# Boom Vang and Preventers (renamed)



## datswite (Sep 28, 2010)

We're wrapping up our refit and will be leaving for a long-term cruise starting this summer. We're heading first to the Caribbean... from there? Who knows?

Anyway, our boat does not have a boom vang. It's setup for mid-boom sheeting. Trying to decide if our precious pennies would better saved than retrofitting a boom vang.

Any thoughts?

Don't Pay the Ransom - Bucking the system one sunset at a time!


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## Faster (Sep 13, 2005)

You definitely want a boom vang. Mid boom sheeting does not 'help' with leech tension when you're broad reaching and running (you'll be doing plenty of reaching in strong breezes and occasionally big seas) A good vang helps to control gybes as well, I'll sound like a broken record but I consider a vang an essential piece of safety gear, even in a small boat.

You have a beefy boat with plenty of power in the rig, as far as I'm concerned a good vang is as essential as a good winch. It need not be a rigid vang, if money is really an issue a simple (but strong) multipart tackle will do in combination with a topping lift, but a rigid vang is cleaner.


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## MikeOReilly (Apr 12, 2010)

I don't have a vang on our current boat, and I wish I did. That said, I get by without an installed vang. We have end-boom sheeting, a long heavy boom, and I use a tackle as a vang/semi-preventer when running off the wind. So yes, I'd prefer an installed vang, but so far we get by pretty well without it.


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## nolatom (Jun 29, 2005)

You can improvise with a preventer and your mainsheet at the lee end of the traveller sharing the load. Problem is, any trim or ease involves two trimming systems, a pain in the neck. And it will not assist in keeping the upper mainsail and leech "down" during a jibe, which is preferable.

So yes to vang. As one who grew up racing, it's a must-have. And it will give you better speed cruising too.

The only disadvantage I can see is if you ever get into an accidental jibe-knockdown, you want the boom end to be able to ride up so the main won't be "overtrimmed" by the ocean against the boom. But vangs are releasable, just make sure you can release it from the cockpit.


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## vega1860 (Dec 18, 2006)

MikeOReilly said:


> I don't have a vang on our current boat, and I wish I did. That said, I get by without an installed vang. We have end-boom sheeting, a long heavy boom, and I use a tackle as a vang/semi-preventer to when running off the wind. So yes, I'd prefer an installed vang, but so far we get by pretty well without it.


Same situation on a Vega with roller reefing main. You need to run a vang/preventer from the end of the boom sailing off the wind. It can be a little awkward, but you do need it.


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## eherlihy (Jan 2, 2007)

To put my answer in context; the boats that I teach on here in SW Florida all have vangs, outhauls, Cunninghams, adjustable split backstays, travelers and a bunch of other stuff. My boat in Rhode Island has a vang, an outhaul, and a traveler (no adjustable backstay, and no Cunningham).

To me, the vang is next in priority after the mainsheet, the outhaul, and the traveler in terms of sail shape, and therefore usefulness. If you plan to motor a lot, save your money for fuel, otherwise spend the $100-$200 on a vang (see here; Garhauer Marine Hardware -10239695), or the $300-$900 on a rigid vang (and ditch the topping lift) (see here; Garhauer Marine Hardware -10239696)


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## RobGallagher (Aug 22, 2001)

I like the "ditch the topping lift" for a solid vang idea. One less thing to go wrong up there, no worries chaffing the main leach, no worries if it breaks and the boom whacks someone.


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## SVAuspicious (Oct 31, 2006)

Faster said:


> A good vang helps to control gybes as well


Pardon? A vang, even moved to the rail or a shroud base is not an effective preventer. Look at the geometry and calculate the force vectors.



RobGallagher said:


> I like the "ditch the topping lift" for a solid vang idea. One less thing to go wrong up there, no worries chaffing the main leach, no worries if it breaks and the boom whacks someone.


Assuming a running topping lift, a solid vang means you can have a spare main halyard without modifying the masthead.


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## Faster (Sep 13, 2005)

SVAuspicious said:


> Pardon? A vang, even moved to the rail or a shroud base is not an effective preventer. Look at the geometry and calculate the force vectors.


Not talking about gybe prevention.. but management. A vang's limitation of boom lift during the gybe can prevent an accidental "goosewing gybe"


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## datswite (Sep 28, 2010)

Thanks for the comments... keep them coming! I'm leaning towards getting one, but, as you might imagine, there are far too many opportunities to spend money you don't have during a refit.

@MikeOReilly - Are you still happy with your Porta-Bote? I appreciated the discussions you've participated in regarding their use as tenders. Frankly, those discussions played a large role in helping us decide to get one. As luck would have it, after we decided that we wanted to get one, they agreed to sign on as partner to our voyage. We got a 10' a few weeks ago, and we're excited to try it out!


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## SVAuspicious (Oct 31, 2006)

Faster said:


> Not talking about gybe prevention.. but management. A vang's limitation of boom lift during the gybe can prevent an accidental "goosewing gybe"


Ah. Thank you. Excellent point. You still need a real preventer.


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## Faster (Sep 13, 2005)

SVAuspicious said:


> Ah. Thank you. Excellent point. You still need a real preventer.


Indeed...


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## eherlihy (Jan 2, 2007)

SVAuspicious said:


> Assuming a running topping lift, a solid vang means you can have a spare main halyard without modifying the masthead.


NIT: not necessarily; the topping lift on my boat is comprised of a SS wire from the top of the mast to about 10' off the cockpit soule. There is an eye on the end of the wire, and a block attached to that eye. There is a line that runs from the goose neck through a shiv at the end of the boom, then to the block, and back to the boom where it is fastened.

