Fuel Economy Mercury F60 ELPT

milflyer · 15 February 2015, 18:38

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

matt h · 15 February 2015, 20:50

0.6 litre per N mile as a guide. good engines and pretty bombproof

milflyer · 15 February 2015, 22:00

Quote:

Originally Posted by matt h

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?)

Wibs · 15 February 2015, 22:12

....don't actually think Matt knows what 4000 rpm looks like.

Christiananthony · 16 February 2015, 11:34

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
Hong Kong

JamesF · 16 February 2015, 13:44

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 5½ 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 ¾ 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.

chris.moody · 16 February 2015, 18:09

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).

matt h · 16 February 2015, 18:14

milflyer · 16 February 2015, 18:24

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!

Christiananthony · 17 February 2015, 01:23

Sorry it should be 0.167 liters per km.

Christiananthony · 17 February 2015, 01:29

The link of the "guy" was : Rigid Inflatable Boats (RIB) - Real World Experience | eBay. To be fair he did say " about 14mpg"

JamesF · 17 February 2015, 14:55

The oft-quoted rule of thumb on here seems to be about 1 litre per nautical mile, which is about 4.4 statute miles per US gallon.

Matth suggested 0.6 L/nmi in the second post — for a similar sized boat with a recent engine. That's 7.3 mpg (statute, US).

I can't believe a figure of 14 mpg (ditto). That's 0.3 L/nmi, which is half what the lowest figures seem to be on here. Of course there will be quite a bit of variation between boats, engines, payload, conditions and people helming, but 7 mpg isn't 'about 14mpg'.

I think he's made a mistake measuring his fuel consumption, or accidentally put a 1 in front of it.

I'd plan for 1 L/nmi, 5½ nautical mpg imperial (or 4½ nautical mpg US), and then be pleasantly surprised if your consumption is better than that. It's much better that way than planning for 14 (or, being more conservative, 10) and being disappointed somewhere out at sea

!

chris.moody · 17 February 2015, 15:29

I think to get better than 0.5 litres per nautical mile you would need either a sub 10hp outboard (they just sip fuel) or a diesel inboard.

PeterM · 17 February 2015, 16:39

I managed in 2013 to do a shade over 82nm on 32L of fuel .

It was a mirror calm day and I trimmed the boat as well as I could and did 22knts the entire way around the IOW having left Poole.

That's with flat (ish) v on my little Avon adventure 4m and a Yam 50EFI purring along behind me ....only coming of the plane twice the entire way.

What's that work out to ? - About 0.39l per NM ?

Got to love EFI

Christiananthony · 18 February 2015, 06:24

Very Good numbers Peter!

There is hope and perhaps credibility to the 14mpg(US) claim. I have the Yam 60 with EFI. Hope to be doing sea trials next week. My Gemini 550 might be a shade heavier at around 300kg for the hull and 120kg for the engine plus extras.

What was your approx displacement at the time and the bottom was antifouled?

chris.moody · 18 February 2015, 08:06

14 mpg (US gallons) works out at approx 0.30 litres per nautical mile.