It depends of quite a few variables you have not stated, but you will do
well with .4 pounds per horsepower hour. Your engines will have constant
speed governors that should have a cap at 2800 rpm. Your engine manual
should state the max rated HP. These engines have ratings between 210 HP and
400 HP depending on their configuration. Your most efficient cruise speed
should be acheived around 2000 RPM. At this speed you should be around .6
max (250 x .6 = 150 HP). So, 150 HP x .4 pounds = 60 lbs . Divide this by 6
pounds per gallon and you have 10 gallons an hour per engine at cruise. with
this, you can work other permutations yourself. But this theoretical boat
with cost you about $50 for every 13 miles you drive it. Think sail boat,
let God blow you about.
Steve

"Old Boat Goat" wrote in message
news:KHu3f.172868$oW2.76925@pd7tw1no...
Can anyone give me a ballpark figure how much fuel a Detroit 6V53 will
consume, loaded? Trying to estimate fuel consumption of twin 6V53s pushing
a 45' hard chine, V-bottom cruiser, 29 gross tons.

TIA

Don