Preventer Rigging -- Lessons from the Platino Disaster

[Dockhead]

Originally Posted by wingssail

On many boats the boom vang system holds the boom up to nearly horizontal and the allowable travel is not enough to let the boom down to the deck.

And on boats with a hydraulic boom vang the gas pressure in the vang cylinder will hold the boom up, and full on mainsheet pressure won't pull it much more than a 1ft. After that it is in danger of breaking.

That's the case even on my boat, with a Selden gas strut, and that one had in-boom furling so a rigid vang. Dropping the boom down on deck was not an option.



Nevertheless, I still cannot imagine at all why one could not have gotten a line around the boom, even from relatively near the mast where the motion of the swinging boom would be much less. A bight around a midships cleat, throw the rope over the boom, back through the cleat and onto a winch. Haul in the line smartly on the roll to limit the snatch load on the line. You wouldn't need to get anywhere near the dangerous end of the boom with the flailing traveler car. You'd need a decently strong line, strong cleat, and strong winch, but surely all of that was available on such a boat.



I wasn't there, and can't even imagine what a 2/3 tonne boom must be like when it's out of control, but still -- why not? Would most definitely work on my boat.


And if that would be impossible, for whatever reasons I cannot imagine, then that means in my opinion that the rig altogether was unfit for purpose -- fundamentally unmanageable.

[Kenomac]

Originally Posted by Dockhead

That's the case even on my boat, with a Selden gas strut, and that one had in-boom furling so a rigid vang. Dropping the boom down on deck was not an option.



Nevertheless, I still cannot imagine at all why one could not have gotten a line around the boom, even from relatively near the mast where the motion of the swinging boom would be much less. A bight around a midships cleat, throw the rope over the boom, back through the cleat and onto a winch. Haul in the line smartly on the roll to limit the snatch load on the line. You wouldn't need to get anywhere near the dangerous end of the boom with the flailing traveler car. You'd need a decently strong line, strong cleat, and strong winch, but surely all of that was available on such a boat.



I wasn't there, and can't even imagine what a 2/3 tonne boom must be like when it's out of control, but still -- why not? Would most definitely work on my boat.


And if that would be impossible, for whatever reasons I cannot imagine, then that means in my opinion that the rig altogether was unfit for purpose -- fundamentally unmanageable.

The answer was in the full report. The surviving crewmember and owner couldn’t figure out a suitable anchor point to lash the boom to after just having watched two friends die and the toerail eyelet get ripped off the boat.

[Dockhead]

Originally Posted by Kenomac

The answer was in the full report. The surviving crewmember and owner couldn’t figure out a suitable anchor point to lash the boom to after just having watched two friends die and the toerail eyelet get ripped off the boat.

I read that, but it doesn't answer the question. The boat surely had midship cleats.


I appreciate that they might have been in shock after the horror of it all, and I wasn't there, and that boom is not like mine, but nevertheless the question remains.


And I say again -- if there was really no means on that boat to get that boom under control, then the rig was not fit for purpose. When the designers specify a 2/3 tonne boom they need to think about such things.


I think the preventer system also needs to be actually engineered, with an analysis of the dynamic loads, as part of the basic design of the rig. Rather than being just improvised, considering the life and death importance of its proper function, so vividly and painfully illustrated by this case. I did some basic engineering calculations on mine when I created it, within the limitations of my abilities, and based on static loads, but I'm now going to have an actual engineer review what I've done.



Another thing we might want to think about is some kind of fuse for the mainsheet traveler. This is going to be severely shock loaded if the boom gets away from the preventer, regardless of whether your mainsheet is poly or dyneema (because of the multiple purchase and relatively short length compared to the preventer). This whole discussion makes me appreciate boom brakes much more, but unfortunately these do not seem to be possible for a rig my size.

[scareygary]

I risk being shredded by posing this question, I suppose. I have only sailed much smaller boats (30'ers) at sea, but I've only used 3 strand twisted nylon for a preventer. I've always thought that one WANTED a bit of 'stretch' in this situation, not unlike with an anchor line. I'd certainly not use dyneema, personally. What is wrong with this thinking? OKay...teach me, but be gentle....

[Tillsbury]

I think there are two schools of thought on this one. The danger of a preventer without stretch is “when the boom does actually go over”. When I first learnt about preventers the thoughts that I came across were that the boom was going to go if they conditions dictated it, and the goal was to make sure that the preventer didn’t cause additional damage to the rig when it happened. The preventer was effectively only holding the boom in lighter conditions when there was a lot of rolling going on. An elastic preventer helps here, in acting somewhat as a boom brake such that nothing terminal happens if you do actually gybe. You can put this together with whatever you have at hand, if the winds are pretty light and the sea state lumpy. Another method is to have a “fuse” somewhere, such that the preventer fails predictably at one point in case of a gybe rather than damage the boom or mast.

The school of thought being shown by some posters here is that the preventer keeps the boom where it’s supposed to be at all times, whatever happens. For this you need great care in selecting high strength in all fittings and lines, and minimum stretch. The goal is that if you get backwinded you never gybe and everything holds.

