Larger boats and GPH averages

Pseudomind

Pseudomind

Active Member
Jul 1, 2008
2,122
Jacksonville, FL
Boat Info
2011 Hurricane with Magic Tilt Trailer
Engines
115 HP Yamaha Four Stroke
I am still trying to close on my 380, I am curious as to your GPH and cruising speed to obtain this GPH. I know most of the larger boats will be diesel, but I am still curious. I am not trying to obtain a gas versus diesel comparison, just to see what a possible length versus GPH possible increase analysis shows.

I am figuring on somewhere between 30 -35 GPH at somewhere around 22-24 knots. I am guessing this will be at RPM wise, 3200 - 3400 range.

Who knows in a few years I might be interested in moving up when I retire. :huh:

I am primarily interested in lets say boats >44 - <60 foot

Hopefully I will have the 2002 Sundancer 380, 8.1s engines before the first of September I have been working on buying, that is if "Hurricane/tropical storm Fay" does not do any damage, as the boat is in a slip at Daytona, Halifax Harbor marina.

Thanks

:thumbsup:
 
Leaving the 380 8.1 out of the equation, and going on your >44 <60 foot range then your numbers may be closer to:
GPH........36 + (44 range nearer the 36 fuel burn 60foot range 50+ furel burn)
Knots......22-24 about right. May increase with boat sze and bigger hp and prop size
RPM........1800 to 2300. Bigger diesels/lower rpm. Your numbers are gasser rpms

Frank W will give you a better, and more detailed answer. Mine are from running my various boats and observing gph on friends larger boats.

Good luck on the 380 purchase, my friend just got an 04' with 105hrs and loves it.

Rich
 
There is no right answer to this one....every model boat and every engine package is different, so there isn't a linear relationship. So, probably the best you can hope for is for others to post their experiences.

I've got Cat 3116's and a 450DA (about 28,000 lbs).......which turns out to be an efficient but rather slow boat by current standards. We normally run the boat at about 75% power, burn 18 or less GPH and run 19-20 kts....speed up to rated cruise of 2400RPM and we are a 21-23 kt boat @ 22.6GPH, depending upon load.
 
Pseudomind said:
I am figuring on somewhere between 30 -35 GPH at somewhere around 22-24 knots. I am guessing this will be at RPM wise, 3200 - 3400 range.
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Thanks

:thumbsup:
Click to expand...

I would estimate 35 GPH, maybe 21 - 22 knots, and more like 35 - 3600 RPM.
 
On my 480 DB, the fuel burn is between 40 and 50 GPH if the engines are running between 1900 and 2100 RPM. This will vary some depending on load and sea conditions but just to give you an idea. Rated cruise on the engines is 2100 RPM and at that RPM, the engines burn a total of 50 GPH. The interesting thing is that it is fairly linear and flat on the GPH vs. RPM between 1900 and 2100 RPM such that the MPG is about the same. So if you go faster, you'll burn more fuel per hour but get their quicker so the total fuel burn is the same as going slower. Below 1900 RPMs, the speed of the boat goes down faster than the fuel burn so the MPG goes down faster. Poking around at 17 knots in a 480 DB is very inefficient.

My speeds are determined by engine load and sea conditions first. That usually means I'm running in the 1900 - 2000 RPM range. In a steep chop, I'm running down in the 1600-1800 RPM range... It ain't always about the fuel burn but making sure the boat isn't getting beat to death.

As a side note, my 480 DB is actually cheaper to run that my 380 DA gas boat was because it is much faster for the given fuel burn. The 480 DB goes 26-27 knots at 2100 RPM and 50 GPH
 
Last edited:
44DB with QSC-500s:

2400 RPM = 80% Load, 26 knots, 40 GPH, 0.63nm/g

Like Gary's the fuel burn is pretty linear. Once on plane, going slower doesn't improve overall fuel economy (in terms of how much fuel I need to burn to get from point A to point B) and going faster doesn't really hurt it, up to and including WOT.

Overall though, the common rail engine is actually less efficient than the older versions. I queried SR on this and they say it is due to environmental requirements imposed on newer engines. I am no genius, but I would've thought that a cleaner burning engine would be more efficient.:smt017

That said, the QSC is smoother, quieter, cleaner (i.e. smoke) and accelerates much faster than the CE version (which my buddy has in his 400 that we run with all the time). As with everything related to boats, it's all trade offs.
 
