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03-24-2019, 07:41 AM
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#1
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Veteran Member
City: Fort Pierce, Fl.
Vessel Name: Leave Um Nuthin
Vessel Model: Cruisers 3950 Aft cabin
Join Date: Aug 2018
Posts: 48
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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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03-24-2019, 07:48 AM
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#2
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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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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03-24-2019, 07:49 AM
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#3
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Enigma
City: Slicker?
Join Date: Oct 2007
Posts: 16,565
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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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RTF
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03-24-2019, 07:52 AM
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#4
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Guru
Vessel Model: Nordic Tug 37
Join Date: Sep 2015
Posts: 1,107
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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
NBs
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03-24-2019, 08:27 AM
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#5
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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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.
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
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03-24-2019, 08:29 AM
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#6
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Valued Technical Contributor
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,785
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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.
David
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03-24-2019, 10:02 AM
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#7
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Veteran Member
City: Fort Pierce, Fl.
Vessel Name: Leave Um Nuthin
Vessel Model: Cruisers 3950 Aft cabin
Join Date: Aug 2018
Posts: 48
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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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03-24-2019, 10:19 AM
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#8
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Guru
City: Sea of Cortez, Mexico
Vessel Name: Irene
Vessel Model: Nordhavn 40II
Join Date: Jan 2016
Posts: 1,235
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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.
__________________
Jeff
MV IRENE
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03-24-2019, 10:45 AM
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#9
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Guru
City: Annapolis
Vessel Name: Ranger
Vessel Model: 58' Sedan Bridge
Join Date: Aug 2013
Posts: 7,088
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Quote:
Originally Posted by Ernie
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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Quote:
Originally Posted by Ernie
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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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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Chesapeake Bay, USA
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03-24-2019, 02:14 PM
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#10
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Guru
City: Rockport
Vessel Name: Ana
Join Date: Jul 2015
Posts: 1,047
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I know exactly how much fuel will be used, more than I can afford.
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03-26-2019, 11:14 AM
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#11
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Guru
City: Qualicum Beach, Vancouver Island
Vessel Name: Capricorn
Vessel Model: Mariner 30 - Sedan Cruiser 1969
Join Date: Feb 2019
Posts: 2,019
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[I semi displacement hull truly planes][/I]
Shallow V hulls will truly plane and they are considered semi-displacement.
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03-26-2019, 12:12 PM
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#12
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Guru
City: Rockport
Vessel Name: Ana
Join Date: Jul 2015
Posts: 1,047
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Quote:
Originally Posted by rsn48
[I semi displacement hull truly planes][/I]
Shallow V hulls will truly plane and they are considered semi-displacement.
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If they're designed to plane how can they be semi-displacement?
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03-26-2019, 12:21 PM
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#13
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Guru
City: Puget Sound
Join Date: Jun 2016
Posts: 631
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Quote:
Originally Posted by OldDan1943
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
FloScan Instrument Co. Inc.
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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Floscan closed their doors about a year ago....
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03-26-2019, 03:04 PM
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#14
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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Quote:
Originally Posted by Ka_sea_ta
Floscan closed their doors about a year ago....
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Ah then, I was correct.
Their site is still up but the company's down.
There may be some units still on the company's shelf or perhaps the installers still have some in inventory?
If you want one, I guess you will have to go hunting.
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
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03-26-2019, 04:07 PM
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#15
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Senior Member
City: MN and FL
Vessel Name: Serendipitous
Vessel Model: Mainship 390, Bayliner 3258, Bayliner 4788
Join Date: Feb 2013
Posts: 285
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Hmmm...plowing water?
Quote:
Originally Posted by Ernie
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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I agree with David and others...8-10kts is too fast for your boat -- or too slow. A Cruisers 3950 aft cabin is built on a planing hull, which is why they gave it 600hp. Your hull will begin 'plowing water' above about 7kts, and continue plowing until you are up on plane, somewhere above 16kts.
My quick guess is ~8gph at 8kts and 13gph (or more) at ~10kts. Your wake (and fuel burn) will be huuuugggge at 10kts. Running angle between 8kts and 10kts will approach 4-5 degrees (which means most of your fuel is being used to make wake, as opposed to making way). You will actually burn less fuel (better miles-per-gallon) and make a smaller wake by getting the boat up on plane.
Your Cruisers is a go-fast boat that needs to stay as close to horizontal as possible, this means going very slow or going very fast. You won't be happy with the performance of a planing hull running at what's politely called the 'transition' speed (plowing water). Handling is goofy, running angles are high, the crew is uncomfortable. Miserable for you, your wallet, and anyone in the path of your wake.... ;-)
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RiverGuy~~
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03-26-2019, 06:54 PM
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#16
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Guru
City: Delaware
Join Date: Mar 2017
Posts: 681
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Have you asked the question over at the Cruiser Yachts Owners Club Forum, www.cruisersyachtsownersclub.com ? I would bet that someone could give you the most economical rpm's to run your boat at both a slow and a fast cruise.
Another alternative might be to peruse the threads over at clubsearay.com While hull shapes might be a bit different, I bet there is a lot of similarity in overall weight and sizes between the cruisers yachts and sea rays. While this wouldn't be an accurate number, its probably close.
Jim
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03-26-2019, 07:45 PM
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#17
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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Quote:
Originally Posted by JLD
Have you asked the question over at the Cruiser Yachts Owners Club Forum, www.cruisersyachtsownersclub.com ? I would bet that someone could give you the most economical rpm's to run your boat at both a slow and a fast cruise.
Another alternative might be to peruse the threads over at clubsearay.com While hull shapes might be a bit different, I bet there is a lot of similarity in overall weight and sizes between the cruisers yachts and sea rays. While this wouldn't be an accurate number, its probably close.
Jim
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I am not sure if I can explain this. Watch your wake. You are supposedly at hull speed when your can make your wake first come together.
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
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03-26-2019, 08:09 PM
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#18
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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Quote:
Originally Posted by JLD
Have you asked the question over at the Cruiser Yachts Owners Club Forum, www.cruisersyachtsownersclub.com ? I would bet that someone could give you the most economical rpm's to run your boat at both a slow and a fast cruise.
Another alternative might be to peruse the threads over at clubsearay.com While hull shapes might be a bit different, I bet there is a lot of similarity in overall weight and sizes between the cruisers yachts and sea rays. While this wouldn't be an accurate number, its probably close.
Jim
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Fule usage is greatly influenced by all the creature comforts you load.
An empty boat always gets better GPH.
Construct your own fuel verses rpm or speed
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
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03-26-2019, 09:48 PM
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#19
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Guru
City: Delaware
Join Date: Mar 2017
Posts: 681
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Quote:
Originally Posted by OldDan1943
Fule usage is greatly influenced by all the creature comforts you load.
An empty boat always gets better GPH.
Construct your own fuel verses rpm or speed
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Absolutely true.
My guess, however, is that the OP doesn't have floscan or something similiar, or he would have done this already.
Jim
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04-01-2019, 01:13 PM
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#20
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Guru
City: Fleming Island, Fl
Vessel Name: Sakura Perdido
Vessel Model: Grand Banks 36 Classic
Join Date: Jul 2016
Posts: 629
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My GB 36, at 7 kts, with the generator running is about 2.5/hr. Without generator is between 1.75 and 2/ hr depending on conditions.
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