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Old 30-03-2008, 11:05   #1
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Advise for Preventer Line Size

I searched the forums, but did not find (I might not be good at these searches) for info about line size for a preventer. My boat is a 36 foot sloop (fairly light displacement) and the preventer will be attached to the end of the boom. What size line should I invest in?

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Old 30-03-2008, 12:21   #2
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I would not use anything bigger than 1/2 inch. A preventer is meant to part if your boom dips into a wave, that way hopefully the boom will not be bent.
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Old 30-03-2008, 13:20   #3
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What he said, you want stretch if you get back winded. And if you carry your boom all the way out you might dip it. We are fractional so this is less aconcern than back winding and preventing accidental gybes
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Old 30-03-2008, 15:11   #4
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Choose an opposite attachemnt point on the boat as close to the bow as possible for the safest lead.
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Old 30-03-2008, 15:22   #5
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On a similar size boat (Nauticat 37) we use a 3/8" line. I would not depend on a line parting. The preventer should be led back to the cockpit.

Agreed that it should led to the foredeck, then back to the cockpit.

Jack
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Old 30-03-2008, 15:41   #6
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You need a line with some stretch in it. It needs to be large enough so you can handle it OK. 3/8 is probably as small as you want for easy hand holding. You don't want a high-tech line in this application, as it will have too little stretch. Evans has a short article on line selection on his site The Right Line for the Job
If you are going to secure the line with a clutch, then you need to also make sure the line size is appropriate for the clutch.

Paul L
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Old 30-03-2008, 16:01   #7
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You need a line with some stretch in it. It needs to be large enough so you can handle it OK. 3/8 is probably as small as you want for easy hand holding. You don't want a high-tech line in this application, as it will have too little stretch. Evans has a short article on line selection on his site The Right Line for the Job
If you are going to secure the line with a clutch, then you need to also make sure the line size is appropriate for the clutch.

Paul L
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Old 30-03-2008, 16:07   #8
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Thanks for the Replies

I am planning on running the preventer from the boom end forward to a block attached to the bow cleat (or a hole I will have to drill through my solid toe rail) and then back to the cockpit. By the way, I have a fractional rig.
Pblais, I am not sure what you mean by lead the line forward to an opposite attachment point. Are you saying, for example if the boom is out to starboard, that the attachment would be on the port side bow?
One last related question, do you guys recommend 2 separate preventers (one line for each side) or is one line used with 2 blocks (one snatch block for each side) a better idea? I am not sure how the logistics for either set up would work in practise.

Thanks again, this forum is great,
Tom
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Old 30-03-2008, 16:29   #9
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I use two preventers port and stbd. with a fractional and swept back spreaders and I don't lead it to the bow but to the tow rail snatch block and back to a secondary winch. And I attach it to mid aft of the mid boom but not at the end. So far so good.

If I were off shore I would rig it to the bow and from the end of the boom.
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Old 30-03-2008, 16:33   #10
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In regards to dual lines, I really like Hal Roths preventer that he details in one of his books. Involves a hefty block shackled to the stem head, and a long line leading aft to the cockpit with a shackle. From the underside of the boom is a line shackled to a bail, the line is the length of the boom so it is cleated off out of the way when not needed.

Tack, go forward and attach the line from the stem to the line on the boom, go back to the cockpit and cleat off.
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Old 30-03-2008, 16:48   #11
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In regards to dual lines, I really like Hal Roths preventer that he details in one of his books. Involves a hefty block shackled to the stem head, and a long line leading aft to the cockpit with a shackle. From the underside of the boom is a line shackled to a bail, the line is the length of the boom so it is cleated off out of the way when not needed.

Tack, go forward and attach the line from the stem to the line on the boom, go back to the cockpit and cleat off. My side decks have enough going on that extra lines being lead aft from the stem are dangerous, and lines lead from the boom to the rail or genoa track make them darn near impassable.

I keep pondering installing a pad eye on each side of the forward hatch with a block block on each. One line runs from the cockpit forward and back. Cut it in half, and splice in a ring, from the ring a line runs aft to a bail on the boom 3/4 of the way back. Thoughts?
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Old 30-03-2008, 17:09   #12
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Firehoser 75,

Have you looked at boom brakes? I have a Walder boom brake and it beats a preventer hands down. Everything is rigged aft and it works on both tacks. I would go with a boom brake any day.
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Old 30-03-2008, 18:47   #13
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Quote:
Originally Posted by Firehoser75 View Post
...
One last related question, do you guys recommend 2 separate preventers (one line for each side) or is one line used with 2 blocks (one snatch block for each side) a better idea? I am not sure how the logistics for either set up would work in practise.
If you are headed offshore, you need to be able to gybe the main without going forward to re-rig the preventer. At least, that is the preferred way of setting this up. This normally takes two preventer lines, or as mentioned above one of the boombrake type devices. I have two lines run from the aft end of the boom to the forward end of the boom with spliced loops in them. These hang on cleats on the boom near the gooseneck. I then have two lines that run from blocks on the bow to clutches near the helm. The lines forward have snap shackles that can be walked forward and hooked to the lines permanently on the boom.

Paul L
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Old 30-03-2008, 20:38   #14
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I know my boat is a bit small, so this may not scale up well, but I use a bungie cord as my preventer. It doesn't stop the gybe, but it slows it down enough that there is no damage and will actually take enough force out of it that I can just hold the boom with one hand to keep it from swinging over if I need to. I imagine this is similar to what a boom brake does, but I'm not sure. Granted, I've only ever tried this in light to moderate winds, not sure how it would react in anything above about 20 knots or so.
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Old 31-03-2008, 04:42   #15
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I have 2 lines either side of the boom going from folding Wichard rings at the boom end to cleats either side of the mast end of the boom that I spliced eyes in. I have a single preventer line going from the cocpit secondary winch to a block at the stem and then back to whichever side I need - depending on which jibe I'm on. I saw this setup somewhere (can't remember where now) and thought it looked good. It works great. Preventer is really good in light winds too - to quieten down a slatting main in left over cross swells. Full length battens help this too. Best part is that I can set it up with the boom way outboard if things got hairy and I forgot the preventer earlier. I use 12mm 3 strand and it has just the right amount of stretch. Yep, its designed to break if I dip the boom.

The other really great idea I finally had set up was an overhead leech line for the main. No more hanging off the end with my wife screaming at me (well not for that now....). Not sure if she is saying get back, or let go!
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