Diesel Usage Cruising the Intracoastal Waterway

[golfcruiser59]

Wondering how much diesel fuel the Caterpillar 3208's use? I live in New York, and would like to take the boat south in the winter. The engines are great, only 500 hrs on them. What kind of mileage can I expect? My tanks hold 400 gallons. Thanks!

[Ram]

I would guess it depends on a lot of thing, how fast, what kind of boat, what HP you have is it Turbo or not? maybe you can go to the website of Cat and find the answers-

[ActiveCaptain]

Wow - that's a difficult question to answer. It's sort of the same thing as, "How much will it cost for food?" A lot depends on the boat and the speed just like food depends on the type of food, how much you go to restaurants, etc.

Give some more info like boat type, displacement, speed you expect to go. From there, the data is pretty well known.

[golfcruiser59]

boat is 43' wellcraft san remo. 375 HP with cruising speed of 18 knots I believe.

[ActiveCaptain]

Originally Posted by golfcruiser59

boat is 43' wellcraft san remo. 375 HP with cruising speed of 18 knots I believe.

A really, really rough estimate based on the engine being properly sized for a non-displacement motorboat is to take the speed in knots and divide it by 2. The gallons per hour will be between that and double that. So I would expect your fuel use to be in the 9-18 gallons per hour range. This estimate is usually too low for faster speeds like you're planning to go - I'm not saying this is an exact way to determine GPH. Obviously, direct measurement is the best way to get your fuel consumption.

Another next step is to figure out how many horsepower is required to push your boat at 18 knots. From that, CAT will have pretty good GPH specs.

[golfcruiser59]

Displacement is 25000lbs

[Alan Brown]

Determining gas mileage in an automobile is a pretty simple thing- Fill your tank, take a trip, then divide the mileage travelled by the fuel used. You could probably do the same with your boat.

[Ram]

I think these number are more real- from a friends post-At 2400rpm, the 3208's in a 32 Topaz will burn about 28gph combined at about 21 knots. Great motors but a lil thirsty - will not get 1mpg. My buddy has a 1987 that we run offshore. Fishes well. I like to call it a big 32. I also have 3208s - 375hp in a 35 Viking - we burn about 30-32 at the same rpm and speed.--
so figure a bit less with your bigger boat--maybe 35 gal an hour to guess

[golfcruiser59]

Originally Posted by Alan Brown

Determining gas mileage in an automobile is a pretty simple thing- Fill your tank, take a trip, then divide the mileage travelled by the fuel used. You could probably do the same with your boat.

Thanks Alan! Lol, yes that is a great idea. But for someone trying to plan a trip that doesn't quite work.

[Randy]

What about installing a fuel flow meter then take it out simulating your cruising for a bit and you've got the answer.

[GordMay]

A Grand Banks 42 with twin Cat 3208 Naturals (210 HP) burns about .
9.6 GPH @ 10 knots - ± 1GPM.

A graph I’ve seen from a Defever manual referenced Caterpillar Data Sheets # TDO339-05 and TD3131-00 (375 HP version); indicating conditions at 77 F temperatures and 29.61 inches of hg barometric pressure, and fuel oil weighing 7.1 pounds per gallon and rated at 19590 BTU per pound.

RPM GPH
1600 4.5
1800 5.2
2000 6.9
2200 9.5
2400 12.1
2600 16.0
2800 21.1

You'll have to calculate your specific speed vs rpm.

[lorenzo b]

I have an 8/71N on a much bigger boat and I burn .8 gal / nm at 1500 rpm doing 7.5 knts. If you keep your speed down to 8 knts you will get twice the milage than you will at planing speed and you won't have people flicking you off on the ICW.

[ActiveCaptain]

lorenzo_b is quite correct. For 4 years we ran our trawler at 1850 RPM pushing us at 8.9 kts burning 8 gallons per hour - just a little better than 1 MPG. 2 years ago we decided to slow her down to 1500 RPM which pushes us at 7.6 knots and burns 3.5 gallons per hour - a little better than 2 MPG. It's not double the fuel savings because we're moving slower but it is a significant saving.

Needless to say, I'm loving 7.6 kts...

[Randy]

Originally Posted by lorenzo b

I have an 8/71N on a much bigger boat and I burn .8 gal / nm at 1500 rpm doing 7.5 knts. If you keep your speed down to 8 knts you will get twice the milage than you will at planing speed and you won't have people flicking you off on the ICW.

I was also wondering about the effects of 18 kts down the ICW would have on the locals!

[cchesley]

I once heard a generic number of about 1 gph / 40 horsepower. Of course it requires that you know how many horses you're using at cruising speed as it isn't as simple as figuring the engine's max hp rating-- you don't usually run at that rate!