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Old 19-07-2021, 07:40   #1
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Jibe preventer rigging

I had an inadvertent jibe and snapped my traveler car on my 49 Jeaneau DS. Any advoce on the easiest and least expensive way to rig a Jibe preventer?
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Old 19-07-2021, 08:19   #2
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Re: Jibe preventer rigging

You've got a downhaul, right? You don't allow slack sheet, right? The arc of the boom during a jibe does not include any brain buckets, right?

You can do it, but the cure may be worse than the problem. A line from the boom to the bow does it. But then, if you jibe, You've got a whopping force from roughly your beam as the boat comes out of you hands and slews toward what was the lee side. That could spoil your day for you. There is an argument to be made for watching for a warning luff very carefully, but when it cannot be prevented, let it go. The boom came across with malice a forethought, but it didn't hit anyone, and you are now before the wind on the other tack.
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Old 19-07-2021, 08:24   #3
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Re: Jibe preventer rigging

Secure a block or low friction ring to a solid point at the bow. Run a line from a winch in the cockpit to that block, then to the end of the boom. I use old spinnaker sheets with shackles. I run two preventers, one for each side of the boom, but they go to the same winch. So when I jibe, I center the main over the cockpit. Change the shackle at the end of the boom and change what line is on the winch, then I complete the jibe.

Assuming you have a solid attachment point at the bow and an available winch, you probably have the lines and blocks already.

What you DON'T want to do is rig a preventer from the middle of the boom to the toerail midship someplace. Booms are not designed for that type of loading, and can break. Preventers need to go to the end of the boom.
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Old 19-07-2021, 08:24   #4
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Re: Jibe preventer rigging

Fasten a long line (3x boom length) to the end of the boom. On a DS49 probably 9mm (or 8mm) polyester double braid will do.

Run the bitter end forward, through some strong point on the leeward rail near or forward of amidships (such as a stanchion base or a snatch block in the toe rail) and back to a winch in the cockpit. Pull it snug. You must be able to release it under load, so beware of putting it on a cleat.

When you wish to jibe, release the preventer in the cockpit, and after the jibe re-lead it on the new leeward side.

When you are not needing a preventer tie the bitter end to the boom near the gooseneck, tight enough so that it does not hang down and snag somebody, then coil and hang the rest.

This solution is cheap, effective, and easy. It does not require more permanent rigging and falderal under the boom like a boom brake.

You can see our preventer in the photo, it is the small dark line running forward from the end of the boom (you can actually see it coming back to the cockpit, right at the bottom of the photo). Pay no mind to the holes in the boom, courtesy of the previous owner.
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Old 19-07-2021, 08:33   #5
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Re: Jibe preventer rigging

There are two theories here of what Giapet asked about. The last two posts deal very well with rigging preventers for intentional jibes. I dealt with what I thought he asked about, which was a preventer in place against unintentional and unexpected jibes.
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Old 19-07-2021, 08:41   #6
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Re: Jibe preventer rigging

Quote:
Originally Posted by tkeithlu View Post
You've got a downhaul, right? You don't allow slack sheet, right? The arc of the boom during a jibe does not include any brain buckets, right?

You can do it, but the cure may be worse than the problem. A line from the boom to the bow does it. But then, if you jibe, You've got a whopping force from roughly your beam as the boat comes out of you hands and slews toward what was the lee side. That could spoil your day for you. There is an argument to be made for watching for a warning luff very carefully, but when it cannot be prevented, let it go. The boom came across with malice a forethought, but it didn't hit anyone, and you are now before the wind on the other tack.
Then someday a something associated with the mainsheet breaks, and the boom goes all the way to the shrouds and takes down the rig. Or kills someone.

It's too easy to say just watch the luff, but after many thousands of miles with a windvane in control, that is a very unreasonable expectation. I have had my prevented main backwinded a number of times, usually during a nighttime squall when a sudden wind shift comes with 30 kt winds. Never was it a dangerous situation. The boat turns, but remains stable, and I ease the preventer on the winch to allow the boom to come across in a controlled way and when I am ready for it. I am then happily on the other tack with no drama.

On the contrary, the times I have had an uncontrolled jibe with no preventer have broken things, could have killed someone (I have a low sweeping boom) and were generally terrifying when it happened, and for a few minutes afterward while getting the boat under control again.

Some boats might not handle having a prevented main backwinded as well as mine. It would probably be a good idea to rig a preventer, and on a mild day intentionally jibe and test it. If the boat doesn't handle it well, maybe look at a boom brake instead.
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Old 19-07-2021, 08:54   #7
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Re: Jibe preventer rigging

Preventer rigging at about 02:30


https://youtu.be/qAhUWCa-KoQ
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Old 19-07-2021, 09:11   #8
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Re: Jibe preventer rigging

Quote:
Originally Posted by tkeithlu View Post
There are two theories here of what Giapet asked about. The last two posts deal very well with rigging preventers for intentional jibes. I dealt with what I thought he asked about, which was a preventer in place against unintentional and unexpected jibes.
I think you might have that backwards. The two comments previous to yours (wingssail and wholybee) both exactly address rigging preventers to deal with accidental or unintentional jibes.

And wholybee's next comment very correctly covers the consequences, with preventer and without, of unintentional jibes.

