Building a Boom Preventer for an Ocean Crossing

Since we will be downwind sailing for around 20 days with 15-25knot trades winds as we cross the Atlantic I wanted to upgrade my boom preventer to make it safer, easier and prevent any gear damage. Previously I just used a single 12mm polyester line which I attached to the mid cleat and would move from side to side when I gybed. I also use the preventer as sort of a vang/kicker to close the leech if I want more power from the main, so making it easier to adjust from the cockpit without going up on deck was important. So I upgraded my preventer with the following:

Two separate port and starboard 12mm polyester preventer lines which I attach and remove when the boom is half way over while standing on the deck next to the helm. This way there is no lazy line that can get caught on anything as we gybe. I have a rubber shock absorber on each line to hopefully prevent anything breaking if we do get an accidental gybe. On the crossing I found that the rubber shock absorber is not really strong enough to reduce the shock load so may just remove it in the future.

On the boom I now have a separate dyneema loop going through the aft padeye. I then built a dyneema strop that is long enough for me to reach and attached that to the loop. I also put a dyneema cover to prevent chafe where it attaches to the preventer line. I used to have soft schackles to attach the preventer line to the strop but changed to these wichard shackles which now allow me to attach and remove with one hand. Need the other hand to hold onto the boat 🙂

The line then goes through a antal loop attached to the mid cleat using a soft shackle. I used to use blocks here but one of the shackles bent over time, so now rely on trusty dyneema to take the load 🙂 To reduce chafe I also installed white plastic tubing on the lifelines and also a dyneema cover on the preventer lines where it rubs against the shrouds.

Finally I have the end of the lines going through a clutch which I also use for my oxley parasailor. I typically use the oxley without the main up, so don’t need the preventer rigged. From here I can tension the preventer using the winch when I want to close the leech.

I also have another preventer line on the other side which I stow on the lifelines ready to used after I gybe.

Review after the Atlantic crossing
On the crossing I optimized the setup in a number of ways which I have updated above. I created a longer dyneema strop to make it easier to reach. I changed from soft shackles to wichard shackles and added chafe gear to the lines where they touch the shrouds. The preventer worked amazingly well on the atlantic crossing:

• Majority of the time we were on autopilot wind mode and never got an accidental gybe even with 100 degree windshifts in squalls. However when we got hit by some squalls when we were motoring in no wind (on heading mode) we did accidentally gybe a couple of times in the windshifts but the preventer held the boom perfectly. It was light winds though, so the forces were not big
• The preventer allowed us to power up the main by closing the leech, easily adding half a knot of speed!
• In light winds and big waves the boom moves up and down a lot, spilling a lot of wind and putting strain on the gooseneck. Tightening the preventer really helped reduce this.

All in all really love the preventer now, we use it all the time even at anchor to keep the boom off the solar panels. Would highly recommend this setup!