Gallons per Hour

Anyone have Cummins 250BDA? Approximately how many Gallons per hour do you burn. At displacement cruise 7knts - if you have a Fast trawler at planing speed. Per side if you have twins.
Trying to get a feel for a boat we are looking at.

Thanks
Tom

Fuel consumption depends on speed, size and weight of the boat, not so much on the engine.

David

We don't know the boat you're talking about, but I'll give you a WAG for 7 kts based on my boat and my 210 Cummins: 5 gph total, 2.5/side.

TWille said:

Anyone have Cummins 250BDA? Approximately how many Gallons per hour do you burn. At displacement cruise 7knts - if you have a Fast trawler at planing speed. Per side if you have twins.
Trying to get a feel for a boat we are looking at.

Thanks
Tom

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Simple rule of thumb is 1 GPH for each 20 HP. If you know the cruising RPM it's pretty easy to find a HP & RPM graph with a propeller HP absorption curve. The absorption curve will give you approximate HP for any RPM. Divide the HP curve value for your RPM by 20, and that should be your maximum burn rate (it may / probably be less). A 250 HP B engine probably cant burn more than 12.5 GPH (250÷20=12.5).

Ted

Ken

Ken E. said:

We don't know the boat you're talking about, but I'll give you a WAG for 7 kts based on my boat and my 210 Cummins: 5 gph total, 2.5/side.

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Thank you to everyone thus far. The boat is a 42ft. 24000lb Taiwanese Trawler - monk clone kinda thing.

Seems like the Hatteras numbers would be close.....

TWille said:

Thank you to everyone thus far. The boat is a 42ft. 24000lb Taiwanese Trawler - monk clone kinda thing.

Seems like the Hatteras numbers would be close.....

Click to expand...

+1

5 gph at 7 kts is a good guess. Monitor your fuel usage and adjust.

TWille said:

Thank you to everyone thus far. The boat is a 42ft. 24000lb Taiwanese Trawler - monk clone kinda thing.

Seems like the Hatteras numbers would be close.....

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I think you will do better depending on stuff. At 7 knots my 45' boat burns 2 GPH. Different motor and lots of optimization. My guess is 3 to 4 GPH, closer to 3.

Ted

I agree that 5 gph at 7 kts sounds high for a 42 foot boat with diesels. 2-3 (total, not per engine) is more likely.

Yea, my guess at 7kts with two 6BTA in a 42 would be 3gph total.

My 34AT (displacement 18,700 dry) at 8knots (Cummins QSB 5.9 rated as 380HP) 1400 RPM, 2.1gph If I drop down to 7.5 knots it will be about 1.6 gph. These are figures from the factory sea trial. At 17 knots, 3000 RPM, 18.1 gph. For sea trials, the factory specifies 1/2 load of water (75gal), fuel 1/2 load (200 gallons) and the 12 volt fridge is on and running.
May I suggest you find a users group for the make and model of your boat and see what info they can provide. Someone might be able to provide you the graph, RPM/speed/gph. Realize, those are "walking around figures" depending on how much you personal stuff you put onboard. Plus, sea state, current and I suspect a few more variables. # and weight of people on board too.

Conclusion: there are many variables involved. And that will result in a "best guess".
If the boat has an accurate/believable flow scan, you can generate your own chart.

If you can’t afford “gallons” per hour you need a smaller boat and/or a FD boat.

Nomad Willy said:

If you can’t afford “gallons” per hour you need a smaller boat and/or a FD boat.

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What he said.....

Nomad Willy said:

If you can’t afford “gallons” per hour you need a smaller boat and/or a FD boat.

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Too funny Eric,

When I had Boomarang with her 4JH3E, I regularly observed ~1 gallon per hour at ~6.5 kts cruise.

Now, with Pelago and a pair of 6BTA's . . . . a bit more, ~17 gallons per hour at ~20 kts economy cruise. Not horrible, but I definitely lost my bragging rights on that deal.

