1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 329Get this manual
BIG FOOT
Trim Tab Adjustment and Replacement
IMPORTANT: The trim tab made of special alloy to aid in protecting the drive shaft housing and gear housing from galvanic corrosion (corrosion and pitting of metal surfaces)Do not paint or place protective coating on the trim tab, or trim tab corrosion protection function will be lostReplace trim tab if 50 (or more) corrodedMark location of old trim tab on anti-ventilation place before removal; install new trim tab in same location1Check trim tab position2Operate boat at the speed at which it would normally be operated3If the boat pulls to the right (starboard), the trailing edge of trim tab must be moved to the rightIf the boat pulls to the left (port)the trailing edge of trim tab must be moved to the left4If necessary, adjust trim tab5Shift engine control into NEUTRAL and turn ignition key to "OFF" position