Using a preventer or boom brake is essential seamanship for downwind sailing, but doing it incorrectly can lead to issues, warns Rachael Sprot.
A properly designed preventer system is just as crucial as any rigging component, yet it is often overlooked, sometimes merely consisting of an old mooring line wrapped around the boom.
As the typical size of cruising yachts, along with mainsails, grows, the importance of a preventer system intensifies. In earlier sections, we examined four incidents from the past two decades where accidental gybes resulted in serious injuries or fatalities among crew members.
These tragedies had various causes but shared common elements such as strong winds and heavy swells, inexperienced helmspersons, fatigue or distraction, and skippers being away from the cockpit.
Two of these incidents involved preventers that failed. Notably, the Platino report highlights the immense loads at play and emphasizes the crucial nature of proper installation and rigging of gybe-prevention equipment. It’s sobering reading that has prompted me to reconsider my practices on my own boat as well as when aboard others’ boats. I hope these articles encourage us all to become more skilled, safety-conscious skippers.
Reflecting on the findings of the reports, I spent a day with Iain Horlock, the chief rigger at Devon’s Jimmy Green Marine, to gain insights on designing a preventer for cruising yachts under 50ft. We used my 36ft Cheoy Lee, Nimrod, to construct a traditional preventer system, and we also tested two alternatives: the Walder Boom Brake and the Wichard Gyb’Easy.
A boom brake or preventer can mitigate the impact of an accidental gybe – critical if your mainsheet crosses the cockpit. Photo: Graham Snook
Rigging a Preventer
What constitutes an effective preventer system? Best practice suggests it should extend from the boom’s end as far forward as possible, a directive reinforced by the Platino report. Key components include a robust attachment point on the boom, the preventer line (which may be split into two segments), and the deck fittings that allow routing back to the cockpit from the bow. I requested Iain’s help in determining the best route and choosing components.
Attachment Point on the Boom
Fortunately, Nimrod’s boom features a superbly designed strong point, provided by a fixed stainless steel bar in a cutout on its underside. This serves as a mainsheet attachment, with ample space for a preventer connection. If you lack a dedicated attachment point, consult your rigger for advice.
There are numerous boom fittings to consider: extra slugs beneath the boom, a handle at the boom’s end, or saddles attached to the boom for routing a strop around it.
Cast boom-end fittings, like this one, are made specifically for preventers and should not serve other purposes.
We confirmed this with Seldén, a mast and spar manufacturer, whose account manager Richard Le Mare advised, “We always suggest setting a preventer from the boom’s aft end to avoid buckling. If your mainsheet is in the boom’s center, the end is still the best spot for a preventer, as the spar is designed to handle downward and sideways force, not the direct lateral force from a preventer.”
He pointed out that older booms may have a cast aluminum boom-end fitting with a large eye or handle, specifically intended for preventer rigging and should be used solely for that purpose. Attachments should be made with rope or soft shackles to avoid damaging the fitting with metal.
Even a deeply reefed main may shift the clew, and thus the gybe’s force, forward along the boom, but maintaining the preventer rigged to the boom’s end will provide better mechanical advantage and prevent the need for rerigging.
Mainsheets or preventers attached in the middle of the boom can break in a gybe.
Preventer Pennant
I’ve always favored having a short ‘half’ preventer, or preventer pennant, permanently rigged to the boom. It lessens workload for when a preventer is needed, making it more likely you’ll complete the remaining setup. It also eliminates the need for someone to connect a line to the boom’s end while underway, which can be challenging and unsafe if the boom is partially eased.
I told Iain the distance from the strong point at the boom’s end to the kicker fitting. He created a pennant of the appropriate length with two spliced eyes. One end was connected with a soft shackle to the strong point, allowing for articulation (which might require anti-chafe for extended passages), while the other linked to a bungee on the kicker fitting to keep it tucked away. Iain chose Dyneema for this to maintain a smaller diameter, minimizing bulk for a line that remains rigged.
It’s worth noting that although we set up just one preventer and pennant during the test, installing one on each side is advisable to avoid needing to swap the preventer when executing an intentional gybe.
The pennant can be connected to the preventer line when required; however, keep in mind that snap shackles aren’t entirely reliable, while bowlines can reduce line strength by as much as 70%.
Preventer Line
For the preventer line itself, Iain prepared a 10mm braided polyester line approximately 1.5 times the boat’s length. He attached a snap shackle at one end for quick connection to the pennant without significant strength loss. The Platino report indicates that snap shackles may not be reliable under dynamic loads, but they outperform bowlines.
While a soft shackle may offer better reliability, we chose to stick with the snap shackle for Nimrod’s size, prioritizing ease of use.
The preventer line can be pre-rigged through its fairleads on the side deck before departure.
