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Old 18 February 2012, 05:27   #21
Portnahaven's Avatar
Country: UK - N Ireland
Town: belfast
Boat name: portnahaven
Make: Red Bay Boats
Length: 7m +
Engine: yamaha 245hp diesel
MMSI: 235089641
Join Date: Aug 2011
Posts: 345
Originally Posted by Dragonhawk ficht View Post
Just what I thought,
So hear goes,

Well i've got a 120 L tank under deck and inline fuel flow reader fitted just after the water seperater, Which gives me a digital flow rate, display built into the rev counter, So I can easily see how many litre's per hour, at whatever rpm, so this is what I get,
1000 rpm uses 4lt per hour, averaging 7 knots, on full tank = 210 nm, depending on tide flow
3200rpm uses 20lt per h, averaging 24 knots, on full tank = 144nm
5000rpm uses 50lt per h, averaging 43 knots, oft = 106 nm
So yea you'll travel much further useing lower rpm, But probably won't do the engine much good,
Strange - that mirrors the fuel consumption very closely in my rig with yamaha diesel.

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Old 18 February 2012, 05:32   #22
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willk's Avatar
Country: Ireland
Make: Redbay Boats
Length: 9m +
Engine: 370hp
Join Date: Feb 2008
Posts: 13,089
...of course, he might simply be trying to calculate his max range for cruising.

I was reading an article in that Motorboat mag about a lad who spent 660k on a sportscruiser. He spends about 12k a year in marina fees. He spent about 2k on fuel last year. Fuel economy and two fridges where his main criteria for selecting the craft

Biff's right, fuel is what Mastercard is for.

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Old 18 February 2012, 05:58   #23
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Nos4r2's Avatar
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,689
Originally Posted by mister p View Post
Very true.......but your engine will have it's most efficient point at peak torque.............This is why acceleration drops of as you approach peak revs......because the efficiency is tailing off.

Got one! Good reply though.

Originally Posted by Low Flyer View Post
Im with Biffer on this one,if you are worried about cost buy a rowing boat,you can go as far as you like then!!And keep the flow meters for how much ale you drink.....
I think you'll find that those who have boats that would benefit from flow meters don't really care what it costs, but would like to know if they've got enough fuel to get to their destination or need to fill up on the way...
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Old 18 February 2012, 06:04   #24
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,840
Flat out 'coz you'll get there quicker.
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Old 18 February 2012, 06:57   #25
Country: Finland
Town: Helsinki
Boat name: SR 5.4
Make: Avon
Length: 4m +
Engine: Toh1 3,5 Yam 90/2S
Join Date: Oct 2009
Posts: 896
After installing the fuel flow learned litle more about "economy" speed of a SR 5.4 and Yam 90(19 inch pich) combination. The good news is as long as mainaining planning speeds liter/nm does not change much from 20 knots to WOT. Slower than that will make it worse and displasement economy is terrible. If remember correctly, roundabout 29 knots was lighly loaded the optimal speed, but differens for faster or slower was generaly speking not much. This is kind of wired, not a typical finding but so it is.

So most of the time I drive as fast as pasengers/conditions/safety permits with no worries of economical speed. Trimming out defenitely improves the economy but not always the handling.

fun on a boat is inversely proportional to size...sort of anyway
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