Ned,
I've just looked at the latest Torqeedo catalogue and the pitch of the speed prop is 12 inches.
I was aware that having higher pitch is going in the wrong direction. I expect under adverse conditions, such a strong wind on the nose, that the advantage of lower pitch would be more noticeable. But on balance the extra thrust in reverse is something that I already appreciate when manoeuvring and is worth more to me than the reduced efficiency in normal running.
It would be nice to be able to do what you did with your skiers and have a few different props to be able to experiment with.
I'm thinking that a 9 inch prop might be a better match for my situation. And if the folks at Torqeedo could design it with good reverse performance in mind, I expect it would be a nice solution for heavier boats.
Cheers
Chris
On 14/03/2010, at 4:45 AM, Ned Farinholt wrote:
Chris,
Did they tell you what the effective pitch of the speed prop is? One would expect it to be greater than the 10 inch on their regular prop. In this case it is not surprising that the speed went down on a heavy boat. You probably are not getting to the motors max rpm or you are getting a lot of slip because of hull speed limiting drag. With no slip and the standard 12 x 10 prop the Cruise 4 would deliver (10in x 1250rpm)/1215 = 10.3 kn. A higher pitch would just make the mismatch worse. I remember 50 years ago going to lower and lower pitch props so we could pull two slalom skiers with a 25 hp Johnson outboard. At about 20 mph max, it all matched and we had great fun.Ned
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