Tightening the topping lift, means a trip to the mast, where I pull on the line that runs through the boom.


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## RobGallagher (Aug 22, 2001)

If you have a topping lift and it's not going to be replaced on your refit, you could always wait on the solid vang. When you do get the solid vang you might find uses for that vang.

A vang with snap shackles on both ends can double as a preventer, MOB retrieval aid, back up mainsheet, lift an outboard, get the dinghy on deck, the list goes on. It's a good thing to have around as for purchase power when you don't want to run back and forth to a winch.

On my last sail of the season the shackle holding my mainsheet to the boom fell apart and bent beyond repair. I keep my old vang/preventer in the cockpit lazarette. A couple of snaps and it got my boom under control and allowed me to continue sailing while I reassembled my mainsheet.


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## SVAuspicious (Oct 31, 2006)

eherlihy said:


> NIT: not necessarily; the topping lift on my boat is comprised of a SS wire from the top of the mast to about 10' off the cockpit soule.


Which is why I cited running topping lifts. My point is that if there is a sheave at the masthead you should use it. If not, and you have a fixed vang, you probably still want something to hold the boom up when a seal fails or for some other reason the vang doesn't work.


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## Omatako (Sep 14, 2003)

SVAuspicious said:


> Pardon? A vang, even moved to the rail or a shroud base is not an effective preventer. Look at the geometry and calculate the force vectors.


So I guess you're talking about taking nthe vang off the base of the mast and moving it to the toe-rail? In that case I agree. I use a 4:1 vang boom to mast base and then another exact copy to the toe rail when running off the wind. Total gybe control.



SVAuspicious said:


> . . . . . you probably still want something to hold the boom up when a seal fails or for some other reason the vang doesn't work.


I'm not familiar with solid vangs having never had one. I always thought they had a beefy spring inside that threatened to push the vang out to max length which was then controlled by a rope block system to keep it at a chosen length/boom height. The above comment suggests that these things may be hydraulic?

I was also thinking about a solid vang but if they're hydraulic I'll pass.


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## TakeFive (Oct 22, 2009)

OK, so the vang-as-preventer question has always bothered me, so I might as well ask it here (hijack alert).

My boat has swept back spreaders, so I can't allow the boom out very far when running, otherwise the mainsail stresses the rig by pushing forward against the spreader and upper shroud. This creates difficult geometry for a preventer, since it's a LONG way from the end of the boom to the bow, and the angle is not all that favorable.

It almost seems like it would be better to remove the vang from the mast base and attach it to the base of a stanchion. Then I'd have 4:1 purchase which could allow me to release the cam cleat under tension. But I've been told that such an arrangement is dangerous. Sounds like opinions here on that arrangement are mixed.

I'd like to hear some further discussion on the pros/cons of doing this, and since we're talking about uses for a boom vang, maybe it's not a hijack after all.

Right now I typically sail in flat enough waters that I don't need a preventer, and I tend to avoid the issue by using genoa/whisker pole with no main if I have to sail DDW. But it would be nice to know what I should do if I find myself in rolly seas and need a preventer.


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## Omatako (Sep 14, 2003)

TakeFive said:


> It almost seems like it would be better to remove the vang from the mast base and attach it to the base of a stanchion. Then I'd have 4:1 purchase which could allow me to release the cam cleat under tension. But I've been told that such an arrangement is dangerous. Sounds like opinions here on that arrangement are mixed.


As mentioned in my earlier post, I use a rope block system as a vang which controls the vertical position of the boom and when running off the wind I have a second identical setup (that I call a preventer) that connects to the same spot on the boom as the vang but the other end goes to the leeward toe rail. That allows total control over crash gybes and sail shape (IMHO). I guess this depends on geometry of your boom and whether you have a toe rail that can be clipped onto.

It's cheap and effective - the only reason I want a solid boom supporter is to be able to dispose of the topping lift for an almost frivolous reason.


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## TakeFive (Oct 22, 2009)

I do not have a toe rail, but I do have a well-placed stanchion with a bail welded to to its base. The angle of attack would be pretty good.

But the attachment point on the boom is only about 1/4 of the way down the boom ('cause that's where vangs attach!). If backwinded, the forces at that point could be pretty high (entire force of the sail concentrated at the one point), and might damage the stanchion or buckle the boom. That's the issue that Auspicious is referring to.


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## Bill-Rangatira (Dec 17, 2006)

TakeFive said:


> I do not have a toe rail, but I do have a well-placed stanchion with a bail welded to to its base. The angle of attack would be pretty good.
> 
> But the attachment point on the boom is only about 1/4 of the way down the boom ('cause that's where vangs attach!). If backwinded, the forces at that point could be pretty high (entire force of the sail concentrated at the one point), and might damage the stanchion or buckle the boom. That's the issue that Auspicious is referring to.


that would be substantial mechanical advantage in favour of the wind
good way to fold bend or snap a boom


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## Jeff_H (Feb 26, 2000)

First of all, I completely agree with the comments that a vang is a necessary piece of safety equipment for the reasons that Faster cited. I don't believe in using a vang taken to the rail for a preventer since as SV Auspicious points out, the forces can be enormous and are likely to pull a fitting out of the deck, over load the hull to deck joint, break the boom or goosneck if the the boom tip catches a wave. 

For coastal cruising in small waves and moderate winds almost preventer set up is workable. But in heavier winds and bigger seas I prefer to have a preventer run from the end of the boom outboard of everything to a turning block at the bow, and back to the cockpit where it can be released easily in a death roll or knockdown, and can be laced on a winch and eased with control if necessary. 

