vang and preventer - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance
 Not a Member? 
  #1  
Old 02-03-2008
Member
 
Join Date: Jan 2003
Posts: 74
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
scosch is on a distinguished road
vang and preventer

Basic question from a learner.
Is there any reason that I cant use one block and tackle to serve as both a vang and preventer and just move the bottom block from the mast to the rail when needed? (I have mid boom sheeting)
The preventer would need more line which is messy but I dont lead them back to cockpit.
Similar enough ratios?
Why not?
Reply With Quote Share with Facebook
  #2  
Old 02-04-2008
Senior Member
 
Join Date: Jun 2005
Location: New Orleans
Posts: 1,860
Thanks: 6
Thanked 23 Times in 21 Posts
Rep Power: 10
nolatom will become famous soon enough
Theoretically you could, but the two things serve different purposes, though they sometimes share them a little.

A vang by definition is rigged on the same pivot point as the boom/gooseneck, so as to keep a steady tension on the leech no matter whether you trim or ease the mainsheet.

A preventer, rigged to the rail, is there primarily to prevent a jibe if you bear off too far past the lee. When trimmed in close, it also tensions the leech. But to keep the same leech tension, you'd have to readjust it every time you ease or trim the mainsheet.

So if you want consistent leech tension (and boom height) and also something to help prevent an accidental jibe, then you need two separate block and tackle systems. Also, you may want the vang tension during a jibe, which is something you can't do with just a preventer, which has to be let go and shifted to the new lee side during and after the jibe.

Even with mid-boom sheeting (and traveler?), which sort of acts like a vang farther out than boom-end sheeting does, you'd still need a vang *and* a preventer if you really want the advantages of both.

Last edited by nolatom; 02-04-2008 at 12:05 AM.
Reply With Quote Share with Facebook
  #3  
Old 02-04-2008
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,277
Thanks: 5
Thanked 25 Times in 17 Posts
Rep Power: 10
billyruffn will become famous soon enough
To add to the good comments in Nolatom's post above, your vang is probably attached to the boom forward of the midpoint. Although some boats will use preventers that are attached at or near the mid point of the boom, doing so increases the risk of breaking the boom. Ideally, a preventer should run from the end of the boom forward to the bow. Booms can break while broad reaching / running downwind with preventers rigged when the boat takes an big roll and the end of the boom drags in the water. When the preventer is attached mid-boom the middle of the boom wants to stay put while force of the water pushes the end of the boom aft. Rigging the preventer to the end of the boom helps balance the force of the water.

I used a mid-boom preventer for years and took some mean jibes with it, including a really violent jibe one night when the Aries decided it didn't like the course we were on while we were screaming along in a 25 knot trade wind (scared the s--t out of me). Nothing broke, but it caused me to rethink the real purpose of the preventer and to re-rig with a more traditional system. My new end-of-boom-to-bow preventer uses more line and is a bit more work to set up and change over when we do jibe, but I think it works better. The end-of-boom set up allows me to get the preventer much tighter (less movement when we do jibe unintentionally).

The system I use now is rigged as follows:

A very stetchy braided line runs the full length of the boom. The end at the gooseneck has an eyesplice. When not in use I cleat this line off near the gooseneck and it lies nicely out of the way. I have two braided lines (one each port and starboard) that run from the cockpit to the bow (on deck), then through strong blocks attached to the bow cleats on either side, then under the lifelines and back on the outside of everything to the shrouds. When the preventer is not in use these the working ends of two lines are clipped to the shrouds. To set up the preventer I un-cleat the line attached to the boom and shackle it to the end of the line that runs to the bow. I have to go to the mast to do this, but don't have go to forward of the mast. I then take up any slack in the preventer from the cockpit. When we change tack, I sheet the main in hard, go forward and re-rig the preventer to the other side. I then jibe the main, trim the sail and then set up the new preventer.


The two weak points in this set up are the block at the bow and the snap shackle that connects the two pieces of line. I oversized both for safety. I would not recommend using just any piece of line for a preventer. Ideally, it should not only be strong, but fairly elastic as well so that the stretch in the line can absorb some of the shock transferred to the rig in an accidental jibe.

Last edited by billyruffn; 02-04-2008 at 01:04 AM.
Reply With Quote Share with Facebook
  #4  
Old 02-04-2008
Omatako's Avatar
Senior Member
 
Join Date: Sep 2003
Location: Auckland New Zealand
Posts: 2,393
Thanks: 0
Thanked 26 Times in 23 Posts
Rep Power: 11
Omatako will become famous soon enough
Quote:
Originally Posted by nolatom View Post
A vang by definition is rigged on the same pivot point as the boom/gooseneck, so as to keep a steady tension on the leech no matter whether you trim or ease the mainsheet.
Not really.

