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Old 04-08-2010, 07:00   #1
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Fuel Consumption

I'm looking for 30' or so cruiser, like Sea Ray Sundancer or Carver. Can you please tell me what average fuel consumption (expences) I can expect? Like miles per gallon? Or hours per gallon?

Also, can you cruise with economy speed and get better fuel expenses per trip?
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Old 04-08-2010, 08:05   #2
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Depends on the individual boat/engines what the fuel consumption will be, and yes, it changes fairly dramatically depending on your speed. Once you're looking at specific boats, be sure to ask and you'll start getting a feel for what to expect. A start - gas engines, which are more common in the smaller, production express boats like what you're talking about, maybe 20-25gph or somewhere in the range of 1 to 1.5mpg.

Every boat has a "sweet spot" where you get the best fuel economy for a given speed. And if you are really looking for economy. Go slow.

Example: the boat I was running last week burned 88 gallons an hour at 25.5 knots. Off plane and idling at about 8 knots, we were burning 6.
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Old 05-08-2010, 16:50   #3
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One thing that you will find is that cheaper boats often have less sophisticated hull shapes, and that they burn more fuel than some of the more expensive brands.

Calls to a couple of dealers or makers should get you some fast numbers for specific boats.
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Old 06-08-2010, 04:01   #4
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Hi Rob's dead right. It all depends how quick you want to go as to how much fuel you'll use.I own a 31' Mariner with two 255HP Mercruisers. I took some some data a little while ago and I hope this could be useful to you.

RPM SPEED KTS Litres Per Hour
1200 6.2 18
1500 7.2 23
1700 7.9 30
2000 8.8 40
2200 10.4 60
2500 13.3 72
2700 15.7 83
3000 18.5 85

I've run this flat out giving 25Kts at 104LPH

Good luck
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Old 09-08-2010, 07:42   #5
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Originally Posted by robw_fl View Post
Depends on the individual boat/engines what the fuel consumption will be, and yes, it changes fairly dramatically depending on your speed. Once you're looking at specific boats, be sure to ask and you'll start getting a feel for what to expect. A start - gas engines, which are more common in the smaller, production express boats like what you're talking about, maybe 20-25gph or somewhere in the range of 1 to 1.5mpg.

Every boat has a "sweet spot" where you get the best fuel economy for a given speed. And if you are really looking for economy. Go slow.

Example: the boat I was running last week burned 88 gallons an hour at 25.5 knots. Off plane and idling at about 8 knots, we were burning 6.
I would say that's about right for that type of boat. Many of the (I hate to use the term) "Sea Ray type" boats are a PITA to operate at low speeds. They wander from side to side and need constant correction. The most inefficient speed is from 8 knots to 20 knots or so before they get on plane.

My boat, a trawler, won't go over 13 knots at WOT but at 7 knots, I'll get over 4 MPG on diesel. Take it up to 11 knots and it drops below 2 MPG.
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Old 09-08-2010, 09:33   #6
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... Many of the (I hate to use the term) "Sea Ray type" boats are a PITA to operate at low speeds. They wander from side to side and need constant correction. The most inefficient speed is from 8 knots to 20 knots or so before they get on plane.
...
I can confirm this. I have a Sea Ray SRV360. It exhibits the "wandering" you mention. But, once you get used to it, you learn to ignore the wandering. Just let it go where it wants. It averages out to going the course you have it aimed. Still, it's annoying.

For my boat, your inefficient speeds are off a little. But your figures may well be for different sized or design boats.

The fuel burn starts to climb at 7-8, but doesn't really get bad until 10. But it planes at something between 14-16. Been so long since I had it on plane, I don't remember exactly. I don't have a fuel flow meter, but on long runs at 8-9 knots I was getting about 1.5MPG. Over 2MPG at 6. Never ran on plane long enough (while measuring) to know, but on a run from Marathon to Cape Coral, it got better than 1MPG. Better than I feared.

For a planing hull with twin 300hp diesels, that's not too bad. But not nearly as good as a trawler.

So, all in all you got it right.

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Old 09-08-2010, 10:41   #7
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Dmitry,

Pay close heed to what's already been said about the "no go" speed range, typically from about 7-8 to 18-20 knots in a 30' deep-V cruiser. This is the speed range where many powerboaters would prefer to cruise, and it's a range where boats of this style tend to exhibit excessive bow rise (thus poor visibility) and extremely high fuel consumption per mile, and where they make their largest (and most dangerous to other boats) wake.

The "wandering" at idle speed is inherent to many broad, deep-V hulls; the design features that allow them to cruise at 20-plus tend to result in poor directional stability at sub-planing speeds. You just have to get used to it- most owners eventually do, once they learn to stop making big steering adjustments to try to compensate. These same design features also make it very hard to run such a hull in no-wake zones; the bow will start to lift and the stern wave will pile up at much lower speeds than you'd find in a hull designed for displacement speeds. A typical 30' deep-V cruiser cannot run more than four to five knots in a no-wake zone without drawing attention from the police and curse words from the kayakers and canoeists.

Flybridge31's measured data appear fairly close to what I've seen reported for other boats of this general size and type. 60 to 100 litres per hour at 15 to 25 knot cruise speed with about 400 to 600 hp is pretty typical.

To summarize: I would only consider a hull of this type if most of your cruising will be at 20-plus knots, ie. open lakes and coastal areas, and if you don't much care about the fuel bill. If that describes you, a heavy deep-V cruiser might be ideal for your needs. If you hate pulling out the credit card at the fuel dock, and don't mind a more sedate pace, look for a hull that's designed for displacement or semi-displacement speeds.
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Old 09-08-2010, 14:13   #8
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... A typical 30' deep-V cruiser cannot run more than four to five knots in a no-wake zone without drawing attention from the police and curse words from the kayakers and canoeists...
An appropriate speed (approximately), for that sized boat (power, sail, whatever), in a "no wake" zone.
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Old 09-08-2010, 15:54   #9
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Dmitry,

What I did when setting up our boat was to go onto a site called, I think, boattest.com. You could then work your way through to a test which gave hull speed/fuel flow curves and see the most economical speed for your hull.

Equally, a lot of these vessels have Mercruiser petrol engines. With FI engines, the rpm/fuel flow curves are a given; it's the hull and drive [prop, etc.] which determines how much grunt you need.

For minimum wash [a requirement leaving our location] and slow speed cruise, I simply ran the revs up 100rpm at a time and looked for a commensurate lineal speed increase. This stopped at 1400rpm/6kt. Next was min rpm for the plane as an economy cruise. Mercury's charts said 3400rpm, but we wouldn't plane easily at this setting so 3500rpm/20.5kt was the compromise. Of the 10 share owners, we were the lowest or 2nd lowest fuel user without any loss of utility or fun.

Hope this helps,

Cheers
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Old 10-08-2010, 02:25   #10
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Originally Posted by Flybridge 31 View Post
Hi Rob's dead right. It all depends how quick you want to go as to how much fuel you'll use.I own a 31' Mariner with two 255HP Mercruisers. I took some some data a little while ago and I hope this could be useful to you.

RPM SPEED KTS Litres Per Hour
1200 6.2 18
1500 7.2 23
1700 7.9 30
2000 8.8 40
2200 10.4 60
2500 13.3 72
2700 15.7 83
3000 18.5 85

I've run this flat out giving 25Kts at 104LPH

Good luck
It is interesting to note that the faster you go the cheaper it is to run per mile once you are on plane. Flat out you will go 0.24 nm on 1 liter versus 0.18 nm/l at 2500 rpm.
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