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Old 17 March 2016, 04:15   #1
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SIB fuel use?

Getting a bit geeky but I know some people like to log these things (me included) and it would be interesting to see how much others use for various engines? SIB's are cheaper to run compare to RIB's but fuel is still used at a fair rate I've found.

I kept the figures for the last eight trips last season. A real mix of longer coastal trips, playing in the waves, kneeboarding and long pootles up rivers.

For my Mercury 15hp 2 smoke the average nautical miles per litre per trip (generally trips of 2 - 4 hours actual moving time) was:

2.6 nm/l
1.5
1.28
1.8
2.3
2.18
2.1
1.9

Average = 1.75 nm/litre

The most accurate average though was a week's use in the Dartmouth area to include a real general mix of river/sea use.

Total distance 122nm, used 64 litres, av speed 5.8 kts/hr, used 3.04 litres hour and achieved 1.9 nm per litre.

If others have figures please post.
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Old 17 March 2016, 16:58   #2
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Originally Posted by Max... View Post
Getting a bit geeky but I know some people like to log these things (me included) and it would be interesting to see how much others use for various engines? SIB's are cheaper to run compare to RIB's but fuel is still used at a fair rate I've found.

I kept the figures for the last eight trips last season. A real mix of longer coastal trips, playing in the waves, kneeboarding and long pootles up rivers.

For my Mercury 15hp 2 smoke the average nautical miles per litre per trip (generally trips of 2 - 4 hours actual moving time) was:

2.6 nm/l
1.5
1.28
1.8
2.3
2.18
2.1
1.9

Average = 1.75 nm/litre

The most accurate average though was a week's use in the Dartmouth area to include a real general mix of river/sea use.

Total distance 122nm, used 64 litres, av speed 5.8 kts/hr, used 3.04 litres hour and achieved 1.9 nm per litre.

If others have figures please post.
By rights we should get the same figures as you. But I've not worked it out to be honest, I have only ever worked on the estimate of 10% of hp, in gallons, at WOT per hour. Always carry twice that amount. Even though we're very rarely always on full throttle and the consumption definitely drops off a lot if we keep it at 2 thirds throttle. So for instance I have a 3 hour round trip at sea planned, that's 4.5 gallons or 20 litres. I'll carry an extra 20, unmixed, then add some of that and mix it at the destination. If I don't use it I put it in the car.
Luckily our local fuel station doesn't seem to care what size jerry can we fill so I'm currently using a 20 litre quicksilver tank and two 10 litre petrol jerry cans. On the other hand our local supermarket refuse to allow delivery into anything other than a 5 litre can...
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Old 18 March 2016, 04:00   #3
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Hi Simon, yes I have used the 10% thing but have calculated it's a bit of an underestimate of fuel at WOT for us - not sure why, maybe the way we drive like hooligans sometimes and thrash these little engines.

It would give 6.75 litres per hour (1.5 x 4.5 litres) but I think 8 might be more accurate at WOT.

To gauge fuel used easiest thing is to weigh your empty fuel container and then weigh the fuel used before/after. 1 litre petrol weighs approx 0.74 kg.

Had 175 views but no other contributions?? Nobody else use any fuel??
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Old 18 March 2016, 04:09   #4
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Max

never done a real trial myself on the SIB but i watched a you-tube video from an Italian supplier for a 3.8 m boat with a 20hp Suzuki lean burn 4st, normal boating as you would going on any trip he got 2lts /hour fuel usage.
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Old 18 March 2016, 05:43   #5
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>>>Nobody else use any fuel??

Well so little I'm not counting!

We tend to do around 20Nm or perhaps up to 25Nm most day out trips, 30Nm would be a long run for us.

So on a basic trip we are 10Nm out and 10Nm back. That tends to use half a 20lit tank so broadly speaking we are around 2Nm/lit which is very close to your figure.

If we are on the potential 30Nm trip I take a 5l can or second 12l tank as spare.

The new Suzuki (perhaps at the dealers today!) only has a 12l tank but I'm damn sure it won't use half the fuel so I'll probably buy a bigger tank.
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Old 18 March 2016, 05:55   #6
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Blimey David, I thought if anyone logged these things it would be you...

Will be interested to see how you get on consumption wise with the Suzuki.
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Old 18 March 2016, 06:13   #7
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>>>thought if anyone logged these things it would be you.

I'm inconsistent!

I have obsessively collected every Motoring Which of the 50/60/70s... I have a drawer with instruction books for every item we have going back 40yrs... all my nails and screws in the garage are sorted in Chinese take away boxes & labelled with type/size...

But my CDs/Albums are not in artist order and I never log fuel consumption.

Selective OCD I reckon.
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Old 18 March 2016, 08:37   #8
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>>> interested to see how you get on consumption wise with the Suzuki.

Yes I'm interested to see how it does. Mind you I might give the results in how much of a tank per day.

Bit like the sort of guy when asked what his car's fuel consumption is will reply "It's excellent... I put 20 worth in on Saturday and it got me to work and back all week with some left over".
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Old 18 March 2016, 08:46   #9
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SIB's are cheaper to run compare to RIB's but fuel is still used at a fair rate I've found
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Had 175 views but no other contributions?? Nobody else use any fuel??
I WAS going to reply to the first observation - but modesty stayed my hand. The second poke broke my resolve!

If my "sums" are correct - you're paying about 54p/Nm at 16kts? and I'm paying about 47p/Nm at 30kts.

Granted, it's commercial diesel but:
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Old 18 March 2016, 08:50   #10
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I WAS going to reply to the first observation - but modesty stayed my hand. The second poke broke my resolve!

If my "sums" are correct - you're paying about 54p/Nm at 16kts? and I'm paying about 47p/Nm at 30kts.

Granted, it's commercial diesel but:
No, on average I'm paying 54p/nm at under 6kts/hr

At least if my maths is correct.

Over a typical weeks use of all sorts (that Devon trip) we did an average speed (moving time only, not floating/anchored and fiddling about etc) of 5.8 kts/hr and for each litre burnt travelled 1.9nm.

And I thought my old Landys' were fuel in-efficient...

I know your typical RIB burns through the old juice pretty quick but gets my goat a little when people say you can "...go a whole week..." on that little (SIB) tank etc and it sips fuel, rollocks they do...
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