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Old 09-12-2004, 21:40   #16
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I guess I'm in the school of thought that you only use them offshore.
I would tend to disagree. There are many times that I've needed them right here in the Sound. I would rather say that you really need them on the larger vessels. Anything over 30' , that boom starts to become fairly powerful especially when out of control.

Once in a choppy conditions, I handed the tiller over to the first mate (her) to go forward and make some genny adjustments (the first mistake) and I got tangled up in the genny sheets. The first mate freaked and let go of the tiller (second mistake). Yes, I was wearing a life jacket! In the meantime the boat took it's own course and wanted to circle. The boom came across with such force that it parted the main track lines. Fortunatly they were old and gave it up instead of ripping out the track mountings or car.

New rules came about on that day!..........................._/)....(\_
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Old 08-01-2009, 12:33   #17
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Preventers

With todays high aspect ratio mains I do not feel it is necessary to attach the preventer to the end of the boom. Valiant yachts (I think a fine off shore boat) attach the preventer at mid-boom along with the main sheet. I have never heard of a Valiant boom bending from dragging the seaway. The preventer lines are much less obstructive than at the extreme end of the boom.
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Old 08-01-2009, 12:52   #18
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In the past I've used the vang tackle as a preventer, attaching it via a strap to the midship cleat (very substantial on my boat) which is located just aft of the chain plates. I'm thinking I'll change this.

I just spliced a shackle into 1/2 into nylon 3-strand. The line is long enough to go from the end of the boom up to the bow and back to the cockpit. At the bow I planned on using a tubular webbing strap to secure a snatch block to the forward bow cleat.

My thought was that when running I'd attach the shackle to the end of the boom, running it forward to the snatch block and back to the cockpit. Take up the slack and cleat it to the stern cleat since I have no free winches.

I've also considered the boom brake but have been put off by all the strings and what seems like persnickety adjustments to get them set right. Of course I'm not really thrilled about hassle of rigging the preventer as I've described either.

Like dinghies, there doesn't seem to be an elegant solution.

Rich
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Old 08-01-2009, 13:01   #19
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That's the way I rigged my preventers-- a 3/8" single braid line shackled to a bail at the end of the boom, run through a block attached well forward and then back to the cockpit. It's a safety issue to be able to make adjustments to the preventer from the cockpit, in my opinion. Changes can be made quickly and without having to go on deck.
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Old 08-01-2009, 13:05   #20
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Jeff is exactly spot on. Emphasis on the small nylon line (5/16 - 3/8" should be ample on most boats). Never use old running rigging lines and never winch the line down tight. They have little to no stretch and may cause something to break. Taking the line all the way forward then back to the cockpit gives plenty of length for lots of stretch.

Every system should have a weakest link and you should carry a spare week link for every system. The weakest link should be the easiest and cheapest thing to replace. Replacing a broken line or block is far cheaper and easier to carry a spare for than a broken boom and ripped up mainsail.

I learned this the hard way. I used to rig my preventer from the middle of the boom, down to a chain-plate on my Columbia 36. On the way down to NZ in 1985, we had an accidental jibe during the passage of a cold front. It snapped the boom in half, ripped up the dodger, tore the mainsail in half and beat the crap out of the boat in about 5 seconds flat. The end of that boom flying around was pretty dangerous too. We sailed the remaining 300 miles under jib alone (which actually wasn't too bad).

I sure wish that they would have had CF back in 1983. It would have saved me a lot of grief. On the other hand, I may have never left after reading some of this stuff.........
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Old 08-01-2009, 14:00   #21
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I have often weighed up the benefits and disadvantages of a preventer but in the end find it unnecessary on our own boat. Once the wind gets strong enough for accidental gybes to become a worry we find that we reach or nearly reach hull speed under genoa alone (and then heavy weather/storm jib alone when conditions become very heavy). Our boom is also well above head height over the short part of the cockpit that it overhangs.

Foresails alone make for very easy dumping of wind if the conditions include heavy gusts too - but some lighter rigs may not stand carrying a lot of foresail alone in heavy wind and sea conditions.

