We’ve all heard the dramatic stories of others and maybe seen the one or two broken booms and masts. But have you ever asked yourself: “Do I really need a dedicated preventer system on my boat?”
Some sailors only race, others only cruise in sheltered waters and others go coastal cruising or even full blown offshore. Now, one could argue that the moderate or occasional coastal sailor doesn’t need a preventer set-up, since one could always use a line to quickly secure the boom to lee if the conditions require it.
However, from experience of others and my own, I strongly advise you to have a preventer system in place that is easily deployed when needed. Without one, the chance that you don’t use one when you really should, will increase exponentially. Without a preventer in place when needed, you risk major damage or injury to boat and crew.
When is a preventer needed?
I’ve seen broken booms and/or preventers even on boats which only sailed in sheltered waters caught out by unpredictable wind shifts or momentary lack of concentration.
A preventer is a good insurance against an accidental gybe. That is when the boom swings rapidly form one side to the other when going on a downwind or near downwind course. While the forces generated in such a scenario are generally very high, an accidental gybe in even mild winds can result in damage to the boom, vang, the boat itself. Also, the boom and mainsheet tackle can swipe a person overboard and/or severely cause injury.
What causes an accidental gybe?
On a downwind course or near downwind course a wind shift or gust or a large wave can suddenly push the bow across the wind, backfill the main and an accidental gybe can occur and cause a serious accident - unless you have a preventer rigged.
A well set-up preventer also reduces the banging noise of the boom in unsteady seas, since it aids the vang in holding the boom from swinging up and down.
What kind of preventer suits my boat best?
There are various systems available for different applications and needs.
When being on a near downwind course, a simple line is attached from the end of the boom to a strong point before the mast.
Disadvantage: The weakness of this temporary set-up is that you need to have a suitable line ready for use at any one time. Also, the boat usually will be already on a set course and you would have to winch-in the boom again to get the line attached to the end. Therefore what happens most, you most likely will attach the preventer at the mid section of the boom since this might still be accessible with the boom out to the lee side of the boat. While still better than nothing, this is not the best solution.
Permanent Preventer Set-up
There are a few different tactics one can use to set up a permanent preventer. However, which one you choose will depend very much on your boat and/or preferences.
The single line set-up A line is being led via a clutch in the cockpit and via blocks to the mast and up to the gooseneck of the boom. From there it will run along the boom to a block attached to the end of the boom and back to the preventer attachment at the boom - clipped in via a snap shackle - ready for deployment. (click to see Single Line Preventer drawing)
Advantage: This set-up provides you with an easy way of just opening the clutch in the cockpit and somebody to walk forward taking the snap shackle off the vang attachment and pulling it forward to a strong point ahead of the mast. Even with the boom right out over the lee side of the boat, the snap shackle on the boom vang attachment should still be within easy reach.
Disadvantage: When gybing, you will have to move the line around the mainsheet tackle to the other side. Again, this can be a bit difficult depending on how far back on the boom the mainsheet blocks are situated. It also presents itself as a single solution only to preventing. And as we all know, the best set-ups on a boat are the ones which have more than one use only.
Dual Line set-up A dual line set-up, while more complex has a few benefits over the single line set-up. To set it up the Dual Line system, you have to run a line preferable from the end of the boom forward to be attached with a snap shackle to the preventer attachment at the boom. Additionally, on either side of the boat there needs to be a line run from the side of the cockpit via a clutch and rollers to a strong point ahead of the mast. (click to see also Dual Line Preventer drawing)
Advantage: Once you are on a downwind or near downwind course you open the clutch near the cockpit of the lee line and go forward to the end of this line at the strong point ahead of the mast. Pulling out the line and then grabbing the snap shackle at the preventer attachment point from the line on the boom (which should be easily reachable). You clip them together, walk to the back and tighten the preventer line.
To avoid the issue of having to feed the line attached to the boom around the mainsheet tackle when gybing, you can set up to lines on the boom, one to port and one to starboard avoiding the hassle of having to feed it around the mainsheet tackle.
Now what about multipurpose use of this system?
Well, having the line on the boom firmly attached to the preventer attachment point serves has a great dual purpose as jackline, when the boom is winched into the mid ship position. Also, on a boat with a selftacker, either one of the side lines can be used to act as a barber hauler or to fix the selftacker car to one side, should one consider to heave to.
On my own boat, I also use the windward line to control the tackline of my Asymmetrical Spinnaker from the cockpit.
Disadvantage: More complex set-up with multiple lines required.
Commercial Products There is a variety of commercial product out there that is designed to help you with controlled gybes and at the same time act as a sort of “quasi” preventer. Many of them are very beneficial to the cruiser and sailor who are prepared to spend some money up-front to avoid major repair work and potentially injury to crew. Some of the systems available work via friction, drum or adjustable Boom brakes. They are definitely worth a look at if you need assistance in controlled gybes and when you lack the set-up of a proper preventer system.