Preventer Rigging -- Lessons from the Platino Disaster

[cyan]

Originally Posted by philaw

I've just read a big chunk of the report, and as a novice its striking to me, not the mistakes that were made, but just how much you need to get right. If 57mm padeyes hadn't been fitted by accident instead of 76mm ones, those people might still be alive. They had a ton of cat 1 gear for MOB situations, but couldn't deploy any of it. They had quality harness life jackets, but the MOB wasn't wearing one. It seems like you need to know the breaking strength of all the components in your rig, including the complicating effect of knots and blocks, and the numbers involved are staggering. A traveller meant to cope with static loads of 2,268kg got broken!? And the mainsheet was flying around the cockpit with these loads, like a cheese wire?! Amongst other things, maybe the boat was just too damn big for them.

Getting the gear right should involve math, but you don't have to be an engineer to use the eye-test. If you simply understand that rigging forces are exponentially higher as the boat gets bigger, then look at a nicely rigged 30 foot boat and expect much MORE than double the hardware capability for a 60 ft boat.

That 2268Kg capable traveller you mentioned? Well, sure, that is the rated static vertical load. BUT- some jackass attached its end-stop with a single M10 bolt of unknown quality to hold the shock load of a ton and a half boom. That just does not pass the eye test. Never mind that one stainless steel bolt can have 5 times the tensile strength of another of the same size, depending on alloy and hardening treatment. (quality $$)

That toe-rail saddle-mounted pad eye? Well, they installed the wrong one that was smaller than specified. Sure, even the larger one was not designed to be used with a preventer with such a boom. But-- that wimpy loop of metal with 6 mm screws just does not pass the eye test on a boat that size, even for use with a jib sheet.

Take a look and see for yourself. Platino's large, thick toe rail saddle-plate was re-fitted for what exactly? To host that thin, wimpy padeye loop??! Tell me if that seems right to you.

[philaw]

Originally Posted by cyan

Getting the gear right should involve math, but you don't have to be an engineer to use the eye-test. If you simply understand that rigging forces are exponentially higher as the boat gets bigger, then look at a nicely rigged 30 foot boat and expect much MORE than double the hardware capability for a 60 ft boat.

That 2268Kg capable traveller you mentioned? Well, sure, that is the rated static vertical load. BUT- some jackass attached its end-stop with a single M10 bolt of unknown quality to hold the shock load of a ton and a half boom. That just does not pass the eye test. Never mind that one stainless steel bolt can have 5 times the tensile strength of another of the same size, depending on alloy and hardening treatment. (quality $$)

That toe-rail saddle-mounted pad eye? Well, they installed the wrong one that was smaller than specified. Sure, even the larger one was not designed to be used with a preventer with such a boom. But-- that wimpy loop of metal with 6 mm screws just does not pass the eye test on a boat that size, even for use with a jib sheet.

Take a look and see for yourself. Platino's large, thick toe rail saddle-plate was re-fitted for what exactly? To host that thin, wimpy padeye loop??! Tell me if that seems right to you.

I totally agree about your 'eye test.' Those fittings seem more like something you'd fit a curtain to than swing 2/3 ton of boom against in a gale. Is part of the problem here the extent to which boats are custom? An idiot can change a standard part on a car with a hangover, but a custom boat requires people to be on the ball.

I've read that airline pilots get specifically trained about overcoming awkwardness/ fears of upsetting the management to cancel flights when needed, and you can see a need for something similar on boats. The guy fitting the pad eye questioned if it was big enough but caved in. Someone else signed off on it. The owner also let it go. Was everyone just following everyone else and trying to avoid making a fuss?

Going back to the airline reference, pilots not getting training specific to the new 737 contributed to the recent crashes. Did the people captaining and crewing this boat know it well enough? The captain didn't understand what fittings he should have and in the report it says how the preventer could have been rigged to the bow, but the captain didn't do it.

I did training in accident investigation, and the methodology essentially always blamed the person at the top, because they hire, train and supervise everyone else. In this case the captain of the vessel and senior people involved in the fitting out of the boat would have had a big finger pointing at them.

[a64pilot]

Originally Posted by Kenomac

If a partially furled, loose footed mail sail was to backwind in 35 knot winds, the force of the sail on the boom would not be exerted on the outermost end of the boom, it would be somewhere near the middle.

Yes, but there is always a but.
Think using a long socket pull handle, the force is centered on the socket, but the longer the pull handle the less force you have to exert to loosen the nut.
Same for a Preventer, the further out the boom, the less force the preventer has to handle.
This of course assumes the pull handle and the boom can handle those forces of course, but one presumes that if the sheet is attached to the end of the boom, then that boom is Engineered for forces on the end of it.