I believe that, done properly and with these caveats taken into account, both are useful. The first in lighter conditions and the second in a well set-up boat.

I suspect the danger might appear when the two are mixed, or when the skipper isn’t clear in his own mind which one is in use. On Platino it seems that elements of the first type were in use, but without the attendant requirements of care and control in heavier conditions.

[Breaking Waves]

Originally Posted by scareygary

I risk being shredded by posing this question, I suppose. I have only sailed much smaller boats (30'ers) at sea, but I've only used 3 strand twisted nylon for a preventer. I've always thought that one WANTED a bit of 'stretch' in this situation, not unlike with an anchor line. I'd certainly not use dyneema, personally. What is wrong with this thinking? OKay...teach me, but be gentle....

There are three “challenges” with nylon.

#1 Is that it is agreeably “soft” on the accidental backing, but can be quite hard when/if the main then snaps back into place. That’s not a problem if it backs, and you catch it and let it thru. But it is not uncommon for the sail to back and then pretty quickly “unback”, sometimes a couple times - with nylon, in that situation it slams back with the elasticity accelerating it.

#2 Is that on long passages it lets the boom and gooseneck move over each wave. That accelerates wear and fatigue (particularly in the “small snap back” phase). A high modulus preventer can “lock it” and avoid that passage. This is pretty much only a concern to those doing repeated long passages.

#3 a “purpose” of a preventer is to prevent anyone getting hit in an accidental jibe. With nylon, the boom will swing a pretty long way, often as far as mid-ships. No-one “should be” standing in that zone, but it is objectively less preventative on this aspect in case someone accidentally is there.

There are size and strength consideration, but they can be properly engineered with nylon.

[DumnMad]

Originally Posted by scareygary

I risk being shredded by posing this question, I suppose. I have only sailed much smaller boats (30'ers) at sea, but I've only used 3 strand twisted nylon for a preventer. I've always thought that one WANTED a bit of 'stretch' in this situation, not unlike with an anchor line. I'd certainly not use dyneema, personally. What is wrong with this thinking? OKay...teach me, but be gentle....

In most cases I think you are right, it reduces the load in the line and on the fittings.

In the Platino case failure of the preventer was prior to the boom getting up speed and momentum. Failure of the line caused by poor purchase angles.
The line broke so Dyneema would be better. But although the Dyneema line may not have broken it may have ripped off fittings.
If it was cleat failure first then sure, nylon stretch would have greatly reduced the load on the cleat.

[model 10]

People have dissed my preventer set-up several times but it has worked well at sea. My understanding is, all the preventer needs is a longer arm than the boom. I have a preventer block lashed to the top shroud chainplate at the hull. The gooseneck is several inches aft of that so the preventer has a longer arm than the boom. I use 3/8" double braid and the line catches on the boom gallows as the boom goes by. It's not to big a deal. It happens to me at night when the auto pilot or windvane fails cause I can't steer for **** in the dark. I've gone round and round in circles with the boom going back and forth, finally giving up and heaving to, a couple of times

[pbmaise]

Originally Posted by a64pilot

One assumes that if a preventer won’t hold in stronger winds, that it’s an inadequate preventer?
Seems to me that stronger winds is exactly where you need one?
Now I’m a newby sailor, I’m not the guy with millions of miles and circumnavigations under my belt, so I go by intuition, which of course can be wrong.

But surely the experienced guys that fit preventers fit ones that are enormously strong?

Yes and no.

The answer to the question is the preventer adequate all depends on wind conditions, sail area, boom area, boom weight, and sea state.

Just a violent sea state along with a heavy boom could be enough to break a preventer without any sails aloft.

It is my belief that people with in boom furlers are tempted to fly more sail area in heavier wind conditions.

Thus in addition to the weight of the boom issue you could, as was this case, be compounding problems by flying too much mylar.

As to the second question... Yes heavy winds should be the reason to have a preventer employed, and if they are too heavy you shouldn't need one since they mainsail is 100% down.

[Joli]

We tend to treat the boom as Breaking Waves describes. Nail it down so it doesn’t move. Earlier this week my wife and I were sailing from Gaspe to Port Hawkesbury and ended up in nasty swells. We secured the boom with a 3/4” line from the boom end to the rail to a winch to stop the main and boom from shaking the rig. This was close reaching in 23 knots, you would think there would have been enough pressure on it from the wind so this wouldn’t be needed but big gear takes a heavy hand to control and the shock loads are enormous. Our main and boom probably weigh over 500#’s.
Platino wasn’t able to secure the boom to prevent the loss of the rig but if they didn’t have a very strong location to secure it to they were in a bad spot.

[RaymondR]

Originally Posted by Dockhead

That's the case even on my boat, with a Selden gas strut, and that one had in-boom furling so a rigid vang. Dropping the boom down on deck was not an option.



Nevertheless, I still cannot imagine at all why one could not have gotten a line around the boom, even from relatively near the mast where the motion of the swinging boom would be much less. A bight around a midships cleat, throw the rope over the boom, back through the cleat and onto a winch. Haul in the line smartly on the roll to limit the snatch load on the line. You wouldn't need to get anywhere near the dangerous end of the boom with the flailing traveler car. You'd need a decently strong line, strong cleat, and strong winch, but surely all of that was available on such a boat.



