Permanently Rigged Preventer

Diagram of permanenetly rigged and engaged preventer system
Edwin G. Fischer
The incidence of injury or death from accidental or premature jibes is unknown but the problem is not insignificant (see World Cruising Sailors Boom Death on 27ft boatNEW).

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 (

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.

Selected Comments from Readers:

Sender: Ian Flint
> Message: Well, it all comes down to being aware and advise crew all the
> time in such situations and especially new ones. The helmsman has the feel
> and would know if the boom might cross over. We always use a preventer in
> tricky situations and generally from near the mainsheet position on the
> boom in the cockpit and to a block near the bow.You can have 2 setups,
> port/starboard or just change over after a gybe. I guess this article
> refers to small boats and probably ok but wouldn't suit bigger yachts.
> Ian

Sender: Chris Daly

Message: I have used this system on my Farr 1220 for the past year having had difficulty with boom brakes. The problem with boom brakes is that they usually require a lot of line tension to perform. I rigged my boom brake with port and starboard lines so that it would act partially as a preventer, but it was never very successful. Since replacing the boom brake with the permanently rigged preventer, I have the best of both worlds. Instead of running the line directly to a bail on the boom, I have use single blocks on the boom to give a 2:1 out haul from the base of the shrouds. The port and starboard lines run back to jammers but are run to the secondary winches for managing jibes. I can jibe single handed with complete control over the boom simply by easing out the line with two turns around the winch. The preventer function is fully operable from the cockpit. This allows the boom to be totally immobilized in its centre position when flaking the main making it much safe to m
anage. The one potential hazard of this system occurs in an unexpected jibe if the preventer is not eased off. This could lead to boom breakage or worse. A possible solution could be to use a 'fuse' in the line, for example a piece of lower breaking strain line to attach the main line to the boom. This idea has made a big difference to safe and easy mainsail control on my boat.