2001 Mercury Mariner 50-60HP Factory Service Manual, Page 456Get this manual
NON-BIGFOOT GEAR HOUSING
Trim Tab Adjustment and Replacement
IMPORTANT: The trim tab is 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 lost1Replace trim tab if 50 (or more) corrodedMark location of old trim tab on anti-ventilation plate before removal; install new trim tab in same location2The trim tab will offset (balance) some of the "steering load" that is caused by "propeller torque" at higher speedsIf at higher speeds the boat turns more easily to the left, loosen bolt, move the trim tab (trailing edge) to the left (when viewed from behind); re-tighten boltTurn trim tab (trailing edge) to the right if the boat turns more easily to the right