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propeller sizing

Posted: July 16th, 2016, 1:08 pm
by nightsky
I've got a Carver 390 with twin Cummins 315 HP engines and 4 blade 23x28 props. I recently sent in the props for balancing and the prop shop said the specs given for HP, WOT(2800), gear ratio (1.96:1) and expected speed (21 kn) didn't add up. On sea trials we achieved 2750 rpms and a speed of 40 KPH (21+ knt). Prop shop claimed that those props should not be pitched higher than 23, so they didn't do anything to them awaiting clarification on the numbers I provided on the spec sheet. It seems to me that the props were performing as expected per Carver for this hull. My question is to any other 390 owners with same engines and 23" diameter, 4-blade props, what do you have your props pitched at and what speed do you achieve at WOT?
thanks in advance

Joe
Pacific Horizons

Re: propeller sizing

Posted: July 16th, 2016, 8:28 pm
by waybomb
2750 rpm wot with a spec of 2800 indicates a very slight reduction in pitch but certainly not to 23 from 28!
I'd leave them as they are.

Re: propeller sizing

Posted: July 17th, 2016, 5:31 pm
by nightsky
waybomb wrote:Source of the post 2750 rpm wot with a spec of 2800 indicates a very slight reduction in pitch but certainly not to 23 from 28!
I'd leave them as they are.

That is my feeling too, although I have to wonder if the stamp on the prop hub was correct at 28 pitch, and if the prop shop confirmed that my props are indeed pitched at 28. Thanks for your input.