Advise for Preventer Line Size

[Sandero]

Mike I am not sure I understand how use use the double lines. Are they used by attaching the single line preventer to one or the other by using s shackle or snap hook onto the eye splice at the forward end? They just wait at the mast where you uncleat one and it becomes the extension to the preventer line?

[GordMay]

Dutchman Boom Brake:
http://www.mvbinfo.com/images/BB_om.pdf

Walder Boom Brake pictured

[Benny]

Whatever line size and system you use make sure the attachment point - pad eye - is heavy and through bolted and backed up with a plate. It doesn't matter how good your system is if the attachment fails.

[MikeNZ]

Hi Defjef, yep you got it right. I have a large snapshackle on the end of the line from the cockpit to the bow and back. Connect it to the shorter line on the side you need. Another thing that works well is to ease the preventer to gybe the main over as you simultaneously haul in on the mainsheet. Mike

[Joli]

I like preventers, they pin you down and make life exciting when you broach to weather. Not to worry though, something will break eventually and you'll pop back up.

[swagman]

Hi Tom,
My suggestion is to forget attaching a preventer to boom end as you'll risk bending your boom midpoint. End point mounting o fpreventers is old school thought - absolutely right when sheet point is equally end boom - not right when sheet point is inboard.
Think about it.
Fit end point preventer, and tension mid point sheet - loads on boom end are pulling it forward and mid point is pulled back. Slop that around for a few days and the boom with crease or in strong stuff, break. Usually at the sheet point.

Better idea is to fix preventer to point at / around sheet point. And if you invest in a velco covered strop you can wind round the boom to fix the preventer to, then you'll not need to worry about the preventer breaking as the velcro strop will open first.

JOHN

PS With boom length on Bavaria 36 the chance of you dipping the boom is absolutely minimal, but dependent on downwind sailing angles - ones always got the risk of an involuntary gybe - so a preventer still makes sense.

[swagman]

Originally Posted by Joli

I like preventers, they pin you down and make life exciting when you broach to weather. Not to worry though, something will break eventually and you'll pop back up.

No where near as much fun as when you broach to leeward with kite and pole underwater and mainsail with preventer still skyward! That ti me is REALLY being pinned down
JOHN

[Joli]

True enough. Nothin better then a sit and spin. Remember the blooper and the fun that could be had when you stuck the pole in the drink and tripped over it? All the stuff is now on the "new" weather side to deal with. Good times for sure

Originally Posted by swagman

No where near as much fun as when you broach to leeward with kite and pole underwater and mainsail with preventer still skyward! That ti me is REALLY being pinned down
JOHN

[Firehoser75]

Swagman,
Thanks for your advise and great explanation of the forces involved with end boom preventer and mid boom sheeting. It makes perfect sense!
I also like the idea of a strong (velcro) mid boom strop to attach the preventer lines to. Also sounds like you are familiar with the Bavaria 36, and that is comforting when considering your advise. I am now also going to investigate a boom brake (Dutchman).
Hopefully I will not experience the windward or the leeward broach! Neither sounds like a whole lot of fun, thank you very much!
Thanks everyone,
Tom

[gmalan]

A preventer is great and I use mine most of the time when going downwind ("gentlemen don't sail to windward", so that's a lot!), but you really don't want it to be the only thing restraining the boom when the poo hits the proverbial...

A preventer's principal role is to keep the boom (and mainsail) from flogging when running in moderate conditions, especially when the main is set by the lee. Under these conditions, the rolling of the boat can make the boom swing back far enough to backwind the main and start off an accidental gybe.

Regardless of how you set it up, during a planned gybe the preventer has to be let off and re-set on the lee side. SO, this is NOT a part of the running rigging that you can (or should) rely on when the going gets rough or you need to do things quickly. This was graphically illustrated to me recently when crewing on a fifty footer in the Sydney - Gold Coast race: with wind gusting to 45 knots we had to gybe, and opted for a "granny gybe" (tacking the bow through the wind) to reduce the strain on the rig. The crew responsible for the preventer was a bit slow throwing it off, resulting in a pad-eye ripped off the bow and a broken preventer line which proceeded to wrap itself around the prop... Thank gawd we didn't attempt a gybe!