I prefer to use a nylon line with a little stretch to it to absorb the shock of the boom hitting the water without over stressing any other part of the boat, but with enough strength and stretch resistance to prevent the boom from getting anywhere near the centerline of the boat during an accidental jibe. 

Jeff


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## wristwister (Mar 20, 2013)

I used to use the vang as a preventer by moving the snap shackle to a stanchion base. Then one day I busted my boom in half. My boat is boom end sheeted so this makes perfect sense: 4:1 force pulling the middle of the boom forward and another 4:1 force pulling the end of the boom back ... and SNAP!


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## Omatako (Sep 14, 2003)

TakeFive said:


> But the attachment point on the boom is only about 1/4 of the way down the boom ('cause that's where vangs attach!). If backwinded, the forces at that point could be pretty high (entire force of the sail concentrated at the one point), and might damage the stanchion or buckle the boom. That's the issue that Auspicious is referring to.


My vang attaching point is also about 1/4 way from the mast - I have back-winded the main in 40 knots and no damage (other than underwear stains ).

I suppose it's individual to each boat and the relative component strength but I also think if the vang and the preventer are both under tension and there is no shock loading, most hulls should be strong enough to resist the pressure from a back-winded main. The main size and power is/should be relative to the component strength.

When I back-winded in a good blow (see above), it momentarily heeled the boat heavily but there was never a suggestion that anything was going to break and the boat recovered pretty quickly. If the boom is allowed to gybe even partially uncontrolled then yes, I would be concerned about equipment damage but not if it is fixed firmly in place.


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## aloof (Dec 21, 2014)

The posts above all make good, and true, points. But in my opinion a vang is completely optional. Many boats don't have them, or don't use them, or they are too frail to do much trim work. My previous boat did not have a vang. And on the current boat it has a small hydraulic leak so I have not been using it much until I can get to a place to replace the seal.

On the boat without a vang the boom height was limited by a fixed piece of strong line (spectra) between the vang fittings. It was loose enough to accommodate reefing and some boom lift for water clearance. The rigid vang on this boat also limits the maximum height of the boom. So avoiding the goosewing gybe, or catching the backstay, does not require a vang. A hydraulic vang can help with this by setting the pressure relief, BTW, hydraulic haters.

Preventers are a completely different subject.

You did not say if your boom and mast had fittings for a vang. Vang fittings require a substantial structure behind them. Screwed on brackets are not going to work for long. Eyeball along the boom sometime in a stiff breeze when the vang is on hard ... the bend can be significant. Many a boom or vang has been broken by forgetting to ease the vang before the mainsheet.

For sail trim, leech tension, your mid-boom traveler may provide almost enough travel. Mid-boom travelers often have much more effective outboard travel than end-boom travelers. Plus, there is no need to do the (slow cruiser) favorite of having the boom all the way out. Mine is never more than 45 degrees from centerline. Because I never sail below 150 degrees apparent the loss of projected sail area is about 3% and my speed (VMG) is far better because the wind pressure is much higher (15% more distance sailed vs. 30% more apparent wind pressure). Plus plus, the risk of accidental gybe is far less reducing the need for all that preventer gear.

So, in summary, I can think of many things one might better spend money on than a vang. Nice to have, but not vital.


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## Faster (Sep 13, 2005)

But you had a Vang, it just wasn't adjustable...

So I rest my case


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## Sailormon6 (May 9, 2002)

aloof said:


> My previous boat did not have a vang....
> 
> On the boat without a vang the boom height was limited by a fixed piece of strong line (spectra) between the vang fittings.


If I'm reading your post correctly, your previous boat had a vang. It just wasn't adjustable. You said the boat had the vang fittings, and you tied a piece of line between them, to prevent the boom from lifting. That's a vang, albeit, not an adjustable one.


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## Classic30 (Aug 29, 2007)

Here's a pic of my boom vang:









I agree there's probably a bit more windage than would be optimum... but it's infinitely adjustable and works well - sometimes.


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## SVAuspicious (Oct 31, 2006)

Omatako said:


> I use a 4:1 vang boom to mast base and then another exact copy to the toe rail when running off the wind. Total gybe control.


Actually not. See below.



Omatako said:


> I'm not familiar with solid vangs having never had one. I always thought they had a beefy spring inside that threatened to push the vang out to max length which was then controlled by a rope block system to keep it at a chosen length/boom height. The above comment suggests that these things may be hydraulic?


It depends on the brand. Some are indeed a big spring. Some have a captured hydraulic damper. Some are entirely hydraulic. Some are even pneumatic. All that I have used have been pretty robust. I've had a few leaky seals on elderly units.



TakeFive said:


> My boat has swept back spreaders, so I can't allow the boom out very far when running, otherwise the mainsail stresses the rig by pushing forward against the spreader and upper shroud.


Your bigger concern is sail chafe. Rig loading should not be a concern.



TakeFive said:


> This creates difficult geometry for a preventer, since it's a LONG way from the end of the boom to the bow, and the angle is not all that favorable.


Not true. See below.



Omatako said:


> As mentioned in my earlier post, I use a rope block system as a vang which controls the vertical position of the boom and when running off the wind I have a second identical setup (that I call a preventer) that connects to the same spot on the boom as the vang but the other end goes to the leeward toe rail. That allows total control over crash gybes and sail shape (IMHO). I guess this depends on geometry of your boom and whether you have a toe rail that can be clipped onto.


