Hi I have a 2001 lund fisherman 1700 with a Yamaha f115 and it is not going as fast as it should. some people tell me its a problem with the prop. I have a 17 pitch prop and would like to know if this is the right prop. it should go 40 or so mph and its only going 28-30 mph its suppose to be about 5600 rpms and its at about 4200-4300 rpms