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Old 27 August 2004, 15:32   #1
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fuel consumption

i know the merits of diesle v fourstroke or fourstroke v twostroke have been covered numerous times but has anyone especially big diesel and fourstroke owners got their economy (or lack of) figures to hand. Im tryin to price how long the extra cost of a diesl would take to pay for itself

oh yeah and what about that diesel thing.. are we gonna get stung for tax?

thanks glen
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Old 27 August 2004, 15:47   #2
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Yam f100 4 stroke

I work on just over 2 galls per hour,I have averaged 1.6 g/hr with lots of displacement speed river work and some 15-25 knot cruising(3-4000 rpm) and some blatting.Have just changed to a 21 inch prop from a 19 which tops out around 5600 revs with 2 adults 1 child or 5000 rpm with 4 adults one child.I reckon on 0.6-0.7 l/mile,but I dont tend to go above 4500 rpm very often,hope this helps,I,ll get my anorack.
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Old 29 August 2004, 08:09   #3
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Quote:
Originally Posted by gtflash
oh yeah and what about that diesel thing.. are we gonna get stung for tax? thanks glen
No, because you will want to use your vote very carefully next year at the general election.

Fuel, 200 hp diesel in a P22 does about a litre a mile @ 25 knots. 2 other advantages to the red stuff, its easily available on the water and much safer.

Pete
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Old 29 August 2004, 14:27   #4
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Timboli
Are you happy with your Yam 100 4stroke - looking at the same on Humber ocean pro.
Was worried about fuel consumption but 2 gallons per hour (8/9 per hour) doesn't seem too bad.
Thanks in advance
Alex
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Old 29 August 2004, 14:33   #5
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Originally Posted by Pete7
No, because you will want to use your vote very carefully next year at the general election.

Fuel, 200 hp diesel in a P22 does about a litre a mile @ 25 knots. 2 other advantages to the red stuff, its easily available on the water and much safer.

Pete
And cheaper .
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Old 29 August 2004, 14:52   #6
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I get around 1.3 miles to the litre of petrol doing around 25 to 30ish knots.

Revs on the Suzuki 140 between 4000 and 4500 which is where the rib/engine seem best.

The last 1500 revs gain another 10 knots, but I daren't ask what amount of fuel that uses - it's fun to give the engine the odd blip to (try and sometimes) overtake a jetski or something, but also running flat out everywhere surely reduces the lifespan of the engine.... not sure by how much though.

At the time I couldn't justify the extra cost for diesel, but the smaller diesels are not too much more, and when I come to replace next I will seriously be considering that alternative path (especially if red diesel remains cheap).

There was negligable price difference between the 150 optimax and the 140 Suzuki, don't think there was anything in it at all actually but somehow I went down the 4s route as opposed to 2s.

-Alex
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Old 30 August 2004, 03:29   #7
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Quote:
Originally Posted by arn.george
Timboli
Are you happy with your Yam 100 4stroke - looking at the same on Humber ocean pro.
Was worried about fuel consumption but 2 gallons per hour (8/9 per hour) doesn't seem too bad.
Thanks in advance
Alex
I am very happy with the f100/humber assault combination as far as economy and speed are concerned,however the ocean pro will be a lot slower with the f100 due to its hull and weight,it obviously depends on what length you are looking at and I dont have personal experience with the ocean pro but humbers figures suggest around 28-30 knots flat out for a 6.3,which means to cruise economicaly at 4500 rpm you wont be going very quickly.
I tend to cruise below 4500,and to maintain this,I would expect to use more fuel,but the average day tends to involve quite a lot of slower speeds also,so my experiences will not neccesarily reflect with another boat and driver.
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Old 30 August 2004, 06:25   #8
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Did around 55nm on Saturday and burnt around 65l of fuel. Half of that was 2 1/2 (kid) up and other half 4 1/2 up. We were doing 20 - 25 kts except through Langstone & Chi Harbours. The flowmeter was reading 30 l/h at 25kts in the usual solent chop, but it is over reading a tad at present. I still need to calibrate it and set the averaging corectly.
I don't think that is too bad for a quad carb 140hp 2 stroke pushing over 1.5 tonnes.
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Old 30 August 2004, 06:37   #9
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Generally we get about 1.3nm/litre cruising at 25-30 kts with 4 on board. It is possible to get 1.4 and even 1.5nm/litre with a light boat as long as you are very conservative with the throttle, but that rarely happens!!

We can get consumption as good as 15litres/hr with 4 on board (this is cruising constantly just above 20 kts-Optimax Smartcraft flowmeter) I know you asked for 4str and diesel figures, but I thought I'd put in some figures for new tech 2 str as they compare well with the 4str figures, Go above 4000 in the Opti though and it all goes down the drain!!
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Old 30 August 2004, 07:22   #10
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At the other end of the scale racing a 7.3 metre race rib at speeds of up to 72 mph in ideal conditions we generally calculate 1.65 litres per nautical mile with a margin for safety!


ps after the cancelled race on Sunday I've got about 210 litres of premixed unleaded with castrol biolube at 50 to 1 in it! Any takers?
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