Might be a good idea to expand on why you think its over propped. Generally you aren't going to get much good advice from a mechanic on whether its over/under propped without a water test. Better to just record the data yourself. Load up the boat in the manner that you typically run it, then record GPS speed at 500rpm increments all the way up to either WOT or max rated RPMs. Record the exact RPM for WOT. Without good data you are just tinkering blind, and props aren't cheap.
If you reach max RPMs and you still have more throttle to go, then you are under-propped. If your boat tops out, and you are well under the rated max RPM range, then you are over propped.
Couple of notes though.
- First things first. Is the engine mounted at the right height. If you feel like the boat is dragging - an engine mounted too low is literally dragging through the water like a parachute. Fix the mounting height (not possible if this is a stern drive)
- Load the boat the way you want it. If the prop was selected based on performance when their was only one person on board, a 1/4 tank of fuel and no other load, then the prop is going to be all wrong if you typically run it with a full tank of fuel, 6 passengers, and a weekend worth of gear.
- Generally I would want my boat slightly under-propped - gives you more versatility to load it up without bogging down the motor, and better low end torque. Most of use aren't running it at WOT much anyway.
If your prop is off by only a slight amount, a good prop shop can adjust it (typically an inch either way, I think). Talk to Pierre at Poco Marine.
