Mercury Racing 500R Operation And Maintenance Manual page 61

FEATURES AND CONTROLS
What Trim Is
The trim angle of an outboard or sterndrive is the angle between the boat
bottom and the propeller shaft formed by moving the engine or sterndrive
closer to the boat transom. This movement is called trimming in or down.
Moving the engine or sterndrive further away from the transom is called
trimming out or up. When a boat is cruising on plane and the trim is adjusted so
that the propeller shaft is parallel to the surface of the water, that is said to be
running at zero trim.
The term "trim" is generally used when referring to adjusting the outboard or
sterndrive within the first 20° range of travel. This is the range used while
operating your boat on plane. The term "tilt" is generally used when referring to
adjusting the outboard or sterndrive further up or out of the water.
How Trim Affects Boat Operation
The trim angle of the outboard or sterndrive has a distinct effect on the planing
angle of the boat, which in turn significantly alters the top speed and handling.
The engine or drive should be trimmed in for best start‑up acceleration and
shortest time to plane. The engine or drive would then be trimmed out for peak
performance. Active Trim automatically handles this transition for you.
61921
Engine or drive properly trimmed
If the engine or drive is trimmed in too far, the bow drops and the boat runs
too wet. In this condition, top speed drops, fuel economy decreases, the boat
may oversteer in one direction or the other (bow steering), and steering torque
will increase (to the right with a right‑hand rotation propeller). Occasionally,
extreme trim down can cause a boat to list to the left (with a right‑hand
propeller).
61922
Engine or drive trimmed in (bow too low)
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