I have a friend who is looking for a spare prop. He has a 1999 Yamaha (OX66) 225 that has a 14 3/4 x 27 prop. He has found a 14.5 x 27 and is wondering what the smaller diameter will do for him. I told him that is may increase the RPMs slightly. He is concerned since he ran a 15 1/4 diameter prop and the boat didn't run right (probably due to the required torque and HP necessary to turn it). Anyone out there think he will have a problem with the .5 decrease in diameter? I don't, but I certainly don't know for sure. Any advice is appreciated.

A 27m or 25T1 Yamaha prop would be best. I'm sure steve will chime in and give best advise.

on the ox66 the pro series props..M's run the best. even a tempest runs well on that boat.
that little of a diameter difference won't hurt anything. but, if the "geometry" is different there may be a slight performance difference between the two props.
some boats with the ox66 runs okay, but you'll find with that boat/motor combo it needs to run higher rpms, like around 6K to make power, therefore the smaller diameter with a higher pitch works the best.
the turbo txp's (3 blade) run great too.

Thanks guys!