boom vang as a preventer

[JBA]

Hello all,
My boom vang is very effective in controlling boom rise on a reach. I have seen comments regarding using a boom vang as a preventer when sailing down wind. Does this technique require additional hardware?

Thanks, JBA

[Bruce Bett]

I bent a boom doing that. Preventers should be attached only at the end of the boom.

Bruce

[Klem]

The best place to attach a preventer is the sheet bail. It is designed to be in the correct place and properly sized for the loads.

[Russell]

Yes a vang can be use as a preventer as well. Basicly you detach it from the mast base fitting then attach it to a a fitting that can handle the loads off of the mast. A decent way to do it is to replace one of the clevis pins on your chain plates with a shackle (seized with wire of course), when you detach your vang you attach it then to the shackle, and now you have a preventer.

However, as already pointed out, this is a BAD spot to rig a preventer. Your preventer is operating very far forward on the boom, so and sudden backwinding is putting a lot a pressure on a nasty pivot point. But, that does not mean never do it, many people are fair weather sailors, if you are out sailing in mild weather, its a fast and easy way to rig a preventer. You just have to use good judgement about the weather. I would say 10 knots and less, you are likely fine with this setup if everything is in bristol condition. This of course changes as your boat gets bigger and loads increase, I would never consider this setup on anything larger then a 30.

As for end of boom vs boom bail, this will depend on your boat. Consider that suggesting a boom bail is appropriate, but a vang is not, in a way is silly, without more details, since on a mid boom sheeting setup the vang is normally only inches forward of the fore most boom bail. We are not talking about a lot of difference there. Also, some cape dorys are design with mid boom and some with end boom sheeting, and a boom section to meet those loads.

End boom preventers, lets face it, are a pain in the ass, and in their own way dangerous. Simply setting them up involves mucking about with things high and outboard. Sure if you are sailing on a flat lake with light winds, its no big deal, but try messing around with the extream end of the boom in 10' seas and 20 knots, scary stuff.

My old boat, a Catalina 30, I always did an end boom preventer, but I never left the Chesapeake on that boat. My current boat, a CD36, I have never once done end of boom preventer on. I have playe with a lot of preventer setups though:

For the first year I use a dutchmen boombrake, attached to the center boom bail and lines forward leading to the shroud chainplates. While I really liked the dutchmen, I always had issues with line chafe due to the boats beam and cabintop height, it would rub on the handrails and stowed dinghy.

After ditching the dutchmen, I experimented a lot, I had a block and tackle I made up just to use as a preventer, similar to what one would do with a vang as preventer setup. But I would attach it to the middle boom bail, much furthur aft then the vang would attach, and down to the shackles in the chainplates I had previously installed for the dutchmen.

Ultimately though, I came to like best a setup with no mainsail for running downwind. I drop the mainsail fully, put a pole on the yankee, let the staysail out the other side, and sicne the staysail has a boom I put a preventer on that running from the end of the staysail boom down to the chainplate in the bowsprit for the forestay. Getting the main out of the picture and avoid the whole preventer problem, fixed the the problem.

Of course this does not help with sloop rigged CDs though. My recommendation, if you are a light wind fair weather sailor, go ahead and use your vang. If you do occationally go out in breezy conditions, make up a block and tackle with shackles on each end, when you need to run downwind, rig one side of that to your aft most bail (on center boom boats) or middle or foremost bail (on aft boom boats). Other end attach to a shackle on a chainplate, easy to rig on demand and places the loads in a reasonable place.

Do not ever attach to a stanchoin base, our CDs do have very beefy looking stanchion bases, with nice support loops on them. But the backing is not up to par, likely fender washers if you are lucky. Best case scenerio you break the bedding and create a new deck leak, worst case you rip the stanchion off.

My 2 cents anyway.

[river-rat]

The end of boom preventer attachment has worked well for me on windy downwind ocean passages. To make rigging it easier I attached a line under the boom from the end to a snap hook a little aft of the boom gooseneck.

Then another line is rigged along the rail from midship to the bow anchor fairlead and back to a cleat on the rail at the cockpit. When on a broad reach, remove the under boom line from the snap hook and tie it to the rail line and you have a line from the boom end to the bow and back to the cockpit cleat. A block is not required at the bow. Just ease the mainsheet beyond desired amount and hand tighten at the cleat, finishing with some sheet trim to finish. If the lines are rigged in advance you don't have to go to the bow in rough weather.

