1992 Montauk 17 with 1992 Evinrude 90-HP V4:
- engine mounting all the way down on transom, lower bolts in slotted tab of motor, upper bolts in fixed holes (appears to be easy job to raise engine), all four bolts are visible in the splashwell
- propeller is a brand new OMC aluminum 13.25 x 17-pitch
- sea trial loading underway: one adult at center console, one adult on cooler seat, two six-year-olds on bow cushion, two cooler stern seats weight about 50-lbs total with items inside, battery at stern port side, no auxiliary engine
- at rest tied to the dock with no people on board, waterline at stern is about 1/4-inch above bottom of splashwell drain tubes when viewed from the astern
- water conditions for trial: perfectly calm, no waves, fresh water
- no bottom paint or anti-fouling
Sea trial observations:
- at speed above approx 25-MPH (SOG per GNSS receiver), boat begins [repeated oscillation of the bow up-and-down or porpoising] with trim up at about 1/4-up from full-down on TRIM gauge
- at WOT, engine RPM at around 5000, trim max-in (down) to avoid porpoising
- boat peed and engine RPM increase slightly at WOT with trim up to around 1/4-up-from full down, but then [repeated oscillation of the bow up-and-down or porpoisng] starts again
- eliminate the purpoising so that boat can be run in the 3000 to 5000 rpm range with lighter steering and better fuel economy and no porpoising
- although I will almost never run at WOT, would like to run motor at its optimum performance which would produce 5500rpm at WOT I have read is the target value for my motor and prop
- Would raising my motor 1.5'' be the best first step?
- If not, what would recommendations be? For example, would a trim tab be recommended?
- Could there be an ulterior [concern] given the static water line of boat?