Props for Yamaha 150 on Tom Cat?

[Doryman]

There's been a discussion recently about the prop on Bob's C25 which inspired me to check out what was installed on my boat. I am a little suspicious now. Here are the specs:

Yamaha 150TXR (HERE is a link to a spec page for this motor)
Props are 15-1/4 x 17 SS

Max HP is developed at 5500 RPM. However, if I run for extended periods at over 4500 rpm the temp goes up a couple of notches (but not what I would call the overheating zone. Is this normal -- should the temp remain constant regardless of the speed? And, I am not sure but I don't think I have ever been able to get the engines to run at 5500 rpm. I can take it out and check -- any other checks I should make? I am taking the boat in for the 100 hour service on the engines next week so would like to have some talking points in hand.

Thanks,
Warren

 

[Larry H]

Warren,

In your owners manual, there should be a spec for 'full throttle operating range'. It may be 4500 to 5500 rpm.

With a normal load in the boat, the motors should run in the range at full throttle. With a lighter load, the rpm should be closer to the max, and a heavy load, closer to the min.

If the props have too much pitch, the motors run slower and will tend to heat up more.

My guess, from your info, is that you need 15 in pitch props, but that's something to discuss with your mechanic.