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Old 07-10-2003, 11:05   #1
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Preventers

Hi all,

Years ago,I sailed with a friend who hated preventers and would not allow them to be used on his boat.The reason for his dislike was the way he had learned to rig them.He would take a line from the outer end of the boom up on to the foredeck where he would lash it to a cleat.Any subsequent adjustment meant that someone had to go forward and release the line.IMO,it's a good idea to fit an eye in the center of the boom.The preventer is taken from this eye through a block on the toe rail at the shrouds, and then back to the spinnaker winch in the cockpit. This way, the preventer can easily be adjusted without anyone having to go forward. Do you use a preventer when sailing downwind,and if so,how do you rig it? Do you use a method similar to the one I use,or have you found another method that works better for you?
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Old 07-10-2003, 14:29   #2
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Preventer ? Is that the same as a Vang?

Enlighten me , Please. And why would ANYONE not want to keep their boom level, if it is the same as a vang. I have used a vang in racing, and the thought of being without one is a total feeling of bewilderment. A skyward pointing boom is , to me , so un-seamanlike , I cringe. If I have gone down the wrong road ( seaway) here, swat me up-side the head- no, not the bathtroom-the part that supposed to think, and I will humbly apologize.
First Law of Appearance, a skyward pointing boom is an obscene gesture !!!
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Old 07-10-2003, 17:36   #3
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Hi Cascade and all,

One of my favorite teachers in school had two sayings that I really liked. He would say," the only bad question,is the one that isn't asked", and "What school does,is teach you how to learn." Well, he must've been talking about me,because I'm still learning,or at least trying to A preventer is different than a vang in the aspect that it's used more as a "safety" device than for sail contol. When sailing downwind, a preventer is sometimes used if there is a danger that the wind might catch the front of the main and cause a "flying" or uncontrolled jibe. A vang can be used as a "preventer",but there are some potential problems.The mast attachment of a tackle type of boomvang can be moved farther outboard,toward the toerail.In heavy seas however,care must be taken that the boom,which is held down by the vang,doesn't slip into the water as the boat rolls.Too much tension on the vang may result in over-flattening the main sail.To maintain sail shape,the topping lift and vang can be adjusted in unison.While a vang attached to a toerail will partially prevent the main from filling on its leeward side and jibing accidentally,it may also cause damage to the rigging if you do jibe uncontrollably. A separate "preventer" line can be rigged from the clew of the main, or an eye attachment at the end of the boom, to a block by the shroud toerail, and then lead aft to a spinnaker winch in the cockpit from where it can be easily adjusted. Now, don't you wish you hadn't asked?

As a footnote to the use of vangs Cascade, I'm not sure how you are using yours,but I always remember a short sailors memory aid to help me with basic mainsail adjustment. You adjust in listed order.

Our - Outhaul
Boats - Backstay
Can - Cunningham
Sail - Mainsheet
The-Topping lift (if necessary)
Virgins-Vang

Forgive me if I'm telling you things you already know

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Old 09-10-2003, 06:31   #4
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First of all preventers should never be rigged to the center of a boom. Few booms are designed with very much transverse bending capacity so that dipping a boom pretty much guarantees bending the boom or damaging the gooseneck. Preventers should be rigged with comparatively small diameter nylon line so that the stretch of the nylon can absorb the impact of a boom end hitting the water. They should be rigged from the aft end of the boom to an attachment point near the bow. They should not be rigged to the clew of the sail itself as that would distort the shape of the sail. They should be rigged so that they can be quickly eased from the cockpit in the case of a deathroll or knockdown.

Preventers should not be installed to work like a vang. Boom vangs control leech tension. Preventers are strictly a safety device and should be rigged so that the pull is as close to horizontal as possible so as to not affect the leech tension. It is a good idea to rig a preventer at deep reach angle to dead downwind when in wave or changable wind conditions.

