The Best Prevention is a Preventer

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Ideally, you don't put yourself in a position where an accidental jibe can happen, but even an experienced sailor can get caught off guard by sudden, violent wind shifts in mountainous coastal areas or in night-time squalls. The most common way to take the fright out of an unintentional jibe involves a preventer, something weve examined in a number of previous reports. Preventers are especially useful when sailing deep downwind in rolly conditions, when exaggerated yawing lets the wind sneak behind the mainsail.

Although preventers are commonly used offshore, they are often misunderstood. Some advice weve seen on the Web is dangerous. There are various ways to rig a preventer line:

swept-back spreaders

1. On a small boat you can relocate the fiddle block with cam cleat on your soft multi-purchase boomvang to the outboard rail, forward of the boom. This will hold the boom down and prevent a jibe. A drawback to this approach is that you will likely have to go forward to release the cam cleat if the mainsail gets backed. A bigger problem is that if the boom dips in the ocean it can bend or break, which is why a bungee of some sort to absorb shock loads is critical if you use this approach. We don't recommend a mid-boom preventer offshore.

2. Rig a temporary end-boom preventer leading to the bow and back to the cockpit. The problem with this approach is that you have to reach the end of the boom to attach the line, potentially dangerous when a sea is running.

3. Our preferred approach is one in which two long preventer pendants (one for each tack) that are slightly shorter than the boom are attached at the boom end and stowed along the boom. When it is time to rig the preventer, the pendant is slipped off the horn cleat near the gooseneck and attached to a pre-rigged preventer control line run through a lead at the bow and back to the cockpit. Offshore sailor and past PS contributor John McCurdy has a video illustrating the use of this arrangement, here: https://goo.gl/XPOAuh

Practical Sailor archives has a number of related articles, including details on setting a preventer:

Headings: The Academy of the Sea, PS September 2004

Offshore Log: Return to the Tropics PS February 2002

Ocean Testing the Best Sailing Gear, PS January 2007

Solid Vang Showdown, February 2006

Swept back spreaders

One detail that is often overlooked in discussions regarding preventers is that swept-back spreaders increase the risk of an accidental jibe while sailing dead down wind. They also make rigging an effective preventer challenging. On a boat with deeply swept back spreaders, like some catamarans, and monohulls without backstays (B&R rigs) the problem is exacerbated.

In recent tests carried out by Practical Sailor, we found that if the preventer line stretches just two percent, the mainsail on a boat with deeply swept back spreaders is liable to backwind. The problem is caused by a combination of two factors: first the tighter sheeting angle on the boom makes it more vulnerable to backwinding; second, the practice of running the control line back to the cockpit makes the line longer, which allows more stretch.

A boat with this configuration might consider using polyester line. Dyneema will stretch even less than, but the stretch in polyester line may be just enough to the keep the boom from breaking.

Darrell Nicholson, editor of Practical Sailor, grew up boating on Miami’s Biscayne Bay on everything from prams to Morgan ketches. Two years out of Emory University, after a brief stint as a sportswriter, he set out from Miami aboard a 60-year-old wooden William Atkin ketch named Tosca. For 10 years, he and writer-photographer Theresa Gibbons explored the Caribbean, crossed the Pacific, and cruised Southeast Asia aboard Tosca, working along the way as journalists and documenting their adventures for various travel and sailing publications, including Cruising World, Sail, Sailing, Cruising Helmsman, and Sailing World. Upon his return to land life, Darrell became the associate editor, then senior editor at Cruising World magazine, where he worked for five years. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.

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