Fuel Burn on DD 671

[cjd]

Looking at a 38'HAt. Convertible. Powered by DD 671 rated at 485 HP. Curious what the cruise speed and max speed would be and expected fuel burn at those speeds. Stated hours are 850
I have been told to tune the HP down a bit to maximize lifespan. What kind of speeds should I expect to lose?
Also need recomendations for any engine surveyers out there near Annapolis MD specializing in these motors.

Thanks CJD

 

[tmorv]

I have a 39C with the same power,basically the same boat. I run my at 1950-2000rpm and 22-24knots average fuel burn is 34-36gph at cruise.

 

[Passages]

I'm always amazed that nearly all boats in the 37-43' range pushed by DD 6-71's (at whatever HP) seem to come in right around 1.5 gallons per mile at cruise.

And once up on plane, economy does not change much whether you are running 70% or 90% WOT. The only reason to not to go 90% all the time is to prolong engine longevity.

Quite a contrast from my old Wellcraft with gas 454's. On that boat if you were to stray from the 3200 rpm sweet spot, you'll pay dearly at the pump.

 

[cjd]

Thanks tmorv.
Passages, What Wellcraft did you have?

 

[Passages]

Passages, What Wellcraft did you have?

1986 St. Tropez. Great boat but became too small when the kids came along.