Your suggestion to "just let it go" is dangerous, very dangerous.
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Old 23-07-2021, 03:16   #9
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Re: Jibe preventer rigging

Depending on the design of your boat I dont see why you cant just run a line to the bow trough a cleat and back to the cockpit.
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Old 23-07-2021, 03:41   #10
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Re: Jibe preventer rigging

Quote:
Originally Posted by wingssail View Post
I think you might have that backwards. The two comments previous to yours (wingssail and wholybee) both exactly address rigging preventers to deal with accidental or unintentional jibes.

And wholybee's next comment very correctly covers the consequences, with preventer and without, of unintentional jibes.

Your suggestion to "just let it go" is dangerous, very dangerous.
+1

Unintentional gybes are incredibly dangerous!

Strange comment coming from you, Keith, as I would consider you one of our resident experts.

Fair winds,
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Old 23-07-2021, 03:48   #11
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Re: Jibe preventer rigging

I have delivered several boats with the Dutchman Boom Brake and I know the inventor. It works a charm.

https://dutchmar.com/dutchman-boom-brake/

no financial interest in the device
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Old 23-07-2021, 04:06   #12
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Re: Jibe preventer rigging

Quote:
Originally Posted by wholybee View Post
Then someday a something associated with the mainsheet breaks, and the boom goes all the way to the shrouds and takes down the rig. Or kills someone.

It's too easy to say just watch the luff, but after many thousands of miles with a windvane in control, that is a very unreasonable expectation. I have had my prevented main backwinded a number of times, usually during a nighttime squall when a sudden wind shift comes with 30 kt winds. Never was it a dangerous situation. The boat turns, but remains stable, and I ease the preventer on the winch to allow the boom to come across in a controlled way and when I am ready for it. I am then happily on the other tack with no drama.

On the contrary, the times I have had an uncontrolled jibe with no preventer have broken things, could have killed someone (I have a low sweeping boom) and were generally terrifying when it happened, and for a few minutes afterward while getting the boat under control again.

Some boats might not handle having a prevented main backwinded as well as mine. It would probably be a good idea to rig a preventer, and on a mild day intentionally jibe and test it. If the boat doesn't handle it well, maybe look at a boom brake instead.

I agree. "Just let it go"? That's a recipe for mayhem, including even losing the rig.


Furthermore, a preventer does more than just hold the boom against a fully backwinded situation. It keeps the boom from flopping around in light wind, which may allow it to be caught backwinded. It also can prevent a slight backwinding from moving the boom back and causing a full backwinded situation.



Preventers? Use them! On my boat, ALWAYS, when the boom is out beyond the rail.


One thing to pay close attention to however is the geometry. There was a case discussed on here where a preventer broke because it was rigged to mid-boom and to some place amidships, creating huge leverage. Someone was killed in that case.


Always rig preventer to the boom end and ALWAYS take it all the way to the bow. The force is doubled at a 30 degree angle -- see: https://www.engineeringtoolbox.com/r...se-d_1507.html.
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Old 23-07-2021, 04:56   #13
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Re: Jibe preventer rigging

if you have a soft vang, could you not run the vang to the toe rail (if you have one) and snug it down. this still would maintain your sail shape pulling down on the boom, and should work as a preventer. if your vang controls are led aft, this might be a problem. and it would necessitate you going forward to release the vang from the toe rail during an intended jibe. which could be dangerous in bad weather.


or using the vang attachment point on the boom and rig a separate preventer to a snatch block on the toe rail aft of the shrouds and then lead that line aft to the cockpit to you can ease the boom around in combination with the mainsheat for an intended jibe



I do understand the physics and if the boom is swinging with force you'd not want a shock load mid boom unless you want to see how a tube folds. but being you'd have your preventer fairly snug, you shouldn't see the shock loads.
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Old 23-07-2021, 05:37   #14
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Re: Jibe preventer rigging

Quote:
Originally Posted by marcjsmith View Post
if you have a soft vang, could you not run the vang to the toe rail (if you have one) and snug it down. this still would maintain your sail shape pulling down on the boom, and should work as a preventer. if your vang controls are led aft, this might be a problem. and it would necessitate you going forward to release the vang from the toe rail during an intended jibe. which could be dangerous in bad weather.

or using the vang attachment point on the boom and rig a separate preventer to a snatch block on the toe rail aft of the shrouds and then lead that line aft to the cockpit to you can ease the boom around in combination with the mainsheat for an intended jibe. . .

Before doing something like that, I suggest you check the geometry of the preventer lead. You can easilyl magnify the force on the preventer by 10x or 20x with a lead like that. Just do the math and you will see. Rigging the preventer as you suggest is exactly how two guys on Platino got killed.



See also:


https://www.morganscloud.com/2018/10...that-can-kill/


"Amidships Preventers -- A Bad Idea That Can Kill", Morgan's Cloud.


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Here is the diagram from the Platino accident report:


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Here's the Platino accident report, which is full of good information about preventers.



So in short, NEVER do this. Preventers should always be rigged to the bow.
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Old 23-07-2021, 05:39   #15
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Re: Jibe preventer rigging

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Originally Posted by Rockinar View Post
Depending on the design of your boat I dont see why you cant just run a line to the bow trough a cleat and back to the cockpit.
You can run the preventer to the bow and then back to the cockpit.

A few considerations:
  • It takes more line, and you have to go farther forward to change it after you jibe (or run two longer lines)
  • The angle is not great if you are using the preventer to "stabilize" the boom in sloppy seas when you don't need it all the way out but still want to hold it in place. The angle to the wide part of the boat is better.
  • The excess line gets into more stuff.
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