Routing
A detailed assessment of the deck fittings’ strength isn’t prudent for most cruising yachts, but an experienced rigger can determine if they’re fit for purpose on a moderately-sized cruising yacht. Inspect beneath your deck fittings to check for reinforcement with backing plates versus just small washers.
For many vessels, bow mooring cleats serve as ideal locations since their backing arrangements can be observed inside the anchor locker and easily reinforced if necessary.
Nimrod, designed in the late 1960s, possesses substantial deck fittings. The bow fairlead is mounted within the toe rail, providing robust support at the preventer’s apex. Open fairleads pose a risk of the line jumping out, hence a proper turning block might be advisable for the long term.
Coil the line onto the guardwires to keep the preventer line out of the way until required.
Both the bow cleats and midships cleats naturally guide the line back to the cockpit, made easier by adding two economical low-friction rings for optimal lead. While snatch blocks would ease flow, they matter less for static loads than for dynamic application, like a spinnaker sheet.
Pre-rigging
We prepared the preventer in Plymouth’s Sutton Harbour. Before embarking on a downwind passage, it’s far safer to rig it at the dock. Clip the end connecting to the pennant to the guardwires amidships for easy access when needed.
Securing it with a thumb knot in the block at the cockpit end, coil the line over the guardwires to keep the cockpit clear.
Even without the boom sheeted in, it was simple to connect the pennant to the preventer line.
TEST 1: The Preventer
We left Plymouth Sound amid a gentle westerly breeze, making for ideal test conditions: enough wind to fill the sail yet light enough for safe experimentation. A preventer should always be connected on a safe point of sail, with an experienced helmsperson at the wheel.
It’s advisable not to ease the mainsheet excessively before attaching the preventer, minimizing potential travel in case of a crash gybe. If short-handed, it’s better to let a novice crew handle deck work while you manage the helm; reaching the boom to attach the preventer to the pennant is straightforward if pre-rigged.
Alternatively, you could heave-to, bringing the preventer to the high side, then gybe out of the heave-to while easing the mainsheet once on a broad reach. All choices depend on specific conditions and your sail plan—the more mainsail deployed, the more challenging it is to come up into the wind.
The preventer held the boom comfortably to windward after the gybe, though this position felt somewhat precarious.
On most boats, it’s necessary to ease the mainsheet adequately for the preventer to clear the forward stanchion posts. Once connected, the preventer must be tensioned sufficiently to minimize dynamic loading during a crash gybe.
With the preventer attached, we executed a gybe. The mainsheet relaxed slightly, indicating some stretch in the preventer system, but the boom remained stable. Although it felt unstable, staying in that position for long wouldn’t be advised; you can either ease the preventer and trim in the main (cautioning that this could risk bending stanchions as the boom’s angle transforms) or gybe back onto the original course.
Wichard Gyb’Easy
TEST 2: Gybing Device – Wichard Gyb’Easy
The Gyb’Easy is a ladder-shaped device with three distinct ‘rungs’ and a pin atop. It serves as a one-size-fits-all solution for boats with mainsails measuring up to 40m², covering cruising yachts around 40ft. It should ideally be placed just aft of the vang bracket; however, on Nimrod, the only feasible attachment was to the vang bracket itself.
A line looped through one rung provides low friction, while looping through both increases friction when tension is needed.
A bight of line is threaded through the rungs and over the pin. The stronger the wind, the more friction is necessary, thus utilizing more rungs of the ladder improves performance.
The line’s two ends should run symmetrically from the boom to the base of the shrouds, passing through a block before returning to the cockpit winches. This setup wasn’t viable for a test on Nimrod, but low-friction rings on midships cleats provided good support instead. Wichard offers a designated line for the device, called ‘Gyb’flex’, intended to absorb shock loads; however, we used a substitute polyester braided line for our testing.
The boom swung too swiftly with just one loop on the Gyb’Easy.
We configured it with two ‘rungs’ and eased the mainsail, applying tension to the Gyb’Easy. During the initial gybe, the boom swung across quickly, yet not at full speed. Clearly, we needed to increase line tension or friction. Thankfully, we had positioned ourselves well at the front of the cockpit, avoiding interference with the mainsheet.
Adding an extra rung with increased tension allowed the Gyb’Easy to effectively manage the gybe.
Iain added a third ‘rung’, adjusting the control line tension. On the second gybe, the boom remained stationary, but easing tension allowed for a controlled boom swing. After further trials, we discovered the optimal setup with minimal resistance yet sufficient line tension, allowing the boom to swing smoothly through the gybe.
Walder Boom Brake
TEST 3: Gybing Device – Walder Boom Brake
The Walder Boom Brake consists of a drum-shaped mechanism around which line is wound two or three times, depending on conditions and the friction level needed. Various sizes are available suitable for mainsails, with the largest applicable for boats over 50ft.