I know many others find the same so it may be worth trying - obviously not a good tactic if one is racing and every second counts, but then the crew is expendable .
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Old 08-01-2009, 14:11   #22
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I have often weighed up the benefits and disadvantages of a preventer but in the end find it unnecessary on our own boat. Once the wind gets strong enough for accidental gybes to become a worry we find that we reach or nearly reach hull speed under genoa alone (and then heavy weather/storm jib alone when conditions become very heavy). Foresails alone make for very easy dumping of wind if the conditions include heavy gusts too - but some lighter rigs may not stand carrying a lot of foresail alone in heavy wind and sea conditions.

I know many others find the same so it may be worth trying - obviously not a good tactic if one is racing and every second counts, but then the crew is expendable .
You're right. It also took me awhile to come to grips with the fact that it isn't efficient to sail straight down-wind anyway (unless you have a lot of wind). I find that sailing on a broad reach will add enough boat speed to compensate for the longer distance (through the water) of jibing down-wind. It's a heck of a lot more comfortable also.
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Old 08-01-2009, 15:22   #23
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Every system should have a weakest link .



My system is a bit of spare double braid from the mainsheet attachment mid boom (modern production boat) to amidships cleat as a turning black and cleated home on the aft mooring cleat.
The weakest link is the attachment to the boom being 2 mm spectra rated at 98kgs wound 4 times so breaking strain is about 400kgs.
It works fine and we have had a gybe of 2 'unannounced' and it worked well snapping after taking some of the power away

I would like one of those $400 boom breaks... but can someone give the $400?
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Old 08-01-2009, 15:27   #24
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My system is a bit of spare bouble braid from the mainsheet atachment mid boom (modern production boat) to amidships cleat as a turning black and cleated home on the aft mooring cleat.
The weakest link is the attachment to the boom being 2 mm spectra rated at 98kgs wound 4 times so breaking strain is about 400kgs.
It works fine and we have had a gybe of 2 'uunanounced' and it worked well snapping after taking some of the power away

I would like one of those $400 boom breaks... but can someone give the the $400?
That's what the nyon braid does..... and it's cheaper......
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Old 09-10-2011, 23:50   #25
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Re: Preventers

Reopening an old thread here, but the same topic.

So it seems to me preventers are important under any wind speed conditions when on direct downwind runs.

The question I have is, what happens when sailing in high wind runs with a preventer, and an accidental gybe occurs? Wouldn't it cause an uncontrolled weather helm roundup/broach from a reversed main, and then a terrible knockdown on the other side? Or what happens? Seems without control of the main, the rudder is useless.

We've already experienced the failed preventer during a race, 40 foot boat with 40 knot winds. We were under heavy winds in a downwind run and using a manually held two purchase preventer. The helmsman took the helm across wind without waiting for the main to be centered. Preventer was not being used for that -- it was only being used for the accidental gybe, not a 90 degree turn. Popped the boom in half. But -- no one was hurt, in part because the preventer prevented the boom for a moment enough for everyone to get down.

I think the next time we are in this situation, that we might try to use just the jib (as discussed in an earlier post).
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Old 10-10-2011, 02:15   #26
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Re: Preventers

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Originally Posted by marksatterfield View Post
Reopening an old thread here, but the same topic.

So it seems to me preventers are important under any wind speed conditions when on direct downwind runs.
Not only direct downwind runs. Whenever the wind is far enough abaft the beam that you start to run out the mainsheet. The key is whether or not there is enough mainsheet out for the boom to crash over in a jibe, not necessarily the exact wind direction. If there is, you need to rig a preventer.


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The question I have is, what happens when sailing in high wind runs with a preventer, and an accidental gybe occurs? Wouldn't it cause an uncontrolled weather helm roundup/broach from a reversed main, and then a terrible knockdown on the other side? Or what happens? Seems without control of the main, the rudder is useless.
No, none of the above. The boom crashes over. Probably to the spot where it should be, so no problem once it's there. The problem is the force with which it crashes over, which can decapitate crew and shred gear.

Does not affect the work of the rudder much.


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We've already experienced the failed preventer during a race, 40 foot boat with 40 knot winds. We were under heavy winds in a downwind run and using a manually held two purchase preventer. The helmsman took the helm across wind without waiting for the main to be centered. Preventer was not being used for that -- it was only being used for the accidental gybe, not a 90 degree turn. Popped the boom in half. But -- no one was hurt, in part because the preventer prevented the boom for a moment enough for everyone to get down.
"Manually held"?! Do you mean you hold the preventer in your hands?! Don't do that! A preventer should be run from the END of the boom to a block or cleat forward of the mast, and back to a winch, if you have a free one, or at worst, to a cleat. The forces exerted on the preventer can be quite high, and you don't want to attempt to absorb them with your hands.

