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Old 03-21-2020, 04:49 PM   #1
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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
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Old 03-21-2020, 05:08 PM   #2
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Fuel consumption depends on speed, size and weight of the boat, not so much on the engine.

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Old 03-21-2020, 05:27 PM   #3
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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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Old 03-21-2020, 05:33 PM   #4
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Originally Posted by TWille View Post
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
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).

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Old 03-21-2020, 05:45 PM   #5
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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.
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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Old 03-21-2020, 05:47 PM   #6
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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.....
+1
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Old 03-21-2020, 05:53 PM   #7
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5 gph at 7 kts is a good guess. Monitor your fuel usage and adjust.
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Old 03-21-2020, 06:17 PM   #8
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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.....
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.

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Old 03-21-2020, 06:19 PM   #9
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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.
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Old 03-21-2020, 06:42 PM   #10
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Yea, my guess at 7kts with two 6BTA in a 42 would be 3gph total.
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Old 03-21-2020, 07:23 PM   #11
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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.
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Old 03-21-2020, 08:15 PM   #12
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If you can’t afford “gallons” per hour you need a smaller boat and/or a FD boat.
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Old 03-21-2020, 11:20 PM   #13
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If you can’t afford “gallons” per hour you need a smaller boat and/or a FD boat.
What he said.....
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Old 03-21-2020, 11:56 PM   #14
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If you can’t afford “gallons” per hour you need a smaller boat and/or a FD boat.
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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Old 03-24-2020, 08:23 PM   #15
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Gph

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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.
- 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.
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Old 03-24-2020, 08:55 PM   #16
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Old 03-24-2020, 09:20 PM   #17
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I will agree....somewhere between 3-4 gallons per hour at 7 knots. Enjoy!!!
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Old 03-24-2020, 10:31 PM   #18
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Now, with Pelago and a pair of 6BTA's . . . . a bit more, ~17 gallons per hour at ~20 kts
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.)
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Old 03-24-2020, 11:03 PM   #19
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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.
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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Old 03-25-2020, 05:39 AM   #20
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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
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."
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