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Old Yesterday, 07:41 AM   #1
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Best guess gph

Alrighty then....not sure where to post this question but will start here. Would anyone out there have a pretty good idea of gph on a 23000lb. boat running twin 3116 cats doing about 8 to 10 knots. Already read on older post that 8kw gen is about 1/2 to 1 gph with the high end being fully loaded. Will only be refrigerator running while underway.
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Old Yesterday, 07:48 AM   #2
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Give more of a description of the boat, especially the length so hull speed can be figured. There can be a vast difference in the burn rate at 8kts and 10kts as for a boat at say 40', at 10kts it will be trying to climb its bow wave and that takes a lot more power.

A typical trawler type boat at 40' at 8kts with 3116 and gennie I'd guess 4-5gph.
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Old Yesterday, 07:49 AM   #3
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Greetings,
Mr. E. Perhaps I am misunderstanding. Can't help you with mains usage but will you be running only a refrigerator with your genny while underway?
If so, might you be better to purchase a cheap inverter to run the fridge rather than underloading your genny? Just a thought...
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Old Yesterday, 07:52 AM   #4
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Hi,

Hi, I speculated about 8kn about 4gal / h and 10kn about 9 gal / h.


Do you know your boat LWL

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Old Yesterday, 08:27 AM   #5
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There used to be a company who made real time fuel usage. I had one installed on my N46. Worked pretty good.

Ah ha, I thought I forgot the company's name but after 3 minutes of digging around shabby memory, it popped to the surface..... Flow Scan

The URL is
http://www.floscan.com/html/blue/recreationalmarine.php
Guessing at your fuel usage is not the smartest thing in the world but, it is a start. Sort of like the manufacture's fuel usage chart and the builder's fuel usage chart.

The easiest example is, if you are cruising north in the Gulf Stream, you will burn less fuel at the same RPMs than if you are cruising south in the Gulf Stream.
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Old Yesterday, 08:29 AM   #6
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To expand a bit on Ski's post above, 10 kts isn't a good speed for a typical 40' twin engine trawler. Even though no semi displacement hull truly planes, at 10 kts it will be mushing though the water trying to climb over its bow wave and will be lugging its engine at that speed.


With twin Cat 3116s a 40' trawler should be able to cruise nicely at 15+ kts. That speed will be kinder to the engine than 10 kts but I would guess 15 gph at 15 kts.


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Old Yesterday, 10:02 AM   #7
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Ok, thanks. Most replies are about what we come up with. 8knots feels good on my boat. We have puttered up and down ICW here a few times seeing what speed feels good and listening to engines. If you listen,they will tell you what they want to run. We in the planning stages for our trip from east side of Florida back to Texas. Again thanks for replies.
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Old Yesterday, 10:19 AM   #8
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Ernie - please tell me what horsepower and rating of the 3116 you have. I can look up the fuel consumption by RPM, please advise your cruise RPM also.
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Old Yesterday, 10:45 AM   #9
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Quote:
Originally Posted by Ernie View Post
Alrighty then....not sure where to post this question but will start here. Would anyone out there have a pretty good idea of gph on a 23000lb. boat running twin 3116 cats doing about 8 to 10 knots. Already read on older post that 8kw gen is about 1/2 to 1 gph with the high end being fully loaded. Will only be refrigerator running while underway.
Quote:
Originally Posted by Ernie View Post
Ok, thanks. Most replies are about what we come up with. 8knots feels good on my boat. We have puttered up and down ICW here a few times seeing what speed feels good and listening to engines. If you listen,they will tell you what they want to run. We in the planning stages for our trip from east side of Florida back to Texas. Again thanks for replies.

From a Yachtworld listing, LWL for a Cruisers 3950 is 29.9'. (Seems low, to me; would have guessed closer to 36-38' or so.)

Anyway, best fuel economy for 30' LWL would likely be at approx 5.5 kts. Above 7.3 kts would most likely be climbing bow wave, and fuel consumption goes quickly north from there.

-Chris
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Old Yesterday, 02:14 PM   #10
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I know exactly how much fuel will be used, more than I can afford.
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