It is essential to run your preventer to whereever the clew of the sail is belayed -- usually the END of the boom, and never to the middle. You will break your boom every time, even without a snap jibe, if the preventer is rigged to the middle.

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I think the next time we are in this situation, that we might try to use just the jib (as discussed in an earlier post).
Our boat is most stable on a run with headsail alone, unless the wind is very light and the mainsail area is needed. That is because the center of effort of the sail is forward of the keel -- making the boat self-stabilizing.
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Old 10-10-2011, 04:43   #27
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Re: Preventers

'It is essential to run your preventer to whereever the clew of the sail is belayed -- usually the END of the boom, and never to the middle. You will break your boom every time, even without a snap jibe, if the preventer is rigged to the middle.'

I'd like to pose an alternative to some of these beliefs.

I've found it really not good to even fit a preventer if your boat is rolling so much you risk dipping the boom. In those kinds of conditions we've learnt to go faster and safer by heading up just a little and sailing the angles.

I've also found when the conditions are lighter and you can sail deeper, but want a preventer to stop the sail coming over, it's not sensible to fit any preventer that cannot break to allow the boom to move before it breaks. We always fitted a preventer with velcro so it held to a point, then let go when it had to. If you are not racing and want cruiser comfort and safety, then a proper boom brake is the answer.

Finally and probably the most contentious here, is my suggestion you should not fit any preventer to your end boom if you've got a modern boat with your main sheeted to mid boom...............

Think about it.

Do this and you create two opposing forces. Winch the preventer to pull the boom end forward, winch your mainsheet to pull mid boom back, and where do you think is taking the strain?

IMHO it is a recipe for disaster we saw in action in the 2007 ARC when maybe 20 boats arrived in St Lucia with creases or broken booms. None said they dipped their booms in the sea. All had end boom preventers and mid boom sheeting.

Do not get me wrong, I agree end boom preventers are right if you've end boom sheeting, but respectfully suggest not otherwise.

Cheers
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Old 10-10-2011, 04:53   #28
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Re: Preventers

Greetings and welcome aboard the CF, marksatterfield.
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Old 10-10-2011, 05:55   #29
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Re: Preventers

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Originally Posted by swagman View Post
'It is essential to run your preventer to whereever the clew of the sail is belayed -- usually the END of the boom, and never to the middle. You will break your boom every time, even without a snap jibe, if the preventer is rigged to the middle.'

I'd like to pose an alternative to some of these beliefs.

I've found it really not good to even fit a preventer if your boat is rolling so much you risk dipping the boom. In those kinds of conditions we've learnt to go faster and safer by heading up just a little and sailing the angles.
I think most people would agree with you here. Dead downwind is anyway no one's best point of sail so most of us will jibe back and forth if we're trying to get there faster.

And whenever there's a risk of dipping the boom end, of course, you are right -- not only no preventer, but no boom hanging out, either. In such cases I furl the mainsail and center the boom.


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I've also found when the conditions are lighter and you can sail deeper, but want a preventer to stop the sail coming over, it's not sensible to fit any preventer that cannot break to allow the boom to move before it breaks. We always fitted a preventer with velcro so it held to a point, then let go when it had to. If you are not racing and want cruiser comfort and safety, then a proper boom brake is the answer.
Why would you want a preventer which is designed to let go, just when you need it most? A preventer which works like that will only make your jibe even more violent -- killing crew members and/or wrecking your boom and other gear.

Some people like boom brakes, and I suppose they have the advantage that they are less work to rig, and in some wind conditions maybe allow you to jibe with less work. But I personally would never rely on one in a jibe. I sail to prevent unintentional jibes -- if I jibe, I want to do it properly, centering the boom and so forth. And if I don't intend to jibe, I want the boom fixed in place, so I can get the boat under control and pointed back where it needs to be pointed. A boom brake is of no benefit in either of these situations.

A jibe is a lot of work on my boat -- the boom is over 20 feet long and the triple-purchase mainsheet is a couple hundred feet long. Well, so what? Who promised that sailing is supposed to be effortless? I would rather do a bit of work and do it properly.

