5% difference in fuel consumption

DavidJ

DavidJ

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At the end of the year I've totted up the fuel that I've put into each tank (i've got two completely separate systems) and over about 3000 litres one engine has used 5% more fuel than the other. Is this within normal engine to engine variation?
Incidently the average total fuel consumption was 51.5 litres/hr which I think is quite good for twin KAD43's on a 37ft Sealine (S37)

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Could be due to a variety of reasons. For example, are you 100% sure that the each tank had the same relative level at the start of the season as now or could be that your rev counters have different accuracies and whilst you think you are setting both engines at same rpm, in fact one may be higher than other. Or could simply be one engine is more efficient than other - do you get more exhaust deposits on one side than the other indicating more unburnt fuel?
Or could be you spend all your time going round in circles?

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Now thats a good question but an easy one to answer....I don't have a genny.
It's made me think though. One alternator looks after the engine batteries only and the other looks after all the anciliaries and will be loaded more especially after running the batteries almost flat on occasions with overnights in bays with the fridge on and power winching etc.

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Which tank looks after the eberspatcher??

Rev counters are never right.

<hr width=100% size=1> <font color=blue>No one can force me to come here.<font color=red> I'm a volunteer!!.<font color=blue>

Haydn
 
My father-in-laws S34 also has KAD43's and one engine uses more fuel than the other. I was told, when I asked about what is acceptable, that the difference should be no more than 10%, so 5% doesn,t seem to bad. My father-in -laws previous boat also used more fuel on one engine than the other even after working out how much fuel the genny took. Wouldn't have thought the heating would affect it in the summer as we never used it.

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Now you know why , when giving a report on new boats the statistics always give after tank size:-
Revs - speed - litres/hr - gals/hr - range. Always qualifying the figures by the wording - "allowing for a 20% margin.

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According to the technical datasheet that is the consumption for 3000 rpm i.e. 25.64 litres/hr per engine. Does that tie in with your cruising speed?

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How about the accuracy of the pumps delivering fuel to your tank maybe if you refuel from different pumps or even at different times the pumps can short deliver or over deliver. Your result could just be the summation of all kinds of little errors. Are both your tanks the same volume?

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