The degree of inefficiency depends on the specific geometry. I cannot conceive of any geometry in which the numbers do not support the proper routing of a preventer from the end of the boom to the bow. See below.



TakeFive said:


> I do not have a toe rail, but I do have a well-placed stanchion with a bail welded to to its base. The angle of attack would be pretty good.


Nope.



TakeFive said:


> But the attachment point on the boom is only about 1/4 of the way down the boom ('cause that's where vangs attach!). If backwinded, the forces at that point could be pretty high (entire force of the sail concentrated at the one point), and might damage the stanchion or buckle the boom. That's the issue that Auspicious is referring to.


The issue I am referring to is avoiding an accidental gybe both causing damage and potentially as a result of damage from overloading.

THIS IS BELOW. *grin*

Here is the engineering.

Let's start with the vang. What we are trying to do is hold the boom down, increasing leech tension and flattening the main sail. Hard on the wind the main sheet provides this function more effectively than anything else. As you head down the vang is the only way to meaningfully effect sail shape in this fashion.

Lets look at the loads. For purposes of this discussion, we'll consider the vang attaches to the boom 4' from the gooseneck, and that the gooseneck is 2-1/2' above the lower vang attachment. For a 100# load on the vang (4:1 vang and a 25# pull to set it) the math isn't too bad. There is some trigonometry.

The angle of the vang to the boom is arctan(2.5/4) = 39 degrees. The down force (which is what we want to impose) is sin(39 degrees)*100# = 63#; compressive force on the boom is cos(39 degrees)*100 = 78#. Efficiency is not great is it? Unintended forces build faster than the desired ones.

Moving on to preventers, the geometry gets more complex as we have to deal with three dimensions and two transformations. The desired force is perpendicular to the boom in the horizontal plane. It is easiest to calculate the X (longitudinal), Y (athwartship), and Z (vertical) components, and then rotate the X and Y plane to the angle of the boom (X' and Y').

The upshot will be that most of the force imposed by a vang or vang-like tackle from a vang attachment on the boom to the toerail or shroud base will be down (which we don't care about for gybe prevention) and boom tension (which we don't care about for gybe prevention).

Compare that scenario to a preventer that runs from the aft end of the boom forward to a turning block or other fairlead at the bow (I use the inside of my bow cleats). Efficiency is still far from perfect but it is much much much better than a connection from just a few feet out the boom to the toerail. In addition, the preventer is just a long piece of line. How convenient!

The math for a particular boat is straightforward but tedious. Someone has to make it worth my while. *grin*

My approach to setting the preventer is as follows:

I run the preventer from the aft end of the boom forward to a bow cleat and back along the side deck to a stern cleat.

Ease the main out until the sail is against the spreaders.

Take up as hard as I can on the preventer and cleat it off.

Use the main sheet to grind the sail off the spreaders, tensioning the preventer in the process more than I could possibly do otherwise.

There is a separate discussion about whether preventers should have some elasticity to absorb shock loads or be as inelastic as possible in order to minimize the development of shock loads. I'm firmly in the inelastic camp. The math is much more complex for that. Empirical data collected by people like Evans Starzinger supports the inelastic approach.


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## wristwister (Mar 20, 2013)

SVAuspicious, I like your preventer arrangement. Beats the heck out of snapping another boom in half (see my above post). This has me also thinking about the jack lines I want to install on deck for some long distance single handing I plan to do this summer. If those preventer lines are of strong line with proper hardware, they could double as jack lines! And hey, maybe they could do triple duty as spinnaker pole foreguys!


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## SVAuspicious (Oct 31, 2006)

I think using the same line for a foreguy and a preventer is fine. I think jacklines should be singlepurpose items. I have dedicated eyes in the deck for my jacklines.


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## Omatako (Sep 14, 2003)

Whilst only an stupid person would contest that a line from boom end to bow is the best solution, it is so only technically-speaking because it is impractical to have it attached all the time and if you're beating into increasingly bad weather then decide to run off because beating is getting dangerous, you will now need to go on the fore-deck to set the preventer up.

Given that one is hopefully always reefed to suit the weather conditions, the energy in the main is commensurately reduced and the boom-to-toerail setup in my experience has always been more than adequate as a gybe preventer. And in my opinion beats going onto the foredeck in wild conditions.

I'm also a little confused by how the line gets to the end of the boom when it is "out there". It must be set while you're beating? And how do you switch it if you *have* to gybe? Back onto the foredeck? In wild weather? Not for me.

I guess we could argue back and forth on this subject for quite a while and never really resolve it. Opinions are opinions. We each have one. I guess those looking for advice just have to decide which one works for them.


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## Omatako (Sep 14, 2003)

wristwister said:


> I used to use the vang as a preventer by moving the snap shackle to a stanchion base. Then one day I busted my boom in half. My boat is boom end sheeted so this makes perfect sense: 4:1 force pulling the middle of the boom forward and another 4:1 force pulling the end of the boom back ... and SNAP!


It's probably a good idea to release the 4:1 holding the boom forward before you crank on the 4:1 to pull it's end backwards.


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## L.A. Sail (Mar 13, 2015)

I'd go with a rigid from Garhauer.


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## JonEisberg (Dec 3, 2010)

Omatako said:


> Whilst only an stupid person would contest that a line from boom end to bow is the best solution, it is so only technically-speaking because it is impractical to have it attached all the time and if you're beating into increasingly bad weather then decide to run off because beating is getting dangerous, you will now need to go on the fore-deck to set the preventer up.
> 
> Given that one is hopefully always reefed to suit the weather conditions, the energy in the main is commensurately reduced and the boom-to-toerail setup in my experience has always been more than adequate as a gybe preventer. And in my opinion beats going onto the foredeck in wild conditions.
> 
> ...


