On a 4 Blade prop you want to start out at 3″ below pad.the easiest way to measure this is to make sure your boat is level and then lower the motor in the vertical position and level it by putting a level on the cav. plate and making it level, then measure from the pad or center of the boat just below the drian plug to the ground, then measure from the center of the prop shaft to ground and subtract the differents and this is your distance from propshaft to pad. This will be a good starting point.
.
