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Know-how: Boom Safety

Zest at sea in 20-plus knots of wind with a preventer rigged from the aft end of the boom

Zest at sea in 20-plus knots of wind with a preventer rigged from the aft end of the boom

Sailing is a remarkably safe activity, despite the potentially dangerous environment in which it takes place. This is undoubtedly due to the safety-conscious attitude of most skippers and their crews. Nonetheless, even the best sailors can still get in trouble when and where they least expect it.

When I was a young Royal Yachting Association (RYA) Yachtmaster instructor, one of the standing orders for all the sea school’s staff was to either have a preventer rigged or the mainsail furled, or be sure and sit next to whoever was at the helm when sailing downwind. My employer clearly recognized the danger of an accidental jibe, both to his reputation and livelihood.

It’s an approach that has served me well over the years and one none of us should ever forget. A blow from the boom or mainsheet in an accidental jibe is one the most common causes of serious injury while sailing. A crash jibe in heavy weather is also an almost certain recipe for damaging the boat or rig.

The classic solution is a line led forward from the boom to stop it crashing across from one side of the boat other: hence the name “jibe preventer.” This should be as much part of the standard package of a boat’s running rigging as the mainsheet. Sadly, this is rarely the case.

Clipping the forward end of the preventer to a point just aft of the vang for stowage when not in use

Clipping the forward end of the preventer to a point just aft of the vang for stowage when not in use

A preventer should run from the aft end of the boom, outside the shrouds, forward to the bow and then back again to the cockpit where it can be easily adjusted. It’s often tempting to attach the preventer to the midpoint of the boom. However, doing so runs the risk a broken boom or gooseneck.

Even worse is taking a preventer from the middle of the boom to the toerail, as the line acts downward, markedly increasing loads compared to one that’s led to the bow. Granted, many have successfully used this arrangement for thousands of miles. However, the risk of significant damage is so great I would never do so.

A preventer should also never be made fast on the foredeck. In order to be free to luff up or jibe to avoid collisions, it must be possible to adjust the line from the cockpit. It’s also important to be able to safely ease a preventer when it’s under load. If it can’t be taken to a convenient winch, a mooring cleat of the kind that allows a rope to be eased with a single turn will suffice.

Zest’s preventer hanging slack under the boom prior to stowing

Zest’s preventer hanging slack under the boom prior to stowing

Different Setups

At its most basic, you probably don’t need any extra fittings or equipment to rig a preventer. On scantily equipped charter boats, for example, I typically use a long mooring line led through the bridge of a foredeck mooring cleat. The line is then brought aft, either to one of the primaries or a mooring cleat on the transom.

In fact, I use this same type of arrangement on Ammos, my 30ft Discovery 3000. The boat is small enough that it’s easy to sheet the mainsail in and attach the preventer to the boom end without any kind of perilous gymnastics. There’s also a straight run along the side decks between the forward and aft mooring cleats. In the 20 years, I’ve owned the boat, I’ve never felt the need to improve on an admittedly basic, but no less effective setup.

Aboard larger yachts, of course, it can be a very different matter, as it’s often impossible to safely reach the end of the boom in any kind of seaway. This is when a permanently rigged two-part preventer makes sense.

The first element in this kind of system consists of a strop roughly two-thirds the length of the boom that’s permanently attached at the aft end, usually with the front end clipped to the vang fitting. The second part runs from the cockpit to the foredeck and then aft outside the guardrail. When not in use, I usually tie the free end of the second part to a stanchion aft of the shrouds where it will be within easy to reach. It then becomes an easy 30-second job connecting two elements when needed, with no need to lean over the lee side of the boat.

Note: just as I would not use a snap shackle on a halyard for attaching a bosun’s chair, I also avoid them with preventers. Instead, the two elements can be joined together with a pair of bowlines, which are quick and easy to tie, even in challenging conditions.

In fact, this is the setup we have on Zest, my partner’s 36ft Rob Humphreys designed one-off. One end is led to a bank of clutches near the companionway and whenever possible is also on the secondary winch. This makes it simple and safe to ease when under load. A little stretch in a preventer can actually be beneficial, so there’s no need to use expensive high-tech ropes. Double-braid polyester, usually the same diameter as the mainsheet, works fine.

Now that you’ve got a preventer rigged, the question becomes what to do if or when you accidentally jibe? Initially, the answer is probably not very much—providing it’s nice and snug. With the wind only marginally on the wrong side of the sail, the forces at work are still fairly minimal, so a quick course correction should serve to bring the boat back on track. To avoid a repeat, steering to a slightly higher heading, say, 20 degrees or so, after you’re back on the correct jibe would also be prudent.

If, on the other hand, you are unable to effect an immediate course correction, or the boat is allowed to deviate further, it will become progressively harder to get back on track. With the mainsail backed the boat will slow, making the rudder less effective at the same time the increasing power in the backed sail is going to make the boat want to luff up that much higher on the new jibe.

When this happens your only option may be to accept the new heading, at least temporarily, and ease the preventer to allow the boom to move over to the new leeward side of the boat in a controlled fashion. This is why it’s so important to be able to safely ease the cockpit end of the preventer when it’s under load.

As you are following through onto your new (temporary) course, sheet the mainsail halfway in, easing the preventer as you do so, then cleat the sheet and traveler securely. A shipmate can then untie the running part of the preventer from the preventer strop on the boom.

Once the boat is settled in on its new course (either your original course or your new unintended course, should you choose to stay on this heading) the two parts of the preventer can be reconnected. On Zest we only have a single line running up to the bow and back, which means it has to be re-led each time we jibe. We could, of course, run a pair of lines down both sides of the boat if we wanted.

A sampling of boom brakes as offered by (from left) Wichard, Walder and Dutchmar

A sampling of boom brakes as offered by (from left) Wichard, Walder and Dutchmar

Boom Brakes

In addition to these kinds of jibe preventers, a number of manufacturers also produce what are collectively called “boom brakes.” Examples include those manufactured and marketed by Sailology, Wichard, Walder and Dutchmar. Boom brakes don’t prevent the boom from running from one side of the boat to the other in the event of an unplanned jibe. However, when correctly set up and adjusted to suit the conditions, they will ensure your boom does so gently and in a controlled manner thereby protecting both the boat and crew from damage or injury.

At the heart of a boom brake system is a compact friction device sitting directly underneath the boom, usually just aft of the vang. A line is then run through the device from one side of the boat to the other. The idea is to create enough friction in the system to slow the movement of the boom sufficiently to keep it from posing any danger.

Adjusting the tension in the line increases or decreases the amount of friction in the system. This in turn allows you to control the speed with which the boom will come around in different wind strengths. One drawback to the boom brake approach is the risk of the boom flying across the boat in an uncontrolled fashion in the event things aren’t properly set up. There’s really no excuse for this kind of thing, though, as one end of the line can be easily led to the cockpit for adjustments.

Although boom brakes are a very neat solution and tens of thousands have been sold over the years, they have yet to gain universal acceptance. I suspect this is partly due to the bullet-proof simplicity of a traditional preventer. Aboard a traditional yacht with a narrow beam, the lines of a boom brake are also typically led well outboard, where they can obstruct passage fore and aft along your side decks. Aboard today’s wider yachts, on the other hand, this is less of a problem as the lines can often be led to the inner edge of your side decks or the top of the cabintrunk. 



Sailology LLC



Photos by Rupert Holmes

June 2021



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