No need to go forward, very simple to configure a setup that can be deployed without going forward of the mast...

One or two lines are fixed to the end of the boom, and led forward towards the gooseneck, with a ring or eye at the forward end... They live stowed there when not in use, held in place either by a small cleat, or bungee hook, whatever...

A combination foreguy and afterguy with a snap shackle joining them lives along the deck, outside of the stanchions, run up to a block clipped to the rail near the bow, then back to the cockpit, either to rope clutches, or cleats... My space is a bit tight, so mine are outboard of the coaming, keeping it all a bit more tidy, anyway...










With the snap shackle always positioned roughly amidships, all you have to do is to take the preventer line off the boom, fix it to the snap shackle, then trim/adjust the preventer from the cockpit...

This arrangement also works wonderfully for setting up a whisker or spinnaker pole, greatly reduces the amount of time to get everything rigged... Frankly, I don't know why everyone doesn't configure something similar...

)


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## SVAuspicious (Oct 31, 2006)

Omatako said:


> Whilst only an stupid person would contest that a line from boom end to bow is the best solution, it is so only technically-speaking because it is impractical to have it attached all the time and if you're beating into increasingly bad weather then decide to run off because beating is getting dangerous, you will now need to go on the fore-deck to set the preventer up.


I always take pause when the word "technically" is used to mean "not really true."

In the first place I go to the foredeck when I need to go to the foredeck and I'm old and creaky. Secondly, back when I only used a long piece of line for my preventer it was set up all the time. It ran from a stern cleat through the bow cleat on the same side and back to hang on a mast cleat.

Others who use this approach may run a preventer down each side of the boat.

I happily stole the brilliant idea of Evans Starzinger and spliced a preventer stub to the aft end of the boom that runs along the bottom of the boom to a spliced in 2" (dimension isn't important) stainless steel ring that stows near the gooseneck. The rest of the preventer goes from a shackle at the mast forward to the bow and back to the stern. Gybing just means disconnecting before and connecting up on the other side after. Evans has published this approach a number of times.



Omatako said:


> Given that one is hopefully always reefed to suit the weather conditions, the energy in the main is commensurately reduced and the boom-to-toerail setup in my experience has always been more than adequate as a gybe preventer.


Main forces even with three deep reefs are substantial. Run the numbers yourself and look at the loads on the toerail for gybing forces. That stanchion bale won't hold. You'll bend if not break a perforated aluminum toerail.



Omatako said:


> I'm also a little confused by how the line gets to the end of the boom when it is "out there". It must be set while you're beating? And how do you switch it if you *have* to gybe? Back onto the foredeck? In wild weather? Not for me.


1. Be prepared.

2. You can always grind the main in to where you can safely reach it.

3. To gybe you go forward OR you run two preventers OR you rig as described above.

Opinions are indeed opinions. The numbers suggest that running gybe prevention to the toerail amidships(ish) is not well-advised. That is data, not opinion.


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## SVAuspicious (Oct 31, 2006)

*sigh* Jon types faster than I do, and has pictures to boot.


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## Shockwave (Feb 4, 2014)

The vang doesn't flatten the main unless you drive the boom into the spar hard enough to bow the rig. Dinghy's do this, cruising boats don't. The vang on a cruising boat is simply twist control.


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## JonEisberg (Dec 3, 2010)

SVAuspicious said:


> *sigh* Jon types faster than I do, and has pictures to boot.


I can assure you, Dave, that is not the case... I simply quit my project, and came in to take a coffee break, before you did... 

It's been so long, I forget where I first got the idea... It wasn't Evans, or John Harries, who's another strong proponent of that 2-part setup... It was probably Steve Dashew, but it may have even been someone like Don Street...

Like you, I only steal from The Best...


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## nolatom (Jun 29, 2005)

JonEisberg said:


> I can assure you, Dave, that is not the case... I simply quit my project, and came in to take a coffee break, before you did...
> 
> It's been so long, I forget where I first got the idea... It wasn't Evans, or John Harries, who's another strong proponent of that 2-part setup... It was probably Steve Dashew, but it may have even been someone like Don Street...
> 
> Like you, I only steal from The Best...


The iceberg was intimidating. I'm inclined to believe whatever you say about preventers. ;-)


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## aloof (Dec 21, 2014)

Sailormon6 said:


> If I'm reading your post correctly, your previous boat had a vang. It just wasn't adjustable. You said the boat had the vang fittings, and you tied a piece of line between them, to prevent the boom from lifting. That's a vang, albeit, not an adjustable one.


It would be a stretch to call it a vang. It was useless for trim. It was not running rigging. It was there only to prevent the boom from hitting the backstay during a wild gybe.

It was very low-cost.


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## aloof (Dec 21, 2014)

So...preventer proponents...I have often wondered what happens in a blow when the preventer takes over from the mainsheet. I have only used preventers, to the toerail, in light rolly conditions to keep things calm. Never when there was enough wind to hold the boom out thru the rolls.

So what happens when you have that preventer rigged, boom way out, and a squall hits at, say, 40 knots and gybes the main? What happens next?


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## Sailormon6 (May 9, 2002)

aloof said:


> It would be a stretch to call it a vang. It was useless for trim. It was not running rigging. It was there only to prevent the boom from hitting the backstay during a wild gybe.
> 
> It was very low-cost.


