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Old 13-11-2019, 13:49   #1
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pre-rigged boom preventer

I was listening to a sailing seminar on the 49 north podcast and they were talking about rigging a boom preventer by permanently running a line from the end of the boom, about the booms length and then connecting it using soft shackles to lines run through blocks rigged forward on either side of the boat and run back to aft cleats. This keeps you from having to reach the end of the boom to tie on a preventer each time you need to use it. Has anyone rigged this? What do you do with the line on the boom end when your not using it? Anybody got pictures?
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Old 13-11-2019, 15:00   #2
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Re: pre-rigged boom preventer

This is a pretty standard way of doing things, so lots of people have things rigged this way.

Best attachment to the end of the boom is with a loop or a strap around the boom, with no hardware to fail.

The line from the end of the boom can just run to the mast and be attached there however works for you, and left hanging just below the boom. Since the line will have a loop in the end, figuring out a tie-off method best suited to your boat should not be challenging.

Any preventer can be subject to very large loads if (when!) the sail is backwinded in a strong wind. All the parts of this system need to be really strong, especially the turning blocks at the bow, they will carry almost 2x the load of the line, and that can come as a powerful "jerk" not a smooth load.
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Old 13-11-2019, 18:19   #3
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Re: pre-rigged boom preventer

Had a J/35 with a preventer rigged spin out next to us in a race last month. Their spinnaker started gyrating in the fairly large waves going dead downwind in a 20-knot breeze. This ended up swinging the boat enough that the main went aback. The preventer kept the boom from decapitating anyone, but the boat ended up broaching, pinned down by the main that was being held, now to windward, and the spinnaker, still flogging and pulling to leeward. They eventually got it sorted out and finished the race. What I learned? : Don’t think that a simply having a preventer rigged is going to solve all the issues that might come up going downwind. Be careful!
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Old 14-11-2019, 20:26   #4
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Re: pre-rigged boom preventer

I have not seen this rig and I'd be curious to see photos also. I am a bit skeptical. One thing that psk reminded me of is to be sure it's easy to pop that preventer free after the gybe and to be able to pay it out quickly in a controlled way, as in a couple turns around a winch. When you say the line is led back to a cleat, which of course it is, but that's the part I'd really like to scrutinize.
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Old 14-11-2019, 21:53   #5
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Re: pre-rigged boom preventer

This is similar to what MOrgan's Cloud / ACC recommends. It is well proven.


The calculations I have seen recommend that the preventer be about the same working load as the genoa sheet gear, and the bow turning block double that. And it must be releasable via a winch, since someday you will be backed anyway.
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Old 14-11-2019, 22:04   #6
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Re: pre-rigged boom preventer

Any concerns/stories about breaking the boom with this set up? I was trying different things last year and in big sea state with light wind, there's a lot of dynamic forces on the boom so it can't be stretchy rope and it has to be taut. Agree with attaching the line to a strap around the boom rather than a hard attachment. One of the padeyes broke right off in a bouncy sea.
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Old 14-11-2019, 22:24   #7
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Re: pre-rigged boom preventer

I have a line with eye splices in each end, twice the length of the boom (less a few inches) tied in the middle to the boom end preventer fitting (where it says "preventer only"). The two ends are held near the mast by a few inches of elastic cord ending in little clips. My preventer lines (one red one green) are kept behind the sprayhood through their clutches. To rig, I take one from in front of the sprayhood, straight to the bow where there's a bullseye strop on the bow cleat, then pull it back outside the shrouds and tie it with a bowline to the preventer line at the mast. Unclip the preventer elastic and haul in. If I'm likely to be gybing I'll run both preventers in one trip.

I figured a low friction ring would be fine at the bow as I don't haul it in under load (it can be tensioned with the mainsheet). Both preventers can be on the cabin top winches to release for gybing.
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Old 15-11-2019, 02:49   #8
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Re: pre-rigged boom preventer

I've added photos of pages from Bill Seifert's book "Essential Passage Making Tips" to my photo album about jacklines, tethers etc. He recommends the system that the OP describes above and the diagrams are pretty good at explaining how to do it.

We intend to install this system (which can be disassembled and stored on the boom when not in use) but for the moment have continuous lines on each side of the boat running from the aft end of the boom, forward to very large fairleads on the bow and then back to cleats on the aft end of the boat. The latter are easy to reach so that the preventer can be released easily and quickly from the cockpit in the event of a broach. A line could also be attached and run to a winch to release the load on the cleat if necessary. We have used the system extensively but fortunately have not experienced any broaches.

Preventers at the aft end of the boom seem to be less frequently associated with broken booms than those attached to the middle of the boom, which we previously used.
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Old 15-11-2019, 06:12   #9
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Re: pre-rigged boom preventer

for the OP - yea, as others have said this is a pretty common and reasonable preventer set-up.

The case history of specific failures suggest a few things:

1. On the 'cleated' end back in the cockpit - yea, you do want to be able to release it under load, which can sometimes be difficult if it is actually 'cleated'. And even thru a clutch or jammer it can often be difficult to pop (and then is not under control) if it is under high load. So, if all you have is a cleat - then you should consider a 'tugboat hitch' (rather than a normal cleating pattern) which is specifically designed to allow controlled release under load (note this is also called a Lighterman’s hitch). The internet instructions will usually show it tied around a bollard - but it can be done around a winch drum or cleat. We always had an unused winch on the preventer side, and used that, but some boats dont have enough winches.

2. Where the preventer line attached to the boom connects to the line run up to the bow and back . . . you want splices rather than knots. Knots weaken the system and there is an actual real history of knots there breaking and people being killed .

3. Where the line turns almost 180 degrees (on the toerail forward) the loads are multiplied and that needs to be the strongest part of the whole system. Properly sized low friction rings and large dyneema strops are good, but the hardware they attach to the boat needs to be equally good. Whimpy padeyes have an actual real history of breaking (And yes people being killed). So, find a good really solid attachment point.

I have actually not seen the boom end break, but I'm sure it does/has in some cases. We always had an aluminum tang welded right thru the boom, with the tang sticking out both sides with attachment holes drilled. This is quite easy for a decent rigger/welder to do and very strong - you have to rip the boom apart for it to break. Otherwise, yea, a dyneema strop is easy to DIY and can also be very strong - you just need to make sure it is secured so it can not slide (foreward) under load (which is usually not too hard to do).

The stretch vs non-stretch question . . . . for offshore passage making you want non-stretch. If it stretches, it will move everytime you go over a wave, which is not great in light air because it unsettles the sail, and also creates fatigue (often concentrated in the gooseneck. For coastal and near-shore sailing it is less clear - you are not typically running in as large swell (in light air) and not running as many wave cycles (fatigue) so the arguments for no stretch are weaker, and some stretch does give you shock absorption which lowers the peak loads . . . .so probably either is fine for coastal but it could be argued that some stretch/elasticity is probably desired (but not a hige amount) and I p[ersonally would say use some polyester for optimal amount.
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Old 15-11-2019, 06:30   #10
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Re: pre-rigged boom preventer

Look from 6:10





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