working out theoretical fuel consumption

Whitelighter

Whitelighter

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I understand the calculation to work out how much fuel an engine will use to produce a specific HP. So I can work out fuel burn at WOT when the engine is producing the full 230hp. But is there a way to work out how much power is being produced at lower RPM, and therefor the fuel used?

If my KAD43's produce 230hp at 3900 rpm, how much are they producing at 2600 rpm?
 
You should be able to find a power and torque graph for that motor somewhere, maybe on the Volvo Penta site. Then you can just read off the HP, Torque & GPH at any given rev range.
 
Hi Jez
There was a spec sheet on boatdiesel.com, just had a look and could not find it.
I did use it to set a spreadsheet up to work out consumption, pm your mail address and Ill send you the excel file tomorrow.
Not sure how accurate it is, its calculated on kad 42 but should not be that much differance

ian
 
Sorry but it does not work like that and unfortunatly manufacturers conditions that produce the graphs are ones you will never match in real life.

To illustrate:
1. You set your revs at 2600, then increase the pitch of propellors, to now do 2600 you will need to raise the required hp and fuel required to maintain 2600.
2. You set your revs at 2600 and take on extra weight; fuel, people, wife's wardrope, boat deeper in the water, greater resistance, more power, and thus more fuel, required to maintain 2600 revs.
3. Weather gets up, are you with or against wind, lots of cavitation, prop up and down, engine trying to maintin revs. HP, speed and fuel all over the place.
4. You fuel and the SG of the fuel is 0.833 instead of 0.837, then you will produce less hp for the same revs.
5. Hull fouling.....

Get the idea the only true trial is your boat in exactly set repeatable conditions.
 
JC is right.thought by your exploits you would have worked it ot by now. On along trip years ago, I think I worked my boat out to 1.3 mpg.

No idea if this was right or not. But where ever I go, I work on 1 mile to gallon and a bit spare. The figgure seems to work for most folk here. It's not a perfect figure, but then the sea is not perfect either. Mane thing is, I tend to arirve at my destination, some times with far more fuel than I'd intended!! /forums/images/graemlins/crazy.gif
 
[ QUOTE ]
Look at the power curve on the engine spec.

I'm willing to bet that your engine will burn 1 gallon per 20hp per hour.

[/ QUOTE ]

Hmm, will run some tests and get back to you. I reckon it is less than that.
 
The upper curve is full throttle for a KAD42.

The lower curve is guesswork as to what you might actually get (transplanting a prop curve from another engine.)

At a guess, 30-35litres an hour per engine at a 2800-3000rpm cruise ?

KAD42.jpg


dv.
 
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