And ten percent of a 15 inch diameter prop would be what?

exactly - -it's not 3 mm


That is way to close for a number of reasons including cavitation.

that's what I thought -- the demo-prop-shop said "it will increase performance
by directing more water aft rather than up" seemed snake-oilish to me.


What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.
well; wrong way -- I have 19pitch now; need to go down in pitch to 17 or 16.
(wot now = 4100, need to get it to 4400-4600)

Thanks
-j