I just put a honda 115hp on a 21 ft starcraft cc and borrowed a prop to see what pitch i would need,this is what i get. At WOT 3500 rpms 33mph with a 15 pitch prop on a 21 ft aluminum vee hull with a new tach.I know the rpms should be between 5000 to 6000 what size do i need?Thanks for a reply.