My brother-in-law has 21 ft C-Dory tug with a 3 cyl. diesel motor. I dont know the size or pitch of the prop, but the boat tops out at an 11-12 mph cruise @ 3000 rpm. He would be happy if he could get 15-16 at 2500 rpm. Could we install a prop that would achieve this? And how could we find out which prop to go to? Thanks...dirt.