Preventer Rigging -- Lessons from the Platino Disaster

[Don C L]

Been thinking about this thread and all the discussion of dealing with a boom. Just came in from a trip, and in the first day the wind went from 5-10 kts to 25 gusts to 30, in a few miles with steep short period 4-6’ swells. I saw it coming so I furled the main. I turned and broad reached for a different anchorage and with the jib I was still doing 6 -7 knots easily with plenty of comfortable control. Never in a million years would I have wanted the main up at all. These days if it is over 15 it’s and I am running or broad reaching, no main. Works for my little boat, but I’d do the same if I had a bigger boat. Point being that cruising you may find your main offers little in running except a big annoying hazard.

[dfelsent]

Gybing by mistake. Hmm. Never done that nor broken anything. Except as crew on an Etchells when the gooseneck fitting blew out. Or on my sloop when the gooseneck fitting bolt backed out and the gooseneck snapped going up wind. Oh yes that uncontrolled gynecology in the north channel near Rathlin. A year later I found out the gooseneck casting was cracked.
And all this with competent experienced crew.
What a nightmare scenario. Makes me rethink preventers and care for sure. Even though I can and could pick up my booms easily.

[Tillsbury]

Originally Posted by Don C L

Been thinking about this thread and all the discussion of dealing with a boom. Just came in from a trip, and in the first day the wind went from 5-10 kts to 25 gusts to 30, in a few miles with steep short period 4-6’ swells. I saw it coming so I furled the main. I turned and broad reached for a different anchorage and with the jib I was still doing 6 -7 knots easily with plenty of comfortable control. Never in a million years would I have wanted the main up at all. These days if it is over 15 it’s and I am running or broad reaching, no main. Works for my little boat, but I’d do the same if I had a bigger boat. Point being that cruising you may find your main offers little in running except a big annoying hazard.

That’s entirely true. Just out of Kaikoura a few months back we were on a broad reach in 10kts and suddenly a steady 40kts piped up, no warning nor forecast. With main straight down and probably no more than 10-15% of the Genoa area out we were storming along at 9kts+. I saw no reason to have any more sail out than that.

[FranklinGray]

I am late to this thread and haven't read all 19 pages yet but one thing I don't see mentioned here is that this happened near NZ. That area is know for large cross swell breaking preventers and travelers. I can see how with the main up the wind doesn't have enough power to hold the boom against the shrouds due to the powerful side swells. Swells there are more powerful than the wind.

With that said, I use a preventer tied to the middle of the boom....just a 7/16th double braid rope led to the midshipmen cleat but do not let the boom out as far. I have back winded it a few times with no problems. Just ease the line out and re-jybe the boat.

Also as others have said, when you are out there, tired, scared, sea-sick on a boat being thrown about taking all your energy just to stand and hold on. NZ seas are not to be taken lightly. What you can do in normal ssas you can't do there.

[FranklinGray]

In seas with cross swell, many sailors prefer to have out at least some main to stable the boat. A stable boat is safer than a rolling boat.

[fxykty]

For those who are interested, the particular features of the passage between NZ and the S Pacific that cause problems is in the first (or last, going the other way) 300-500 miles north of NZ. It’s called the ‘dangerous middle’. It’s one of the reasons that NZ introduced their Cat 1 certificate for NZ boats and crews. Though the Platino disaster is an example of the inadequacy of regulation in the face of complacency. It’s also a reason why NZ-designed cruising sail boats are optimised for sailing.

There’s the primary E quarter swell from the trades with a secondary W quarter swell coming out of the Tasman Sea. Layered on top of that is a N quarter swell from any recent tropical depression.

What makes the cross-swells difficult is the Three Kings Ridge heading north 300 miles from the northern most point of NZ, rising up to 300m depth with 3000-4000m on either side.

3-6 m swells with 2-4 m cross swells are generally just fine in the open ocean. With the shallowing and especially if significant added wind energy (30 knots plus) the swells stand up and shorten their period dramatically. Hence the need to time your passage carefully and pay especial attention to transiting the dangerous middle.

Heading north, it’s the beginning of the passage so plan your departure generally on the back of a low.

