2001 Mercury Mariner 50-60HP Factory Service Manual, Page 49Get this manual
GENERAL INFORMATION
NOTE: Trim tab adjustment will have little effect reducing steering torque if the outboard is installed with the anti-ventilation plate approximately inches (50mm) or more above the boat bottomOperate your boat at normal cruising speed, trimmed to desired positionTurn your boat left and right and note the direction the boat turns more easilyIf adjustment is necessary, loosen trim tab bolt and make small adjustments at timeIf the boat turns more easily to the left, move the trailing edge of trim tab to the leftIf the boat turns more easily to the right move the trailing edge of trim tab to the rightRetighten bolt and retest