Also, if you really get the boat out of shape and the main is backwinded, you need to release the preventer pretty smartly, and if you can't, it needs to be fail-safe - i.e the line should break at a lowish force rather than a high one (this is where the boom brake comes in). Imagine the 2 tonnes of force in a 1/2in preventer being released instantaneously when it breaks! I use 8mm polyester braid (stretchy) for my preventer (33ft Carter) and it runs all the way to the stem, through a snatchblock and back to a jammer on the cabin top where I can reach it from the cockpit and put it on a winch to set and (most importantly) ease off gradually when necessary.

A boom brake has a number advantages:

• The forces on the boom are controlled by friction, so you can never over-stress the boom with a boom brake.
• Depending on how you set it up, it can assist your boom vang by pulling down on the boom, or can even be an emergency main-sheet.

My boom brake is very simple - a figure 8 "rescue descender" used for rock climbing which i got off EBay for $45 and 20ft of 1/2in polyester braid. The line is shackled to the starboard toe-rail and runs through the figure 8 to the other toerail, through a block shackled to the toe rail and then back up to the cabin top jammers via a free sheave in the line organiser. I use a winch to grind it on. Because of the set-up, it effectively has a 2:1 purchase.

There's a photo of the boom brake on my blog at S.V. Sunny Spells · Running Rigging.

The boom brake does create a bit of an obstacle on the side decks, but you get used to it pretty quickly. I run my jacklines OVER the boombrake lines, which also keeps the tether hooks off the deck, at least over that area. However, having an intermediate "catch point" in your jacklines is not such a bad thing - if you get washed along the deck you'll get stopped midway rather than dangling over the transom!

[Easterly-30]

Sansom Trophy braid 3/8" has a breaking strength of 3000 lbs. Regarding the snatch block at the bow for the preventer: what size block are you talking about? I.e. what working load is that block expected to be in relation to the strength of the line?

Also, why not put a short length of line with a breaking strength rated below the breaking strength of the preventer line so your good preventer line or turning block doesn't break? Use it like a fuse in an electrical circuit.

[Steve Pope]

Mike could you post a sketch of your set up.

[Jim Cate]

Well, here is another approach that has worked for us on three different boats now.

We rig a three part tackle permanently on each side of the boat. Outboard ends are made fast to a strong (!) point near the chainplates, inboard ends go to the boom somewhere near the midpoint. The falls are lead back to the cockpit via a clutch, and thence to a secondary winch. This way one always has a preventer rigged, and so it gets used all the time... no going forward or snapping on lines when it's ugly out. This set up also works as a very powerful vang. When gybing, one can ease the boom over under perfect control, using the winch as a snubber. I first used this setup on my Yankee-30 years ago when involved in single-handed offshore racing, and it was so cool that we've used it on all o ur cruising boats.

On Insatiable II which is a fractional rig w/ swept-back spreaders and a 19 foot boom, the attachment point is farther forward than I'd really like (only about 1/3 of the length from the mast), but it has worked ok for 30k miles now. Incidentally, we now use webbing "bales" for all boom attachments these days: three wraps of 2 inch webbing, sewn in place around the boom, and with appropriate D-rings for attaching shackles to. They spread the load out on the boom a bit, last about three years in the tropics, and cost almost nothing.

I expect that this system will get razzed by the traditionalists, but it works well for us.

Cheers,

Jim and Ann s/v Insatiable II lying Gladstone Qld Oz

[svtaipan]

Hello Jim.
Pretty much what we do too. Question though. What size line are you using?
Cheers
Kris n David
TAIPAN