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Old 25-07-2019, 06:49   #16
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by a64pilot View Post
Donít believe me, try it, point directly into the wind under motor and loosen the sheet and see what happens.
That depends on the windspeed and sea state.
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Old 25-07-2019, 07:12   #17
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Preventer Rigging -- Lessons from the Platino Disaster

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That depends on the windspeed and sea state.


Explain please.
If either is horribly high will you have the main up?
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Old 25-07-2019, 07:18   #18
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by Kenomac View Post
Dockhead,

Donít 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 wonít hold, something will break.

Well, it will hold, and up to 50 knots with the whole mainsail up, provided the force is not increased by dynamic loads. I've done the calculation.


It's really important to have the preventer on quite tight so that the boom can't swing and build up momentum and create a snatch load. Then all bets are off.
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Old 25-07-2019, 07:22   #19
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by El Pinguino View Post
The massiveness of the boom indeed..... and the area between cabin and the helm was all being swept by the mainsheet and traveler combo..... so not as simple as tossing a line over the boom although that was attempted....and then reeling it in...... and I don't think the three of them just sat around waiting for the rig to come down....


From the report...

The boom was 8.6 metres long and weighed 678kg with the mainsail furled inside it. A length of the mainsheet was hanging from the end of the boom and the traveler car (which had broken free of its track) was still attached to the end of the mainsheet. The traveler car was 350mm long, weighed just over two kg and the crew described it as acting like a wrecking ball as it quickly caused substantial damage to the rear of the yacht.
After making their way to the helm station, the Owner and the surviving crewmember watched the motion of the boom and lay on the deck each time it swung past. The damage that occurred in the initial few minutes included the following, which happened in close proximity to the two men:
 The helm console (where the hydraulic sail handling controls were mounted) was smashed off of its pedestal while the Owner was at the wheel. This happened before he was able to finish furling all of the mainsail or any of the headsail (the headsail remained half furled as it had been set). The surviving crewmember soon realised that the broken helm console was interfering with the steering wheel, making it even more difficult to turn. He used his legs to push the console away until he was later able to tie it back from the wheel.
 The bimini was smashed off while the two men were beneath it. This was left hanging by one webbing strap which the surviving crewmember cut to allow it to fall overboard and out of the way.
 The cockpit table was torn from the deck and propelled over the side.
 The steering wheel was buckled and one of its spokes was broken, adding to the difficulty in
turning the wheel.
 The life lines at the rear of the yacht were knocked down on the starboard side.

Platinoís crew were unable to regain control of the boom following the failure of the preventer and mainsheet traveler. The surviving crewmember did attempt to lasso the boom by throwing a line over it as it swung across the rear of the yacht. However, he was unsure what he would tie the line to, if he had been successful. The two men took turns at steering the yacht and were able to subdue the boomís motion somewhat at times. This was achieved by adjusting the yachtís heading in an attempt to both restrict the rolling motion and keep the boom in contact with the water on one side or the other.
Despite the crewís efforts, the boom continued to swing from side to side throughout the day. The surviving crewmember stated that the force was sufficient to cause the entire boat to shake as the boom repeatedly impacted on the shrouds.

The actual cause of the initial gybe was not down to a rogue wave as the owner thought but a leak on the hydraulic steering.....

PS... the weight of boom and sail was 678kg....nearer to 3/4 of a tonne than a 1/4 of a tonne... about the weight of a small car....



I wasn't there, and I can't even imagine the behavior of an almost 700kg boom, so I won't argue about this. I'm glad I wasn't there!!


Another point in favor of a ketch rig -- reducing the size and weight of all this stuff.
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Dash me with amorous wet . . . . I can repay you."
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Old 25-07-2019, 07:35   #20
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by a64pilot View Post
Explain please.
If either is horribly high will you have the main up?
They were in gale conditions, gusting to 48kt, with 2meter sea from the south and 3meter swell from the north. Even with no mainsail up, and pointed more or less into the wind (ever try to do that in seas like that?) the boom would swing wildly from side to side. Our boat is smaller than theirs (33t vs 36t) and I would not want any crew to be in the way of an unrestrained boom in those conditions.

