.hr per gallon.


Enjoy!

Andy Beach
Hi

Thank you, so based on that theory 320hp / 12 = 26.66 gallons per hour
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