How to arm the boom restraint well (and avoid tragedy)


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The boom breakage on the X-4.3 Agecanonix, based on initial “unofficial” reconstructions, may have been caused by an unintentional gybe (“chinese gybe”) with the boom braked by the restraint (frame taken from video released by German newspaper Bild).

The tragedy aboard the X4.3 “Agecanonix” at the ARC, and the death of a French crew member, Max Delannoy, due to impact with the boom, again puts the focus back on crew safety.

Boom restraint is an essential and necessary maneuver for safety in aft gaits and to avert uncontrolled mainsail passage over the new tack in the event of an unintentional gybe. We asked “guru” Davide Zerbinati (surveyor, boat builder, yachtsman and author of monumental volumes on shipboard work) to help us to understand how to properly arm this maneuver, how the boom brake alternatively works, what the risks of improper installation are, and what should be done to increase crew safety.

Boom retention, everything you need to know

David, what was the dynamics of the accident at the ARC?

It appears to be an unfortunate unintentional jibe, but we cannot speculate until World Cruising Club technicians determine the exact dynamics of the accident.

What is known is that the accident occurred in challenging conditions, with a three- to four-meter crosswave and winds between 30 and 40 knots. We do not know under what circumstances and with what sequence, we only know that the boom, or a piece of the already broken boom, struck the victim in the head.

What is boom restraint and why is it so important for safety?

For safety, With that sea, at 3,000-mile ocean voyage, at load-bearing gaits, it is essential to arm the restraint Of the boom. The restraint is a line that binds the boom, preventing it from swinging over the new walls in the event of an unintentional gybe (the “chinese gybe,” ed.), an event that, in waves and ocean winds, subjects the mast and boat to stresses with often disastrous consequences, including dismasting.

It should also be remembered that the restraint locks the boom and preserves the trope and rigging from the stresses of the mainsail. We do not know whether and how it was armed on Agecanonix, however, it is known that improper installation of the restraint, may not be effective or be the cause of the boom itself breaking.

VIDEO – How it is armed restraint of the boom on Davide Zerbinati’s boat

How to properly arm the boom restraint?

A line running from or near the end of the boom (varea) to the bow on a bollard. Or rather, with a loop equipped with a block to return to the cockpit, on a winch or bollard, with which it can be adjusted.

When you have the mainsail open aft, the sail should not touch the spreaders or shrouds, but once the restraint is secured you will recover a bit of mainsheet. The best-equipped boats already have two retentions set up.

boom restraint

The advantage of having the maneuver on a winch is that you can fine-tune it, but it is also easier to leave in an emergency.

Shown is a basic diagram of a boom restraint (boom preventer in English).

What lines to use and how to attach to the boom?

The retaining line must be larger in diameter than the mainsheet because the mainsheet passes through demisting blocks, while the retaining line is a direct maneuver. To give an idea, on a 50-foot boat the restraint is accomplished with a 16mm dyneema line; on a 45-footer, 12 or 14mm, also dyneema.

Some boats already provide it, Selden provides it, Hallberg-Rassy provides it as an option. Ideally, it is best to use a loop around the boom, or a strap, as opposed to the classic carabiner. On some boats there is a hook, a hook that can be anchored to the gunwale or on special padeyes(eyebolts, ed.) on deck.

What happens in gybing with boom restraint?

If the boat goes into an involuntary gybe, the restraint goes into tension, restraining the boom. If you cannot get back to the previous tack in time, you must slowly let go of the restraint, and recover with the sheet to get the boom over the new tack and resume steering the boat. This is why restraint must be easily and quickly adjustable. So it goes without saying that if you fix the restraint in bollard, it should be tied with a simple knot, which should also be untied under tension.

What mistakes are likely to break the boom?

If the restraint is wrongly attached to the center of the boom, it will create a deflection in the center of the beam-boom, which can easily break the boom itself. The anchor point should not be the same as the block of sheet (it will not hold the stresses), or a metal-to-metal joint with a shackle.

The anchorage of a restraint can be made with a webbed dyneema textile loop wrapped to the varea. Recent tests by Practical Sailor magazine have shown that on modern boats with very quartered spreaders, since they cannot open the mainsail much, the working angle of the restraining lever arm is less, so a restraining line elasticity of only 2 percent is sufficient to gybe the boat (this is why dyneema, a static line with low elasticity, is recommended). Other issues then arise on small boats, which can easily find themselves with the boom in the water. The latter, if held, could break or damage the tree.

What to do if the boom breaks?

It is conceivable that with a hacksaw and a few rivets, a crew may find a makeshift solution to repair a broken boom, however, having the mainsail on board, which is rigged even without a boom, may allow them to continue sailing and get to safety.

What is boom brake and when is it used?

On small to medium-sized boats, an alternative to restraint is a boom brake, for example the one from Walder. It has a different function; it does not constrain the boom, but slows its swing, converting the boom’s kinetic energy into heat through the friction of the lines passing through its structure.

boom brake at the boom restraint post

I boom brakes are metal components in which a line runs, with friction (in Walder’s case, the line is coiled along a drum). Tensioning the sheet increases the friction and thus the braking force of the device. The base of the moorings are often used as the anchor point, and the brake is attached to the center of the boom.

Are failures in the equipment predictable?

Those with only Mediterranean sailing experience have difficulty understanding the effects of 3-, 4-, or 5-meter ocean waves and the mechanical stress reported by all equipment. Every day, or at shift change, an inspection tour called “hands, eyes, binoculars.” By observing and touching the equipment, one can detect cracks, shackles coming loose, play on the structures, premonitory signs of failure.

Prevention and boat preparation are essential: for example, those without ocean experience tend to underestimate the effects of rigid spring or mechanical vang, which, due to prolonged wave stresses, risks fracturing the boom at the very point of vang attachment. Some boats replace the piston with a classic textile vang. Adjustments are also important, a good adjustment of the vang for example, can reduce some mechanical stresses on the limb.

How to increase crew safety and avoid tragedies?

When moving toward the bow, you pass upwind, obviously tied up, and always crouching. Where you sit in the cockpit is also important for safety. In dismastings, fortunately, the mast almost always falls to the side, and thus the cockpit is a safe zone, but what often happens is the breakage of a block that under tension goes to hit those on board.

The further aft you are from maneuvering, the safer you are. Modern racing boats with cockpit covers, think IMOCAs, also protect the skipper from these events. However, it is essential for safety that all crew know what to do and how to move, and how to conduct the boat safely to continue sailing in case of an accident. There are incredible stories of deaths of the skipper on board, and crew members, who did not even know how to use the VHF.

Is it safer for the crew to stay below deck?

When you are in waves of 3, 4 or 5 meters, it is like sitting on the mechanical bull. Those at the helm struggle to stand. It is hardly conceivable to stay below deck for long in those conditions: you will need to find a safe position in the cockpit, where you are always pointing feet and holding on with your hands. It is not easy even for the most experienced crews.


Davide Zerbinati

Who is Davide Zerbinati

Davide Zerbinati is a sailor, Engineer and Nautical Architect, CEO of Valle Scrivia Srl company specializing in supplies for long-range sailing and safety on board. In his activities since 1998 has appraised about 5,000 boats, more than 1,000 models, and supervised about 100 refitting. He is skipper of the Stadtship 54 Aluaka, a boat with which he won the Leg 1 of the Las Palmas-Mindelo (Cape Verde) leg and the Mindelo-Santa Lucia leg at ARC+ and ready for new adventures and formations.


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