Preventer Rigging -- Lessons from the Platino Disaster

[a64pilot]

I believe the only thing that is really different between a preventer and a brake is the controlled release upon hitting an adjustable point.
That wouldn’t be too hard to Engineer, whether it be a winch that will slip at an adjustable point or something similar.
I’d bet that if a sailboat winch were designed in the 21st Century it would be required to have a load point where it would slowly release. Think floor jack for an automobile, if you try to pick up something heavy enough that may collapse the jack, the fluid will just release through the valve, you can’t overload one.
Or your windlass for your anchor, mine and I assume others if you apply an excessive force, the clutch will slip and the chain will slowly be let out, or if the motor is driving it, it just slips.
Apply that process to a preventer on a big boat, and it will release similar to a brake, before something breaks.
At some point the thought process of I’ll build it so strong it can’t break becomes too heavy and expensive, then the thought changes to either a controlled release or a controlled failure mode.

[RaymondR]

The first fatality in this incident occurred because the preventer failed. One way or another this is always going to be a possibility with any system which requires human input for it's integrity of operation.

This fact leads to consideration of which is the more appropriate philosophy - prevention or mitigation?

Other factors intrude.

I don't use the main running down wind in heavy breezes but even in the light breezes I do the results of a back wind with a preventer in use are still fairly spectacular with the boat overpowering the rudder and consequent lying abeam with everything under great strain whilst I disconnect the autopilot and release the sheet and furl the genoa, Just loosening the preventer leads to nasty complications with the windward shrouds.

Employing a boom brake to allow the boom and main sail to swing across generally does result in the boat going onto a reach however since both sails are now set on the same beam just bringing the boat into the wind tames everything whilst generating far less stress on both crew and rig.

Having now pondered on how one would best implement this on a big boat I have decided that from an engineering viewpoint the utilization of an A frame type structure as the boom vang to carry the high torsional forces down to the deck and hydraulic rams with a double relief/metering valve system would best serve as a set and forget arrangement.

[Kamell]

Originally Posted by Kenomac

Dockhead,

Don’t fool yourself into thinking your preventer will hold if your main sail becomes backwinded. The forces are intense, something will break as I witnessed firsthand. The preventer is really intended just to keep the boom in place so its not flopping about due to the swell motion and help prevent a gybe. After the gybe becomes inevitable.... it won’t hold, something will break.

This is an apt statement. The word "preventer" requires heavy qualification; what exactly is being prevented?
When running, a preventer will keep the boom in place, especially when seas are bucking the rig back and forth a bit. Note: the top half of a mast of 40 feet, when pitching about by 30 degrees or so, can move tens of feet in seconds, and in lighter winds can actually momentarily exceed the apparent wind speed. The preventer can help keep the boom stable even if the sail itself is puffing in and out a bit.

But if there is sufficient wind, and one loses their bearing and backwinds, the force is often sufficient to break a component of the preventer sytem (Cleat, shackle or line itself). Plus, if the boom is not sheeted back firmly enough against the preventer, there may be play in the system that results in an extra shockload.

As a rule, do not rely upon electronic autopilot systems when on a run or broad reach, as the risk of a sudden erroneous course correction is there. These systems cannot respond to seas or sudden changes in wind direction.

I think of the preventer system as a three-way vector system. The topping lift (or main), sheet and preventer all converge under similar tension at the end of the boom, ensuring the boom is fixed in place in all directions. A similar three-way fixed point theory applies to proper poling out of the headsail and/or spinnaker.

Has anyone here ever used a snubber on the preventer to absorb sudden shockloads? (asking for a friend)

[Kamell]

One more thing: I have a cutter rig equipped with the requisite car rails for the staysail which are conveniently not in use when on a run. I have set the cars to the extreme fore of the rail (on the cabin top about four feet forward of the mast and eighteen inches inboard, and run a preventer from the point the sheet is fixed to the boom, forward through the car, and back to the staysail winches in the cockpit. This allows me to adjust the sheet and preventer simultaneously and fine tune both the height and position of my boom. The rail and car are much stronger than a pad eye or cleat. also, I can have a lazy preventer on the leeward side for easy gybing and resetting. No crawling around under that boom to move preventers.
I was able to run quite comfortably in a significant and variable following sea with a very stable boom.

[Dockhead]

Originally Posted by Kenomac

Dockhead,

Don’t fool yourself into thinking your preventer will hold if your main sail becomes backwinded. The forces are intense, something will break as I witnessed firsthand. The preventer is really intended just to keep the boom in place so its not flopping about due to the swell motion and help prevent a gybe. After the gybe becomes inevitable.... it won’t hold, something will break.

