The purpose for tilt and trim options on outboard engines is boating safety. Without the ability to adjust hull angle to match sea conditions and planing speeds, broaching can occur. Broaching happens when a watercraft violently changes its heading from side to side, which can throw passengers overboard or cause the watercraft to capsize.
When the propeller is angled toward the hull, the bow will drop. When boating upwind in this scenario, this keeps the bow heavy to prevent lifting. In rough seas, a low bow has an easier time carving through choppy waves.
In agreeable sea conditions, neutral trim is most efficient. The bottom of the cavitation plate should be parallel with the water surface and the propeller should be vertical with little to no angle. This position lowers the bow, but less so than with trimming in.
Angling the propeller away from the hull causes the bow to lift. It can cause dangerous bouncing if extremely angled out. Moderate angles can be used to thrust into top speeds or gain clearance through shallow water. Outboards can be fully tilted forward to be removed from the water if needed.
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