Preventer Rigging -- Lessons from the Platino Disaster

[a64pilot]

Originally Posted by accomplice

No, it wouldn't be. I'm thinking about the forces on the attachment points. With the boom attachment that far forward, I'd be worried about the forces involved on a bigger boat.

I don’t understand, what wouldn’t be?
I agree on attachment points. I believe my weak link is where the brake attaches to the boom. I’d like to find a stronger fitting, mine slide in a track bottom of the boom, I’d like to find a nice investment cast piece, mine is a loop welded to a plate that slides into the track.
Although as a brake releases and not holds, the forces ought to be much lesser.

[Ericson38]

Originally Posted by accomplice

No, it wouldn't be. I'm thinking about the forces on the attachment points. With the boom attachment that far forward, I'd be worried about the forces involved on a bigger boat.

My mid ship cleat lines up with the boom's preventer bail. In the vertical plane, there would be a lot of downforce, resisted by the sail itself as well as the topping lift. In the horizontal plane, the system has much better angles than the boat in the report.

[AJ_n_Audrey]

A couple of years ago, sailing downwind at night, the autopilot ram ripped away from its base. I had a preventer rigged from the end of the boom through the bow chock to the capstan. The boat fell off before we could grab the wheel, and the accidental gybe did not break the preventer line (spare halyard, fyi), but it did break the bow chock. A lot of force there.

[cpisz]

I have never seen a better example of why we should have a boom brake. They do not have to be expensive. A $50 figure 8 boom brake could have save a life. It just needs to slow the boom enough to prevent major damage and maybe time to duck. I just don't like the idea of getting backwinded with a fixed preventer. I have had it happen and it is quite unpleasant.

[Kenomac]

Some of you should go back and review post #3. Our preventer broke in an instant, the forces in play on a 53ft boat are intense compared to 30-40ft boats. On our 63ft 36 ton boat, the forces in play are mind-boggling and impressive to say the least. The mast is 90ft tall and the sail area larger than most houses. In 50 knots of wind, us humans on a boat like the one abandoned... are like a flea on an elephants behind. You absolutely can’t imagine what will happen when you encounter those forces...unless you’ve been there. A boom brake on a 36 ton boat won’t work, that’s why you don’t see them in use or being sold.

[accomplice]

Originally Posted by a64pilot

I don’t understand, what wouldn’t be?
I agree on attachment points. I believe my weak link is where the brake attaches to the boom. I’d like to find a stronger fitting, mine slide in a track bottom of the boom, I’d like to find a nice investment cast piece, mine is a loop welded to a plate that slides into the track.
Although as a brake releases and not holds, the forces ought to be much lesser.

Sorry for the ambiguity: the downforce on the main would not be insignificant. As to the loading of the attachment points, though, my back of the envelope indicates forces larger than the specs on any of our other running rigging.

[a64pilot]

I would assume any kind of brake for a boat that size would be a custom design, don’t think anything off the shelf would work?

There is something about that schematic of the accident boat that doesn’t look right too, don’t know if it mast placement or boom size or what, but it looks like where the boom is on the drawing would put it at least in contact with the shrouds?
But with the preventer both that far out on the boom and the attachment point that close inboard, surely they had to know it was inherently very weak?
What broke, the line or the attachment points? Was the line also undersized? It would seem no one thought out how strong the forces would be, or didn’t take the need of a preventer seriously?

Then finally, it seems the experienced sailing crowd isn’t impressed with brakes, so maybe we are missing something?

[accomplice]

Originally Posted by cpisz

I have never seen a better example of why we should have a boom brake. They do not have to be expensive. A $50 figure 8 boom brake could have save a life. It just needs to slow the boom enough to prevent major damage and maybe time to duck. I just don't like the idea of getting backwinded with a fixed preventer. I have had it happen and it is quite unpleasant.

As Kenomac said, that might work on a smaller boat. To manage the forces, the attachment point would need to be in the aft half of the boom, preferably all the way aft. On most boats it isn't practical to rig a brake there.

[Cheechako]

Originally Posted by accomplice

Two reasons: First, off the wind in anything but calm seas the roll of the hull can backwind the main and the boom will slam about -- not a gybe, but large shock loads and a jarring experience. Second, because an accidental gybe can be catastrophic (as described in Platino report), precautions should be taken to avoid it. Saying, "I'll stay on top of things" is prone to human error and is of limited viability on multi-day offshore passages with multiple crew. I can watch something closely for a few hours -- not for a few days.

Yeah, still, just not comfortable in high winds using a preventer of any kind. I'll adjust course if necessary, get rid of so much roll which is ugly anyway, etc. The loads can be huge as people mentioned and I just dont like it. But then, I'm a pretty conservative sailor, or maybe fearful is a better word!.

[accomplice]

Originally Posted by a64pilot

What broke, the line or the attachment points? Was the line also undersized? It would seem no one thought out how strong the forces would be, or didn’t take the need of a preventer seriously?

