Boom Brakes and Preventers

Gybe wipe out!

When sailing down wind we eventually may find ourselves having to perform the dreaded gybe.  Depending on conditions and wind strengths, this can be relatively painless or really scary. A violent gybe, which causes the boom to crash from one side of the boat to the other, can cause major damage. In some instances the boom and its attachments can break or bend, the mast can break or bend, and/or the standing rigging can be shock-loaded causing premature fatigue or even failure.

Dutchman Boom Brake

If the gybe is intended, there are some techniques to minimize this ‘shock-loading’. One, is to grab the entire main sheet tackle as a whole and help ‘yank’ it over to the new gybe; this is a tricky technique and should be well practiced in light air. When using this method make sure to keep your head, hands and feet clear of the boom or any associated lines. The trick is to hold onto the tackle until the sails back-fills, then letting the tackle run smoothly through the hands (while wearing gloves), acting as a brake. The second method is to trim in the main sheet through the gybe and release it (quickly!) on the new tack. The second method is less preferred, as it can cause the boat to round up if you don’t release it at just the right moment.

To help make things easier let’s talk about what are some good hardware/ rigging solutions:

The boom brake will surely solve all of your gybing woes. It is exactly as it sounds, a device that provides a braking-action by applying friction to a line that is rigged athwartships. There are several manufacturers of boom brakes worth checking out: WalderFleming, Dutchman, and Wichard, just to mention a few. The only downside I see with these systems is that the line that has to be rigged athwartships and if you are not careful, can trip you up on your way forward. There can be several ways to rig your boom brake so make sure you ask your local rigger what set-up suits your boat optimally.

Proper Boom Preventer System, click image to link to Sail Magazine's article on preventers.
Proper Boom Preventer System, click image to link to Sail Magazine’s article on preventers.

The boom preventer is a more traditional, highly effective method that can, if rigged properly, leave your deck clutter free. The preventer, unlike the boom brake, is to be rigged to the very outboard end of the boom via a pad eye and pendant(see diagram). Many people come up with their own inventions but do not realize that taking shortcuts can lead to boom failure. Here are some tips to rigging your boom preventer properly:

  • always use an outboard attachment point
  • the attachment point should be a heavy duty pad eye that is through bolted and not just drilled and tapped
  • the boom should have a high-strength pendant spanning the length of the boom so that you can access the inboard-end easily when the mainsail is eased all the way out
  • the inboard end of the pendant needs to have an eye to accept the shackle of the preventer control line
  • the preventer control line should be stowed at the shrouds, go forward to a turning block on the bow and lead aft via lead blocks back to the cockpit, thus keeping the deck clutter free
  • the control line should be long enough so that when it needs to be released (in a jam) it can allow the boom gybe across to the other side in a controlled fashion
  • the cleating mechanism for the preventer control line should be one that can be easily released in case of emergencies!

Whether choosing a good boom brake system or a properly configured preventer system, take time to ensure that it is rigged correctly and you are well practiced at using it in varying conditions. Both systems should use a stretchy line material like nylon (or at the very least a stretchy polyester) to minimize shock loading. The boom brake offers you an effective ‘set it and forget it’ method that shouldn’t require you to leave the safety of your cockpit once rigged. It can however clutter amidships and create a potentially hazardous situation if you do ever need to go forward. The boom preventer can be controlled from the cockpit as well, however it will require you to go forward to the shrouds to rig the system so that it can be used.

Remember you can always leave a comment if you a have a question or a thought. Thanks for the read and we’ll talk to you again tomorrow…

10 thoughts on “Boom Brakes and Preventers

  1. A very informative article. Do you have any guidance on the working loads that will be involved and how to calculate them for different boats?

    1. Hi John,

      I do not, it’s probably harder than we think to calculate shock loads for a gybing boom. However, the manufacturer will typically provide a sizing recommendation for the appropriate boom break. Our, in-house preventer system will generally come in two sizes small, mono-hulls 38 and under, and large for monohulls 39-50. We will provide custom consideration to heavier boats, as well as boats that fall right near the top of the small kit if they are a very displacement laden.

      Hope that helps and thanks for the read!


  2. What form of nylon line would you recommend for the preventer line, three strand or double braid? For the preventer pennant would you recommend nylon as well? Thanks!

    1. Hi Avery!!

      Thanks for commenting. Although we look for something abrasion resistant yet stretchy you are not limited to Nylon. It can be Dacron for the control line. Also, it can be three strand, I would just choose what suits the boat. With that, here’s what we use. Nylon double braid for the control line and Dyneema for the boom pendant because it’s easy to access the inside of the line where we bury a chock chord so that can be retracting. This serves to stow the line neatly against the side of the boom.

      To answer your question, the genius of this system is in the design and less in the materials.


  3. Is there any advantage/disadvantage to having both a preventer and a brake installed on on a 50 foot sloop

    1. Hi Bruce,

      Not that I can think of. It’s usually one or the other in my experience. Depending on how you use/rig a boom preventer it can be used as a boom break as well.

      Thank for the question and I hope this helps.


  4. also, as to the padeye on the boom, does it have to be attached on either side (lateral) of the boom or can I just have one on the underside of the boom?

    1. One on the underside should work as well. It is preferred to have through bolted pad eyes on the side as it will reduce the tendency for the boom to twist, but I think you’ll be fine. What kind of boat is it and whaybisze is it? Just be sure that the pad eye is outboard as far as it can be.


  5. if no turning block forward, can I use a snatch block attached to either side of the bow cleats?

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