Fuel Consumption

[DaCostaGreene]

3.4 gallons p/hour at 20 knots on a 30 footer with a 160hp D3.

My question is - is that good?

Nick

 

[Whitelighter]

I would say it is very good. Unless the boat is a bit ugly or a bit crap to be on, in which case it's alot.

 

[DaCostaGreene]

Not ugly when in the water, could be off putting at first glance when hard standing.

Stability is second to none, really excellent.

 

[duncan]

that would be a lightweight cat then...............

nothing short of amazing for a conventional planning cruiser - erring on the unbelieviable!

1.1m/pl on a 25ft / 2.5 ton boat is considered excellent

1.3m p/l for a 30ft cruiser would be stunning

however - achieveing 20 knots from 160hp on a 30 ft craft suggests it's got to be a displacement multihull built v v light and a max speed>?

 

[LeytonC]

what revs [is|are] the engine(s) running at?

 

[DaCostaGreene]

1.8 tonnes (weight)

30ft and the 3000RPM, yes it is a Cat

 

[duncan]

are well there you go - many 21ft boats with 4 people and a good picnic will make 1.8 tonnes!

GC1's grab bag is 800kg

 

[DaCostaGreene]

And they'll also drink alot more too.

1.8 tonne 21 footer with 4 and a picnic, how much do you think it would drink? Assuming that its a planing monohull

 

[duncan]

8 stella's an hour?

more seriously with the same engine / drive about the same consumption at the same speed.

couple of people reengined small boats with the 150 TDI mercruser unit and were reporting similar consumption - they also had another 15 knots or so available too.

 

[DaCostaGreene]

But this is a 30ft displacement cruiser, not a planing sports boat - with about another 10 knots to go (top speed around 30knots) - baring in mind this is just diesal. With Petrol outboards the figures are not to disimilair.

Something to think about? A sports fisher, weekend cruiser, rivers,ocean, day trips, charter plus an atlantic crossing to come. What with fuel costs going up n'all that, a likely candidate for market leader??

 

[duncan]

yep a likely market leader

sounds similar to the 8m cat we were suggesting this power / engine config for earlier in the year.

30 knots 30ft and displacement don;t seem to match even for a cat though!

 

[DaCostaGreene]

I suppose you could class it as a semi-displacement. The air lifts the boat slightly. Imagine if it were fitted with Hydrofoils too!!

 

[LeytonC]

In that case its almost exactly what i would expect the engine to burn based on D3 160 based on 1 gallon per hour per 20hp (which is a common assumption), using the forumula (ok, so its a bit higher - but hard to take into account drive losses, so assumed vp figures for leg)

((((actual revs/rated power revs)^3)*rated power)/20)

this gives us

((((3000/4000)^3)*155)/20) = 3.27 gph.

(assuming 8hp loss in transmission (which volvo penta do))

 

[DaCostaGreene]

The actual figure (so please excuse me if my maths is wrong) is 18.6 litres per hour - I think that translates to 3.4 gph

Help.

 

[LeytonC]

1 Litre = 0.21997 gallons - ok clunky way round but meh, which would make

18.6 * 0.22 = 4.1 gph

 

[Whitelighter]

I agree Leton (thanks for the Soltron BTW)

1 gallon = 4.54litres, so 18.6/4.54 = 4.09gph

 

[DaCostaGreene]

Rather than Volvo Penta figures, I'd suggest figures from other Boat manufacturers rather than engine manufacturers, as Volvo may be a little OTT, IMHO.

 

[duncan]

I suspect that the volvo figures will be spot on for an engine on a test bed!

 

[LeytonC]

i am only taking hp at the prop from vp, NOT any fuel figures - i am using the general 20hp per (gallon per hour) rule, which pretty much does work for *most* diesel engines.

 

[LeytonC]

you are welcome!! - i rounded to 1 decimal place, /forums/images/graemlins/smile.gif