I wasn't there, and can't even imagine what a 2/3 tonne boom must be like when it's out of control, but still -- why not? Would most definitely work on my boat.


And if that would be impossible, for whatever reasons I cannot imagine, then that means in my opinion that the rig altogether was unfit for purpose -- fundamentally unmanageable.

Taking one of the genoa sheets of and taking it over the top of the boom to the sheet block on the other side would probably have been sufficient. Another possibility if the gooseneck and vang arrangements allow is to use the topping lift to hoist the boom vertical against the mast.

And, if the problem with the steering was that the autopilot was still engaged either turning it of at the main breaker or removing the connector of the solenoid valve would have solved the problem.

[cyan]

Originally Posted by Dockhead

Nevertheless, I still cannot imagine at all why one could not have gotten a line around the boom, even from relatively near the mast where the motion of the swinging boom would be much less. A bight around a midships cleat, throw the rope over the boom, back through the cleat and onto a winch. Haul in the line smartly on the roll to limit the snatch load on the line. You wouldn't need to get anywhere near the dangerous end of the boom with the flailing traveler car. You'd need a decently strong line, strong cleat, and strong winch, but surely all of that was available on such a boat.

Yeah, the report is lacking here. The rig stayed up for more than 8 hours after the crash gybe. A failed lasso attempt was noted, along with an unanswered question of where even to secure such a lasso.

BUT...

That is a LONG time to come up with zero good solutions. (though it's hard to imagine the effects of such trauma) The report stated that the foreward hatch, the only safe way to get to the foredeck, was blocked by the tender. That doesn't sound like an 8 hour insurmountable problem, especially when your friend is in the water and it's still daylight. (one dead, let's try hard to avoid making it two?) There seemed to be an attitude of defeat, as the three survivors were sure the rig would collapse and "hoped it would come down during daylight". Maybe understandable, but you would hope somebody would respond by refusing to give up, as the captain believed she had even marked the mob position.

The other thing missing from the report (or I missed it) is even an estimated reefing amount of the main at the time of the accident. The 3D computer simulation of preventer loading shows the boom furled maybe 50%? I'm curious because in my experience it's easy to judge main overpowering by heeling amount, but not so much if your beam reach is flirting with DDW. The mono seems more like a catamaran at that point, where you might want to reef by the numbers and not by feel? (ok, maybe no main at all in 30-35 knots, 120 degrees)

[a64pilot]

Originally Posted by Dockhead

This whole discussion makes me appreciate boom brakes much more, but unfortunately these do not seem to be possible for a rig my size.

No, they are definitely possible, just likely not a relatively inexpensive thing that can be safely “thrown together” like it can be on a smaller boat like mine.
It would likely require some customization, possibly even a different system entirely, and that gets expensive.
But it certainly can be done.
With the kind of money these boats cost, I assume the need isn’t considered to exist, or they would have them.
In this accident the mass of the boom if anything may have done more to prevent the preventer breaking, it wasn’t a hinderance until after the boom was loose. Even if it were a lighter weight boom it may have been just as deadly.


In truth, and I don’t want to get the Cat people upset, but I would assume that it’s not rocket science to design a system that would loosen a sheet on the main of a cat when forces exceeded a certain amount too, and yet that’s not done, but escape hatches are fitted.
Yes, I know that high winds are not the only force that can capsize a boat.
It may be that the legal aspect of having a safety system that can’t possibly protect in all situations drives the decision?

[jmh2002]

Originally Posted by a64pilot

In truth, and I don’t want to get the Cat people upset, but I would assume that it’s not rocket science to design a system that would loosen a sheet on the main of a cat when forces exceeded a certain amount too, and yet that’s not done, but escape hatches are fitted.

These systems already exist. But you are right, they not fitted as standard.

Having said that there are a lot of things not fitted as standard in general. Even a boat marketed as a blue water cruiser is generally not really setup for full time live aboard cruising.

The motoring industry seems to have come a long way in this regard, with ABS, Airbags, etc, and in Europe it is quite common to see relatively normal priced cars already with front 'radar' for automatic braking and other safety related functions.

The marine industry is still quite far from that level though.

[Ericson38]

Originally Posted by RaymondR

Taking one of the genoa sheets of and taking it over the top of the boom to the sheet block on the other side would probably have been sufficient. Another possibility if the gooseneck and vang arrangements allow is to use the topping lift to hoist the boom vertical against the mast.

And, if the problem with the steering was that the autopilot was still engaged either turning it of at the main breaker or removing the connector of the solenoid valve would have solved the problem.

Don't know where their genoa sheets were, being used, furled up, etc, but I keep a 100 foot of 5/8 stay-set-x and many snatch blocks (large) in the hanging locker/nav station area. Having this bridge deck traveler sounded like a compromise. I had one on an Ericson 30+ in the 80's. Yes, in the way, but large main with a LOW Kenyon Sparcraft boom.