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Old 17 February 2012, 15:31   #11
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Originally Posted by HUMBER P4VWL View Post
What is the most economical speed per mile to run at?

Is it the speed to maintain planing ability, whatever your boat/engine?

Or is it slightly quicker to have less boat in the water as long as you're not pushing your engine to its limits?

C'mon techies.
It's the one where it does the most MPG
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Old 17 February 2012, 16:05   #12
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Usually the most efficient compromise (economy versus speed) is around peak engine torque. However this varies according to prop, leg gearing, weight, hull length etc. 4000-4500 is usually near it. Have a look at the testing done by Ribeye and Yamaha a few years ago which may give you a better idea.

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Old 17 February 2012, 16:22   #13
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A little bit of trim can give you a couple of gallons an hour.
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Old 17 February 2012, 17:13   #14
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still aye nobbur yew mean? i fownd diss - doo yew fink itts is?

That would be a 'Cardinal' bunnet. Rules & regs state you must wear one if you are stationary for any length of time
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Old 17 February 2012, 17:38   #15
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That would be a 'Cardinal' bunnet. Rules & regs state you must wear one if you are stationary for any length of time
like 6 months
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Old 17 February 2012, 17:45   #16
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I though shall I post or not but thought I thought. What the hell give it a go. My answer turned out to be. Who cares. You can't put a price on fun and happiness
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Old 17 February 2012, 18:50   #17
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Quote:
Originally Posted by Nos4r2 View Post
It's the one where it does the most MPG
Very true.......but your engine will have it's most efficient point at peak torque.
If you then match the prop to maximise it's thrust at this same speed for the particular vessel then you will be at max mpg.
Now on a rib you will have two max mpg's. One for displacement and one for planing. Your prop will be matched for planing efficiency but you could have it matched for displacement and regear your transmission.
So........engine efficiency is fixed.
It is mated to suit your hull by prop pitch and slip for best economy if you so wish.
Economy is often forgone for maximum speed and so props will not generally be fitted to make the most of a particular engine's torque for the hull it is fitted to. Esp. on RIBs.
A tug however will generally have it's prop suited to best engine torque.
Torque is the rate of change of engine speed. When this rate is high, acceleration at this point is high because the engine is at it's most efficient. In water this point can be maintained because of fluid coupling despite variations in load. Gears or torque converters assist in getting engines to this sweet spot and keeping them there. This is why acceleration drops of as you approach peak revs......because the efficiency is tailing off.
Cool?
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Old 17 February 2012, 18:56   #18
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like 6 months

admirulty rools

arfter sikks munfs hee becums a azard too navigashun an az succh iz lykely too bee blowen upp bi de royul mareens orr uvver nobburs wiv mor ekslposivs thann comon sence (reed royul enjineers, ira, wna, hizbolla an de menia strait oister cachers.
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Old 17 February 2012, 20:02   #19
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I though shall I post or not but thought I thought. What the hell give it a go. My answer turned out to be. Who cares. You can't put a price on fun and happiness
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,
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Old 18 February 2012, 05:59   #20
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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.....
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