So it depends on where the weak link would occur, cause there is a weak link. I’d suppose you would want the sail to be the weak link, that would I assume be safer than either the preventer breaking and or the boom breaking.

[Breaking Waves]

Originally Posted by Kenomac

Stuff happens out there

Ken, that section you quoted was NOT 'stuff happening out there'. It was stuff not done properly in preparation. The autopilot never ever being checked. You want a lesson - check your autopilot before every single passage. That should be basic. Check that the bolts are all tight and the hydraulic oil is topped up and not leaking. Takes like 5 minutes and should never be skipped. And there are a bunch of other safety-critical systems which should be very carefully checked before every passage.


"even when people do everything the correct way. Qualified marine technicians and engineers signed off on every part of the refit"

The preventer and the traveler were NOT done the correct way. Do you know for a fact the preventer, set up in that way, had 'qualified technicians and engineers sign off on it?' I honestly doubt it.

If you have actually read the full report (lol) you will remember the crew (without the skipper) rigged it on the 2nd night. They used a crap piece of old line for the 'extension' and they tied it in with a knot. Despite their 'experience', they did not seem to appreciate the likely loads at all. And the actually padeyes used/installed were already lower strength than specified for their outboard jib sheeting purpose and were NOT specified for preventer loads. The tradesman installing the padeyes even questioned their appropriateness because they did not pass a sniff test - but someone (in the refit yard) unidentified in the report incorrectly confirmed they were correct.

And those traveler end-stops - there was a serious QA screw up there in the 'engineering' - got to guess someone ordered something out of a catalog without doing any engineering, probably without knowing about the boom weight.

the experienced crew had no way of knowing what was about to come their way.

Sure they did, or should have. You get hammered about half the time you sail either way on this passage.

everyone should learn from what happened to lessen the possibility of a repeat.

Yes, exactly, and this was a human failure first and a technical failure second - there is definitely an important lesson there.

and #1 you need to take this sort of passage seriously - you need to do proper preparation and maintenance and inspection and make sure that safety-critical systems pass the sniff test. And then #2 on passage, you need to pay attention, not ignore signals of impending failure, and you need to sail the boat defensively so when stuff happens you have some margin for failure.

breaking wave

[Tillsbury]

Originally Posted by cyan

Getting the gear right should involve math, but you don't have to be an engineer to use the eye-test. If you simply understand that rigging forces are exponentially higher as the boat gets bigger, then look at a nicely rigged 30 foot boat and expect much MORE than double the hardware capability for a 60 ft boat.

That 2268Kg capable traveller you mentioned? Well, sure, that is the rated static vertical load. BUT- some jackass attached its end-stop with a single M10 bolt of unknown quality to hold the shock load of a ton and a half boom. That just does not pass the eye test. Never mind that one stainless steel bolt can have 5 times the tensile strength of another of the same size, depending on alloy and hardening treatment. (quality $$)

That toe-rail saddle-mounted pad eye? Well, they installed the wrong one that was smaller than specified. Sure, even the larger one was not designed to be used with a preventer with such a boom. But-- that wimpy loop of metal with 6 mm screws just does not pass the eye test on a boat that size, even for use with a jib sheet.

Take a look and see for yourself. Platino's large, thick toe rail saddle-plate was re-fitted for what exactly? To host that thin, wimpy padeye loop??! Tell me if that seems right to you.

And here we are back at basic seamanship. Looking at that pad eye I was thinking it would do to lash a dinghy down but not much else. And then while I was writing that sentence I got a little iffy -- I would probably check the weather forecast and only use it to lash the dinghy if we weren't expecting a storm...

You don't need maths to do that.

[Ericson38]

Originally Posted by a64pilot

Yes, but there is always a but.
Think using a long socket pull handle, the force is centered on the socket, but the longer the pull handle the less force you have to exert to loosen the nut.
Same for a Preventer, the further out the boom, the less force the preventer has to handle.
This of course assumes the pull handle and the boom can handle those forces of course, but one presumes that if the sheet is attached to the end of the boom, then that boom is Engineered for forces on the end of it.

So it depends on where the weak link would occur, cause there is a weak link. I’d suppose you would want the sail to be the weak link, that would I assume be safer than either the preventer breaking and or the boom breaking.

End Boom main sheets pull mainly down, and the horizontal angle is close to 90 degrees.

A preventer tied to the boom end and the bow will pull at the boom sideways and attempt to rotate it, putting large side loads into the gooseneck.

In my case, when the boom is at close to 90 off the centerline (just before hitting the shrouds) the mid boom preventer attachment hovers directly over the mid ship cleats, and the location along the boom is just about centered within the sail area it is controlling side forces from. The effective length of the preventer is then about 6 feet. Rig has a traveler car on boom, Forespar, roller furling in mast.

