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Old 07-02-2016, 12:52   #1
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Preventer Rigging?

I have always rigged my preventer the old-fashioned way Ė take a length of 12mm rope, tie one end with a bowline through the end loop of the boom, lead that around a midship cleat, and back to a winch. Voila.

Then this summer I realized with horror that the angle is all wrong. It pulls mostly DOWN on the boom, which means a strong impulse back will snap the preventer. All these years Iíve been doing it wrong!
I have just installed strong padeyes on the rail forward, from where I think I should have a much better lead.

I am going to make up a low friction eye with a dyneema strop (which I learned to splice last year, hurrah) to use as a snatch block.
But it got me thinking that there must be a better way to rig the preventer. With a sea running, itís a PITA to stand on your toes and tie that bowline through the boom end loop, and the other end of the preventer takes up a precious winch.

How do others do it? Maybe splice a loop through the boom end, and use a snap shackle at the end of the preventer? Or rig it premanently?
If the latter, how would you store it? I donít fancy leaving a hank of rope hanging off the end of the boom at all times. I guess it could be led further up the boom and hung there. Or maybe just a snap shackle?
Any tips?

Another preventer question: It seems to me that your preventer doesnít actually need to be as strong as all that Ė itís purpose is to keep the boom from slewing around and generating snatch loads. If itís held in place, it donít produce enormous forces. So why not use a somewhat smaller, easier to handle line? Iím thinking of downsizing from 12mm to 10mm. Or maybe 10mm Dyneema for lightness and strength, hmmm? Maybe with the cover stripped off half of it?


And while weíre at it Ė letís talk about furling lines. I use 12mm double braid, which is heavy and bulky and fills up the furling drum. Now why such big line for this? I have big Selden S400 Furlex furlers, but they donít generate forces which would challenge 10mm double braid, I donít think.
What do you guys use on your furlers? Maybe here again some 10mm cruising Dyneema with the cover half stripped off would be cool Ė very light and easy to handle, and much less bulky in the drum, and plenty strong enough. Hmm?
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Old 07-02-2016, 19:12   #2
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Re: Preventer Rigging?

I have a snap shackle to a bale on the end of the boom. The line goes forward to a snatch block on the toe rail and then back to a cleat at the cockpit. Lives in a locker when not in use. I dont want more clutter than necessary.
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Old 07-02-2016, 19:19   #3
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Re: Preventer Rigging?

I use 5/16" warp speed for my furler. Think you'd want to have some stretch in the preventer. Now I rarely rig a preventer, but I used to use a big snubber around the boom to the preventer, a couple of feet from the end of the boom.
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Old 07-02-2016, 19:33   #4
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Re: Preventer Rigging?

Quote:
Originally Posted by Dockhead View Post
Preventer's ; How do others do it?

why not use a somewhat smaller, easier to handle line?

What do you guys use on your furlers? Maybe here again some 10mm cruising Dyneema with the cover half stripped off would be cool
Regarding Preventers . . . the first question is whether you want to redesign your boom and deck layout. The best solution I have seen is: preventor line with trigger shackle, led to block let into side or underside of boom, line running forward, and down to deck and back to winch/clutch. You stow the line with the shackle clipped to the forward end of the boom. To set it, you release the clutch, and take the line forward and clip it to a strong point. If you have two of the port and starboard you can leave both set and jibe from the cockpit.

If you dont want to redesign your boom and deck layout . . . then probably the best technique is lines fixed to aft end of boom, and led forward, stowed at forward end. With lines running from winches up the side decks to a strong turning point and back, stowed near the stays with trigger shackles. You clip the side deck lines to the boom lines to set the preventors.

In either case you need to make sure the prevent or does not bear on the upper lifeline when the preventer is set and the main has accidentally jibed, and it is nice if they do not also bear on the stays. I bent stanchions twice on Hawk before I got this sorted out.

As to line size - for the furler - yes, definitely use stripped dyneema for the part in the drum, with a cover where it has to be winched or clutched under load. For the preventor same thing. And yes, in both cases, 10mm dyneema is probably more than string enough.
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Old 07-02-2016, 19:44   #5
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Re: Preventer Rigging?

Heavy duty Shockles brand bungee with carbiners on each end. One end clipped to boom end bail, other to a 4:1 block and tackle, other end of tackle clipped to padeye aft of midships (for spin sheet block), tail led to cockpit. I use it for a preventer and to tweak the main (sort of like a boom vang). This gives some flex to the system to reduce shock loading, but the bungee is strong so still tweaks it down tight.

Accidentally field tested this rig once in moderately heavy weather (35 kts, 8 ft seas...periodically bigger). A big sea came up behind us and shifted the stern enough for an accidental jibe. Traveller was all the way to port side (catamaran). Preventer rig survived long enough to ease the load mostly back onto the mainsheet/traveller before some of the hardware exploded (you can see temporary lashing in attached pic). As a result, jibe was not very violent.

I think having some flex in the system is good so that, in the case of an accidental jibe, you dont get caught with the main held over to the new windward side...further encouraging the boat to to turn.
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Old 07-02-2016, 19:44   #6
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Re: Preventer Rigging?