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Old 09-10-2003, 07:51   #5
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Jeff,

Just for clarification,I wasn't suggesting that a vang be permanently used as preventer. I was trying to illustrate a comparison of using a vang (which the original poster referred to), to a separate dedicated preventer line. Thus the statement "A vang can be used as a "preventer", but there are some potential problems." Also, as far as attaching the line to the clew of the sail, I agree that it's not the best method,but it is a method if other means are unavailable. Perhaps my comments were to vague,but I was trying to explain the purpose of a preventer rather than the ideal installation. I'm curious as to why you feel it's necessary to run the preventer line from the end of the boom,all the way to an attachment point at the bow. It seems like a lot more hardware would be needed to provide a good angle for the line back to the cockpit? In my orignal post here,I mentioned installing an eye at the center of the boom for a prevernter attachment. I always thought that the forces exerted at that point would be no more than what is exerted on it when the mainsheet is attached there.Is that not true? On my boat,there was already an attachment eye at the end of the boom.I use a line with a shackle on it that I attach to it with.Then I run the line to a snatch block close to the shroud toerail, and then back to a cockpit winch. This layout gives me a good angle back to the winch,and does so with a minimum amount of hardware. Also, I can rig the preventer very quickly. This setup has always worked good for me on my boat.Please explain your reasoning.Thanks!

Stede
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Old 29-11-2004, 09:29   #6
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Boom Brakes?

Resurrecting an old thread....

Anyone have experience with boombrakes like the one from HotWire? ServoBrake
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Old 01-12-2004, 09:45   #7
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Combining the two isn't unheard of...

Hi, Stede - hope you and your wife had a pleasant Thanksgiving, and that you got a bit of sailing in, too.

I bow to Jeff's trimming prowess but, in the grubby world of small crews and practical arrangements, I don't think it's a terrible thing to use a combination vang/preventer. In fact, I think you'll find this recommended in ANNAPOLIS BOOK OF SEAMANSHIP 3RD ED by John Rousmaniere, a person who isn't too unconcerned about sail trim.

Given your preferences in a boat and your plans to sail singlehanded or short-handed and offshore, I think you'll have to juggle three somewhat related but mutually exclusive systems: vang, preventer and boom brake. The last two don't exactly perform the same function because you may want to prevent the boom from jibing if you momentarily lose directional control, rather than the jibe being allowed but controlled.

I've not been happy with what we've been doing on WHOOSH, and it's complicated by the fact I don't have secondary cockpit winches. Consequently, I'd welcome Jeff and others commenting on what follows... I've been using a 4:1 tackle with a cam cleat and leading the vang/preventer to an adjustable fore/aft bail on the genoa track. The lead is both down but also forward somewhat, with the boom connection point being perhaps 2/3 of the distance from the gooseneck on its own beefy bail. I have to go on deck to deal with the vang/preventor and would like to modify the arrangement to at least be able to allow its release from the cockpit. I'm sold on location of the boom attachment point (given the deck plan) and I like Jeff's suggestion of moving to nylon; I've been using dacron double braid. A longer length line plus defeating the cam cleat will solve the cockpit-release problem, as I added cockpit coaming horn cleats suitable for use with the vang/preventer. After the gybe, I would need to go on deck to move the vang/preventer to the other side.

As for the boom brake, I've looked at a number of products (including ServoBrake) but haven't opted to carry one for a combination of reasons: none are simple given the string involved, most require careful adjustment to be effective, all add cost to the kitty as the dollar continues to plummet, and there's already a fair amount of string being pulled as it is. So far, we've found the vang/preventer is keeping us out of trouble provided we use it...which is most of the time we're sailing. And WRT Servo-Brake, be sure to price out the whole system, as installed. It's low initial price is misleading given the blocks and line you'll need.

Jack
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Old 01-12-2004, 15:36   #8
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Post vangs and preventers

IMHO not sure there is a perfect answer here.

On my Moody 47 I have a rigid vang that controlls boom height when running and a seperate 4:1 block and tackle that I use as a preventer rigged about 1/2 way back on the boom which I lead to the toerail as a preventer. I tend not to lock it down hard but keep it tight enough that momentum can not build up for a jibe.

Technically a preventer rigged from the back of the boom to the front of the boat is the best way as it stops the boom from jibing but still allows it to rise if you dip the boom. You can rig this several ways however one of the most unique I have seen was a line led through the boom and then aft to a rope clutch for the tail and a block out the bottom of the boom with a snap shackle that you could lead forward. This way you clip it forward and all adjustments are from the cockpit except when you want to jibe.


