Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 33Get this manual
Trim "In" Angle Adjustment Some outboard boats, particularly some bass boats,
are built with greater than normal transom angle which will allow the outboard to be trimmed further Uin" or Th is greater trim under" capability is desirable to improve acceleration, reduce the angle and time spent in bow high boat, altitude during planing off and in some cases, may be necessary to
Trim Tab Adjustment
Propeller steering torque will cause your boat to pun in one directionThis steering torque is normal th ing that results from your outboard not being trimmed so the propeller shaft is parallel to the water surfaceThe trim tab can help to compensate for this steering torque in many cases and can be adjusted within lim its to reduce any unequal steering effort