Gph

LarryM said:

Too funny Eric,

When I had Boomarang with her 4JH3E, I regularly observed ~1 gallon per hour at ~6.5 kts cruise.

Now, with Pelago and a pair of 6BTA's . . . . a bit more, ~17 gallons per hour at ~20 kts economy cruise. Not horrible, but I definitely lost my bragging rights on that deal.

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- I can afford all the GPH i need, I am some one who is moving from the sailing side to to the trawler side (shall we say dark?) Just trying to be thoughtful about this. I am used to .5gph at 7knts

A very heartfelt Thank you to all who went out to there way to supply legit info to this conversation.

We will all be dead soon enough. You can't take it with you. You either spend it in full enjoyment, or your heirs will. And trust me, they would not appreciate it as much as you because they didn't earn it.

I will agree....somewhere between 3-4 gallons per hour at 7 knots. Enjoy!!!

LarryM said:

Now, with Pelago and a pair of 6BTA's . . . . a bit more, ~17 gallons per hour at ~20 kts

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I'm in the same category, Larry! My max rpm is 3300 but I never push her that hard. (That would give me 22 knots.)

OldDan1943 said:

My 34AT (displacement 18,700 dry) at 8knots (Cummins QSB 5.9 rated as 380HP) 1400 RPM, 2.1gph If I drop down to 7.5 knots it will be about 1.6 gph. These are figures from the factory sea trial. At 17 knots, 3000 RPM, 18.1 gph. For sea trials, the factory specifies 1/2 load of water (75gal), fuel 1/2 load (200 gallons) and the 12 volt fridge is on and running.
May I suggest you find a users group for the make and model of your boat and see what info they can provide. Someone might be able to provide you the graph, RPM/speed/gph. Realize, those are "walking around figures" depending on how much you personal stuff you put onboard. Plus, sea state, current and I suspect a few more variables. # and weight of people on board too.

Conclusion: there are many variables involved. And that will result in a "best guess".
If the boat has an accurate/believable flow scan, you can generate your own chart.

Click to expand...

Dan, yours should be a poster boat for why trawlers should go slow.

1.6 GPH @ 7.5knots gets you 15 nautical miles in two hours
2.1 GPH @ 8knots gets you 16 nautical miles in two hours
OR
18.1 GPH @ 17knots to get 17 nautical miles in an hour

Soo-Valley said:

Dan, yours should be a poster boat for why trawlers should go slow.

1.6 GPH @ 7.5knots gets you 15 nautical miles in two hours
2.1 GPH @ 8knots gets you 16 nautical miles in two hours
OR
18.1 GPH @ 17knots to get 17 nautical miles in an hour

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Steve, as has been pointed out to me many times, "You dont have a trawler. You have a tug." SHRUG
Every boat, no matter the design, has a 'sweet spot' when it come to fuel efficiency. Mine, I think, is about 7-7.5 knots. As the owner, I can make the decision, fast (WOT), medium, slow and very slow. LOL I am not excited about 17 knots and not happy moving at 2knts. Am I racing the tide, racing for pier position, getting to the fuel dock before it closes, reaching my destination before it gets dark. These and other things influence the 'how fast'.
Just as one considers the 'sweet spot' for the fuel burn, there is a 'sweet spot' for sea state.
SO MANY things we must consider each moment ....
My Nordhavn carried 1000 gallons of fuel.... when outside of the ICW, WOT was my usual decision.... With the AT and its 400 gal of fuel, the fuel burn rate is more important, to me. My guiding principle is, "Leave early, arrive early."

Soo-Valley said:

Dan, yours should be a poster boat for why trawlers should go slow.

1.6 GPH @ 7.5knots gets you 15 nautical miles in two hours
2.1 GPH @ 8knots gets you 16 nautical miles in two hours
OR
18.1 GPH @ 17knots to get 17 nautical miles in an hour

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Hey....17kts@18gph sounds fairly efficient to me!!!...and it is 17kts to go 34nautical miles in two hours. You must work in marketing or work for the media...