[Ericson38]

Originally Posted by Ericson38

End Boom main sheets pull mainly down, and the horizontal angle is close to 90 degrees.

A preventer tied to the boom end and the bow will pull at the boom sideways and attempt to rotate it, putting large side loads into the gooseneck.

In my case, when the boom is at close to 90 off the centerline (just before hitting the shrouds) the mid boom preventer attachment hovers directly over the mid ship cleats, and the location along the boom is just about centered within the sail area it is controlling side forces from. The effective length of the preventer is then about 6 feet. Rig has a traveler car on boom, Forespar, roller furling in mast.

There's the mid boat cleat (just forward of the boarding gate) adjacent to the preventer bail on the main boom.

[Jim Cate]

End Boom main sheets pull mainly down, and the horizontal angle is close to 90 degrees.

True when close hauled and the boom is near the centerline. When the boom is eased well out, beyond the range of the traveller, the pull is more nearly horizontal than vertical... varying greatly between different boats.

Jim

[El Pinguino]

Originally Posted by Jim Cate

True when close hauled and the boom is near the centerline. When the boom is eased well out, beyond the range of the traveller, the pull is more nearly horizontal than vertical... varying greatly between different boats.

Jim

Quite so..... and when the boom is out near the shrouds is the time you really need a preventer. So with my preventer leading to a point maybe a metre and a half back from the bow, the traveller aft of the helm, and the vang cranked hard down the boom is about as imobilised as it can get... which means no shock loadings... no problems.

[RaymondR]

Originally Posted by Jim Cate

True when close hauled and the boom is near the centerline. When the boom is eased well out, beyond the range of the traveller, the pull is more nearly horizontal than vertical... varying greatly between different boats.

Jim

Since there is a lot of strain on the main sheet and traveler and considerable shock loading when a hard driven, close hauled vessel pitches into short seas one wonders whether the sheet arrangement was fit for purpose even had it not failed on a jibe.

[MartinR]

Originally Posted by Tillsbury

and only use it to lash the dinghy if we weren't expecting a storm...

Only a small dinghy.

It is not very hard to see if fittings are sufficient if you can envision the forces. These are not.

[MartinR]

Originally Posted by RaymondR

Since there is a lot of strain on the main sheet and traveler and considerable shock loading when a hard driven, close hauled vessel pitches into short seas one wonders whether the sheet arrangement was fit for purpose even had it not failed on a jibe.

Obviously not, as it broke. I think also, in modern times, the shock loads are exaggerated by using Dyneema sheets. Once upon a time we used sheets that were somewhat flexible, but Dyneema is in fashion now. Obviously perfectl for halyards, but I can not see any good reason to use it for sheets.

[Dockhead]

Originally Posted by MartinR

Obviously not, as it broke. I think also, in modern times, the shock loads are exaggerated by using Dyneema sheets. Once upon a time we used sheets that were somewhat flexible, but Dyneema is in fashion now. Obviously perfectl for halyards, but I can not see any good reason to use it for sheets.

There are plenty of good reasons -- better control of the sail, lighter and more flexible cordage being easier to handle. All my running rigging is Dyneema. Even the furling lines.


But you are right about the shock loading and maybe we need some kind of fuse to deal with that.

[jmh2002]

Originally Posted by MartinR

Obviously not, as it broke. I think also, in modern times, the shock loads are exaggerated by using Dyneema sheets. Once upon a time we used sheets that were somewhat flexible, but Dyneema is in fashion now. Obviously perfect for halyards, but I can not see any good reason to use it for sheets.

As I'm sure you know the 'good reason' to use Dyneema or variants is to immediately convert wind force into boatspeed, instead of wasting this energy with rope stretch.

I don't see a problem with this in general, however I do agree with your point that the loads are then transferred to another part of the boat (or sails) and this needs be understood and accounted for.

And of course there are some applications where you do want some stretch, eg: anchor chain snubber.

In general it often appears to be people's lack of full understanding rather than a problem with gear or technology itself.

Remember when GPS came out and boats kept running aground on coral reefs? It wasn't really the fault of the GPS but instead that people didn't understand that the charts were no longer sufficiently accurate to work with this GPS.

[MartinR]

Originally Posted by jmh2002

As I'm sure you know the 'good reason' to use Dyneema or variants is to immediately convert wind force into boatspeed, instead of wasting this energy with rope stretch.

Yes, of course, for racing this is obviously a big advantage. But I doubt you would get any noticeable increase of speed on a cruising boat. The energy wasted in rope stretch is extremely low. But, yes, the foil profile is better maintained with Dyneema. For racing, 0.1% in speed gain means a world, for cruising basically nothing. Also, most cruising boats fittings are not designed to take the shock loads from Dyneema. Racing boats are. Needs thinking about.