Marine Propeller Pitch Selection
The pitch to swap to so the engine reaches the top of its rated RPM band at wide-open throttle: each inch of pitch changes WOT RPM by ~200 rpm, so pitch change = (target - current WOT RPM) / rpm-per-inch and new pitch = current - change. A 19 in prop hitting 5000 rpm against a 5400 target drops to a 17 in prop; a boat over-revving to 6000 goes up to 22 in. Under-rev needs less pitch, over-rev needs more. A selection aid; a WOT test with the new prop and the dealer's prop chart govern.
Formula and source
pitch_change = (target_wot_rpm - current_wot_rpm) / rpm_per_inch; new_pitch = current_pitch - pitch_change; default rpm_per_inch = 200.
Marine propeller pitch selection, standard boating / outboard-manufacturer practice (Mercury / Yamaha prop selection guides) by name; the ~200 rpm per inch of pitch rule of thumb.
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