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  • 1 Post By John Rousmaniere
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Old 10-12-2004
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John Rousmaniere is on a distinguished road
Deadly Serious about Booms


Downwind legs can give a crew a chance for a breather, but special attention is still needed to make sure the boom doesn't live up to its name.
Because few things can so suddenly spoil a day’s fun—or end a sailor’s life—as easily as a vicious whack on the head, not enough can be said about taming the boom. If you have your doubts, just remember this number—16. That’s the number of deaths proved to have been caused by flying booms or whipping main sheets over the past 21 years. This evidence is not anecdotal. My friend Edwin G. Fischer, M.D., a neurosurgeon at Harvard Medical School and Beth Israel Hospital in Boston, a widely experienced offshore sailor and fleet surgeon of the Cruising Club of America, has been tracking boom-related fatalities since the late 1980s.

I first heard Gary talk about the problem at a safety-at-sea seminar in Newport in 1990. His presentation was memorable not so much for any one of the many dry medical details that he presented, but for the inescapable conclusion that a sharp blow to the head is to be avoided at all cost. Gary methodically described the trauma suffered by the brain during a hard smack so grimly that his listeners were left convinced that, away from a good hospital, this is a problem that even a specialist cannot competently address.


Light air is no time to drop you guard. An errant wave or wake can spell trouble for innattentive crew members.
What triggered his concern was an accident in the previous year’s Marion-Bermuda Race. In a boat full of doctors, during an accidental jibe, the helmsman (a pediatrician) had received a hard blow on the head from the mainsheet, and not even the neurosurgeon who was the boat’s skipper could save him. The only action the survivors could take was to place the body aboard the Russian ship that responded to their SOS.

While Gary’s data—which can only cover part of the grim record—are not specific as to the conditions, I bet that few of the 16 fatalities took place offshore and in gales. In my own experience the boom is most dangerous when a jibe or hard roll is least expected, when we let down our guard. Consider, for example, the familiar scenario of an easy light-air run, a distracted or novice steerer, and a passing powerboat. Because that’s when most sailors let down their guard, a swinging boom then may be as dangerous as one in a wild jibe in 30 knots.

The practical lessons to be learned can be grouped into four categories:

  • Never take the boom for granted. Always know where it is. After all, this is the second most dangerous item on any boat (the first being a full liquor locker). Personal attention is everything—focused attention. In one accident, a crew member on a boat running square in rough weather on San Francisco Bay became annoyed that a preventer had not been rigged to hold out the boom. Walking aft to lecture the skipper, he was so distracted by the larger problem that he neglected to keep an eye on the boom itself, which flipped across and killed him.
  • Control your jibes. Don’t jibe or tack unless the crew is ready. This is a matter of technique, including training the crew, having competent people at the helm, and avoiding sailing on a dead run, when accidental jibes often happen.
  • Don’t expose crew to a mainsheet swinging across the boat. This may require redesigning the block system. A block over the cockpit will inevitably cause a slack sheet to lasso a sailor by the head. Of the 16 fatalities in Gary Fischer’s data base, three were caused by mainsheets. Autopsies revealed injuries to the high cervical cord.
  • Control the boom. Every boat—whether racing or cruising—larger than about 20 feet should have a device for stopping or controlling the boom’s swing. Here we’re talking about preventers and restrainers—a subject in itself.


On this transoceanic racer, the preventer (rigged with a webbing strap around the boom) gives an extra margin of safety when traveling wing-on-wing in heavy air.
A boom preventer
stops a swing. A better term might be "boom guy" because, like a spinnaker pole’s foreguy and afterguy, the line holds a spar in a fixed position. This is a line running from the boom forward to the side deck near the chainplates or to the bow, through a hefty block, and finally back to the cockpit near the mainsheet so it can be adjusted every time you ease or trim the sail. I always rig two permanent preventers or boom guys— port and starboard—so nobody has to go on deck after a jibe, in the way of the boom, to rig a new one.

A preventer line should be at least the diameter of the main sheet and should have some "give" so the boom or gooseneck won’t break in an accidental jibe. Nylon, which is stretchy, is an excellent material for a preventer. Dacron line usually is suitable so long as there’s a rubber or nylon strap on the boom. A way to keep the preventer from breaking the boom is to put a "weak link" somewhere in the system. Matt Pederson, of that font of good seamanship the Sailing Foundation of Seattle (which invented the Life Sling), tells me that on Doug Fryer’s Night Runner in the Victoria-Maui Race, they rigged the preventer pretty much the way I do—a line through a sturdy block on each side near the chainplates and then back to the cockpit—but with one difference. "Instead of hooking the shackle directly to the padeye, we attached it with several lashings of light line. That way, if the load on the vang gets too high the lashings break (instead of the boom bending), acting as sort of a mechanical fuse. The exact number of turns of the lashings is found by trial and error. We started out with four and broke it in light air and choppy seas. We then changed it to six turns and this worked perfectly."

There are two types of preventers—one led part of the way forward and the other to the bow. The first one, which is the simplest, is the typical rig for daysailing, racing, or near-shore cruising. Tie or shackle the lines (port and starboard) to the boom about one-third to one-half of the distance aft of the gooseneck, preferably to a reinforced location like the boom vang fitting or mainsheet fitting (even with stretchy material, the load can be powerful). Lead each line to a side deck through a sturdy block attached to a though-bolted fitting on the rail forward of the chainplates (where the shrouds meet the deck), and then aft to the cockpit to a winch or cleat. Never rig a preventer using a turnbuckle or flimsy eye on a stanchion base, each of which will surely break in an accidental jibe. In this system, the preventer is led down as well as forward, and so serves in part as a boom vang to tighten the mainsail leech and make the sail set better.

The other preventer is the traditional offshore rig leading from the end of the boom to the bow. Because it provides no downward pull, it allows the boom to rise to keep it from dragging in a large ocean swell. This preventer takes more time and agility to set up than the combination type. It's often carried on boats making long tradewind passages.


The heavy loads that develop aboard boats in big breezes demand respect. Clear communication between the helmsman, trimmers, and the rest of the crew is the keystone to controlling the boom. 
A boom restrainer
slows the boom’s swing. It is a line running from rail to rail through a high-friction block on the boom. The best-known restrainer is the Dutchman Boom Brake, which has been around for a long time and has many fans.

There’s another type of boom restrainer called the "puller-outer" or "out puller." It’s used by boats making long, square, fast runs under symmetrical spinnakers (for instance in the Transpac Race). While not absolutely stopping the boom from coming across, the puller-outer at least controls this dangerous spar while also easing steering in dicey conditions.

The puller-outer is a sturdy line led through a block on the end of the main boom. It serves as an outhaul for the spinnaker sheet. On one end is a block that the spinnaker sheet is led through. The sheet then leads forward and down to and through a block on the leeward rail. Finally, the sheet goes back to a winch for trimming. When running in strong winds, the floating block is hauled well out under the boom to spread and flatten the spinnaker, making the sail less likely to swing around. The spinnaker pole is over-squared, as well. Stabilizing the chute this way always vastly improves steering. And because the sheet leads down and forward, the boom is held out so long as there’s a load on the sheet. In a broach to leeward and an accidental jibe, easing the sheet dumps the spinnaker and allows the boom to swing across without risking a dismasting. 

Any of these four rigs—the two preventers and the two restrainers—are well worth trying by any crew that wants to avoid becoming number 17 on Dr. Gary Fischer’s list.

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