Rough guide to HP per meter of RIB

[Channel Ribs]

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!

[Downhilldai]

Originally Posted by Channel Ribs

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.

[martini]

Wouldn't fancy having 220hp on my 8.5, I've got over double that and could do with a bit more!

[Erin]

Certainly looks a little light at the 6.5m mark. Would have thought 175 would be more like it as a minimum.

[martini]

Originally Posted by Erin

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

[Erin]

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.

[Channel Ribs]

Originally Posted by martini

I've got over double that and could do with a bit more!

Twins require a whole other guideline!

[martini]

Originally Posted by Channel Ribs

Twins require a whole other guideline!

And air-deployable hulls yet another

[martini]

Originally Posted by Erin

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