Secure the Boom Brake to a strong point on the boom near the kicker strap attachment.
We utilized the Walder 203, recommended for boats up to 12m or 8 tonnes. It can replace the kicker or be positioned behind a rigid vang.
Setting up the line on the Boom Brake takes time, but it can be pre-fed and left in the locker or rigged before departure.
Similar to the Gyb’Easy, the Boom Brake requires a robust attachment point at the chainplates or toe rail near the shrouds. One end can be secured running back to a cockpit winch on the opposite side for tensioning.
Tension can be adapted during the gybe to assist the boom’s transition when necessary.
During our first gybe, the Boom Brake performed effectively, likely due to our experience with line tensioning from the Gyb’Easy test. However, since we had rigged it asymmetrically by tying off to one side, performance varied between gybes.
With the control line leading to a winch on the windward side, in lighter conditions, it tended to draw the boom towards the centerline while tensioning. If rigged to winches on both sides, tension on the leeward line could be maintained more effectively, avoiding this issue, particularly with more mainsail pressure.
Overall, the Boom Brake functioned well, smoothly dissipating gybe energy.
Rachael sailed 100 miles to Roscoff on a broad reach to familiarize herself with her new preventer setup mid-channel.
Preventers and Boom Brake Verdict
All three setups performed admirably, and I would feel comfortable using any of them for downwind sailing.
Preventers are advantageous as they are straightforward, cost-effective to install, and a pennant left rigged to the boom is far less intrusive compared to other two devices. However, traditional preventers complicate gybing since they must be removed first, followed by mainsheet tensioning, and then re-rigging post-gybe. This necessitates someone to leave the cockpit each time a gybe is executed.
If you opt for a preventer, it’s advisable to rig pennants and lines on both sides, allowing for a quick swap without needing to go to the foredeck. The trade-off is increased lines in the cockpit, with potential hazards posed by slack lines dangling from the boom during gybes. If you have practical solutions for managing this, YM would love to hear them.
Three weeks after our test, I sailed from Plymouth to Roscoff while on a broad reach. The preventer held the boom steady in 2m seas, enabling me to release it and maneuver behind a few ships when necessary. After just 20 hours, the line had chafed in the fairlead, indicating the need for protective measures. I purchased inexpensive firehose online, which also doubles as effective chafe protection for mooring lines. Moving a turning block sufficiently far forward would be difficult, and I favor the sturdiness of a fairlead.
Avoid going forward in rough conditions to rig a preventer if you can help it.
When properly configured, friction systems simplify gybing. They’re more versatile too, as they don’t necessitate complete mainsail easing and can prevent boom swinging on other points of sail in rolly seas, which pose hazards even in lighter winds. They do not hold the boom to windward after a gybe like a preventer does, potentially placing you in a precarious situation that may fail suddenly. Conversely, boom brakes permit a gentler boom transition, often preferable to a full preventer.
However, we determined these systems ideally require two cockpit winches. If a headsail is poled out and you have a guy and downhaul rigged, you may not have sufficient winches available for this setup. They also need strong attachment points near the shrouds, not all boats may have.
The Walder Boom Brake felt like the more robust apparatus, yet I appreciated the Gyb’Easy’s simplicity and found it easier to adjust friction settings compared to the Boom Brake. There’s significant slack in the mainsheet while gybing, so, although the gybe should happen gradually, crew must be briefed to keep clear. We unanimously agreed that you need to be familiar with your boat and any system before relying on it during challenging conditions.
I remain skeptical about trusting these systems to gybe safely with the mainsheet loosened in winds exceeding 20 knots; however, they serve as safety backups rather than replacing proper sailing techniques during a gybe.
Choose a Preventer That Suits You
Ultimately, your choice will hinge on your boat, crew, and sailing style. According to Iain at Jimmy Green, “A preventer system is inherently tailored to individual circumstances since each deck layout varies.” For occasional inshore use or offshore runs on the same gybe, a traditional preventer offers the simplest solution, especially with heavy-displacement cruisers more prone to deeper downwind angles and fewer gybes.
If I were sailing a more contemporary boat equipped with an asymmetric sail that favors reaching downwind and allows for increased gybing, I would lean towards the Boom Brake or Gyb’Easy. For trade wind journeys across the Atlantic on ships over 40ft, I would strongly consider the Boom Brake, particularly if my crew were inexperienced.
“I’d be cautious about crafting a preventer system intended to withstand high loads,” warned Iain. “At some point, something will give.”
None of these systems guarantee the prevention of the damaging effects of a crash gybe, but they do enhance the likelihood of avoiding such incidents.
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