It isn't a stretch at all. By definition, a boom vang is "a strap or line which exerts downward pressure on the boom near where it joins the mast of a fore-and-aft rigged sailboat." (Wikipedia) The purpose of a boom vang (sometimes called a "kicking strap") is to prevent the boom from rising up when sailing downwind or during a gybe.

As Jeff and others have said, a vang is a valuable safety device.


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## MikeOReilly (Apr 12, 2010)

Jon/SVAuspicious, with your preventer setup (as stolen from Starzinger), do you leave the unused line running from cockpit to bow to foremast lying on the deck & cabin? Or is it secured in some way? I get the end-boom to gooseneck connection, but the other part seems like a hazard if it's just lying on the deck. I must be missing something...

I currently run our preventers from the end-boom to a turning block attached to unused chainplates at the shrouds. Solid connection, plus this allows me to store our preventer lines neatly coiled, but ready for use, on our mid-ship belaying pins. We have a long boom (18') so the vectors seem to work, although I can see where it would be better from the bow, but only if the unused line along the deck and up over the cabin could be secured in some way.


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## JonEisberg (Dec 3, 2010)

aloof said:


> So...preventer proponents...I have often wondered what happens in a blow when the preventer takes over from the mainsheet. I have only used preventers, to the toerail, in light rolly conditions to keep things calm. Never when there was enough wind to hold the boom out thru the rolls.
> 
> So what happens when you have that preventer rigged, boom way out, and a squall hits at, say, 40 knots and gybes the main? What happens next?


I've yet to have that happen, so I can't say for sure... But I would hope prior to getting hit by a 40-knot squall, I would have been sufficiently alert to have reefed the main so that the consequences of an accidental gybe would be no more severe than one under a full main in more moderate conditions 

I've yet to have a failure or breakage of a preventer, it has always held during those occasions when the main has been backwinded... However, in any situation where the preventer might not stand up to the forces involved, I can't see where the consequences would be any _WORSE_ than an unrestrained accidental gybe, beyond the possible parting of the preventer line, or the breakage of a block or shackle or other component of the system... And, even in the event of such a failure, it still seems that the acceleration of the boom coming across would have been diminished at the outset, until the point of failure, at least...


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## JonEisberg (Dec 3, 2010)

MikeOReilly said:


> Jon/SVAuspicious, with your preventer setup (as stolen from Starzinger), do you leave the unused line running from cockpit to bow to foremast lying on the deck & cabin? Or is it secured in some way? I get the end-boom to gooseneck connection, but the other part seems like a hazard if it's just lying on the deck. I must be missing something...
> 
> I currently run our preventers from the end-boom to a turning block attached to unused chainplates at the shrouds. Solid connection, plus this allows me to store our preventer lines neatly coiled, but ready for use, on our mid-ship belaying pins. We have a long boom (18') so the vectors seem to work, although I can see where it would be better from the bow, but only if the unused line along the deck and up over the cabin could be secured in some way.


Everything is run outside of the stanchions, I often have enough crap lying on deck, as it is... 

The red line is the afterguy, the green becomes the foreguy or preventer once the line on the boom is clipped to the snap shackle. The only "excess line" is all back in the cockpit...

I'd suggest you consider taking your preventer much further forward, hard to imagine how it's "preventing" much of anything taken to the base of the shrouds, when run from the end of the boom with the main fully eased... Also, wouldn't it have to be run through or beneath the lifelines when it is rigged? Sometimes running a sheet or other running rigging through lifelines is unavoidable, but I think it's generally not the greatest idea, if there is an alternative...


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## SVAuspicious (Oct 31, 2006)

aloof said:


> So what happens when you have that preventer rigged, boom way out, and a squall hits at, say, 40 knots and gybes the main? What happens next?


Unfortunately I can tell you. *sigh* This is why I am now picky about crew, and *always* rig a preventer offshore.

Without a preventer, heading downwind, when an idiot crew ignores the autopilot beeping off course the boom slams back and forth against the rigging - generally shrouds. Battens break at a minimum.

With a good solid preventer the main backwinds, all the elasticity is taken up, the boat shudders badly waking everyone, the boat heels remarkably, the skipper boils into the cockpit and depending on conditions takes one of two actions. If there is still boat speed you steer back to the appropriate course and the boat settles down. If there is no steerage, grind the main in and ease the preventer together (remember the loads are HUGE) and get the boat moving again.



MikeOReilly said:


> Jon/SVAuspicious, with your preventer setup (as stolen from Starzinger), do you leave the unused line running from cockpit to bow to foremast lying on the deck & cabin? Or is it secured in some way?


Jon has pictures of his two lines clipped to one another.

Mine preventer, when not in use, has a snap shackle clipped to a ring on the mast, all the slack taken up at the stern cleat, and the extra line coiled and hung from the pushpit above the stern cleat.


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## aeventyr60 (Jun 29, 2011)

On mikereilly's boat he can run it through the forward hawse hole, and then back inside along his generous bulwarks to a either a cleat or a clutch.


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## TakeFive (Oct 22, 2009)

Guys,

This is exactly the kind of preventer advice that I was looking for. I can now really visualize coming up with something that works for my little boat - and it's really no different from your big boats.

Here's my (somewhat naive) question: What kind of fitting do you recommend at the end of the boom to attach the preventer? (I have mid-boom sheeting, not end-boom.) It sounds like most of you you use a single line on the boom, and shackle that line to two preventers near the mast, depending on which side the boom is on. Should I attache a bail at the end of my boom, or do you have some other recommendation?