Just so happens that yesterday due to a pilot brain fart, my main did get backwinded in about 25-28 knots of breeze. An odd wave in lively sea conditions threw the stern out, and the pilot didn't catch it. I was sailing a bit by the lee which made it easier to happen; must be more careful about that in the future.


My preventer was on good and tight as I always keep it -- to eliminate snatch loads. Run to the bow cleat and back to a winch. Kicker on hard and outhaul on hard to eliminate most slack in the sail -- that's how I sail DDW with the mainsail.


So in the event with the main suddenly backwinded, everything held just fine, and the preventer successfully dealt with the loads and did its job.



Don't know what that would be like in 40 knots of wind, but I wouldn't use the preventered out main sail in 40 knots of wind.

[SailRedemption]

Originally Posted by Dockhead

Just so happens that yesterday due to a pilot brain fart, my main did get backwinded in about 25-28 knots of breeze. An odd wave in lively sea conditions threw the stern out, and the pilot didn't catch it. I was sailing a bit by the lee which made it easier to happen; must be more careful about that in the future.


My preventer was on good and tight as I always keep it -- to eliminate snatch loads. Run to the bow cleat and back to a winch. Kicker on hard and outhaul on hard to eliminate most slack in the sail -- that's how I sail DDW with the mainsail.


So in the event with the main suddenly backwinded, everything held just fine, and the preventer successfully dealt with the loads and did its job.



Don't know what that would be like in 40 knots of wind, but I wouldn't use the preventered out main sail in 40 knots of wind.

Even if you did have it out, it would undoubtedly be reefed further reducing the load on the preventer.

If the winds were lighter would you still have had a tight outhaul and vang(I assume what you call a kicker?)? Or do you keep the main tight going DW in all wind?

[wingssail]

Originally Posted by Kenomac

Dockhead,

Don’t fool yourself into thinking your preventer will hold if your main sail becomes backwinded. The forces are intense, something will break as I witnessed firsthand. The preventer is really intended just to keep the boom in place so its not flopping about due to the swell motion and help prevent a gybe. After the gybe becomes inevitable.... it won’t hold, something will break.

As mentioned previously and described by dockhead yesterday, this is not an absolute "something will break" is not always true.

In 27 knots of wind my boat jibed, through my error, and the backwinded main, held by a preventer, kept the boat nearly horizontal for several minutes and no part of the rig or preventer system broke, (however after some time the mainsail tore badly). This preventer was a 6 mm polyester double braid line led from the end of the boom to a stanchion base! near the shroud and then back to a cleat in the cockpit.

The report by dockhead above, is another example.

When a vessel can be "knocked down" in gusty weather without breaking something it stands to reason that a vessel which has been jibed can also be held down, in the opposite direction, without breaking something. The key is to avoid the shock load at the instant of the jibe. As dockhead states, the sail and boom must be held tightly in place. A snubber could also relieve the shock loads.

[Dockhead]

Originally Posted by SailRedemption

Even if you did have it out, it would undoubtedly be reefed further reducing the load on the preventer.

If the winds were lighter would you still have had a tight outhaul and vang(I assume what you call a kicker?)? Or do you keep the main tight going DW in all wind?

When going DDW, the sail is operating all in drag mode, no lift, so it seems to me that it doesn't need any shape. Furthermore, I don't need it bellying out and rubbing on the spreaders. So yes, I always keep it good and tight and flat when going DDW. YMMV!


Kicker = vang -- yes.

[jmh2002]

Originally Posted by Dockhead

When going DDW, the sail is operating all in drag mode, no lift, so it seems to me that it doesn't need any shape. Furthermore, I don't need it bellying out and rubbing on the spreaders. So yes, I always keep it good and tight and flat when going DDW. YMMV!.

This may make sense from a cruising point of view but when racing the outhaul (and downhaul, etc - boat dependant) is generally eased when rounding the top mark and heading downwind - it's faster - except in the case of heavy air and wanting to depower the mainsail as much as possible.

[MartinR]

Yes, there is more drag to a rounder shape.

[Dockhead]

OK, that makes sense.

Originally Posted by jmh2002

This may make sense from a cruising point of view but when racing the outhaul (and downhaul, etc - boat dependant) is generally eased when rounding the top mark and heading downwind - it's faster - except in the case of heavy air and wanting to depower the mainsail as much as possible.

[carstenb]

Coming late to this discussion. We've cruised about 20,000nm over the past 3 years. We always have our boom brake set and we set an end boom to forward cleat preventer when sailing downwind.

