One liter per mile - what speed for your RIB?

[Channel Ribs]

I think most of us are familiar with the idea that a RIB should be expected to yield 1:1 on passage, ie not at a high speed but a comfortable planing pace.

We have just spent some time tweaking our own 90HP 4/S + 6.25m setup, not sure how much of an improvement has been made yet but 1:1 used to be achieved at around 20kn. (You can see why I felt the need for a tweak.)

So what speed do you get, is 1 liter per mile realistic?

[Zubenelgenubi]

1 L per hour? Doesnt sound realistic to me even at idle.

[Channel Ribs]

Originally Posted by Zubenelgenubi

1 L per hour? Doesnt sound realistic to me even at idle.

Booger! I meant per mile, d'Oh

[Erin]

I think they use a different unit of measurement in Alderney to the rest of us. For example, ask somenone how much they've had to drink, and if they say a pint or two, they actually mean about a gallon

[Zubenelgenubi]

I think 1 L per mile is certainly achievable, I was out yesterday & did about 30 miles & used about 25L of fuel, most of the time at about 30kn, all approximations of course. My 90 2 stroke is very economical.

[Channel Ribs]

Originally Posted by erin

i think they use a different unit of measurement in alderney to the rest of us. For example, ask somenone how much they've had to drink, and if they say a pint or two, they actually mean about a gallon :d

[Zubenelgenubi]

Originally Posted by Erin

I think they use a different unit of measurement in Alderney to the rest of us. For example, ask somenone how much they've had to drink, and if they say a pint or two, they actually mean about a gallon

Sound like a "quiet night" in Ireland, ie about 6 to 8 pints!!

[Channel Ribs]

Originally Posted by Zubenelgenubi

Sound like a "quiet night" in Ireland, ie about 6 to 8 pints!!

It is not the quantity, it is the way it is measured. "A couple of pints" can mean anything. Time is also a fluid concept round here, days can last weeks and months go on for a lifetime.

[9D280]

2 I can remember-

1) 35 (Nautical) Miles, 30L Fuel, 19-20 Knts.
It was an Sr4 / Suz DT25, so not too good a comparison to your 90!

1) 24 (Nautical) Miles, 30L Fuel, Consisting of 1/2 hr pootling about with a lot of stop - go, followed by 20-24 Knts for 20 odd miles, 2 miles of which were at WOT.
That was with an old not particularly well tuned 2-pot Yam 55 Premix on the Humber


There was a thread about fuel consumption, will try to find it later if someone doesnlt get there first.

[Leapy]

Did a Mylor-Fowey-Mylor flat sea run in the summer...Ribcraft 5.3, Suzuki DF90 (2009 spec 1500cc), 3 up.

Distance travelled: 53.2 imperial miles
Average speed including mooring, tootling around Fowey etc: 19.2mph
Cruising speed at sea: 25mph, give or take
Fuel consumption measured tank full to tank full: 9.13mpg (2.00 miles per litre)

[Cypman]

Cruising at circa 25kts in a Humber Ocean Pro 6.3m with a Suzy DF140 resulted in a fuel burn of around 17 ltrs. Even at 30kts I was bettering 1 ltr per mile.

[Channel Ribs]

Thanks for all the responses so far, this will also really help with the Alderney Cannonball Challenge.

Summary so far:-

Zubenelgenubi: 30nm:25L @30kn (90 2/S) = 0.83 lpm
9D280: 35nm:30L @20kn (25 4/S) = 0.86 lpm
9D280: 24nm:30L @mixed (55 2/S) = 1.25 lpm
Leapy: 46nm:26L @20kn (90 4/S) = 0.57 lpm
Cypman: ?nm:17L @25kn (140 4/S) = ?
Cypman: ?nm:? @30kn (140 4/S) = <1 lpm

[two stroke mick]

Etec 60 hp on DR 490 varies from 1.5 nm/ltr to 1.7 nm/lt at 18-20 kn

TSM

[Channel Ribs]

Summary so far, with estimated 1:1 speeds in bold at the end:-

Zubenelgenubi: 30nm:25L @30kn (90 2/S) = 0.83 lpm 33kn
9D280: 35nm:30L @20kn (25 4/S) = 0.86 lpm 22kn
9D280: 24nm:30L @mixed (55 2/S) = 1.25 lpm 20kn
Leapy: 46nm:26L @20kn (90 4/S) = 0.57 lpm 25kn
Cypman: ?nm:? @30kn (140 4/S) = <1 lpm 35kn
TSM: ?:? @20kn (60 E) = 0.75 lpm 25kn

It seems fair to say that, so far, speeds of between 25 and 30 knots are realistic for most outboards.

[jwalker]

Something spooky about rib fuel consumption I reckon. My boats have done about 1lt a mile no matter what engine was on the back and even my current boat weighing in at about 3tons with a diesel still does about 1lt per mile.
Folk talk about how economical modern engines are, how 4 strokes are better that 2 strokes, how new tech 2s are better than old but they all seem to be around the 1lt/mile. Except Leapy, of course.

[GordyP]

I get about 1.3 ltr/mile at 40 knots, no idea what speed I'd be going to get it to 1ltr/mile.

[Leapy]

Originally Posted by malthouse

Leapy: 46nm:26L @20kn (90 4/S) = 0.57 lpm 30kn

Should be 20kn

[Leapy]

Originally Posted by jwalker

Something spooky about rib fuel consumption I reckon. My boats have done about 1lt a mile no matter what engine was on the back and even my current boat weighing in at about 3tons with a diesel still does about 1lt per mile.
Folk talk about how economical modern engines are, how 4 strokes are better that 2 strokes, how new tech 2s are better than old but they all seem to be around the 1lt/mile. Except Leapy, of course.

All I can say about my own figures is that the measurements are tank brim full to tank brim full and the mileages comes from the GPS. The figures I quoted for that trip are consistent with the figures I've got for the whole of the boat ownership.

I'm happy with their accuracy

[Channel Ribs]

Originally Posted by Leapy

Should be 20kn

Cheers Leapy, will you settle for 25 though as I am trying to adjust to the theoretical speed where 1:1 is reached?

[Channel Ribs]

Originally Posted by GordyP

I get about 1.3 ltr/mile at 40 knots, no idea what speed I'd be going to get it to 1ltr/mile.

You've never tried going 35 then?