Hatteras 67 CPMY burn rates

[madhatter1]

My 34 is 1.15 smpg cruising at 24 knots. The 46 is half that at 19-20 knots. I honestly have no real idea what either is at Hull speed. Guessing 34 is 2.5 to 3 and maybe the 46 is close to the magical 1!

[Sadey]

velocity in knots = 1.35 x the square root of the waterline length in feet.
The trick is the water line length. I don’t have it on any schematic so I estimate my WLL at 58’ so about 10.2kts

[Hat52MY]

Well 2-3 years ago fuel was a non issue, but with diesel approaching $5 bucks, actual operating costs out weigh everything else. Especially when the whole reason of owning a boat this size is to be able to use it for diving and a live aboard. Anyone can afford to buy an F86 Sabre jet, the 16K an hour operating cost on the other hand is the problem.

Quote Originally Posted by Hat52MY
After 12 years of ownership, in the grand scheme of owning and running a Hatteras to the islands, I find fuel to be the cheapest of ownership. And what Pascal said....

Even at $5 a gallon with 500hrs a year, which is highly unlikely as most boats are lucky put on 100hrs a year. In the grand scheme of ownership, fuel is a variable expense, and in my experience is one of the cheaper line items of owing and operating the boat. Even at 500 hrs of run time a year, that averages out to $3.3k per month. Putting it in perspective, you'll pay$3k a month for a good marina in South Florida. We have consistently budgeted $10K a year for fuel and with pricing fluctuations over the years, this has kept us on budget.

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[Freeebird]

First off these big MY’s roll like pigs. Not the best choice for a dive boat. Better off to get a CC for that purpose. I was just helping Freebird deliver a 58 series11 wide body. We took maybe a 3-4’ seas on the beam lamps broke furniture went flying boat looked like a bomb hit it. True the stabilizers were inop but they’re not effective at anchor or drift diving either.
As far as fuel burn you’ll hear people regurgitate this 1mpg figure at hull speed. Anyone with half a brain should understand that a boat doesn’t run on rails tracks tires. It operates in a medium of wind waves zig zagging drivers and autopilots. I know my boat will burn more total fuel when it’s rough than calm and sometimes it’s considerable. I’m a charter fisherman so I really only operate 2 speeds 2100 and 850 which is 42 and 12 gph respectively. 850 is out trolling speed which is about 8-9 knots that’s with 525 hp 12/71’s. That’s kinda close to 1 if you’re talking statue mpg. FWIW we just delivered that 58 with 650 hp8/92’s 10 days 1000 mi from basically Tampa Florida to the Mississippi Tennessee line. We ran every day at 1300 rpm which yielded 11 smph I kept pretty detailed logs on running time and estimated fuel burn at a conservative 12gph. We topped the tanks at Apalatchacola fl and then at Demopolis Ms the aft fuel gage was inop and the fwd suspect. Bird with his 1 mpg estimated the aft tank would take 300 gal my time and fuel flow estimate was 369. We put 454 gallons in a 508 gallon tank. Kinda a holy chit moment that close to running out we did have about 100 gal in the fwd tank but both engines were running off the aft which wouldn’t have been a good thing to have both die at once. In any event when I ran the actual hard numbers we were at 16 gph a far cry from 1 smpg. So take all these numbers with a grain of salt because what you will see in the real world probably won’t be the same.

First, you’re wrong.

The engines are the 735HP versions, we ran at 1,250 which gave us hull speed of 11.3MPH. Yes, MPH. We never got a true baseline because we started with an unknown quantity of fuel. Had we not been fighting that flood current of 3-4MPH, we could have gotten an accurate figure. We were not “a far cry from 1smpg” except for when we were fighting the current.

I’ve run enough of these things to verify they WILL get 1MPG (or damn near) on slack water, but not with 12V71TI’s which was the topic of this thread.

[rsmith]

I’ll just bite my tongue and roll my eyes.

First, you’re wrong.

The engines are the 735HP versions, we ran at 1,250 which gave us hull speed of 11.3MPH. Yes, MPH. We never got a true baseline because we started with an unknown quantity of fuel. Had we not been fighting that flood current of 3-4MPH, we could have gotten an accurate figure. We were not “a far cry from 1smpg” except for when we were fighting the current.

