I'm looking to replace my prop - it was sized by Ribcraft for a relatively heavy commercial load (10 passengers and 250 kgs fuel) - but now tends to be used much more lightly loaded. I can over-rev the engine by 300rpm - and would like to get that back down to 3800 at WOT!!
The current SS prop is three bladed - so I could just increase pitch - but was wondering whether anyone has played with 4 or 5 bladed props, and what effect they've had?
From what I've read on that engine ( www.boatdiesel.com well worth the fee) You are pitched perfectly. Don't mess with it. I considered purchasing a hard boat with that Yanmar (an Albin 28) and the recommendation was to pitch for 4000+ rpm to prevent overloading.
Four blade would be good, five blades are good for getting over turbo lag and spinning the engine up but you do loose top end speed. 4 blade is a good all rounder, we prop lots of heavy boats with 4 blade props. Also with a 4 blade you might find you need one pitch down from a three to keep the rpm up, so for your boat i would suggest keeping the same pitch and going to a four blade as it will reduce the revs naturally.
Flight Speed? That's happened at much less revs than that!!
Thanks everyone for all the advice - it's good to hear views and opinions from those that know and have tried things. It sounds like I'm not far away from being propped right - but maybe try a 4 bladed prop.