FWIW, currently if I'm near DDW and solid breezes, I'll often avoid a gybe by dropping my main and running on genoa alone with a whisker pole. If I have a lot of space I'll avoid DDW entirely, but on my narrow river I sometimes have narrow space (need to stay out of the channel if big ships are around), so sometimes no choice but to run DDW due to traffic.


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## MikeOReilly (Apr 12, 2010)

JonEisberg said:


> Everything is run outside of the stanchions, I often have enough crap lying on deck, as it is...
> 
> The red line is the afterguy, the green becomes the foreguy or preventer once the line on the boom is clipped to the snap shackle. The only "excess line" is all back in the cockpit...
> 
> I'd suggest you consider taking your preventer much further forward, hard to imagine how it's "preventing" much of anything taken to the base of the shrouds, when run from the end of the boom with the main fully eased... Also, wouldn't it have to be run through or beneath the lifelines when it is rigged? Sometimes running a sheet or other running rigging through lifelines is unavoidable, but I think it's generally not the greatest idea, if there is an alternative...


Thanks Jon. I get it ... I think . Your deck is very cluttered though -- not something I would want. I prefer a clean working space when moving around, especially at night, but if it works for you, then great.

My preventer certainly does prevent. The angle is not as good as it would be if it were run from the bow, but the force vector certainly does exist to prevent a jybe. Sorry I don't have pics. With our long boom (18') and the fact that we're never more that ~50-60 degrees off the centre line, makes it work fine.



SVAuspicious said:


> Unfortunately I can tell you. *sigh* This is why I am now picky about crew, and *always* rig a preventer offshore.


We prevent whenever the we're sailing with wind past the beam ... always. It's one of our boat rules. This means we always have the preventer rigged and ready should things go off the rails. But mainly we simply can't afford an accidental jybe. With our very large main, it would lead to very bad things .



SVAuspicious said:


> Mine preventer, when not in use, has a snap shackle clipped to a ring on the mast, all the slack taken up at the stern cleat, and the extra line coiled and hung from the pushpit above the stern cleat.


It's where to attach the foreguy when not in use that I'm not clear on. If it's clipped to the mast it would mean clutter on the foredeck, and would get in the way of my staysail.

How about clipping it to a shroud? To engage the preventer I'd take the line off the cockpit cleat, then walk forward, unclip the foreguy at the shroud and connect it to the end-boom line that is stored at the gooseneck (or there abouts).



aeventyr60 said:


> On mikereilly's boat he can run it through the forward hawse hole, and then back inside along his generous bulwarks to a either a cleat or a clutch.


I could ... do you think the cap rail and toerail bulwarks were meant to take that kind of vertical-component load? Probably OK... I'll play with it.

Thanks guys


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## MikeOReilly (Apr 12, 2010)

TakeFive said:


> Here's my (somewhat naive) question: What kind of fitting do you recommend at the end of the boom to attach the preventer? (I have mid-boom sheeting, not end-boom.) It sounds like most of you you use a single line on the boom, and shackle that line to two preventers near the mast, depending on which side the boom is on. Should I attache a bail at the end of my boom, or do you have some other recommendation?


The experts may have better ideas, but I looked up Evans Starzinger's description and he suggests installing a couple of tangs near the end-boom. That should work for you.


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## SVAuspicious (Oct 31, 2006)

TakeFive said:


> Here's my (somewhat naive) question: What kind of fitting do you recommend at the end of the boom to attach the preventer?


I have a bail at the end of my boom specifically for the preventer. If your boom isn't so fitted adding one is pretty straightforward.



MikeOReilly said:


> It's where to attach the foreguy when not in use that I'm not clear on. If it's clipped to the mast it would mean clutter on the foredeck, and would get in the way of my staysail.


Offshore I run the preventer (when not being used) over the inverted dinghy and under the bagged staysail to a ring on the mast. A shroud would be fine as well.



MikeOReilly said:


> I could ... do you think the cap rail and toerail bulwarks were meant to take that kind of vertical-component load? Probably OK... I'll play with it.


They better be able to take that load - on most boats they are part of the deck-hull joint.


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## TakeFive (Oct 22, 2009)

What, exactly, is a tang? My generation thinks it is an orange drink. :laugher


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## MikeOReilly (Apr 12, 2010)

TakeFive said:


> What, exactly, is a tang? My generation thinks it is an orange drink. :laugher


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## TakeFive (Oct 22, 2009)

Any single attachment point under the boom will cause twist. Is this a problem? Any way to avoid it?


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## SVAuspicious (Oct 31, 2006)

A good sized bail and a good sized shackle. I use a Yale Loup between.


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## TakeFive (Oct 22, 2009)

So I think I will add a bail to the bottom of the boom, attached with a through-bolt in the same way the bails are for the vang and mid-boom mainsheet. This will cause some twist in the boom due to the location at the bottom, so I hope that is not a problem.

One other complication that I just realized - my mid-boom sheeting will interfere with a jibe if I only run a single line to the gooseneck. So I either need two lines going forward to the gooseneck, or run a single line only to the mainsheet bail, and the rest of the preventer shackles onto it at that point. What I don't know (since my boom is stored away right now) is whether I would be able to reach the attachment point with the boom extended out on a run. It might be too far over the side of the boat. I need to do some measurements as soon as raise may mast and put everything back together.


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## datswite (Sep 28, 2010)

Great discussion on preventers... talk about thread drift! 

I suppose I got enough opinions on vangs to answer my question, though. Like most things, opinions vary - however, this camp tends toward having a vang.