Then finally, it seems the experienced sailing crowd isn’t impressed with brakes, so maybe we are missing something?

They used a two part preventer, with a pennant fixed to the boom and a second line bent to the first using a bowline in each. The pennant was first lead through a snatch block attached to a padeye bolted to the rail. I believe they had two failures -- first was that the other line (not pennant -- not sure what you'd call it) failed. Then the bowline in the pennant was held by the snatch block. The second failure was when the padeye let go.

While the lines were (obviously) undersized, the report identified several factors, including undersized line, line weakened by a bowline, and miscommunication that lead to an undersized padeye -- but the primary factor was the arrangement that attached too far forward on the boom and too far aft on deck. They also noted inappropriate use of a snap shackle and poorly considered angle of deflection through the block.

As skipper of a larger boat, the things I'll do differently from reading this are:
* Always use a strong (spectra) line for preventer (I've already learned this -- but need to ensure crew follows this).
* Get the best angle you can for the preventer -- aft on the boom, forward on deck -- my typical attachment point was 60% back on boom and 60% forward on deck, I will switch to 95% back on boom and 95% forward on deck.
* Train crew in use of MOB recovery equipment or discuss more thoroughly what it does.
* Alter PFD protocol to include whenever called on deck for emergencies.
* More regularly check autopilot hydraulic fluid level.

[RaymondR]

Originally Posted by accomplice

In a storm situation, sure. This was downwind sailing in force 8.

Well for me in the boats I sail in force 8 is storm sailing. Perhaps not in a bigger vessel but the sloop rig with it's relatively large main sail down wind sailing in high winds with the main is probably the trickiest and riskiest point of sail.

How you set up the boat for down wind sailing is largely a matter of personal preference and related to your own level of experience with the vessel in various sea states, risk assessment is largely a matter or ones own experiences and perceptions of probability and consequences of an action.

If the vessel is stable and tracks well down wind I would be more likely to employ the main down wind than if it moved around violently under wave action.

Being a senior citizen, single hander and starting to have less agility I tend to leave the main down and the boom securely prevented from any swinging motion on down wind legs on windy days.

From a fit-for-purpose design viewpoint I would not want a piece of gear as heavy as the boom on the subject vessel free swinging nor would I be comfortable with the Rube Goldberg preventer and boom brake arrangements we employ on smaller vessels - it is a recipe for disaster.

[accomplice]

Originally Posted by Cheechako

Yeah, still, just not comfortable in high winds using a preventer of any kind. I'll adjust course if necessary, get rid of so much roll which is ugly anyway, etc. The loads can be huge as people mentioned and I just dont like it. But then, I'm a pretty conservative sailor, or maybe fearful is a better word!.

I'm not sure force 8 would be enough for me to alter course, but at some point when the wind builds I would definitely want to be headed deep off the wind. With even a small bit of mainsail up, I would want a preventer. I've found on our boat, though, that the most stable and comfortable situation for high winds is downwind being pulled by stay sail alone.

I believe the conservative thing to do is shorten sail and check the preventer.

[Don C L]

Wow, I had not read that before. To your query Dockhead, I think it is clear, and the report confirms, your set-up is the best that can be done, the weak link in your system then may be the gooseneck the farther out the boom goes, the load will be transferred to the gooseneck at its weakest angle. Also, unless it is a freak wave or wind, the main will probably be reefed. I tend to agree though that a big gybe WILL break something in there, or at least I always expect that something WILL break. Most I see are rigged to stout chainplates near the rail up to mid-boom but that's on smaller boats. As far as corralling a swinging boom, one of that size and weight is way dangerous. Imagine actually getting a line around a swinging telephone pole and then lashing it to something in time? Ugh, a lot to go wrong there. May be possible to do safely, but I have my doubts. I had that stint crewing on a 65 footer and I would not have cared to try to stop that boom from doing whatever it cared to do, and it did not have in-boom furling. Still, I am wondering how the boom started swinging back and forth initially anyway. In this case I suppose the confused sea state turned the boat downwind instead of rounding up allowing the boom to return from the gybe? This part from the report is one I don't get: "The preventer failed and the boom swung violently across the back of the boat and out to the port side. The yacht was now out of control and the boom quickly swung back to the starboard side."
I am guessing it went "out of control" because the AP did not allow the boat to round up and kept turning it downwind?

