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Old 06 February 2011, 08:34   #1
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Rough guide to HP per meter of RIB

Following on from the random though process here...

4 horsepower for every 10cm of RIB over 3m looks like this:-

4m 40hp
4.5 60
5 80
5.5 100
6 120
6.5 140
7 160
7.5 180
8 200
8.5 220

I have more rules of thumbs than thumbs as it is, but this seems quite neat on first glance. Our last boat was a 6.25m Ocean and it was underpowered at 90HP, I reckoned 130HP would have been ideal.

Sorry is this should have been in the Engines section, or indeed the Bilges!
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Old 06 February 2011, 08:38   #2
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Sorry is this should have been in the Engines section, or indeed the Bilges!
Bilges!

It seems to work ok up to 5.5m, but loses its way from there.
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Old 06 February 2011, 08:46   #3
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Wouldn't fancy having 220hp on my 8.5, I've got over double that and could do with a bit more!
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Old 06 February 2011, 08:47   #4
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Certainly looks a little light at the 6.5m mark. Would have thought 175 would be more like it as a minimum.
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Old 06 February 2011, 08:57   #5
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Certainly looks a little light at the 6.5m mark. Would have thought 175 would be more like it as a minimum.
My Crompton was good for 42/43kts with 150hp

Too many variables in this rule of thumb

Here's another one for ya, hp/3=l/hr@cruising speed
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Old 06 February 2011, 09:11   #6
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Nope, still a bit out.

Matt's theory: 200/3 = 67.

Reality: 35kts = say 1.2l/nm = 42litres/hr

Theorum failed

Probably works with a 2-stroke though.
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Old 06 February 2011, 09:23   #7
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I've got over double that and could do with a bit more!
Twins require a whole other guideline!
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Old 06 February 2011, 09:25   #8
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Twins require a whole other guideline!
And air-deployable hulls yet another
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Old 06 February 2011, 09:27   #9
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Nope, still a bit out.

Matt's theory: 200/3 = 67.

Reality: 35kts = say 1.2l/nm = 42litres/hr

Theorum failed

Probably works with a 2-stroke though.
Might've been WOT then, you know what my memory's like
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