prop selecton/outboard operation

[fishnpbr]

I have a merc 115 4S. The max rpm range at wot is 5800-6400. I have noticed that when I run a 17 prop the rpm's only get to 5600 at wot. When I run a 15 prop I can hit 6400 rpm's with a little throttle left over. I actually lose a little speed with the 15 and the higher rpm's. Don't understand that. Is it best for the motor to run in the upper end rpm range. I'm not at all concerned with speed just what would be best for the motor. Any thoughts.

[john warren]

i would go with the lower rpm prop if your getting more usable power out of it.

[WALLEYE MIKE]

Changing from a 17" prop to a 15" prop (same type of prop) should only be a difference of 400 RPM or so. 15" prop should give you a better hole shot and would get you speed down for trolling over a 17"prop. 17" prop will give you a little more top end speed.

[fishnpbr]

Would running the 17 at 5600 rpm wot be considered lugging the motor?