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Old 15 February 2015, 13:38   #1
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Fuel Economy Mercury F60 ELPT

Hi folk ... Can anyone offer a "guideline" fuel usage on a 2010 model fitted to a 5m Humber Assault RIB.

Normal operating RPM range 4000 +/- 500

Many thanks

John
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Old 15 February 2015, 15:50   #2
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0.6 litre per N mile as a guide. good engines and pretty bombproof
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Old 15 February 2015, 17:00   #3
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Quote:
Originally Posted by matt h View Post
0.6 litre per N mile as a guide. good engines and pretty bombproof
Hi Matt, greatly appreciated (presuming that figure was at 4000 RPM?)
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Old 15 February 2015, 17:12   #4
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....don't actually think Matt knows what 4000 rpm looks like.

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Old 16 February 2015, 06:34   #5
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Hi John,

I read about a guy that got (or so he claimed) 14 miles per US gallon at 28mph in a Nautica 16 and a 45hp 4 stoke Honda. I think if my math is right 14mpg is 0.174 liters per kilometer.

Anyone else confirm or deny these numbers? Im very curious myself and will be relaunching my Gemini 550 with a Yamaha 60 soon and do some testing.


Cheers,
Christian
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Old 16 February 2015, 08:44   #6
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I presume a Nautica 16 is 16ft long, or 4.9m.

We took our Ribcraft 4.8 with a 2008 Honda BF50 was on a run last year — unusual, because it's normally a sailing club safety boat and normally the third choice. About 5 miles up the coast to another sailing club, all-day loiter with a couple of very short high-speed blasts on safety boat duty, then back home. Total fuel consumption was roughly 15L, (4 US gallons). Total distance probably somewhere between 12 and 16 miles, so we managed between 3 and 4 nautical miles per US gallon.

Given that the BF45 is a much older motor, it isn't going to beat a BF50 by a factor of 4.

The claim sounds like nonsense to me.

Edit: Here's some more back-of-the-envelope calculations.

28 mph 14 mpg = 2 US gallons per hour.
The density of petrol is roughly 6 lb per US gallon, so 12 lb/hr.
Assume that he's using power to do this: 34hp.
Brake-specific fuel consumption (smaller is better) is 12 34 = 0.35 lb/hr/hp

For an early-90s petrol engine with carburettors, I'd expect 0.45 lb/hr/hp at best.

Assuming half power, the figure is a more reasonable 0.53 lb/hr/hp, but I'm convinced that you won't get a boat of that size to that speed on 28hp.
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Old 16 February 2015, 13:09   #7
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I manage 0.66 litres per nautical mile on a 4m Searider with honda BF50, but I never cruise at 4000 rpm. Usually cruise at 4500 to 5000, and often take her up to 5750 rpm.

Matt's figure sounds quite reasonable to me, not that he has ever helmed at anything other than WOT or idling (during the bits where the prop is out the water).
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Old 16 February 2015, 13:14   #8
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Old 16 February 2015, 13:24   #9
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Hi Chris

Thanks for your note ... 0.6 is sounding a good starting point. With a number of excellent locations to go to e.g. Guernsey, Alderney and St.Malo to name a few with "interesting" seas 4000RPM / 20Kts is a fair (IMHO) conservative and planning figure with a RIB / Engine I don't know yet ... Not ready to be bitten or loose my fillings yet LOL!
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Old 16 February 2015, 20:23   #10
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Sorry it should be 0.167 liters per km.
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