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Old 15 March 2019, 14:09   #1
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Real life running/fuel costs

Leaving aside the initial purchase price, perceived sea keeping and berthing costs, what are the likely fuel consumption differences between a 6m with a 115 Mercury and a 6.5 with a Suzuki 150? Not worried about top speed, interested in range and economy. Thinking on a cruising speed in the mid to high 20 knots. Both ribs are by XS if that helps in anyway.

Any thoughts gratefully received.
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Old 15 March 2019, 14:31   #2
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Not a Suzuki but a 150hp Mariner (Mercury) on a 6.5mtr Coastline.

Most economical cruising speed is 24 knots. Consumption around 0.8ltr/nm.

The Suzuki might be marginally better but there won't be a huge difference

Actual daily figures from a week last year......

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Old 15 March 2019, 14:37   #3
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Range is my thing.

Oddly enough, I suspect that range will be similarish. Obviously we'd need to know what the tank capacities are!
In VERY general terms, I'd say 115hp is a bit light for 6m and likely requiring a heavy throttle hand, whereas 150hp is very balanced for your required cruising speeds. L/Nm may work out very close.

As regards costs - in that spectrum, your fuel mileage costs will be the least of your worries. Fixed annual costs per mile will be the big influence, the more miles you do, the cheaper it is!
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Old 15 March 2019, 14:53   #4
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Thanks Last Tango, exactly the sort of answer I was hoping for.

Agree with your thinking Wilk, but the purchase and annual cost I can justify and live with. The plan is to be out as often as I can and to do some long distance trips [being retired has some benefits] so the actual cost per outing has a bearing on choice of size. That and keeping the wife on side!
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Old 15 March 2019, 16:38   #5
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Ive found this calculator to be pretty accurate, it can be set in metric or imperial Fuel consumption calculator - MerCruiser - Volvo Penta - Crusader - Mercury - Evinrude - Honda Marine - Yamaha Marine - Suzuki Marine - Tohatsu - Johnson - Outboards | GPH MPG LPH KPL
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Old 16 March 2019, 02:33   #6
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Quote:
Originally Posted by 36valley View Post
Leaving aside the initial purchase price, perceived sea keeping and berthing costs, what are the likely fuel consumption differences between a 6m with a 115 Mercury and a 6.5 with a Suzuki 150? Not worried about top speed, interested in range and economy. Thinking on a cruising speed in the mid to high 20 knots. Both ribs are by XS if that helps in anyway.

Any thoughts gratefully received.
All this burn data in my view is misleading as in real terms people don't use their boat that much to notice the fuel usage difference. My rule of thumb is on a normal half - 1 day out in the rib I use 30 - 40 of petrol and that is on a 60 hp old 2 stroke. Regarding range always carry about 20 - 40 ltrs in cans unless you have a huge tank
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Old 16 March 2019, 02:39   #7
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Passage planning?
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Old 16 March 2019, 02:44   #8
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Passage planning?
Perhaps one might like to expand
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Old 16 March 2019, 04:26   #9
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OP - If you are interested in range because you want to make long trips then focusing on cost per mile may not serve you well. Clearly it's important to buy an economical engine, but it's also vital (IMO) to consider other factors as well. It's a piece of string really...
  • Every engine/boat combo has a sweet spot for speed v economy.
  • Different boats handle waves differently.
  • Your boat needs to be able to achieve the engine's sweet spot in the weather you will travel in.
  • Long cruises tend to mean encountering mixed conditions.
  • Larger boats generally have larger tanks.
  • Loads will effect the range considerably
  • Because the engine will be run harder
IMO take the bigger boat/engine combo and forget about the "fuel economy".
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Old 16 March 2019, 05:19   #10
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On a 6m I'd think a 115HP will be a bit underpowered for economic cruising in the high 20kt band.

The extra 0.5m will also made a ride difference in any kind of seas.

If budget allows - as you say it will, I'd go for the larger engine every time. Not only will it be generally running at lower revs for the same speed as a smaller one, but if ever you need extra power, you have it.

I think that many people who opt for a smaller engine often spend a lot of time thinking "what might have been with the larger one" and that can spoil the enjoyment for a long time: few think I should have gone for the smaller unit.

For these reasons I'd go for the 6.5 with the 150 given the choice, and everything else being equal

LT
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