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Old 17-12-2009, 06:43   #1
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Boom Preventer

I have searched the site and am not able to find information on a Boom Preventor.

I am looking for information and better an illustration (easier for me to understand) on how to set one up on my boat, 33 foot. I would like to control it from the cockpit with the boom on either side of the boat.

I have seen preventors set up as needed, but are cumbersome to change from one side to the other.
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Old 17-12-2009, 07:30   #2
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I'd suggest running a line from a strong point on the boom (perhaps about 1 foot from the end, depending on your boat) to a block secured sufficiently far forward and outboard on the side deck, with the end led back to the cockpit. Same on other side. You can slack one and bring up the other when you jibe.
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Old 17-12-2009, 08:14   #3
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I suggest you look at getting a dutchman boom brake. It works with the boom in any position and is easily controlled from the cockpit with a single line.
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Old 17-12-2009, 08:16   #4
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I asked the same question before, and here is what I was told and have now used in practise.
If your mainsheet attaches to the end of the boom, then attach your preventer lines here. If you have midboom sheeting, then you are better to attach your preventer lines closer to midboom, otherwise you increase the risk of bending or even breaking the boom. Think sheet pulling on the middle of the boom in one direction and preventer pulling on the boom from the end in the opposite direction. Then factor in the added forces applied by high winds and in the event of the boat rolling or broaching, the boom end entering the water. Problem???
As Sneuman says, attach the turning block well forward of the shrouds. I use my bow cleats, but if you have holes in your toe rail, some people attach a snatch block to this. Then run the line back to the cockpit for total control of the preventer. I suggest setting up and getting used to the preventers in fairly light winds, just so you are sure they are set up right for your boat.

Good luck,
Tom
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Old 17-12-2009, 10:30   #5
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With the blocks attached to the toe rails, one on each side, you leave one slack when not in use?

Are the toe rails strong enough to support the stress?

Do the lines get tangle up when not in use?
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Old 17-12-2009, 10:37   #6
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Quote:
Originally Posted by landonshaw View Post
With the blocks attached to the toe rails, one on each side, you leave one slack when not in use?

Are the toe rails strong enough to support the stress?

Do the lines get tangle up when not in use?
The toe rail would work, and certainly should be able to handle the stress, but it wouldn't have to be on the toe rail.

Yeah, it's two more lines to get fouled, for sure, but I'd simply take the preventors off and stow them when not in use. You're only going to need them for the small percentage of the time you're running dead -- or nearly dead -- downwind, which shouldn't be your preferred point of sail anyway.
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Old 17-12-2009, 11:03   #7
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Would it be reasonable to use your boom vang out at the end of the boom (close to mainsheet) run to a more forward point to hold it down and out? I used to use mine when I would go wing on wing shackled to the middle cleat. I only used it in light airs but it seemed like it would be strong enough to keep the boom over in heavier winds. Any reason not to do that? It was very easy to just unclip the snap shackle on the boom then jibe and hook it back up on the other side.

Jim
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Old 17-12-2009, 11:45   #8
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The way I rigged a preventer in my last boat was from somewhere around mid boom down to the toe rail. Not far foward but about to the shrouds came as I recall. That not only acted as a preventer but the downward angle of the pull also significantly flattened the main, allowing me to ease the sheet a little further and present a larger surface area to the wind and a little more speed. Seems like running the preventer way forward would not add this benefit or would the combined vector of the sheet and preventer still result in significant down force?

Now I sort of rigged this myself, without any expert help so not sure if this is the proper way to do it or if it introduces any risks or problems. Any comments or advise on this technique would be appreciated.
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Old 17-12-2009, 12:34   #9
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not for big boats

Quote:
Originally Posted by jkleins View Post
Would it be reasonable to use your boom vang out at the end of the boom (close to mainsheet) run to a more forward point to hold it down and out? I used to use mine when I would go wing on wing shackled to the middle cleat. I only used it in light airs but it seemed like it would be strong enough to keep the boom over in heavier winds. Any reason not to do that? It was very easy to just unclip the snap shackle on the boom then jibe and hook it back up on the other side.
Jim, that's an okay option for small boats, but not for big boats because you'll have no way to control the boom during a gybe.

Your point about only using the preventer in light airs is well taken, and I would venture further to say that skilled sailors would never need to use a preventer other than in light airs. But should the wind come up while you're using the vang as a preventer you would find yourself in trouble because when you return the vang to its proper position in preparation for a gybe you're going to sky the boom.