In flat seas the boom may settle amidship pointed into a moderate wind. In that kind of sea, settle would not be a word I'd use to describe the boom. Furthermore, even in flat seas (which they were not), trying to hold the bow to the wind gusting to 48kt would be a challenge even if the steering were not damaged.

The difference in forces between a 10t boat and a 36t boat are significant, compounded by force 8 winds and significant sea state.
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Old 25-07-2019, 07:39   #21
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by Dockhead View Post
It's really important to have the preventer on quite tight so that the boom can't swing and build up momentum and create a snatch load. Then all bets are off.
Yes!

Our standard practice is to drop the main sheet further than the point of sail calls for, even if it puts the sail against the spreaders, then secure the preventer, then tighten the main sheet such that the preventer is in significant tension. If the boom were allowed any movement from a backwinded sail, the situation could get dangerous fast.
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Old 25-07-2019, 08:04   #22
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Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by accomplice View Post
They were in gale conditions, gusting to 48kt, with 2meter sea from the south and 3meter swell from the north. Even with no mainsail up, and pointed more or less into the wind (ever try to do that in seas like that?) the boom would swing wildly from side to side. Our boat is smaller than theirs (33t vs 36t) and I would not want any crew to be in the way of an unrestrained boom in those conditions.



In flat seas the boom may settle amidship pointed into a moderate wind. In that kind of sea, settle would not be a word I'd use to describe the boom. Furthermore, even in flat seas (which they were not), trying to hold the bow to the wind gusting to 48kt would be a challenge even if the steering were not damaged.



The difference in forces between a 10t boat and a 36t boat are significant, compounded by force 8 winds and significant sea state.


To be honest in 48 kt winds, my main wonít be up, and being a smaller boat with just a Mom and Pop crew we may be laying to a drogue.

Of course itís easy to say that, but as winds have a tendency to catch you by surprise itís not possible to arm chair quarterback it.
But yes, even my little boat can handle 2 to 3 meter seas on the bow, may have to hand steer it as my autopilot isnít high speed, and you donít get an indication of it becoming overwhelmed, that is what let to my accidental Gybe, and the sea conditions werenít of course as bad as this incident, but neither were the winds.

What Iím questioning is, is dropping sail when you have no control of the boom the best action?

I assume they were somewhat downwind, and when the preventer let go the boom came across and the combination of mass and velocity tore the car off of the traveller, then the boom should have continued on and slammed against the stay, making one Hell of a boom, but if they could have held a downwind course, it should have stayed there, pinned against the stay.
I think in my incident it came over and slammed into the other stay before I figured out that I need to hold a downwind course until I got the Genoa in and could turn into the wind and try to control the boom.

Maybe it was the pilot in me that thought turn into the wind and ďfeatherĒ the main?

Iím making an assumption that in this accident the crew was pretty much decimated immediately. Iím assuming the owner may not have been much of the working crew, and possibly the skipper if he or she was the spouse of the owner, maybe the boat was primarily sailed /handled by the crew, of which 2/3rds were gone?

Lot of assumptions there, I may well be wrong.

Then just as a further guess, Iíd guess that their action to furl the sail would have worked better on a boat that had in mast furling as opposed to in boom or a conventional rig where you drop the sail onto the boom. But by very significantly increasing both the mass of the boom and decreasing its aerodynamic dampening may not have been the best course of action.
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Old 25-07-2019, 08:15   #23
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by a64pilot View Post
To be honest in 48 kt winds, my main wonít be up, and being a smaller boat with just a Mom and Pop crew we may be laying to a drogue.

Of course itís easy to say that, but as winds have a tendency to catch you by surprise itís not possible to arm chair quarterback it.
But yes, even my little boat can handle 2 to 3 meter seas on the bow, may have to hand steer it as my autopilot isnít high speed, and you donít get an indication of it becoming overwhelmed, that is what let to my accidental Gybe, and the sea conditions werenít of course as bad as this incident, but neither were the winds.
On your boat, with 2meter seas from one direction and 3 meter seas from another, what would happen to the boom if unrestrained?

In my experience, most boats will experience significant roll motion in confused seas. An unrestrained boom is susceptible to swing in the presence of roll.