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Finally and probably the most contentious here, is my suggestion you should not fit any preventer to your end boom if you've got a modern boat with your main sheeted to mid boom...............

Think about it.

Do this and you create two opposing forces. Winch the preventer to pull the boom end forward, winch your mainsheet to pull mid boom back, and where do you think is taking the strain?

IMHO it is a recipe for disaster we saw in action in the 2007 ARC when maybe 20 boats arrived in St Lucia with creases or broken booms. None said they dipped their booms in the sea. All had end boom preventers and mid boom sheeting.

Do not get me wrong, I agree end boom preventers are right if you've end boom sheeting, but respectfully suggest not otherwise.

Cheers
JOHN
But this is not logical at all -- it's not the mainsheet which provides the opposing force to the preventer in a jibe. It's the sail. So the violent force from a gibe is transmitted to the boom at the clew and has nothing to do with where the sheet is belayed. Obviously the closer to the clew the point of attachment of the preventer is, the less bending moment is induced in the boom if you have a violent jibe while your preventer is rigged. Mid-boom preventers are a recipe for a broken boom for this exact reason.

If you saw broken booms on mid-boom sheeted boats, it was because of the mid-boom sheeting, NOT because of how the preventer was rigged. If you don't have your preventer rigged, or if your preventer slips or breaks, and the boom goes over, the boom WILL break if it is sheeted mid-boom. That's why I categorically don't like mid-boom sheeting, which IMHO is a lazy way to cut down the length of the main sheet, at the expense of safety. Where you sheet is not as important as where you rig your preventer, because a properly rigged and strong enough preventer -- rigged at the end of the boom -- will protect the boom from a violent incident with the mainsheet. Still, the mainsheet is the second line of defense, so I would never have a boat with mid-boom sheeting, personally.

Obviously if you do have mid-boom sheeting and you rig your preventer at the end of the boom, you should avoid rigging the preventer with a huge amount of pre-tension on it -- that will bend the boom and hurt your sail trim. But you don't actually need any pre-tension at all on the preventer for it to work properly, as long as it has close to zero slack in it.
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Old 10-10-2011, 06:31   #30
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Re: Preventers

I am surprised this is such a contentious issue.

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Originally Posted by marksatterfield View Post
So it seems to me preventers are important under any wind speed conditions when on direct downwind runs.

We use preventers in two situations: #1 in light wind with a swell (in any wind angle) which causes the boom to move/slam and roll air our of the mainsail. A preventer in this situation saves wear on the gooseneck and sail and keeps the boat moving. I can't see how anyone would not agree with this application. #2 when sailing deep with the possibility of an accidental jybe (in any wind strength). I understand for some boats this could be a problem either because the boat will dip the boom in the water (generally on quite old designs with extra long and low booms) or because in an accidental jybe the rudder will get overwhelmed by the main and just lie on its side (generally IOR designs and usually when sailed with rather more mainsail for the wind speed up than a cruiser would typically use). If your boat has either of these two tendencies you can use a 'fuse' (light line which will break before your boom breaks) and we know racers who do this.

The question I have is, what happens when sailing in high wind runs with a preventer, and an accidental gybe occurs? Wouldn't it cause an uncontrolled weather helm roundup/broach from a reversed main, and then a terrible knockdown on the other side? Or what happens? Seems without control of the main, the rudder is useless.

However no boat I personally have ever sailed had either tendency. (honestly if we were sailing in conditions where I thought we had a serious chance of dipping the boom I would do something different with the sail plan. That can't be good semanship preventer or no) On our boats, the preventer catches the main from coming across and slamming into the other side. It just sits there backed against the preventer, waiting for you to either ease the preventer to allow the jybe or steer back onto course. The preventer just works as you might expect to prevent an accidental jybe and does not cause any bad behavior at all.
We happen to use a spectra very low stretch preventer, which we find superior in boat situations. In situation #1 (light air/big swell) a stretchy preventer will allow the boom to roll a little (as it stretched) which causes gooseneck and sail wear and allows the air to be rolled out of the sail. And in situation #2 a no stretch preventer does not allow the boom to move in an accidental jybe so there is no slamming/shock load while a stretchy preventer will allow the boom to move (quite far with a nylon preventer) and then it will slam back to its old position when the wind comes back to the proper side.

As to location, end of boom is always best but mid-boom is sometimes more convenient and works on many boats (but does pose more bending loading on the boom)
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