I have a 30' custom built semi-displacement boat w/ the etec 150. Prop is 15.5x11 alum. The boat weighs 9800 lbs. with no water and 40 gal fuel. Fuel tank 180 gal, water 130 gal. capacity. I am getting 5200 RPM at WOT now @18 mph. Not concerned about speed since 98% of the time will be rumming at 8-9 mph. Should I be concerned about the RPM's at WOT? Model # E150DPXAB
Your Evinrude E-TEC 150 HP has a red-line of 6000 rpm and an optimal full-throttle rpm range about 5700 rpm.
The 11" pitch prop is the smallest that Evinrude produces for that motor. Perhaps you can have a competent propeller shop re-pitch it to 9" to raise the rpm to the recommended range. There may be other companies that manufacture props with 9" pitch or close to it that may be of help to you.
A boat that size, plus being semi-displacement, puts a tremendous load on the motor and the engine should be propped toward the higher end of the rpm range for best results and long service life.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.