Of course, we're conservative sailors - whenever the wind is over 15 knots (sometimes before, depending on sea state) we reef and we almost always go directly to our second reef (we find that we don't go much slower and everything is much much easier, squalls etc when we are in our second reef.

Of course we're double-handing and that means single-handing when the other person is sleeping (half the time). So nighttime squalls, confused seas etc have to be handled alone and being in the second reef means life is much easier.

We don't worry about dipping our boom in the water - we have backward pointing spreaders and Capri is not a boat that wallows.

I might worry about the gooseneck if severe loads came into play - but if the gooseneck goes then the problems are major. Not sure how we would handle that situation.

As far as I know, no one makes boom brakes for really big boas - but they do make them for our size - 40 feet

[Cpt Pat]

Originally Posted by Kamell

Has anyone here ever used a snubber on the preventer to absorb sudden shockloads? (asking for a friend)

I won't use a preventer on my boat under any circumstances! They are an accident waiting to happen. They are a lubberly kluge. If I'm sailing so close to dead downwind that I might need a preventer - I fly twin jibs instead, and take in my main.

And to keep the boom from flopping, I use a Dutchman boom brake. It won't "prevent" the boom from swinging due to a backwinded main, but it will slow it down enough to prevent damage (especially to your skull) and will stop the boom from flopping in light winds or a slight backwinded-main condition. If the main is fully inflated while taken aback in heavy airs, you want the main to swing over in a controlled fashion. The alternative (if the preventer doesn't fail) is a knockdown and the boat being pushed astern and athwart against the rudder. That's how people fall overboard and how rudders get destroyed. Backwinding the main is how people used to "back boats up" before "sailboats" (wind-assisted motor vessels) had engines.

With preventers, as crew (never as skipper) I have personally seen a boom bent nearly in half when it "dipped" into the sea, a lower shroud and mainsheet block destroyed by a preventer failure and resulting crash gybe, and half a dozen knock-downs caused by a prevented main when it got heavily backwinded. I've also heard direct accounts of many bent booms/failed deck fittings and read of many injury-accidents involving preventer failures; including this one that could easily have resulted in death were it not for an incredible effort by the California Air National Guard.

Excerpt:

At about 5 AM Michael Kalahar and another crew member were on watch when a sudden swell twisted the vessel sideways back winding the main and causing the sail to travel hard to port. In doing so, the force of the reloaded sail shredded the preventer line allowing the main sail to travel at high speed across the cockpit and swing the mainsheet across the face of Michael Kalahar thus throwing him against the port side winch with the sheet wrapped around his throat and face.

https://web.archive.org/web/20140116...n-Pacific.html

Preventers are pure evil.

[Cpt Pat]

(session timed out)

Some alert Ham radio operators assisted in getting aid for S/V Wind Child. Remember that frequency: 14.300 MHz. There's nearly always someone listening. If you have an HF radio that operates on the 20 meter Ham band, it's your best bet when no one answers on the marine bands.

Story here: SV Wind Child

-Patrick
N8QH

[Dockhead]

Originally Posted by Kamell

. . . As a rule, do not rely upon electronic autopilot systems when on a run or broad reach, as the risk of a sudden erroneous course correction is there. These systems cannot respond to seas or sudden changes in wind direction.. . .

Maybe on smaller boats, but above a certain size no one hand steers a cruising boat once you're out of the harbour. I don't know about yours, by my powerful hydraulic pilot with computer by B&G normally responds very well to rough sea conditions, and in wind mode, changes in wind direction.



When you're on a really tricky point of sail like sailing wing on wing with the main a bit by the lee, it's good to be behind the helm at least to override the pilot if it makes a mistake. Wind mode on the pilot is good for this.

Originally Posted by Kamell

. . . Has anyone here ever used a snubber on the preventer to absorb sudden shockloads? (asking for a friend)

The problem with this is geometry. If your preventer is rigged to a bow cleat (rather than to a strut a la Open 60's), the geometry is not favorable unless the boom is right out. If you let the boom move, the forces on the preventer are magnified quickly.


Much better practice, I would say, is to prevent the shock loads in the first places, by having the preventer on good and tight and having the sail pretty flat (even if that reduces its power).


And of course avoiding getting the main backwinded. I don't use the main at all going downwind over about a F6. Not just because of the risk of getting it backwinded, but also because of the risk of dipping the boom once the sea gets up, and because of the risk of a broach from having the CE so far back. I would not have been using the main in this case except we had been sailing in much lighter conditions; the squall blew up suddenly. I should have immediately started getting rid of the main; good lesson for the future.