In my experience, the block system that goes from the boom to the base of the mast (a lot of modern boats use a block system in tandem with a sprung telescope or hydraulic rams) to control tension of the leech is called a kicker and is not the same thing as a vang.

A vang is a preventer and is connected between the boom and the rail when running off the wind. The kicker stops the boom from lifting when the main sheet is eased but the vang holds the boom to the side to "prevent" crash jibes.

Billyruffn, your system is very rare. I can't recall ever seeing one like that. How would one experience an "accidental jibe" with this system connected?

Andre

Last edited by Faster; 12-07-2011 at 09:46 AM. Reason: fixed quote
Reply With Quote Share with Facebook
  #5  
Old 02-04-2008
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
Andre-

The Boom Vang is usually a block and tackle that goes to the mast base and is used to control the mainsail shape. It is generally called a kicker if it is a solid vang, not just a block and tackle, and can support the boom in place of a topping lift.

Most boom vangs are not preventers, and are not connected to the rail. Most preventers don't help with sail shape all that much either, since they're mainly pulling forward on the boom, rather than down.

IMHO, a boom brake makes a lot more sense than does a preventer. In many situations, a preventer can become a serious problem and often can result in the boat being knocked down or pinned down, and then can only be released under a high load, which is fairly dangerous to do. A boom brake allows the boom to move, but at a fairly low speed, where it is not going to be a danger to people in the case of an accidental gybe.

Most modern boom brakes are also adjustable in tension for the wind conditions and are often controlled by a line lead aft to the cockpit.
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Share with Facebook
  #6  
Old 02-04-2008
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,277
Thanks: 5
Thanked 25 Times in 17 Posts
Rep Power: 10
billyruffn will become famous soon enough
Omatako wrote:

Billyruffn, your system is very rare. I can't recall ever seeing one like that. How would one experience an "accidental jibe" with this system connected?

------

I was using an incorrect term. I was referring to the mainsail going aback -- you're right, technically you don't jibe unless the boom comes across. I've never had a jibe with the preventer rigged, but frequently had the sails unexpectedly go aback. When the wind's up and the swells are big that's no fun either.
Reply With Quote Share with Facebook
  #7  
Old 02-04-2008
JohnRPollard's Avatar
Moderator
 
Join Date: Mar 2007
Location: Chesapeake
Posts: 5,680
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 10
JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough
Quote:
Originally Posted by scosch View Post
Basic question from a learner.
Is there any reason that I cant use one block and tackle to serve as both a vang and preventer and just move the bottom block from the mast to the rail when needed? (I have mid boom sheeting) The preventer would need more line which is messy but I dont lead them back to cockpit. Similar enough ratios? Why not?
Scosch, The short answer is "yes you can" use your vang as a preventer. This is not the ideal arrangement -- better to have a separate preventer that you can deploy when necessary -- but it is better than running without a preventer at all. Many many sailors do exactly as you describe.

Quote:
Originally Posted by Omatako View Post
In my experience, the block system that goes from the boom to the base of the mast (a lot of modern boats use a block system in tandem with a sprung telescope or hydraulic rams) to control tension of the leech is called a kicker and is not the same thing as a vang.Andre
Omatako, Not wishing to get into an etymological debate here, but I think this may be a question of regional differences in terminology and usage. In North America, the distinction between a vang and kicker is more-or-less as SailingDog describes in his post above. "Preventer" is a more general term used to describe any device that is deployed to prevent the boom from jibing unintentionally when sailing off the wind. They can resemble the same block and tackle system often employed for the vang or can be rigged in other ways such as Billyruffn described above.


Quote:
Originally Posted by billyruffn View Post
My new end-of-boom-to-bow preventer uses more line and is a bit more work to set up and change over when we do jibe, but I think it works better. The end-of-boom set up allows me to get the preventer much tighter (less movement when we do jibe unintentionally).
Billyruffn, Your end-of-boom preventer is more often seen on boats sailing off-shore or making longer coastal passages. It seems to be a preferred arrangement for many experienced off-shore sailors. Personally, I have never been comfortable with this approach.

One important consideration when rigging a preventer is that while it may succeed at preventing a sudden accidental jibe, it may not be able to prevent a jibe altogether. In certain heavy wind and sea-state conditions, the sail may become backwinded and overpower the vessel's ability to correct its course. With an end-of-boom-to-bow preventer, the crew is then left with two options: (1) allow the boat to continue spinning up into the wind before releasing the preventer line (which would probably entail a very dramatic broach); or (2) if sea-state or limits on navigation do not permit option (1), the preventer must be eased and the boom allowed to jibe across.

