Cruising Revs

[blimp]

Just a quick question.

Haven't had the rib long enough yet to know what my fuel consumption is, but any suggestion what would be an efficient cruise rate in terms of rpm? Perhaps even slow cruise, and, fast cruise?

If it helps any bit:
At WOT I'm doing about 48mph for 4900-5000rpm
At 4500rpm I'm doing about 40mph
It's a Yamaha 150HPDi pushing a Cobra 6.65m

[OceanEco]

3800-4000rpm

[benc]

WOT on that engine should be between 5000-5500 - what propellor do you have?

[blimp]

19" on at the moment - had been told that a 21" prop would give better performance at top end, but when I enquired further I was told that it would bugger acceleration which I'm going to need for wakeboarding during the Summer. I seem to remember reading on some yamaha site that WOT was 4500-5500, so I just assumed that I was fine, being slap-bang in the middle of the range!! Now I'm confused

[benc]

Well, I have two of the same engine, with 23" props.

My acceleration is incredible, and top speed... about 55knots...

Is your prop stainless or Ali?

[blimp]

stainless! - might well go up to the 21" then

[benc]

If you weren't so far away, i'd let you try one of mine You should be able to find one around though, let us know how you get on

[blimp]

Thanks Benc - what about the other important dimensions - pitch... and the like?

[benc]

19"/21" etc.. is the pitch - I have the standard yamaha 23" pitch propellors - I want to change mine for some from steel developments at some point, but can't justify it at the moment.

[benc]

Just thinking about it, im talking utter nonsense.. if your propellor was too small, then the engine would rev higher... unless its hitting a rev limiter.

Maybe you have the engine too high on the boat?

I am sure with a 19", its under prop'd but I am not sure why you wouldnt be getting higher revs