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Old 20-03-2017, 16:32   #1
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1GPH at Low 20's Knots??

Hello all,
I was perusing boats for sale, and stumbled upon a 46' Ocean Sunliner with twin 450 GM 6V71-T Idiesel's (900hp total) that the ad claimed 1GPH when cruising at the low "20's".

This sounded WAY too good to be true, so in the interest of truth, I ask if that is even remotely possible? I mean we all want fuel economy, but at 20kts?? is there something 'special' about the Ocean sunliner hull that would allow even close to this? does anyone have any thoughts, other than "the broker wanted attention"??

b
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Old 20-03-2017, 16:42   #2
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Re: 1GPH at Low 20's Knots??

Not even a remote possibility. 6v-71 detroits will consume a gallon per hour at idle........
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Old 20-03-2017, 16:42   #3
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Re: 1GPH at Low 20's Knots??

Even 1 GPM would be great mileage on a boat that size. I don't think you could even idle 900hp engines in 1GPH.
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Old 20-03-2017, 16:43   #4
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Re: 1GPH at Low 20's Knots??

I think it would be more likely to build a perpetual motion machine than to get over 20 kts on 1 gph on a 46' boat. I doubt you could get those results with a 46" model boat.

I burn that much to get 6.5 kts in a 42', 25,000 lbs boat.
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Old 20-03-2017, 16:55   #5
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Re: 1GPH at Low 20's Knots??

Even if he left off a 2 in front of the 1 for 21 gallons an hour I think he would be being very optimistic. He either mistyped something or he is lying.
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Old 20-03-2017, 16:58   #6
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Re: 1GPH at Low 20's Knots??

Left a couple of zeros out...
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Old 20-03-2017, 17:01   #7
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Re: 1GPH at Low 20's Knots??

Quote:
Originally Posted by Brian_D View Post
Hello all,
I was perusing boats for sale, and stumbled upon a 46' Ocean Sunliner with twin 450 GM 6V71-T Idiesel's (900hp total) that the ad claimed 1GPH when cruising at the low "20's".

This sounded WAY too good to be true, so in the interest of truth, I ask if that is even remotely possible? I mean we all want fuel economy, but at 20kts?? is there something 'special' about the Ocean sunliner hull that would allow even close to this? does anyone have any thoughts, other than "the broker wanted attention"??

b
perhaps the add was suggesting per motor.
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Old 20-03-2017, 17:14   #8
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Re: 1GPH at Low 20's Knots??

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Originally Posted by downunder View Post
perhaps the add was suggesting per motor.
or per cylinder
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Old 20-03-2017, 17:14   #9
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Re: 1GPH at Low 20's Knots??

Maybe he moved the decimal point the wrong way.
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Old 20-03-2017, 17:31   #10
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Re: 1GPH at Low 20's Knots??

I think my dinghy can do it, maybe.
For reference if I remember right my little 21' CC boat with a single 175 OB would burn 8.5 GPH at about that speed, about 20+ GPH at full tilt
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Old 20-03-2017, 18:08   #11
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Re: 1GPH at Low 20's Knots??

I think you are reading alternative facts.

Same boat and engines on another advert are saying 19 gallons/hour @ 19 mph cruise speed. Even that would be stretching the truth a bit.
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Old 20-03-2017, 18:17   #12
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Re: 1GPH at Low 20's Knots??

I have a very nice bridge from Florida to the Bahamas for sale.
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Old 20-03-2017, 18:46   #13
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Re: 1GPH at Low 20's Knots??

StuM would spot the problem immediately.

It was a units check failure.

Cross out hours and put in minutes (or maybe seconds) and I reckon the number sounds about right.
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Old 20-03-2017, 18:51   #14
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Re: 1GPH at Low 20's Knots??

I think it is possible if going down hill.
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Old 20-03-2017, 19:33   #15
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Re: 1GPH at Low 20's Knots??

I've run and rebuilt DDs all my life. A rule of thumb on natural 71s is a gallon an hour at maximum continuous hp. Turbo models like 671TI can burn 2-3x or more fuel.
My boat has early 671 naturals and burns a total of about 8.5 gallons @ 10kts. I have a semi planning hull. If I had 2000 hp I could plane.
6v71s as opposed to IL671s seem to have a poor reliability reputation.
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