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Old 28 December 2011, 17:09   #1
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Country: UK - England
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Help please

Merry crimbo all

Took my 5.4 rib out today got a old but very good ( said service guy) yam 70hp 2stroker she dos 30 knots 3 up is this good or poor as she only revs to 5000 rpm trimmed up Also my fuel consumption seems a bit much wot for 25-30 min will empty a 22ltr tank is this right?
If anyone could help me I would appreciate the advice
Thanks mark
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Old 28 December 2011, 17:26   #2
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3 up, 30knots and 5000 rpm sounds like the pitch is about right for 1 or 2 up-it'll be quicker and rev higher with less load.
You might want to drop a couple of inches in pitch if you're going to be using the boat 3 up all the time.

Oh, and yes, that's how much fuel you'll use at WOT.
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Old 28 December 2011, 17:35   #3
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Thanks Nos4r2

If I run this boat at 3500 rpm I get about 20kn 3 up how much fuel do you think I would burn
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Old 28 December 2011, 17:41   #4
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Quote:
Originally Posted by Bulldog View Post
Thanks Nos4r2

If I run this boat at 3500 rpm I get about 20kn 3 up how much fuel do you think I would burn
1 liter per Nm or a touch less
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Old 28 December 2011, 17:41   #5
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Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
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MMSI: 235090687/235055163
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Quote:
Originally Posted by Bulldog View Post
Thanks Nos4r2

If I run this boat at 3500 rpm I get about 20kn 3 up how much fuel do you think I would burn
Try it and find out-there's no set formula for usage except a rough idea for WOT usage.

willk might be right, but you'll only find out by checking it yourself.
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Old 29 December 2011, 04:18   #6
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Each engine / boat / load combo will have its "economic point". Only very rarely I would expect it to be below 3500rpm for a boat like that.

The best I've managed to record is 0.82L/ nautical mile at a rolling average around 20-21 knots / 4300-ish rpm, 2 up. The boat clocks in around the 440Kg mark.

Somewhere in the depths of this section is a "fuel economy" thread. If nobody has it handily bookmarked, I'll try to dig it out later.
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