Pseudomind said:
I am still trying to close on my 380, I am curious as to your GPH and cruising speed to obtain this GPH. I know most of the larger boats will be diesel, but I am still curious. I am not trying to obtain a gas versus diesel comparison, just to see what a possible length versus GPH possible increase analysis shows.

I am figuring on somewhere between 30 -35 GPH at somewhere around 22-24 knots. I am guessing this will be at RPM wise, 3200 - 3400 range.

Who knows in a few years I might be interested in moving up when I retire. :huh:

I am primarily interested in lets say boats >44 - <60 foot

Hopefully I will have the 2002 Sundancer 380, 8.1s engines before the first of September I have been working on buying, that is if "Hurricane/tropical storm Fay" does not do any damage, as the boat is in a slip at Daytona, Halifax Harbor marina.

Thanks

:thumbsup:
Click to expand...

Our 38DA has the 8.1L Horizons and you are right on about the gas consumption. We get about 30~33GPH at 20~22MPH with an average load (3~5 people, 1/2 gas, 1/2 water, 1/2 waste levels). Even with this consumption we really like the boat. Someday we may move up with the big boys like Frank and others, but for now I am really happy with the 38DA.

Good luck on your purchase,

Mike
 
The 38DA is a smaller and lighter boat than the 380DA... I personally think the 380DA needs DIESEL power but that's a different ball-removing thread.
 
fwiw, The QSM's in my 480 burn fuel at exactly the rate predicted by the Cummins fuel burn/RPM graph in their literature. As measured by the digital display, and the amount of fuel needed to fill her up vs predicted to be needed by the electronics.

I cruise at ave 24k at 1960 RPM. That seems to be the sweet spot for my motors.
 
What accounts for the greater rate of fuel burn per hp with the larger diesels?
If the 500's burn 40 gph, why would my 3208's (355 hp)burn only 22 gph?
Less than a 50% increase in hp, but an 80% increase in fuel used. Is it typical that the greater the hp, more fuel- per horsepower, is required?
In other words, it seems as though as the engines get larger they get less efficient.

Can anyone 'splain to me?
 
I think the first indication will be to simply look at the comparable weights of the boats. When they get big, they get big and heavy (in a good way) in a hurry. 6' longer, 2' wider, 2' taller - that's a lot of boat.
 
I have come to realize my best fuel consumption is between 1,700 and 1,750rpm for the 56. Sea Ray recommend a crusing speed of 2,100rpm which is completely absurd IMO unless you have unlimited funds!

Here are some numbers on my boat that I recorded this past weekend trying to figure out my best consumption speed (I used a combination of the engines manufacturers publish data and three boat test I found of similar sized boats with the same engine configurations). The boat has MAN 10-cylinders and with 3/4 fuel and water weighted in at 71,000lbs:

1,500rpm = 19knots = approx 33 gal/hr. = .575nmpg
1,700rpm = 24knots = approx 45 gal/hr. = .533nmpg
1,900rpm = 28knots = approx 58 gal/hr. = .483nmpg
2,100rpm = 31knots = approx 75 gal/hr. = .413nmpg

Although I get better fuel consumotion at 1,500rpm, the turbos aren't singing and the boat isn't yet near full torque (1,700rpm according to MAN), so I feel that I am lugging the diesels. I only use this speed if the seas are heavy as the boat seems to plow through anything without recognition.

I'd be super interested to see if anyone in a 560 with the 800HP 3406E Cats care to share their data!
 
Frank,

I noticed that you had 3116's in your DA at 28,000 lb. It seemed like you got pretty decent Nmpg for a boat that heavy. I was looking at the 370EC (18,000lb) with these engines and wondering what the Nmpg would be with the3116's. Most of the ones I see are 300 or 350hp.
I saw your favorable comments about this boat in another thread about the AJ290 and all of a sudden I got hooked on the idea of going quite a bit larger then I had been looking for. I was looking at gas powered AJ290's. I liked the look of the 370EC hardtop and the room it had but wondered how fuel efficient it was compared to the AJ290.
Thanks

Mike Katsoris
 
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