Heading south, you’re depending on a long range forecast. Boats will often stage from Minerva Reefs to shorten the distance/time. Regardless of whether you’re coming from Tonga or New Caledonia, aim for a point just north of the Three Kings Ridge, slightly west of due north from Cape Reinga.

You’re hooped if you get a SE (low pressure system passing through) but way more likely in late October/early November is NE/E from the summer high located to the NE of NZ. Oftentimes you can get a strong SW from the low sitting in the central Tasman Sea, which is butted up against the summer high. In either case, expect power close reaching with relatively steep and breaking waves on top of confused swells.

[Yoty]

"Perfect Planning Prevents P..s Poor Performance".
Tattoo on eyeballs ! 6P's.
No PLAN, regardless of sea miles etc, is planning to fail.
Sadly, the best experience/brains trust on board had their world rocked, HARD and DEADLY,....NO PLAN.

[Montanan]

Hi all, been following this interesting thread. I recently spotted this Youtube video about a unique [at least to me] type of preventer system which seems to remove the issue of running the preventer line all the way to the bow and back to the cockpit and also allows the boom to rise a bit, to ease off during a gust if the vang is not pulling downward hard.

I haven't done a force analysis on this system yet; I have a bit of an initial gut feeling that the load onto the gooseneck might become significant as the taughtness of the preventer appears to be directly in line with the boom, and not like a bow mounted preventer line which provides for a more wide angle from the boom end vectoring the pull forward from the boom and not directly into the gooseneck. Please give that consideration in your analysis and reasoning.

What are your impressions and thoughts of this scheme of preventer? Seeking guidance and knowledgeable perspectives.

https://www.youtube.com/watch?v=twFlPo9yTQ4

All the best.

[Dockhead]

Originally Posted by Montanan

Hi all, been following this interesting thread. I recently spotted this Youtube video about a unique [at least to me] type of preventer system which seems to remove the issue of running the preventer line all the way to the bow and back to the cockpit and also allows the boom to rise a bit, to ease off during a gust if the vang is not pulling downward hard.

I haven't done a force analysis on this system yet; I have a bit of an initial gut feeling that the load onto the gooseneck might become significant as the taughtness of the preventer appears to be directly in line with the boom, and not like a bow mounted preventer line which provides for a more wide angle from the boom end vectoring the pull forward from the boom and not directly into the gooseneck. Please give that consideration in your analysis and reasoning.

What are your impressions and thoughts of this scheme of preventer? Seeking guidance and knowledgeable perspectives.

All the best.

You can do a "force analysis" in your mind very easily. Can you picture "lever arm" in your mind?



I could break that with one hand on the end of the boom. That's the silliest piece of rigging I've ever seen.

[Montanan]

Originally Posted by Dockhead

You can do a "force analysis" in your mind very easily. Can you picture "lever arm" in your mind?



I could break that with one hand on the end of the boom. That's the silliest piece of rigging I've ever seen.

Thanks Dockhead for your quick and reasoned reply. So my gut sense was properly alerting, not unlike the Platino Disaster then awaiting to happen again. The tension load on the fairleads mounted to the mast and likewise to the car on the boom and to the gooseneck and each of those components mounting to the mast could be immense. Best have some strong backing plates inside the mast and inside the boom so as to allow the compression of the fairlead load pulled by the roped towards the boom and the load on the boom towards the gooseneck to be sustainable. Otherwise I could see the compression axial load through the boom and mast to be collapsing.
Basically it appears to provide for a doubling of the load of the wind into those components but limited to those components and the line and cam clutch. If those components and their mounts are robust and the boom has solid compression strength then perhaps the system is viable. Definitely requires a thorough force and component strength analysis.

I'll give that it certainly is simple and uncluttering which would lend to it being readily used whereas other systems require more action and thus may not be deployed. Better to have a deployed preventer than no preventer just so long as the system is designed to prevent the preventer from becoming destructive in its own regard.

So maybe this is anything but Sail Safe as their brand name implies, or if well built it could be quite safe.

I perceive that any preventer system should also be backed up with a robust boom brake system.

Regards.

