Hi,
I've got a 115 Merc 4 stroke pushing an 17.5 aluminum fishing boat. I wanted more top end speed and was thinking of a 21 pitch prop. My hesitation is the Spitfire 4 blade 21 pitch says for engines 135 hp - 300 hp.
My 17 pitch 4 blade aluminum runs 6400 rpm at 40 mph
My 19 pitch 4 blade...