I am not personnaly enthralled with the boom brakes, just do not like the way the rig up.

my 2 cents on this topic.
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Old 02-12-2004, 12:29   #9
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Rigging a block and tackle from the deck to the mid boom as a preventer is generally considered not to be a great idea offshore. If the boom dips into the water, it is very likely to do damage. This can be mitigated with some kind of rubber strop that could work as a shock absorber.

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Old 02-12-2004, 21:49   #10
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Boy, you guys are fancy! We usually need a preventer only on lite wind downwind runs when the winds are fickle. Then we just send the nephew topsides with a line & tell him to hold on & don't let the boom slam back. BTW he is 6'4" & 280lbs. Interesting thoughts though, I think a more effective one could be rigged thru one of the forward eyepads back to an un-used pulley on the traveler set-up, & into the cockpit . Hmmm Will have to let the nephew know he's been replaced.
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Old 03-12-2004, 02:45   #11
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Just echoing Jeff H's comments.
The originall post refered to "NOT wanting to go forward" and one would asume from that comment that the weather and sea condition was not good. So in that situation, a preventer needs to be fitted to the end of the Boom. If attached part way down the Boom and if the Boom should take a plunge, then some seriouse damage may occur.
To answer Stede's comment about the stress on the Boom from mainsheet. The stress applied to the Boom via the sail is along the entire foot of the sail and thus the length of the Boom. The attachment point of the mainsheet system on a large Boom, is usually multiple point attachment. Often two and even three points. The bending force is in a verticle plain and large Booms are often shaped so as they can take a greater load in the verticle. But the force applied to the Boom when it gets dunked is usually horizontal. Plus the shape of the sail at that moment can also be trying to bend the Boom horizontally. So the Boom can be damaged. Plus if the attachment point is part way down the Boom, the goose neck will also recieve the respective force on the otherside of the fulcrum point. So it takes a loading that it was never desind to take.
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Old 03-12-2004, 13:36   #12
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Here's a useful summary on the choices...

For those following this thread, you might find it interesting/helpful to read John Rousmaniere's Sailnet article on vang/preventers and 'offshore' preventers. You can find it at:
http://www.sailnet.com/collections/s...r%20Seamanship

Before crossing the Atlantic in 2003, I installed 2 thur-bolted bails on the end of our main boom, the intent being to use them with an offshore preventer. The nylon line I planned to use is still coiled up in the port sail locker. Perhaps when we begin to see a possibility of rolling the boom into a heavy sea, I'd rig the forward preventer in lieu of the vang/preventer I've been using...but the latter is much easier to live with. OTOH the changes I mentioned above to keep me off the deck when needing to gybe are painfully apparent.

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Old 08-12-2004, 21:31   #13
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The latter may seem easier, but will do more harm than good. . The set up at the aft end of the boom is the only way to go. Less stress, less hassel, & easier to control in variable winds. The vang is not really set up to take the stress of sudden wind-shifts.....Do you wan't to borrow my nephew! He makes a great Boom-Butt!
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Old 09-12-2004, 11:18   #14
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If I were designing a preventer set up I would use a single nylon line on either side of the boat, with each led from the end of the boom to a turning block on the foredeck and back to a cleat on the cabin top at the cockpit. I would rig retractor lines on shock chord at the base of the mast to store the preventers parrellel to the boom when not in use. Jibing the working preventer would be easy to release prior to the jibe and the making them up preventer on the new jibe would be easy from the cockpit. You should not need any more than a 1:1 purchase set up hand tight, but you will need a winch to ease the line should you get backed. The long length of the nylong line acts as a shock absorber.

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Old 09-12-2004, 13:53   #15
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I guess I'm in the school of thought that you only use them offshore.

The mainsheet boom bale(?) Loop thing, attaches near the end of the boom on our boat. So, I just tied an old halyard with a boline to the boom bale, ran it forward to a block on the toe rail and back to a spare winch. When we jybed, I'd pull it out of the block and run it to the other side. If we were going to jybe more than 2 times a day, I ran two of 'em. (Pereformance setup)

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