The problem with option (2) is that following this course of action will require easing the preventer line until it bears up hard against the shrouds, placing enormous lateral loads on them. And this will occur at about the same moment that the angle of the line from the bow to the boom-end will lose most of its purchase (i.e. mechanical advantage), so the preventer will no longer be able to overcome the tremendous leverage being exerted on the boom via the backwinded sail. At that point the only option will be to release the preventer entirely and let the boom jibe violently. In addition to risking damage to the boom or the leeward rigging with the jibe, there is risk that the windward rigging, probably the spreader, will be damaged if the preventer line is permitted to bear up against the shroud prior to release.

For these reasons, I prefer the mid-boom preventer that is secured to the reinforced portion of the boom where the vang attaches, and led outboard to the point of maximum beam just aft of the shrouds. To prevent shock-loading the boom, the preventer line can be stretchy and can be secured to the boom via a shockles or similar high-strength elastic material.

As SailingDog mentioned, the best all-around solution may be to rig a sturdy break that simply permits a slow controlled jibe rather than preventing it altogether.
Reply With Quote Share with Facebook
  #8  
Old 02-04-2008
Plumper's Avatar
Sailor
 
Join Date: Nov 2007
Location: Vancouver Island
Posts: 845
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
Plumper is on a distinguished road
I think that the term "kicker" comes from the British word kicking strap which is the same as a boom vang or "vang". The two do the same job. As for using a vang as a preventer, it is very common and sometimes termed a prevang.

The job of the preventer is to prevent accidental boom jibes but expecting it to work in high winds or extreme conditions is looking for trouble. I believe that preventers are best when used when the boat is rolling and the boom may flop from one side to the other (especially in light airs). Expecting it to hold the boom in place in strong winds when the full force of the wind hits the back of the sail is unreasonable. Something is going to give. Hopefully the preventer will be the weak point, not the boom. In those high wind or extreme conditions the boom brake becomes the device of choice because it allows the boom to cross the centreline but dissipates the powerful boom breaking, sail ripping, gooseneck snapping forces. When sailing off the wind in extreme conditions, particular care should be taken to avoid jibing and in those conditions I would not use a prevang. In lighter airs where the boom will not stay in place because of rolling a prevang is perfect.

Gaz
__________________
There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
Shakespeare, Julius Caesar IV, iii, 217
Reply With Quote Share with Facebook
  #9  
Old 02-04-2008
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,277
Thanks: 5
Thanked 25 Times in 17 Posts
Rep Power: 10
billyruffn will become famous soon enough
JohnRPollard wrote:

In certain heavy wind and sea-state conditions, the sail may become backwinded and overpower the vessel's ability to correct its course.
----------------
John,

I think the reason offshore sailors use the end boom preventer is that they are often more at risk of jibing because normally don't have someone at the wheel / tiller at all times (relying instead on autopilots or self-steering wind vanes) and, more to the point, they are frequently dealing with larger seas which can increase the tendency for the boat to roll heavily when sailing down wind, thus increasing the risk of sticking the end of the boom in the water.

Coastal sailors don't have to deal with these circumstances quite so often and mid-boom preventers or boom brakes may be the preferable option. As I indicated in an earlier post, I used a mid-boom preventer for several years and it does make it much easier to release the preventer in a controlled manner when the mainsail goes aback.

Fortunately, I haven't yet experience the situation you describe -- with the sail aback, preventer holding the boom from jibing and the rudder unable to bring the boat back down wind -- but I can imagine it happening. As you suggest, the recovery would be challenging, but so far I've found that the combination of easing the preventer while recovering the slack in the mainsheet and helm action can usually get things back to where you want them. I think there's also a lot to be said for keeping the sail area appropriate to the conditions at hand and having a human being driving the boat (or at least sitting at the helm prepared to react) when the wind and sea state get up. After all, an attentive helmsman is probably the best "preventer" there is.
Reply With Quote Share with Facebook
  #10  
Old 02-04-2008
Member
 
Join Date: Jan 2003
Posts: 74
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
scosch is on a distinguished road
wow, thanks

thanks for your replies, kind of a can of worms, like a lot of topics between sailors. I was glad to learn it all but I was particularily glad to hear one reply that suggested that what I wanted to do was reasonable if not perfect.
Im trying to sneak up on all the equipment I need to avoid making mistakes, and moving the vang to the rail when necessary seemed a good start. thanks again.
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Boom Preventer or Not? cditzen Seamanship & Navigation 18 10-10-2011 06:34 PM
Deadly Serious about Booms John Rousmaniere Seamanship Articles 0 10-12-2004 08:00 PM
Boom Vang z1nonlyone Gear & Maintenance 5 08-21-2003 08:51 AM
Boom Vangs SailNet Racing Articles 0 10-04-2000 08:00 PM
Control the Wicked Boom John Rousmaniere Gear and Maintenance Articles 0 05-06-1999 08:00 PM


All times are GMT -4. The time now is 02:21 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.