Better, and actually simpler, just to rig a proper preventer.
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Old 17-12-2009, 13:27   #10
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G'Day All,

On our last three boats (30,36 and 46 ft LOA) I have rigged permanent tackles that I call "vang/preventers". In all three cases they have consisted of a three part tackle that leads from a point near mid-boom to a strong point on the deck near the shroud chainplates, with the fall lead to the cockpit and usually to a secondary winch.
On the first two boats which were masthead rigs with fairly short booms, the attachment point was the previous boomvang attachment. On I-two, a fractional rig with a 6 metre boom, the attachment is a strop made of two inch webbing, located about 1/3 of the way out from the mast. These are left permanently rigged.

In practice, when sailing off the wind at all we tension the leeward tackle. This acts as a powerful vang, operating with a much better angle than a conventional setup thus generating far less compression loading on the gooseneck as well as acting as a preventer. When we gybe, we use the tackle to ease the boom across under control -- this works well, even under fairly harsh conditions.

We feel that by having the preventers always rigged, we always use them, and thus gain a considerable margin of safety. The spectre of breaking the boom does loom, but in all our years and miles, we have yet to dig the boom into the sea. One time, when I-two was new to us, we got caught aback in a violent windshift in a thunderstorm, just as I was attempting to tuck in a quick reef. To my horror, the boom bent like a bow, and I feared for it, but in the end not much happened. We were left with a barely perceptable curve in the boom, but with a loose-footed mainsail we've just left it as is for the subsequent 7 years.

The tackles are yet another bit of string that encumbers ones progress forwards, but we feel that this is a small price to pay for the security against accidental gybes. When cruising, we find many of our routes lead to sailing wing and wing with a poled-out genoa and nearly DDW. With either a windvane or an autopilot steering, one does get gybed now and then, but with the preventer set, nothing significant happens! The main fills on the "wrong" side briefly, the pilot corrects its course, and soon it simply refills on the correct side and you continue on course... no worries, mate! INcidentally, on I-two the mains'l is about 60 square metres in area, so the loads are substantial.

Cheers,

Jim and Ann s/v Insatiable II lying Burnett River, Queensland, Oz
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Old 17-12-2009, 14:34   #11
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A nylon line from the boom, far out, towards the bow.

Inshore the gadget from Ronstan.

b.
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Old 17-12-2009, 14:48   #12
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Jim,

Sounds like you and I have nearly identical set ups with similar results.

I have boom end sheeting but have a bail about 2/3's out the boom where I attach a couple of handy billies, one lead to each side. I have a gallows on the aft end of the coach roof, at the forward end of the cockpit and the bail is just forward of that. I have no other vang.

I find that this arrangement suits my needs. I sail solo and I don't want the boom flopping around where it wants to go. It does take some attention to detail and remembering to fiddle with them before gybing and also to balance the loads between the sheet and the vangs.

But it provides such a sense of security when running dead downwind. No nagging fear of a gybe.
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Old 17-12-2009, 14:51   #13
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Off-shore, off the wind, I use a boom brake and a preventer. The preventer lines are permanently attached to the end of the boom , led forward to a cleat on the boom. When in use, the line is removed from the cleat run to a block forward on the deck and then aft. There is no need to rig the other line as it will only get in the way. My mainsail is about 850 sqft so the "belt and suspenders" approach is justified.
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Old 18-12-2009, 11:32   #14
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The key is to look at what needs you are trying to meet. We sail short-handed, sometimes in a lumpy sea, sometimes with directionally unstable wind (IOW offshore) and so keeping control of the main - and protecting the crew when s/he is doing something on deck - can be very important. That's why we ended up using the same approach as Jim, which we first saw being used on Amels and proudly stole. The real beauty of what Jim describes is how much control it gives one of the main - not just being able to shape the sail but also safely jibing it in heavy air or a lumpy seaway.

The biggest disadvantage of this arrangement is that one can't really run the boom out as far as is typical (e.g. on a broad reach) as the lifelines will interfere with the run of the preventer's tackle. We think that's a small price to pay. I screwed a bail on the back side of the mast, a short distance below the gooseneck, and the two tackles are dead-ended there and lie just under the boom (with lines coiled and hung) when the boat's settled in some where for a while.

To repeat: "We feel that by having the preventers always rigged, we always use them, and thus gain a considerable margin of safety."

Jack
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Old 18-12-2009, 12:55   #15
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I googled 'bill seifert preventer' since I know it's in his book. Google came back with:
Offshore Sailing: 200 Essential ... - Google Books

which has the relevant part of the book (I'm not sure how it's legal for Google to do it this way).
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