Preventer

A line or tackle rigged to the boom or spar to prevent unwanted movement, particularly to stop a boom from swinging dangerously during an accidental gybe.

A preventer is an essential safety feature in sailing, designed to stabilise the boom and reduce the risk of injury or damage during certain manoeuvres or in challenging conditions. The boom, which extends horizontally from the mast and holds the foot of the mainsail, can swing violently across the deck during an accidental gybe. This sudden movement can pose a serious hazard to crew members and equipment. A preventer secures the boom, typically using a line led forward from the boom to a fixed point on the deck or mast base, then back to a cleat or winch. This arrangement ensures the boom remains restrained, even if the wind shifts unpredictably.

Preventers are particularly useful when sailing downwind when the risk of an accidental gybe is highest. They are also employed in heavy seas to stabilise the boom and reduce strain on the rigging. While a preventer can significantly enhance safety, it must be rigged and handled with care. Improperly set preventers can create hazards, such as difficulty in releasing the line quickly if needed. For this reason, many sailors opt for quick-release mechanisms or use a vang/preventer combination to maintain control. Understanding the correct use of a preventer is a key skill for safe and efficient sailing.