The accidental gybe and how to prevent it
1The lesson in plain words
An accidental gybe can injure crew and break gear. Keep the wind clearly opposite the boom, leave room for wind shifts and rig a preventer.
What happens
An accidental gybe happens when the wind gets behind the mainsail from the wrong side and throws the boom across without anyone choosing it. The boom can hit a head with enough force to cause serious injury or knock someone overboard. The mainsheet sweeps the cockpit, and the shock can break the boom, the gooseneck (its fitting on the mast) or the rig.
Sailing by the lee
On a run, wind coming from the boom side means you are sailing by the lee. A wave, wind shift or steering error can throw the boom across. Check the apparent-wind indicator. A lifting or fluttering leech, the mainsail's back edge, is another warning. A collapsing headsail may simply be blanketed by the main: check wind direction.
Steering to prevent it
Keep the apparent wind clearly on the side opposite the boom. Allow for yaw, the boat swinging from side to side, and wind shifts. Concentrate on steering; make small corrections early and watch the wind indicator. Head farther up onto a broad reach, with the wind over your rear quarter, if waves push you towards a gybe.
The preventer
A preventer is a line that holds the boom out so it cannot swing across. Rig it from the outer end of the boom, forward to a strong point or block near the bow, and back to the cockpit. Use strong fittings and a cockpit release that works under load. A line from mid-boom straight down to the rail can break the boom if the boat rolls the boom into the sea.
Boom brake and crew
A boom brake is a friction device that lets the boom cross slowly instead of stopping it. It is an alternative to a preventer and is useful when sailing short-handed. Whatever you rig, keep everyone's head below the boom on a run, and never sit or stand in the mainsheet's path. Control the boom with the mainsheet before easing the preventer for a gybe; rig it again on the new side.
2Key data
- By the lee
- Wind on the same side as the boom on a run
- Safer running angle
- Wind opposite the boom; allow a margin for yaw and wind shifts
- Preventer lead
- Boom end → forward block → back to the cockpit
- Boom brake
- Lets the boom cross slowly under friction
3Key points
- 1
An accidental gybe can injure crew and break the boom or rig.
- 2
Danger zone: sailing by the lee, wind on the boom side on a run.
- 3
Watch wind direction and the mainsail leech; a collapsing headsail alone does not prove you are by the lee.
- 4
Rig a preventer from the boom end forward and back to the cockpit.
- 5
Keep heads low; control the boom with the mainsheet before easing the preventer for a gybe.
4Frequent mistakes
Wrong: Tie the preventer from the middle of the boom to the nearest cleat.
Right: Lead it from the boom end, forward, then back to the cockpit. A short mid-boom lead can snap the boom.
Wrong: A preventer can be left on through a gybe.
Right: Control the boom with the mainsheet, then ease the preventer. Gybing against it can pin the main aback and knock the boat down.
5Practice case & exam keys
Offshore, running in a long swell with 18 knots of true wind from dead astern. The boom is out to starboard. The helm keeps losing concentration and the genoa, a large overlapping headsail, collapses every few minutes.
Show the answer
Relieve the distracted helm. A collapsing genoa alone does not prove you are by the lee. With the boom to starboard, head up enough to keep the wind clearly over the port quarter, allowing for yaw in the swell and wind shifts. Rig a preventer with a cockpit release that works under load. Keep everyone clear of the boom and mainsheet.
Exam keys
- Accidental gybe: boom crosses uncontrolled; serious injury and rig damage.
- By the lee: wind from the boom side. Check wind direction; headsail collapse alone is not proof.
- Preventer: boom end, forward, back to cockpit; use a release that works under load.
- Keep wind clearly opposite the boom; allow for yaw and shifts. Control boom before easing preventer.
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