What's the radius of the bare furler drum vs full? I think there is a significant difference on mine giving a not insignificant difference in purchase, especially where the you're winching in the biggest part of the sail.

If you're using an oversize winch then maybe you don't care.
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Old 07-02-2016, 19:47   #7
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Re: Preventer Rigging?

A good system has been designed for Morgan's Cloud, you can get the details from their website. As i understand it, they have a permanent line running both sides of the boom with an eye at the forward end. It is held in place with a piece of shock cord until required. When required it is connected via a shackle to a line running forward to a block near the bow and back through a clutch to a winch. The connection is performed easily at the base of the mast and all lines are rigged permanently. When it is time to jybe, the leeward preventer is removed and reattached to the boom, the jybe is executed and the new leeward line is attached. It makes sense to me but there is more detail on their website.
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Old 08-02-2016, 02:37   #8
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Re: Preventer Rigging?

I use a line from the boom forward and down through an eye at the front corner of the coach roof, up through a shackle on one of the forward halyards, down through an eye on the other side of the coach roof and back to the boom. The preventer is put into use by winching the halyard tight.


Always rigged ready for use, easy to put on and off by tightening or loosing the halyard and does not require one to leave the cockpit.
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Old 08-02-2016, 02:48   #9
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Re: Preventer Rigging?

Fat furling lines are not there for ultimate strength but to make it easy on your hands and the winch.
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Old 08-02-2016, 04:27   #10
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Re: Preventer Rigging?

Quote:
Originally Posted by Dockhead View Post
But it got me thinking that there must be a better way to rig the preventer. With a sea running, itís a PITA to stand on your toes and tie that bowline through the boom end loop, and the other end of the preventer takes up a precious winch.

How do others do it? Maybe splice a loop through the boom end, and use a snap shackle at the end of the preventer?
That's pretty much what I have - preventers permanently rigged on the toe rails and a short line with eyes each end, one of which cow hitches around the end of the boom and the other end gets easily attached to the preventers with a snap shackle from the comfort of the cockpit.

Also, I find it handy having the preventers available in light airs - between the sheet, preventer and topping lift (which goes down to a cleat on the backstay so is easily adjustable from the cockpit) you can lock off the boom wherever you want and give the main some belly without the weight of the boom.
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Old 08-02-2016, 05:18   #11
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Re: Preventer Rigging?

It seems like the major problem is in the angles with the original setup. If your going to vector the force through the cap rail with the new setup it seems like a shock absorber (bungie) might be desired. Perhaps some consideration should be given to what portion of the preventer is sacrificial. It shouldn't be the rail I would think. Perhaps the pin size in the car or the block on the rail is best. No line ends whipping about at a time when things are happening quickly.
I use 10mm line on my Yankee furler. Plenty strong, low friction leading aft. If furling under load its on a winch, if no load, that's what gloves are for.
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Old 08-02-2016, 14:43   #12
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Re: Preventer Rigging?

I have a loose-footed mainsail so I just tie the end of a dockline around the boom near the sheet bail, and lead the line to a bow cleat and back to a cockpit winch. The stretch in the dockline makes it possible to have the preventer really taut, to prevent the boom from moving. In case of an accidental gybe, the stretch avoids shock-loading the rig.

Alain
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Old 08-02-2016, 16:25   #13
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Re: Preventer Rigging?

I have 2 lines permanently installed on either side of the boom
They are 7/8 the length of the boom and are lashed tightly to a small cleat when not in use.
I then run two 1/2 inch nylon lines (think stretch) from cockpit down each side to blocks on my forward cleats and then outside everything back to midship cleats where they reside when not in use.
So, it's a stroll to midship cleats loosen off the 1/2 inch line, step up to mast, connect this line to the permenant and stroll back to cockpit. Tension up as necessary.
Gybing is equally carefree.
Also if wing and wing with Genoa and staysail, I use boom as a poor man's pole and use preventer and main sheet to fix position of boom as appropriate.
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Old 08-02-2016, 18:26   #14
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Re: Preventer Rigging?

Agree with others to use two small lines "parked" on the boom to attach to. I bring my main preventers all the way forward to blocks on the toe rail then all the way back over deck to Lewmar line stoppers which slip at a load that is below line strength. These stoppers are blocks of three at each side and used for jib furler etc. as well.
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Old 09-02-2016, 08:55   #15
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Re: Preventer Rigging?

We did not have a traveler on our Whitby. There were two strong padeyes at each aft corner just behind the cockpit. Beefy snap shackles on the boom end were on 5:1 purchase blocks with a cleat on the bottom. When sailing we kept both sheets on and would take out the slack of the windward one while the leeward one was snugged up. This effectively became a semi-preventer especially when we were gybing as we would snug up the windward one as we brought the boom over gradually (in strong winds) but loosing the windward side a bit at a time. Of course if you had a radical change in course there would be some slack. For downwind sailing we would rig a traditional preventer with snatch blocks on the rail led to an attachment on the boom and the bitter end led to a winch in the cockpit (or just tied off or to a clutch) if we needed both winches for anything. It all worked great for us but not something perpetual sail tweekers would like.
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