Permanently Rigged Preventer
The incidence of injury or death from accidental or premature jibes is unknown but the problem is not insignificant (see Sail-World.com World Cruising Sailors Boom Death on 27ft boat). 
'Diagram of permanenetly rigged and engaged preventer system'
Edwin G. Fischer
Click Here to view large photo
The immediacy and seriousness of such accidents became apparent to the author during the 1989 Marion Bermuda Race when a pediatrician at the helm of a fellow neurosurgeon's boat had a fatal head injury during an accidental jibe at night. He was struck by the mainsheet as it whipped across the cockpit. The binnacle was also badly damaged by the mainsheet. The boom and mainsheet are eqaually dangerous during an uncontrolled jibe.
From an incomplete list of 18 fatal head and/or neck injuries that occurred on "offshore" yachts during accidental jibes, a surprising number occurred in various racing venues, as follows.
1979 SORC boom injury
1981 Practice - USCG Academy Sailing Team boom injury
1989 Marion Bermuda Race mainsheet injury
1992 Cowe's Week mainsheet injury
1996 Antigua Race Week mainsheet injury
1998 Ft. Lauderdale-Key West Race boom injury
2007 Atlantic Rally for Cruisers (ARC) boom or mainsheet injury
In addition, in 1990 a midshipman at the US Naval Academy was in coma after a head injury during an accidental jibe and his recovery was not good enough to return to school.
Accidental jibes can be avoided only if a preventer is always in place and engaged. Phil Garland, of Hall Rigging Bristol, Rhode Island, USA), designed such a preventer system that the author and his crew have used on a Morris 46 in five Newport Bermuda Races and 2 roundtrip transatlantic passages from Newport, Rhode Island to the British Isles. The system has been recommended strongly to participants in the Newport Bermuda Race (www.bermudarace.com).
A. Equipment
a. A pad-eye or bail on the undersurface of the boom, aft of the vang (about 1/3rd the distance from the gooseneck to the boom end, but the exact location is not critical)
b. Two blocks on the deck, one on each side, located in the vicinity of the shrouds (will vary with the boat)
c. Two line stoppers, one each side, located by the cockpit in easy reach of the helmsman
d. Two lines long enough (about half the length of the boom plus the distance from the deck block to the line stopper, plus several extra feet)
B. Set-Up
a. Both preventer lines start at the pad eye or bail on the boom, one running forward to the block and then aft to the line stopper on the starboard side, the other running similarly on the port side.
b. On our Morris 46, a piece of PVC tubing on the aft lower shroud prevents line chafe.
C. Operation
a. The entire system can be run by the helmsman: releasing the old leeward line from the stopper before or during the jibe and tightening the line in the stopper on the other side after the jibe.
b. The helmsman can also trim the line as the mainsheet is let out or taken in.
c. Occasionally, one of the lines hangs up on a Dorade.
d. Upwind both lines are slack and do not need attention.
e. The initial force of the jibe is minor compared to the full force of the jibe after the accelerating boom has crossed the centerline.
by Fischer, MD Edwin G.
Sanctuary Point, WA