[Dockhead]

Originally Posted by Montanan

Thanks Dockhead for your quick and reasoned reply. So my gut sense was properly alerting, not unlike the Platino Disaster then awaiting to happen again. The tension load on the fairleads mounted to the mast and likewise to the car on the boom and to the gooseneck and each of those components mounting to the mast could be immense. Best have some strong backing plates inside the mast and inside the boom so as to allow the compression of the fairlead load pulled by the roped towards the boom and the load on the boom towards the gooseneck to be sustainable. Otherwise I could see the compression axial load through the boom and mast to be collapsing.
Basically it appears to provide for a doubling of the load of the wind into those components but limited to those components and the line and cam clutch. If those components and their mounts are robust and the boom has solid compression strength then perhaps the system is viable. Definitely requires a thorough force and component strength analysis.

I'll give that it certainly is simple and uncluttering which would lend to it being readily used whereas other systems require more action and thus may not be deployed. Better to have a deployed preventer than no preventer just so long as the system is designed to prevent the preventer from becoming destructive in its own regard.

So maybe this is anything but Sail Safe as their brand name implies, or if well built it could be quite safe.

I perceive that any preventer system should also be backed up with a robust boom brake system.

Regards.

If those angles would only double the loads, the system would work.


But it's vastly more than double:





The angle is only a couple of degrees. If someone came up with that crazy piece of rigging for the very purpose of breaking the gooseneck and twisting or ripping the mast up, you would would say that it was well designed for the purpose.


No amount of backing plates or whatever could make that work as a preventer. It's exactly the same error as the design of the Platino preventer, except even worse

[Montanan]

Originally Posted by Dockhead

If those angles would only double the loads, the system would work.


But it's vastly more than double:


Attachment 197914


The angle is only a couple of degrees. If someone came up with that crazy piece of rigging for the very purpose of breaking the gooseneck and twisting or ripping the mast up, you would would say that it was well designed for the purpose.


No amount of backing plates or whatever could make that work as a preventer. It's exactly the same error as the design of the Platino preventer, except even worse

Got it now. I am clearly being slow witted this morning.

So scratch that system unless one wished to have their by a KaBoom.

[accomplice]

Back of the envelope static analysis for a backwinded main of 100m^2 in 35kts.

The force on the sail would be as follows:

100 m^2 [sail size] * (1.229 kg/m^3) [density of air] * ( (35 knots) * (0.5 m/sec/knot))^2 * 0.102kg-f/Newton= 3.8kg-f.

Assuming that CE for the (reefed to 100 m^2) sail is 2 meters aft on a 7meter boom, and that the preventer line is around a mast of 1/10meter radius, that would multiply the force by 20x.

Thus the preventer line in that scenario would experience approximately 75kg static load. (Of course, dynamic loads could be much higher)

Even a static analysis shows they're going to need a stronger line, much stronger attachment points and clutch. They're off by 1-2 orders of magnitude.

[Montanan]

Originally Posted by accomplice

Back of the envelope static analysis for a backwinded main of 100m^2 in 35kts.

The force on the sail would be as follows:

100 m^2 [sail size] * (1.229 kg/m^3) [density of air] * ( (35 knots) * (0.5 m/sec/knot))^2 * 0.102kg-f/Newton= 3.8kg-f.

Assuming that CE for the (reefed to 100 m^2) sail is 2 meters aft on a 7meter boom, and that the preventer line is around a mast of 1/10meter radius, that would multiply the force by 20x.

Thus the preventer line in that scenario would experience approximately 75kg static load. (Of course, dynamic loads could be much higher)

Even a static analysis shows they're going to need a stronger line, much stronger attachment points and clutch. They're off by 1-2 orders of magnitude.

Ah, but then what's an added zero or two.

Whoa, that much more than nothing, Who Knew!

Thanks much for the analysis. Great envelope, far better than the napkin the system was apparently drawn up on.

[Tillsbury]

Looks like great way to slice your mast apart at the gooseneck. Any force applied at the end of the boom would be multiplied so many times at the mast fitting I would agree with Dockhead: a decent shove even by hand would likely damage something quite significant. If they sell any of these, expect them to come up in maritime reports in the future.