Preventer Rigging -- Lessons from the Platino Disaster

[Dockhead]

Originally Posted by jmh2002

. . . And my default recommendation is serious full batten mainsails, mast track system, and a nice slab reefing setup. No in mast or in boom. The external slab reefing is just so bullet proof and easily fixable or able to be jury rigged while cruising with normal blocks and lines that are carried onboard. . . .

I think slab reefing would be my default choice, as well, and perhaps the advantages of in-mast become less important with a split rig where you might not need to vary sail area of individual sails as much.


However, in-mast is still worth thinking about -- it is by far the safest and fastest way to vary sail area of a main or mizzen sail. I've been living with in-mast furling now for 10 years, and I've gone from hating the idea of it as I was buying this boat, to appreciating it more and more with each year which goes by, and with every storm and every tough situation I go through with it. When the chips are down and a gale has blown up and it's o-dark hundred, and you find yourself in big sea conditions and you have to reduce the main NOW, and going onto the icy deck would be to take your life in your hands, there is just nothing, I mean nothing, like in-mast furling. Like with the ketch rig there is a penalty in ultimate performance, but like with the ketch rig, it matters little if you are starting with an easily driven hull which does not require ultimate horsepower to keep it moving through the water.



Boom furling is now permanently off any list of furling systems to consider for me, after this.

[jmh2002]

Originally Posted by Dockhead

...the life and death function of keeping that massive beast under control -- was left by the designer for the crew to improvise out of old leftover cordage. That is just total malpractice as far as I'm concerned.

Yes, as it is on many boats. You are totally correct.

[boom23]

Originally Posted by Dockhead

However, in-mast is still worth thinking about -- it is by far the safest and fastest way to vary sail area of a main or mizzen sail. I've been living with in-mast furling now for 10 years, and I've gone from hating the idea of it as I was buying this boat, to appreciating it more and more with each year which goes by, and with every storm and every tough situation I go through with it. When the chips are down and a gale has blown up and it's o-dark hundred, and you find yourself in big sea conditions and you have to reduce the main NOW, and going onto the icy deck would be to take your life in your hands, there is just nothing, I mean nothing, like in-mast furling. Like with the ketch rig there is a penalty in ultimate performance, but like with the ketch rig, it matters little if you are starting with an easily driven hull which does not require ultimate horsepower to keep it moving through the water.

Boom furling is now permanently off any list of furling systems to consider for me, after this.

One more vote for booms above crew heads and in-mast furling. It's a fact that the in-mast mainsail might not have the best shape or power but, in my opinion, the ease of use outweighs its drawbacks.

On my current boat (Amel 50) the boom is pretty chunky, but it's well over the center cockpit enclosure and aft deck. In addition, the factory provided a preventer attachment point on the boom and the actual preventer setup. Even with that, when I'm in situations that might cause accidental jibes, I furl the mainsail and only use the Genoa, or other headsail. It's safer and easier for my wife and I to handle.

Practice safe sailing everyone.

Great info in this thread!

[Dockhead]

Originally Posted by boom23

. . . In addition, the factory provided a preventer attachment point on the boom and the actual preventer setup. . . . .

Bravo to Henri Amel!!


That is the way boat design should be done -- focussing on -- and solving -- the core design issues, particularly those with such safety implications, rather than the neato blue spreader lights and other style features . . .

[boom23]

Originally Posted by Dockhead

Bravo to Henri Amel!!


That is the way boat design should be done -- focussing on -- and solving -- the core design issues, particularly those with such safety implications, rather than the neato blue spreader lights and other style features . . .

I strongly believe that, at least upscale, blue water boat manufacturers should provide a cruise-ready boat. The manufacturers know, or should know, their products the best. Boom control is a very old problem. We should not have to debate about how to deal with this issue. Maybe I'm naive, but the older I get the more intolerant I get with incompetence or incomplete solutions. It doesn't take that much more to make a better product especially regarding issues that existed since the boom was developed.

[rgleason]

For smaller boats an end of boom bolt-on brake using the "preventor" lines, might be ideal if properly designed.

Alternatively, fitting some properly engineered elastic (like the mooring) as a part of each preventor line will reduce peak loads significantly and thus reduce failure of geer.

[transmitterdan]

I don't like an elastic preventer. I want the boom to be "still" and not moving about on a stretchy line. Also, stretchy nylon heats up as it elongates. That's where the kinetic energy goes (it has to go somewhere). A boom that doesn't move has zero kinetic energy.

[rgleason]

TDan I agree that the line should not be strechy, the idea is to have a very strong stretchy link that starts to stretch only when the jibe forces exceed some high value, and the amount of motion would not need to be too much, just enough to help reduce peak loading on the line and fittings. Some weak elastic is not going to work. It should be engineered for different sized mains. I think I would rather have the preventer hold than be dealing with a boom that let go unintemtionally.

