Mercury Optimax Models 135, 150, Direct Fuel Injection., Page 54Get this manual
OUTBOARD MOTOR INSTALLATION
Trim Tab Adjustment
Propeller steering torque may cause your boat to pull in one directionThis steering torque results from your outboard not being trimmed so the propeller shaft is parallel to the water surfaceThe trim tab can help compensate for this steering torque and can be adjusted within limits to reduce any unequal steering effort
Models Without Power Steering
Operate 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 until trim tab moves freely (does not rub against locking ridges)DO NOT strike tab to make adjustmentsMake 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 rightPosition trim tab in one of the locating grooves BEFORE tightening bolt to prevent damage to holding mechanismTorque bolt to 40 lb-ft (54 Nm) and retest