Baker said:

Hey....17kts@18gph sounds fairly efficient to me!!!...and it is 17kts to go 34nautical miles in two hours. You must work in marketing or work for the media...

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Yeah, really. I wish that were all I burned at 17 kts...

Baker said:

Hey....17kts@18gph sounds fairly efficient to me!!!...and it is 17kts to go 34nautical miles in two hours. You must work in marketing or work for the media...

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you must be confused.
In one hour 17 nautical miles using 18 gallons

but slow down and it takes you approx 2 hours to make the same distance using about 4 gallons.

That is using approx 14 gallons less to cover same distance going slower.
What did I miss?

Soo-Valley said:

you must be confused.
In one hour 17 nautical miles using 18 gallons

but slow down and it takes you approx 2 hours to make the same distance using about 4 gallons.

That is using approx 14 gallons less to cover same distance going slower.
What did I miss?

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What you missed is you said "it takes so and so amount to TWO HOURS"
ANd then you said "It takes so and so amount to go TWO HOURS"
ANd then you said "It takes so and so amount to go ONE HOUR"!!!!.....as if to magnify your point by your reduced comparison. Yes it is the same. But it reeks or a marketing gimick or something the media would do to amplify their point. And I was certainly just poking fun at you. So since you question me I will question you....why did you use only a one hour examply when you used two hour examples for the more efficient speeds?...

Baker said:

What you missed is you said "it takes so and so amount to TWO HOURS"
ANd then you said "It takes so and so amount to go TWO HOURS"
ANd then you said "It takes so and so amount to go ONE HOUR"!!!!.....as if to magnify your point by your reduced comparison. Yes it is the same. But it reeks or a marketing gimick or something the media would do to amplify their point. And I was certainly just poking fun at you. So since you question me I will question you....why did you use only a one hour examply when you used two hour examples for the more efficient speeds?...

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For convenience of course, to bring a fixed distance attainable in the shortest period of time as presented into a comparison of different velocities and comparative digestion of fluid volumes to attain that same fixed distance.
Now you can apply any constant to each scenario for greater coefficient.

To be super accurate the measurements should all be taken in a 12 hr period of time, running each speed out and back..... and returning for refueling frequently to keep the fuel weight reasonable the same..... noting the tide for each run. BUT, who has the time and desire and wants to be that accurate.
I have always been stumped for why this is reported with the 12vt fridge running.

OldDan1943 said:

To be super accurate the measurements should all be taken in a 12 hr period of time, running each speed out and back..... and returning for refueling frequently to keep the fuel weight reasonable the same..... noting the tide for each run. BUT, who has the time and desire and wants to be that accurate.
I have always been stumped for why this is reported with the 12vt fridge running.

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You don't drink beer?

Soo-Valley said:

You don't drink beer?

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Maybe 2 beers each year but, dont get between me and my red wine or cognac.

Plus, I dont 'serve' while underway. If there is a casualty I dont need drunk help.
The bar will open upon returning to my slip and properly tied up or anchored for the night.

OldDan1943 said:

Maybe 2 beers each year but, dont get between me and my red wine or cognac.

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I understand why you don't see the need to run the fridge.

OCDiver says 1 gallon per 20 hp. Hmmm, I have to question that. Sounds way high. That would put my 36 TT with 120 F.L. at 6 gls per hour. I don't burn half that. In fact I burn between 2 and 3 per hour.

People sometimes look at me funny when I can't quote a litany of GPHs and MPGs or GPMs.
Seriously, who cares. A heavy season of cruising requires me to buy a few hundred gallons of diesel. A season filled with other commitments just saw me top off the tanks at the end of the season for storage.

The first few years I owned the boat I was very concerned that my fuel was getting old. I had spent a lot of time doing other projects than cruising.

pete