Preventer Rigging -- Lessons from the Platino Disaster

[Kenomac]

Originally Posted by Joli

Haven’t posted here in a long, long time.

That said. It’s foolish to push a large boat in heavy conditions with a small crew. A sixty some foot boat in 35 true will easily sail at 12 knots with just a staysail. No reason to push the boat unless it’s fully crewed with capable sailors.

A 65ft boat on a beam reach in 30-35 knot wind, will be traveling at 8-9 knots with a partially furled mainsail... not 12 knots. They would have been experiencing the feeling of 20-25 knot wind in the cockpit behind the dodger with a moderate heel, nothing out of the ordinary and certainly not expecting what was about to occur when the steering failed.

Here’s what 40 knots from the stern looks like on a 53ft sailboat running on bare poles aided by the engine at 2100rpm for steering and battery charging. The seas are 2-3 meters just like in the report.

https://m.youtube.com/watch?v=HAKLm8vaR2k

[Tillsbury]

Originally Posted by cyan

Fascinating report. One has to wonder if the attitude was too casual regarding the preventer rigging, not understanding the forces.
When racing downwing on a much smaller (35ft) boat, we would sometimes use human-preventers, leaning on the boom for short legs in rolling seaas with maybe 15-20 knots. Dangerous, sure, but also maybe breeding contempt for the exponential scaling of the forces on larger boats.

These points stood out to me in the report...

Equipment:

1. preventer at very bad angle - leverage multiplied forces more than 10 times
2. insufficient (and old, history-unknown) extender line connected to the preventer pennant
3. insufficient preventer extender connection method (2 bowlines, weakening line strength by 70%)
4. autopilot hydraulic leak (not detected)- no low fluid alarm in system
5. bad hydraulic ram installation with plastic block on un-reinforced GRP that partially failed
6. undersized padeye installed by mistake- installer even noted it looked too small

Humans:

1. bad call: large main, decent winds, on super heavy boom broad reaching in very confused seas
2. too much relying on autopilot in rough conditions
3. didn't notice that the crippled autopilot system was occasionally failing to hold course at times during 3 hours before accident
4. noted the preventer angle was not ideal but assumed they had to do it that way apparently due to pennant length
5. survivors collectively very surprised that traveller gave way on crash gybe, clearly not understanding the forces involved

You missed:

Traveller moved to dangerous position without sufficient engineering input.
Traveller stops held by just one (!) M10 bolt of uncertain material and specification and source. Even so it held until the second crash gybe, but a traveller stop properly built for such a large rig could well have lasted a few more gybes, enough time to get the boat back under control. The failure of that bolt was the proximate cause of a bad situation turning into total loss of control and a dismasting.

[Breaking Waves]

Originally Posted by Kenomac

my assesment .... I completely disagree with yours.

your privilege. does not bother me at all.

It does seem a bit odd you would completely disagree with me because I have agreed with a few of your points (like the cascade) - lol.

I just hope whatever you take away here makes you and your vessel safer.

I seriously doubt you read the entire report to come to your conclusions.

Again your privilege, but you would be wrong (again).

Had the hydraulic steering not failed,

Autopilots do fail. This is hopefully not common but is not unanticipated on ocean passage. Some from improper installation, some from wear. I have seen (at sea) seals leak, brushes go bad, fluxgates and control heads die and wire connections vibrate loose. I've fixed all those at sea.

Checking the autopilot should be a standard regular procedure. This crew NEVER (ever) checked the level of the header tank - the simplest possible check.

Also, the crew should be sensitive to the feeling of the boat at sea - is it comfortable and stable? If it is not then they need to take action to make it so. Reducing sail appropriately would be one of those actions, but it would also, in this case, probably have led them to understand they had a steering problem approximately 3 hours before the incident (according to the report). They then could have switched to hand steering, and diagnosed/fixed the autopilot (or just topped up the header tank and put a continuous watch on it).

The conditions were not out of the ordinary for a 36 ton sailboat to easily handle.

These conditions were out of the ordinary for this crew in this boat - which is the relevant factor. Frankly, any boat, no matter the size, sailing north from NZ should be well prepared for these conditions - 30'ers to 150'ers - it's much more about the crew and their capability than it is the boat size.

