Wayne.B wrote:
On Wed, 08 Nov 2006 11:36:48 -0500, DSK wrote:

We burn about 1 3/4 gph cruising about 7 to 7.5 knots. The
boat will (in theory) go 8.5 but fuel consumption starts
getting up into the 5gph range and we make a loke of wake
and foam and noise, for not a lot of speed gained.

Here's another data point:

On our Grand Banks 49 we average about 1 gallon per mile on extended
cruises unless we make a really concious effort to economize which can
save an additional 10 to 20%. That includes about 4 hours per day of
generator time, running on both engines, and using active stabilizers
virtually 100% of the time. Our average speed is about 8.5 kts,
slowing to about 7.9 if we are really trying to stretch the fuel.

This doesn't seem quite right to me - my catamaran, which weighs about
15% of what your trawler weighs, uses almost as much fuel.

If you boat displaces 60000 pounds, then it will need about 60 HP to
get over 7 knots, 90 hp to get to 8.5 knots. Looking at specs for
various Caterpillar engines, the gallons/hour at 60 hp is 3+ gals.
Using two smaller engines doesn't help that much, though at least they
can idle with lower consumption.

Your number only make sense if you spend more time on average using
you engines to run the A/C than propel the boat.