A more detailed reading of the report showed that a further complication in hand-steering the boat may have been that the autopilot was not disengaged, but was low on fluid and operating poorly as a result. Perhaps it wasn't working well enough to conclude it was on, but was working well enough to inhibit hand steering.
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Old 25-07-2019, 08:16   #24
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Re: Preventer Rigging -- Lessons from the Platino Disaster

Great discussion, and thanks Dockhead for the link to the report.

We rig our preventer as recommended (from the end of the boom to a cleat on the bow). My question is, would a boom brake help at mitigating the shocking loads when an accidental gybe breaks the preventer? Things may still break but if I can reduce the number of things that break... well, everything counts. (as clarification, I'm not referring to the boat involved in the accident since the loads are not near average of what I would see in my boat).
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Old 25-07-2019, 08:22   #25
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by Dockhead View Post
Well, it will hold, and up to 50 knots with the whole mainsail up, provided the force is not increased by dynamic loads. I've done the calculation.


It's really important to have the preventer on quite tight so that the boom can't swing and build up momentum and create a snatch load. Then all bets are off.
You’re sadly mistaken....something WILL break. Ours was tight.
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Old 25-07-2019, 08:30   #26
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by accomplice View Post
On your boat, with 2meter seas from one direction and 3 meter seas from another, what would happen to the boom if unrestrained?



In my experience, most boats will experience significant roll motion in confused seas. An unrestrained boom is susceptible to swing in the presence of roll.



A more detailed reading of the report showed that a further complication in hand-steering the boat may have been that the autopilot was not disengaged, but was low on fluid and operating poorly as a result. Perhaps it wasn't working well enough to conclude it was on, but was working well enough to inhibit hand steering.


Your probably right,thankfully I have never experienced those seas and hope to not.

However Iím questioning if greatly increasing the mass of the swinging object and reducing the tendency of the sail to either feather if into the wind or be pinned against a stay is the best course of action prior to gaining some kind of control over the boom?
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Old 25-07-2019, 08:30   #27
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Don’t believe me, try it, point directly into the wind under motor and loosen the sheet and see what happens.
I own a 36 ton sailboat. It would be super stupid if I was to do what you suggest in 3 meter seas and 48 knot winds.... which I have encountered... just like the boat was in... which was ultimately abandonded.
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Old 25-07-2019, 08:38   #28
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Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by Ivanvet View Post
Great discussion, and thanks Dockhead for the link to the report.

We rig our preventer as recommended (from the end of the boom to a cleat on the bow). My question is, would a boom brake help at mitigating the shocking loads when an accidental gybe breaks the preventer? Things may still break but if I can reduce the number of things that break... well, everything counts. (as clarification, I'm not referring to the boat involved in the accident since the loads are not near average of what I would see in my boat).


That is what Iím hanging my hat on. That something that gives in a controlled manner is preferable to something that holds fast but can suddenly let loose.
I have a tendency to think that an irresistible force and an immovable object can build horrendous forces and something may let loose
However itís contrary to majority opinion, it seems the majority of salty sailors seem to think of brakes as unnecessary gimmicks. Maybe a little harsh but you get the idea.
I wouldnít want a preventer and a brake, the sudden load imparted on a brake after a preventer let go, may likely overwhelm and break it.

Rigging a brake may not be an inexpensive proposition, in my case it was a few hundred dollars and the brake was already on board, and was a half days work.
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Old 25-07-2019, 08:43   #29
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Re: Preventer Rigging -- Lessons from the Platino Disaster

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Originally Posted by Ivanvet View Post
Great discussion, and thanks Dockhead for the link to the report.

We rig our preventer as recommended (from the end of the boom to a cleat on the bow). My question is, would a boom brake help at mitigating the shocking loads when an accidental gybe breaks the preventer? Things may still break but if I can reduce the number of things that break... well, everything counts. (as clarification, I'm not referring to the boat involved in the accident since the loads are not near average of what I would see in my boat).
Excellent point. We tried to rig a boom brake onto our 53 three years ago, and I do think it would have made a difference. But there was no way to do it.
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Old 25-07-2019, 08:51   #30
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Re: Preventer Rigging -- Lessons from the Platino Disaster

As far as dynamic loads, your getting them and they are quite large, the ďloosenessĒ of the sail will impart a significant dynamic load. There is no way that I know of to get around that.
When that sail backwinds and ďpopsĒ tight itís an initial shock load.
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