You seem to imply you think bigger boats are safer in these sorts of conditions - and they can ofc be more stable when things are going well but I would just comment that when things go wrong on bigger boats they tend to be more difficult to resolve and more dangerous, and they tend to require a greater level of competence (both in operation and maintenance) to handle safely. I personally have always been a bit suspect of the 60' size range, because it is really too small for good professional crew and too big for many amateur sailors to deal with (and yes I ofc know there are counterexamples of amateurs who use 60'ers well, but in my experience many more who struggle with this boat size).

it’s highly unlikely any of the other cascade events would have happened,

I believe you are fixated on the proximate cause and overlooking the root cause. Fixing a proximate cause typically does not stop other related bad things from eventually happening. That is common in amateur incident analysis. So, be it, it is not worth debating with you.
[/COLOR]

.

breaking wave

[jmh2002]

Originally Posted by RaymondR

The system you propose is exactly what I use as a boom brake on my boat except I rig it on both sides using a single line and use a halyard in the middle where it passes over the coach roof to pull it tight. I don't use blocks down at the toerail but friction fittings made using large thimbles. If I want to prevent the boom from moving if the main is back winded I run a line from the boom end to the most forward cleat as the report recommends.

Originally Posted by jmh2002

Also an important note here which often gets missed. Padeyes, shackles, etc, and even blocks are designed to take load in a certain orientation. The safe working load can reduce substantially at other orientations, or the gear can even fail totally at a much lower load than expected if used in an incorrect orientation.

This problem is getting better now that boats are moving to soft shackles, etc but the concept still needs to be correctly understood.

From my post here: http://www.cruisersforum.com/forums/...ml#post2939434

I appreciate that you have stated you use this arrangement as 'friction fittings' so I am just using your post as a general example rather specifically about your setup.

But it does well illustrate the kind of thing I was talking about. In this type of case, depending on the line material itself, it is possible that the 'bend radius' of the line when passed through this type of thimble is beyond the design limitations of the line.

In short the line can end up being 'point loaded' at the thimble.

It is therefore possible, especially under extreme load (say, as a preventer is shock loaded...), that the line could fail at this point way below it's normal safe working load.

Again, RaymondR's post was just used as an example here because it's often easy just to run a line somehow without considering all of the consequences of how it is run and what can happen under load.

Many deck hardware and line manufacturers have nice diagrams explaining this vs the various percentages of load.

[RaymondR]

I have considered making some other type of arrangement, say something like a block with a fixed, ie non rotating, sheave but since what you see in the image works ok decided it was not worth the bother. However, if I had a boat with a monster boom which weighed half a ton I'd most certainly have something very industrial.

[jmh2002]

Yes, in your case possibly everything is sufficiently oversized relative to the boat loads that it might not matter.

I'm not convinced about the padeye arrangement either, but I also can't see everything in the photo to properly assess it. However possibly it's sufficiently oversized too.

[Joli]

Originally Posted by Kenomac

A 65ft boat on a beam reach in 30-35 knot wind, will be traveling at 8-9 knots with a partially furled mainsail... not 12 knots. They would have been experiencing the feeling of 20-25 knot wind in the cockpit behind the dodger with a moderate heel, nothing out of the ordinary and certainly not expecting what was about to occur when the steering failed.

Here’s what 40 knots from the stern looks like on a 53ft sailboat running on bare poles aided by the engine at 2100rpm for steering and battery charging. The seas are 2-3 meters just like in the report.

It must be an AWFULLY SLOW 65’ boat to only do 8~9 knots in 35 true.

[Ericson38]

Originally Posted by jmh2002

From my post here: http://www.cruisersforum.com/forums/...ml#post2939434


But it does well illustrate the kind of thing I was talking about. In this type of case, depending on the line material itself, it is possible that the 'bend radius' of the line when passed through this type of thimble is beyond the design limitations of the line.

In short the line can end up being 'point loaded' at the thimble.

I think in this case the thimble he uses is better than bowline loop to bowline loop, or a snap shackle jaw (for sure). Maybe a sharper turn than a larger radius block pulley, but you wouldn't want a block-pulley to reverse that line anyway. Simpler is better. I do wonder how that fitment is attached to the hull on the caprail. Is it long screwed in, or bolts and backing plates on the underside of the deck.

[Joli]

Originally Posted by Breaking Waves

breaking wave

Evan?

[accomplice]

Originally Posted by Joli

It must be an AWFULLY SLOW 65’ boat to only do 8~9 knots in 35 true.