[DumnMad]

Quote:
Originally Posted by a64pilot View Post
Dockhead you keep getting back to the mass of the boom, however I feel certain that any system that couldn’t handle the mass, couldn’t handle a back winded sail either.
My reasoning is the mass isn’t what broke the preventer, without movement mass isn’t much of a force, it’s mass and velocity, and it didn’t have any velocity until after the preventer broke.

Originally Posted by Dockhead

The logic here seems kind of broken -- or maybe I'm just not understanding what you're saying.

In any case, that boom needed to be under control, and it wasn't. That pathetic preventer had no chance. Neither the designer nor the crew appreciated the challenge.
I think that's right, and surely "systems safety analysis" should be part of the design process even if it's not totally formalized.
A 2/3 tonne boom is just not safe at all if it is controlled only by an improvised preventer, which may be drastically mis-improvised as this one was. If you really must have a boom like that, then I guess you need some kind of hydraulic brake on it.
For me this is where the ketch rig comes in. I just wouldn't want any part of a boom like that, hydraulic brake or not.

Some have a mechanic's mind, force required to tighten a nut.
Some have a builder mind, momentum needed to drive a nail.

In steel pile driving, in which I have considerable experience, a 1tonne hammer will comfortably drive a 40 tonne capacity pile. i.e. 1tonne hammer can apply a 40tonne load to the pile.
Its less about the weight of the boom and more about keeping it tightly controlled.

[sailingharry]

Originally Posted by a64pilot

depending on velocity, even a lightweight boom of only a few hundred lbs will kill.

A family friend was killed by a boom on a 35' boat. The dent was 2 or 3 inches deep. The similar sized boom on my Sabre 34 weighs maybe 30 pounds, not "a few hundred." A moving boom is a lot of force!

[a64pilot]

Originally Posted by sailingharry

A family friend was killed by a boom on a 35' boat. The dent was 2 or 3 inches deep. The similar sized boom on my Sabre 34 weighs maybe 30 pounds, not "a few hundred." A moving boom is a lot of force!

I understand, but it may well have had a lot of energy imparted into that 30 lbs by the aerodynamic forces of the sail.
Not to sound too stupid, but we drive very heavy boats with those sails, they are a force to be reckoned with.
Any sail when your underway is like a wound up spring holding enormous force, let something break or an accidental Gybe and those forces are released.
I’ve seen it once on my little boat in not really that bad of weather, I don’t need to see it again, especially in bad weather, I’m a believer.
https://www.alleydog.com/glossary/de...Trial+Learning

[DumnMad]

Originally Posted by a64pilot

I understand, but it may well have had a lot of energy imparted into that 30 lbs by the aerodynamic forces of the sail.
Not to sound too stupid, but we drive very heavy boats with those sails, they are a force to be reckoned with.
Any sail when your underway is like a wound up spring holding enormous force, let something break or an accidental Gybe and those forces are released.
I’ve seen it once on my little boat in not really that bad of weather, I don’t need to see it again, especially in bad weather, I’m a believer.
https://www.alleydog.com/glossary/de...Trial+Learning

The wind in the sail gives the boom its speed. The force is not so great because the sail is giving way.
Like the pile driver - a 30lb boom could apply a 1000lb impact against something rigid if swinging fast enough.

It only takes a 2lb hammer to smash someones skull........Its the momentum

[sailingharry]

A64, you may have misread my post as disagreeing with you. The opposite was true -- I was endorsing your "even smaller boats" thought, and providing real-world observations that you were more right than you stated. We are in agreement!

[transmitterdan]

Originally Posted by rgleason

TDan I agree that the line should not be strechy, the idea is to have a very strong stretchy link that starts to stretch only when the jibe forces exceed some high value, and the amount of motion would not need to be too much, just enough to help reduce peak loading on the line and fittings. Some weak elastic is not going to work. It should be engineered for different sized mains. I think I would rather have the preventer hold than be dealing with a boom that let go unintemtionally.

Stretch helps peak loading if and only if there is already unavoidable momentum. But it does not reduce peak loads coming from the wind itself as long as the boom is held fixed.

Springy line helps with anchoring because there is unavoidable momentum.

[rgleason]

Momentim. Yes, we need to think about the momentum applied to the back of the sail, as it can travel 2-3' feet or more with the boom held stationary, as the jibe is beginning. When the sail fetches up, there is impact loading much like a hammer, but somewhat softer, with loads brought down to the boom and to the mast. These loads must be greater than just the force of the wind. That is why I think a very very strong, elastic that will not stretch at all under normal loads but will stretch a small amount, say 1-2' as the momentum jibe loads are dissapated, would help to prevent impact loading from damaging the sail and or gear.