Fuel Consumption

[rjbathgate]

Hey,

Realise this is very much a how long is a piece of string, fluffy question, but I was just wondering if anyone could give some 'ideas' on what I should expect for fuel consumption:

5.05m RIB
60HP 2 Stroke Mercury Outboard

Cruising at 4000rpm at 20 - 22 knots

What kind of distance (or fuel consumption per hour) should I expect, roughly?

Cheers

[sarahscottiedog]

I once read on here that reguardless of your outfit, is always seems to work out at a sensible cruising speed for your boat they all seem to drink about 1 litre per mile. Most people I have spoken to agree that this is a pritty good rough guide.
My current boat has a digital fuel consumption guage and agrees with this through out the middle 80% of planing speeds, only at the very top and bottom 10% is it much different.

[C-NUMB]

I have old boat magazine test where a 60 hp 2st mercury was tested. At WOT(5300 rpm) consumption 26,8 l/h and at 4300 rpm 16,1 l/h. I this case 4300 rpm equals to a speed of 21 knots. So as an indicative figure roundabout 0,8 l/nm might be close to truth, lightly loaded.

[Hightower]

In light of the above facts in the post above, I've deleted my post.

[rjbathgate]

Hey,

Cheers for all the replies

Will go play with the numbers!

Ta

[davej]

I have almost exactly your rig, ie a 60hp merc 2S on a tornado 5mtr and while I have never really actually calculated the fuel burn reckon its less than 1ltr/hr.

Davej

[rjbathgate]

Originally Posted by davej

I have almost exactly your rig, ie a 60hp merc 2S on a tornado 5mtr and while I have never really actually calculated the fuel burn reckon its less than 1ltr/hr.

Davej

do you mean 1 litre per hour?

That's 20 nautical miles on 1 litre of fuel...?! Getting 500 nautical miles out of one jerry can of 25litres sounds a bit wonderful....

Do you mean 1 litre / nautical mile?

[mikeripon]

Hi i was lead to believe that if you half the horse power of an engine, ie 60hp =30 ltrs at full throttle for 1 hour, but for most messing around you can further half the figure again 15ltrs per hour for your average hour out playing etc. This is also meant to take into account a bit spare for the safety factor.
Its a pretty rough guide but a quick one to work out if you have enough fuel to go out for the afternoon?

[starnetman2001]

For me, I think it unlikely that a rough rule would work for all.

There are just so many variables.

Deep V hull or fast planing.
Length of Hull (More hull in the water = more drag)
Load
Speed.
2 or 4 Stroke.
RPM, (While 4 strokes use less fuel at lower RPM 2 Strokes can use more)
Engine economy.
Driver
Prop size
And swell size

I think the only sure fire way is to test your RIG. Get a feel of what it uses under whatever load (Also helps with early diags). Ask people who have the same hull and similar sized engines.

Just my opinion

[BogMonster]

Originally Posted by mikeripon

Hi i was lead to believe that if you half the horse power of an engine, ie 60hp =30 ltrs at full throttle for 1 hour, but for most messing around you can further half the figure again 15ltrs per hour for your average hour out playing etc. This is also meant to take into account a bit spare for the safety factor.
Its a pretty rough guide but a quick one to work out if you have enough fuel to go out for the afternoon?

I think that's fairly pessimistic but would certainly give a safety factor.

My 150hp Etec would give 75L/hr at full throttle on that calculation (not as bad as that I don't think - I can't say I have ever looked but I think it's more like 50-55) half that would be 37.5L/hr at which consumption rate you would have to be cruising at somewhere north of 35 knots all the time.

I'd say my typical average consumption is no more than 20L/hr in mixed use this would be some cruising 20-25kt some fast cruising 30-35 knots some pootling around and the odd WOT blast.

You certainly shouldn't run out of fuel using that rule of thumb anyway

[two stroke mick]

60 HP etec on 4.9m valaint rib uses 13 lt per hr at a crusing rate of 18-20 kn (I use the figure of 0.75 lt per hr actual usage and a theroical usage of 1 lt per hr this gives me a safe buffer of 25% approx.

TSM