60' LOA might be 50' LWL. Hull speed approx 9.5kt. If you're not sailing full throttle you rarely make hull speed, particularly in sloppy seas.

[Kenomac]

Originally Posted by Joli

Haven’t posted here in a long, long time.

That said. It’s foolish to push a large boat in heavy conditions with a small crew. A sixty some foot boat in 35 true will easily sail at 12 knots with just a staysail. No reason to push the boat unless it’s fully crewed with capable sailors.

Originally Posted by Joli

It must be an AWFULLY SLOW 65’ boat to only do 8~9 knots in 35 true.

Your statements contradict. First you say “It’s foolish” to push the boat in conditions of 35 knot winds, then you respond by wondering why the boat is not being pushed beyond its 9.5kt hull speed in 35 knot winds.

Personally, we’d most likely be sailing comfortably along with a main sail furled down to about 30% with our staysail fully deployed expecting to be making 8-9 knots in 35 knot winds on a 64ft 36 ton boat.

Now after thoroughly digesting the report, a helmsman will be behind the wheel at all times... just in case., and someone will be checking the hydraulic fluid more often.

[Joli]

No contradiction at all, hull speed is only a number easily outdistanced. There is no reason for a short handed crew to be carrying all the sail they were in those conditions. That size boat should easily sail in the low teens with that breeze aft of the beam. Our boat Joli, is a powerful 61 footer with a waterline to truck dimension of 93’. We understand higher winds and have pressed the boat into the high teens. The loads at those speeds are very high and we respect them IMMENSELY! We’ve owned and have sailed this boat for 20 years, sometimes racing it, mostly cruising it, my wife and I. As Breaking Waves states, a 60’ boat is an odd size boat for a couple and small amateur crews, they can easily get into trouble with it. We’ve not had trouble with Joli, knock wood, but understand it’s extremely powerful and have seen the loads since we’ve raced it. There is no way my wife and I will be broad reaches with ANY main with gusts of 48 knots. That’s foolish for any small crew on a boat of this size.


At the end of the day what happened is a tragedy that could have been avoided if the crew was more knowledgeable, fearful, aware of the power of the boat they were sailing.


I’m done, be safe everyone.

[Kenomac]

Joli,

We are basically in agreement following your last post. I would not be sailing with a main sail either if the wind was gusting higher than 35 knots.

[jmorrison146]

Originally Posted by Kenomac

Bad things can happen even when you do everything correctly. Our preventer on our 53 broke three weeks ago even though it was rigged the correct way... from the end of the boom, the preventer run all the way forward to the bow cleat. All it took was a 15 knot wind from dead astern, then punching in a goto heading on the chartplotter. The boat suddenly and without warning turned itself 60 degrees to starboard due to an auto pilot compass malfunction, then before I could get behind the helm and hit standby... snap! The preventer broke.

Fortunately, nothing else broke, nobody was hurt and only a forward stanchion was slightly bent. But stuff happens, and that’s one great feature of a center cockpit boat... it places you in a very safe location when things do go wrong. The entire gybe occured in less than maybe 5-10 seconds.

I’m convinced now after the fact, that it was better that the preventer broke as it slowed the boom coming across, then to have held and possibly broken the boom or ripped the sail in half.

This may not have been an autopilot malfunction. On my Simrad system, you must first select "Restart" under the "Navigation" function so that the track line for the selected waypoint resets to the current position of the boat. If not, when you select the "Go To" function the autopilot tries to regain the track displayed and will make a major turn to go there. After even a few minutes of sailing with a waypoint entered the boat will be left or right of track by several yards.

[Kenomac]

Originally Posted by jmorrison146

This may not have been an autopilot malfunction. On my Simrad system, you must first select "Restart" under the "Navigation" function so that the track line for the selected waypoint resets to the current position of the boat. If not, when you select the "Go To" function the autopilot tries to regain the track displayed and will make a major turn to go there. After even a few minutes of sailing with a waypoint entered the boat will be left or right of track by several yards.

Thanks for the suggestion, but it was definitely an auto pilot compass malfunction. I need to get the electronic compass fixed, replaced or recalibrated, it’s off by 45 degrees since the mishap.

The electronic compass decided to somehow recalibrate itself by 45 degrees at exactly the wrong moment.