Fuel burn on Volvo D12

[DavidParky]

I am considering buying an Atlantis 50HT 2007. The boat has the Volvo D12 775hp engines and I wondered if anyone has real life experience of the fuel burn at cruising speeds. Also any views on the boat itself would be welcome. Thanks

 

[Portofino]

Very similar 12.8 L i 6 but a bit older none CR and a bit less @ 700 .
The burn graph is not linear it’s curved at the RHS goes up at the last few 100 rpm s .
Cruise is the rpm the engines and boat feels and sounds best .Not scientific I know .
Some American sport fisher forums suggest never really go over 80:% load in the interest of longevity and to be fair its that point the burn rate starts to curve upwards faster on a graph .
So for me they seem to sit on full boost around 1800 rpm .WOT for me is bit lower than yours - 2250 ish .
I often do just under say 1780 rpm were load is from 75/77 % depending on fouling and fluids carried .
Looking at 80 or just over say 85/87 L hr per side .My smaller hull does 28/29 knots cruise .

1950 is a 100 , 2000 over 110 and near WOT iirc I have seen 140 per side . But I never really go there unless testing it once a year .


Word of caution those internet engine manufacturers figures on a test bed are over optimistic.
There is no gear box + boat attached .So it’s good you enquire .

I could lower it down to 67-75 L/ hr if I throttle back to 1600 / 1650 is but the boat slows and the boost starts to drop .
It’s on a kinda plateau anyhow so while it looks likes the L/ hr has dropped it has the extra time according to the plotter to reach the destination means the total for the trip is pretty much the same .So may as well rev up to the sweat spot of 1780 rpm 80-85 L / hr and get everything else like EGT s etc at the optimal levels .

Summary around 80 L / hr per side .

What speed this achieves depends on the hull .That’s not what you are asking .

Best to keep them under 1800 rpm ( or maybe 1900 if the wot is 2350:? ) if you can .Best stay out of north of 2000 rpm were the burn rate shoots up .

What does the brochure say at 1800 / 1900 rpm ? Could that be cruise .
Is 80 + L / hr per side acceptable?

 

[DavidParky]

That is really useful. Agree re manufacturers figures - they run for ever on a thimble full! Many thanks for the prompt reply. If anyone has a view on the boat please do share.

 

[SC35]

Manufacturer's figures at calculated propeller load.

 

[oldgit]

Manufacturer's figures at calculated propeller load.

View attachment 120527

as a comparison a Rodman 41 with pair of D6 (375 HP) IPS was consuming 160 litres per hour at more or less WOT and 30 knots, according to the on board fuel burn calculator.

 

[DavidParky]

Thanks guys, as ever real life information really useful. A random additional question but does anyone have a boat in Greece if so what sort of price are you paying for marine diesel per litre? My quick research suggested 60-70p. Thanks

 

[Chris H]

My old pig iron MAN 800’s are about 100L/hr per side.

 

[BruceK]

A theoretical 0.181 kg burn per hp of a normally aspirated engine seems to validate the chart above.
e.g. say at cruising speed you are using 600hp of the 775
(1 litre of diesel being 874g)
(fuel efficiency gained through turbo charging etc ~20%)

0.181 / 0.874 x (600x0.800) = 99litres per hour