A preventer’s principal role is to keep the boom (and mainsail) from flogging when running in moderate conditions, especially when the main is set by the lee. Under these conditions, the rolling of the boat can make the boom swing back far enough to backwind the main and start off an accidental gybe.
A preventer is great and I use mine (read details of Sunny Spells’ preventer in this post) most of the time when going downwind (“gentlemen don’t sail to windward”, so that’s a lot!), but you really don’t want it to be the only thing restraining the boom when the poo hits the proverbial…
Regardless of how you set it up, during a planned gybe the preventer has to be let off and re-set on the lee side. SO, this is NOT a part of the running rigging that you can (or should) rely on when the going gets rough or you need to do things quickly. This was graphically illustrated to me recently when crewing on a fifty footer in the Sydney – Gold Coast race: with wind gusting to 45 knots we had to gybe, and opted for a “granny gybe” (tacking the bow through the wind) to reduce the strain on the rig. The crew responsible for the preventer was a bit slow throwing it off, resulting in a pad-eye ripped off the bow and a broken preventer line which proceeded to wrap itself around the prop… Thank gawd we didn’t attempt a gybe!
Also, if you really get the boat out of shape and the main is backwinded, you need to release the preventer pretty smartly, and if you can’t, it needs to be fail-safe – i.e the line should break at a lowish force rather than a high one (this is where the boom brake comes in). Imagine the 2 tonnes of force in a 1/2in preventer being released instantaneously when it breaks! A recent post on CruisersForum suggested using a velcro strop to attach the preventer to the boom – this sounds very sensible as it would allow the preventer to release in an emergency without breaking anything.
Before I left Sydney for Hamilton Island in May, I rigged a boom brake (details in an earlier post here) to control the boom during gybing especially when sailing short-janded. The boom on a sail boat can be lethal:
- Earlier this year a man was killed off the Queensland coast when he was struck in the chest by the boom on S/V De Ja Vu during an accidental gybe. He was sailing with his wife who was brought to shore by rescue helicopter after the accident.
- The boom striking one of the crew members is thought to have contributed to the disappearance of three yachtsmen in the Whitsundays in April 2007.
The boom brake was initially a bit of an obstacle on the side decks, but I got used to it pretty quickly. I initially thought I might unshackle it from the toe-rails when it’s not in use, but never got to the point where I felt it necessary (we were running most of the time though).
I run my jacklines OVER the boombrake lines, which also keeps the tether hooks off the deck, at least over that area. However, having an intermediate “catch point” in your jacklines (by running them uner the boom brake) is not such a bad thing – if you get washed along the deck by a “green one” you’ll get stopped midway rather than dangling over the transom! It’s just the clipping and unclipping (on a dark and stormy night…) that becomes an issue.