The lines can be tied together when on a reach so there should be little danger of a gybe.

If a gybe to the other tack is expected a line to the bow needs to be rigged on both sides of the boat. If the boat starts to round up with a lot of heel the vang can be released to allow the boom to raise, depowering the rig and keeping the boom out of the water.

[Boyd]

I find that when running, the main blankets the jib and puts a lot of helm into the situation. I typically drop the main and sail with just the jib. She runs like on rails barely requiring helm.

Two caveats, I never run dead down wind prefering to gibe if required.

I usually give up on the main if the wind is much astern of the beam. This is a function of wind speed. Light wind is worse as the jib collapses periodically. As the wind moves behind the beam, the main adds so much helm that I have about the same speed with it down as up.

That said if the wind is up beyond 25 then I am probably using the working jib and a reefed main. Under these conditions the main doesnt blanket the jib as bad which gives me more latitude on keeping the main up. However it still reaches a point where having the main up is more trouble than its worth.

The downside is its almost impossible to gibe in light winds without the main up or resorting to using the engine. In close quarters or short legs, I just have to endure keeping the main up.

Hence the issue of a preventer doesnt come up.

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

[Bruce Bett]

Sorry about the somewhat curt nature of my earlier post. Since replacing my bent boom I have taken to rigging my preventer as follows. I run a short line from the bail at the stern end of my boom to the to the snap shackle on the boom end of my vang. When the vang is clipped to the bail on the boom then the line just hangs there. When I deploy the preventer I unfasten the vang from the bail, leaving it clipped to the line. I then carry the vang froward and attach it usually to a bow cleat. This is almost as easy as using the vang as a preventer and, since the attachment is at the end of the boom, it is less likely to result in damage to the rig.

Bruce

[Duncan]

With enough torque acting to bend a boom, now I am worrying about using a preventer at all. Let's say the preventer is so strongly attached that the boom is not going to bend - what is going to bend/break? A shroud or stay? A deck fitting?

Could it be better to have a sacrificial piece somewhere, so that the preventer would let go before damaging something else?

I've always considered a preventer as a way to safeguard crew, i.e. to prevent nuisance gybes. Now I am thinking about what happens when the boom rolls in the water, and twists things around.

[Al Levesque]

Consider that the preventer will act on the boom much the same as the main sheet and should not cause any more damage than the sheet would. On the other hand, if the main is suddenly backwinded and is allowed to swing to the opposite side, the momentum acquired during the swing will be far more dangerous than not swinging.

[Klem]

The question about what is going to break is a good one. I have broken two preventers, once a line (1" 3 strand on a larger boat) and once a fitting (3/4" steel bolt again on a larger vessel) both in really rolly conditions offshore. What is going to break really depends on the relative strength of what you are using. One thing to consider is that if the conditions are bad enough to break your preventer, an accidental gybe will be even more likely to break something so either you need a stronger preventer or you should be doing something different. I use a line with a little stretch to it for preventers to absorb the shock and then put a good amount of preload on it. This is effective in keeping the boom from swinging around and provides some give for that really bad roll.

Back to the discussion on where to attach the preventer, something that makes a huge difference is how the sail is attached to the boom. If you have a loose-footed sail, all of the loading on the boom occurs at the very end and that is where your preventer should be attached (this is also where your sheet bail should be). However, if you have a full footed sail that distributes the load over the boom, attaching to the end of the boom can be just as bad as using the vang attachment depending on how the boom is constructed. For this reason, I suggested the boom bail above because everything is designed for it to carry the load. The issue with end of boom attachment is that although you have a greater mechanical advantage and this is better for your preventer gear, it puts a much larger bending moment on the boom than mid boom. From an engineering standpoint, bending stress will be greatly reduced if you distribute the load on either side of the attachment point. Regardless of where the boom bail is, it is critical that it does not create a stress concentration that will cause a failure. Since the designer has already done the work for you, I would suggest using the boom bail unless you have switched to a loose-footed sail and retained mid boom sheeting which is not a good idea to start with. There are a few boats out there that have sheeting extremely far forward on the boom due to space constraints for the traveler and it may be better to attach to the end of the boom on these but the boom should be designed for you to attach to the bail anyways.