And I too wonder why they had so much trouble rounding up, though it sounded like the traveller car flying around damaged the helm and made it dangerous to be in the cockpit. Anyway I was left with a lot of questions after reading.
That pad eye attachment was sure a joke, and the angle and the pennant, well the whole thing; I am surprised they were all ok with it as the report says. And then relying on the AP off the wind with no one near the helm... I don't know, that gives me the willies imagining it. I mean I know APs can do remarkably well but, maybe it's my experiences with off the wind issues that I get REAL attentive when running/broad reaching... heck I don't even trust a person at the helm let alone an AP unless I know they really know what they are doing. There was a cascade of events there due to the AP failure, the poor design of the preventer system and the mainsheet traveller in the cockpit like it was. I am not sure anyone ever sat in the cockpit and said, ok, what if we get a violent gybe? The most haunting and troublesome thing for me in that report though is that apparently no one took charge of the MOB, (no flotation device thrown, no reporting of location till later, no one maintaining visual,) which to my mind should absolutely have been the priority... but this is Monday morning quarterbacking...

[Ericson38]

Originally Posted by Don C L

Wow, I had not read that before. To your query Dockhead, I think it is clear, and the report confirms, your set-up is the best that can be done, the weak link in your system then may be the gooseneck the farther out the boom goes, the load will be transferred to the gooseneck at its weakest angle. Also, unless it is a freak wave or wind, the main will probably be reefed. I tend to agree though that a big gybe WILL break something in there, or at least I always expect that something WILL break. Most I see are rigged to stout chainplates near the rail up to mid-boom but that's on smaller boats. As far as corralling a swinging boom, one of that size and weight is way dangerous. Imagine actually getting a line around a swinging telephone pole and then lashing it to something in time? Ugh, a lot to go wrong there. May be possible to do safely, but I have my doubts. I had that stint crewing on a 65 footer and I would not have cared to try to stop that boom from doing whatever it cared to do, and it did not have in-boom furling. Still, I am wondering how the boom started swinging back and forth initially anyway. In this case I suppose the confused sea state turned the boat downwind instead of rounding up allowing the boom to return from the gybe? And I too wonder why they had so much trouble rounding up, though it sounded like the traveller car flying around damaged the helm and made it dangerous to be in the cockpit. Anyway I was left with a lot of questions after reading.
That pad eye attachment was sure a joke, and the angle and the pennant, well the whole thing; I am surprised they were all ok with it as the report says. And then relying on the AP off the wind with no one near the helm... I don't know, that gives me the willies imagining it. I mean I know APs can do remarkably well but, maybe it's my experiences with off the wind issues that I get REAL attentive when running/broad reaching... heck I don't even trust a person at the helm let alone an AP unless I know they really know what they are doing. There was a cascade of events there due to the AP failure, the poor design of the preventer system and the mainsheet traveller in the cockpit like it was. I am not sure anyone ever sat in the cockpit and said, ok, what if we get a violent gybe? The most haunting and troublesome thing for me in that report though is that apparently no one took charge of the MOB, (no flotation device thrown, no reporting of location till later, no one maintaining visual,) which to my mind should absolutely have been the priority... but this is Monday morning quarterbacking...

Yes, the pad eye attachment on the rail looks like jewelry more than substantial attachments would. Our running back pad eyes are really large, just a foot back from the aft lowers.

I also think an end boom preventer is going to transfer a lot of load into the gooseneck on a jerk force slam, and think a mid boom preventer would to a better job at overall force control and secure the boom, which is a beam. For sure, end boom preventers would have the best chance at not parting on their end of the battle, but unlike an end boom sheet, the end boom preventer is going to throw a lot of force back into the gooseneck, since the other end of the preventer is led forward at an acute angle, forcing the gooseneck forward and to the opposite side.

[Suijin]

Originally Posted by a64pilot

I don’t understand then why they furled the sail before they had some way to control the boom.
I know my boat is a much smaller boat and the forces etc are less, but with the engine running and her nose pointed into 30+ kts of wind, the sail just luffed and the boom was pretty much controllable, swinging yes of course, but not slamming into the shrouds. taking the sail down of course reduces the dampening of the sail, and increases the mass of the boom, both you don’t want.

"On the morning of June 13, Platino was 305 nautical miles NNE of Cape Reinga and sailing downwind on a broad reach2, in high wind, to gale conditions and a confused sea."

You said you you can throw your boom over your shoulder and carry it. We both have cutter rigs, so relatively short booms (mine is @ 12') but while I can carry my boom on my shoulder it is *heavy*, relatively speaking, probably 70 lbs. Even that, whipping around, out of control, slinging a traveller car around like a wrecking ball in 35-45 knots of wind in a confused sea and impaired steering, and no way to fully douse the main...I think believing that flicking on the engine and heading into the wind makes everything settle down to manageable conditions is a bit of wishful thinking.

This is one of my nightmare scenarios, having been on a boat (Valiant 42) and experiencing a hard gybe offshore during a squall. The boom was not even far enough out for a preventer. The force of the gybe did significant damage to several attachments points on the boom, some of them overbuilt.

This story is about a catastrophic failure leading to a gybe on a big boat. I think it's worth discussing, perhaps in a separate thread, tactics and hardware solutions for dealing with more common scenarios (squalls, broaches, etc) that lead to the same issues.