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## JonEisberg (Dec 3, 2010)

MikeOReilly said:


> Thanks Jon. I get it ... I think . Your deck is very cluttered though -- not something I would want. I prefer a clean working space when moving around, especially at night, but if it works for you, then great.


Nah, my decks are not quite as bad as they might look  That double yellow line is for the Code 0 furler, it's only there when that sail is being flown... The rest of all those lines, with the exception of the jackline, are no further inboard than the lifelines themselves...

BTW, if you never ease your boom more than 50-60 degrees off centerline, I'd say you definitely want to configure a bulletproof preventer setup... What, have you replaced the original rig on your Rafiki with a B&R, or something? 

Here's a pic that shows how the part of the preventer that lives on the boom is stowed at the gooseneck, the yellow elastomer cord works well for that chore...


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## aeventyr60 (Jun 29, 2011)

"*My preventer certainly does prevent. The angle is not as good as it would be if it were run from the bow, but the force vector certainly does exist to prevent a jybe. Sorry I don't have pics. With our long boom (18') and the fact that we're never more that ~50-60 degrees off the centre line, makes it work fine. *"

Mike,

When you get going in the trades, you may find you will dip that 18' foot boom in the swell...another good reason to lead that preventer forward. You will be rolling side to side in the trade wind swells. More like a milk shake the the milk run.


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## MikeOReilly (Apr 12, 2010)

Thanks guys. Always lots to learn. Not sure what a B&R is Jon, but it's the same rig. I haven't actually measured our angle with a protractor, but as I say, we tend not to ease the main out very far. We can get some big rolly stuff on the Great Lakes too, which is another reason I like to keep the boom in closer. 

I'm definitely going to change the preventer connection to the Starzinger approach. That looks great. I'll also play with running the preventer through the forward hawse scuppers. It will give me a better angle. I'm not convinced it will make a substantive difference, but if I can keep the lines running uncluttered and stored clean it would be a more powerful connection.


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## CapnRon47 (Jul 29, 2007)

Jon,
Since this thread has already been 'sidetracked' to preventers let me ask; the line from the bow to the end of the boom runs outside the lifelines but the line aft, from the bow, runs inside them and will rub up against the stanchions for the rigging when under tension, do you worry about that chafe and how do you deal with it?

thanks,
Ron


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## JonEisberg (Dec 3, 2010)

CapnRon47 said:


> Jon,
> Since this thread has already been 'sidetracked' to preventers let me ask; the line from the bow to the end of the boom runs outside the lifelines but the line aft, from the bow, runs inside them and will rub up against the stanchions for the rigging when under tension, do you worry about that chafe and how do you deal with it?
> 
> thanks,
> Ron


No, everything runs outside the stanchion bases, including the part of the line run back to the cockpit... There is no concern over "chafe", as there is no movement of the line against anything, once either the preventer or the foreguy is set, and adjusted... And the stanchion bases are smooth polished stainless, anyway, hard to imagine much in the way of chafe even if the line was sawing back and forth along them...

The only thing I might sometimes have to tweak, is if heading up closer to a reach, and my relatively short boom is trimmed more inboard, the preventer might begin to make contact with the lifelines forward of the shrouds. If that starts to be a concern, it's easily dealt with by either twinging the preventer down to the rail further aft with a snatch block, or moving the turning block further aft (I don't know how people sail without perforated aluminum toerails, I'm spoiled forever in that regard ) But by the time the boom is brought far enough inboard for such an adjustment to be made, unless the sea state is exceptionally sloppy, it's generally about time to be able to dispense with the preventer, anyway...


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## CapnRon47 (Jul 29, 2007)

Jon,
thanks, that is what I was thinking but just wanted to confirm with you. I don't have perforated aluminum toerails, I do have hefty forward SS cleats that I could run the preventer line thru the eye and under the lifeline back to (eventually) attach to the boom. I also have a track on the toerail that extends about 3' forward of my shroud stanchions, but still about 3' aft from those bow cleats. I am concerned these are not far enough forward to give a good angle to the end of the boom for the preventer.










I will have to work out what that angle is for both cases and look at the ratio of the loads.

regards,
Ron


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## SVAuspicious (Oct 31, 2006)

JonEisberg said:


> No, everything runs outside the stanchion bases, including the part of the line run back to the cockpit.


Choices. Horses for courses. I fun the working end of my preventer inboard of the stanchions and outboard of the shrouds. The shroud covers make dandy low-friction fairleads. By the time my preventer succumbs to UV there is still no sign of chafe.



JonEisberg said:


> I don't know how people sail without perforated aluminum toerails, I'm spoiled forever in that regard.


One manages. *grin* I'm happy to have bulwarks tall enough to jamb the entire width of my foot into. There are times when I do envy the flexibility perforated toerails bring but I don't want to give up my bulwarks either. I think Magnus Rassy would never speak to me again if I screwed a perforated toerail on top of his lovely teak caprails. *grin*


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## CapnRon47 (Jul 29, 2007)

All, thanks for this thread. I am trying to size the equipment for a preventer. what kind of loads might I expect with these dimensions: P: 36.6 ft, E: 13.3 ft main area: 244 sq ft.?

thanks,
Ron


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## Cal2-27 (Apr 7, 2015)

I read this entire thread and I still have no idea how to rig a preventer on to my boat lol

I need to brush up on my nautical nomenclature as well....

Could someone possibly dumb down the Evans Starzinger method for a gybe preventer?

Thanks for all the info (and your patience with the newbies!!)


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