I’ve run enough of these things to verify they WILL get 1MPG (or damn near) on slack water, but not with 12V71TI’s which was the topic of this thread.

[SamBellows]

First, you’re wrong.

The engines are the 735HP versions, we ran at 1,250 which gave us hull speed of 11.3MPH. Yes, MPH. We never got a true baseline because we started with an unknown quantity of fuel. Had we not been fighting that flood current of 3-4MPH, we could have gotten an accurate figure. We were not “a far cry from 1smpg” except for when we were fighting the current.

I’ve run enough of these things to verify they WILL get 1MPG (or damn near) on slack water, but not with 12V71TI’s which was the topic of this thread.

So, with the 12v71TI's it has, what should I expect? Typically I am told only a ''poor' or ''idiot'' is concerned with the burn rate and ''Its never used enough to be concerned with fuel consumption and if you can afford one you should be happy with it even if it uses 10,000 gal an hour''. I was actually told that by the way, not on here. That is a fallacy in my opinion. Perhaps the reason a lot of boats are not used is because the owner never asked the important question before purchase.

I have a reason for wanting a boat and not being able to run it as intended negates the whole reason of owning the thing to start with.

[cww]

So, with the 12v71TI's it has, what should I expect? Typically I am told only a ''poor' or ''idiot'' is concerned with the burn rate and ''Its never used enough to be concerned with fuel consumption and if you can afford one you should be happy with it even if it uses 10,000 gal an hour''. I was actually told that by the way, not on here. That is a fallacy in my opinion. Perhaps the reason a lot of boats are not used is because the owner never asked the important question before purchase.

I have a reason for wanting a boat and not being able to run it as intended negates the whole reason of owning the thing to start with.

I don't get this.

You're talking to dozens of people who own these boats on this forum. You don't like the answers, so you keep saying they aren't answering the question. That's silly. You've already got multiple replies from people who have that boat telling you the burn rates (e.g., 12gph at 10 knots is mentioned above), but you seem obsessed with disproving or griping about the advice you've heard that fuel is the least of your worries with a boat this size.

The problem is that advice is not wrong. When you have multiple people who have these boats telling you the same thing then is the issue really them? To put it another way, if you're this concerned with fuel burn, a 90,000lb 70ft boat with giant V12 diesels is probably not the boat for you. It's going to burn a lot of fuel (1mpg or less). Everyone has said that.

[Freeebird]

I’ll just bite my tongue and roll my eyes.

You do whatever makes you happy.

[Freeebird]

So, with the 12v71TI's it has, what should I expect? Typically I am told only a ''poor' or ''idiot'' is concerned with the burn rate and ''Its never used enough to be concerned with fuel consumption and if you can afford one you should be happy with it even if it uses 10,000 gal an hour''. I was actually told that by the way, not on here. That is a fallacy in my opinion. Perhaps the reason a lot of boats are not used is because the owner never asked the important question before purchase.

I have a reason for wanting a boat and not being able to run it as intended negates the whole reason of owning the thing to start with.

Not sure why you quoted my reply to Scott, but as Chris said, I think your question has pretty much been answered as to what to expect in terms of fuel usage. All you have to do now is decide if that's a number you can live with. If not, your only real option is to go smaller, much smaller.

[Freeebird]

I don’t see this as troll material, but I will add one thing.

As I’ve said on here before, GPH is a useless figure unless you’re talking about a generator. They do their job at a constant rate, and the only thing that moves is the hour meter and the internal parts.

Miles per gallon is all that matters when you’re talking about dollars spent at the fuel pump and getting a boat from point A to point B. I’m guessing that’s why Scott wanted to bite his tongue and roll his eyes at my claim as he’s a clock watcher. Have you ever seen a car or truck manufacturer list GPH on a window sticker?

When I calculate fuel burn/range, I top the tanks, run a measured distance on flat water, top them again and do the math. My start and stop times have zero to do with that equation. Current and wind will obviously skew those numbers, but that’s easily calculated IF you maintain the same RPM that gives you hull speed on flat water. Head into either and push the throttles up to compensate, and your numbers will change dramatically.