Preventer Rigging -- Lessons from the Platino Disaster

[wlange]

This thread made me think of “boom brakes”. Anybody out there have much experience with these? I recently purchased a Walder boom brake after reading a lot of reviews and watching some videos of people using them. As some have posted above, preventers don’t really seem to prevent anything. At best, it may give you a second or two to get the helm over (if you are at the helm and paying attention) or else ease the preventer quickly to control the gybe. Once gybed, you simply can’t sit back with the preventer loaded up waiting for stuff to start breaking. In theory, the brake makes sense to me as it won’t prevent a gybe but allow it to happen in a more orderly fashion. I say “theory” as I have yet to put mine to a real world test. Any experiences people have had with brakes, especially Walder type, would be interested to hear. Thank ahead of time for any comments.

[SteveSadler]

When I crewed the 156' schooner Invader, Long Beach to Hawaii, The captain rigged a nylon anchor rode from boom end to anchor windlass. Having done several big boat deliveries with the captain, (owner of Windjammer Cruises), We discussed the acute angle, stretch, and lack of sufficient tension on the preventer, and he explained, "nothing will prevent the boom from jibing if we it's backwinded, we just want to slow it down to prevent damage."
With todays materials and tech we can certainly try, but with such huge shock loads, something is bound to fail. Introducing some stretch in the system seems a simple answer.

[sailorboy1]

The past couple of months I've been looking pretty hard into boom brakes. I see no reason why a boom brake wouldn't/couldn't be rigged if using a preventer. I see a big plus to having a preventer that will break way before the rigging and a brake to control/softener the slam when it does.

[jmh2002]

Originally Posted by SteveSadler

When I crewed the 156' schooner Invader, Long Beach to Hawaii, The captain rigged a nylon anchor rode from boom end to anchor windlass. Having done several big boat deliveries with the captain, (owner of Windjammer Cruises), We discussed the acute angle, stretch, and lack of sufficient tension on the preventer, and he explained, "nothing will prevent the boom from jibing if we it's backwinded, we just want to slow it down to prevent damage."
With todays materials and tech we can certainly try, but with such huge shock loads, something is bound to fail. Introducing some stretch in the system seems a simple answer.

No, no, and no.

https://en.wikipedia.org/wiki/Fantome_(schooner)

Do you refer to the same Windjammer organisation?

Nylon, no, WAY too much stretch, indicating that the Captain was already making poorly considered choices.

Originally Posted by SteveSadler

"nothing will prevent the boom from jibing if we it's backwinded,

Nonsense. I have been completely backwinded on a 130ft yacht, mast down, rail deep down, huge round down, but no gybe, and no damage, apart from the crew's egos.

Originally Posted by SteveSadler

With todays materials and tech we can certainly try, but with such huge shock loads, something is bound to fail. Introducing some stretch in the system seems a simple answer.

There will be minimal shock load with the right gear at the right tension.

It's unfortunate that being a cruising forum, there is a real lack of knowledge, experience, and sailing ability here, and instead a lot of "some guy told me this"... leading to a lot of disinformation.

[SteveSadler]

JMH If you disagree, at least provide a reason other than no no no!
Shock loads are why things break, as in the case here, elasticity greatly lessens the load.
Didn't you use a nylon snubber on your anchor chain so many years ago? Do you remember why?
Finally, lets keep your personal insults out of the forum, they and their authors aren't welcome here.

[wingssail]

Originally Posted by Kenomac

Dockhead,

Don’t 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 won’t hold, something will break.

I certainly understand what you are saying but I do have experience contrary to that.

Of course my boat is smaller, but my mainsail is 750 sq ft (70sq mt). While sailing in a building wind from behind I (stupidly) steered the boat into a gybe in 27knots of true wind, while sailing with mainsail alone at 7 knots.

A preventer was rigged. It was (is) 3/8 double braid dacron tied to the end of the boom and led to a stanchion base bail!! halfway up the foredeck then back to a cleat in the cockpit.

The angle of the preventer to the end of the boom was approx 40 degrees.

The gybe took all slack out of the preventer, spun the boat around beam to the wind, and then pushed the boat over on it's side and held it there, heeled to about 70-80 degrees, and forward motion was stopped.

But nothing in the preventer system broke. Nor anything else on the boat except that the mainsail itself gave way after about 5 minutes and began tearing vertically from the middle of the boom up. Within 10 minutes the mainsail was shredded, not surprising because we knew the sail was on it's last legs.

It took us a long time to release the pressure (even as the main itself relieved some of the pressure by ripping) because the remaining pressure on the cleated line made it hard to release. It should have been on a winch. I couldn't leave the helm and Judy was below when this happened. Once she gained the deck and we cast off the preventer the boom then swung farther over past the centerline and fetching up against the running backstay and check stay (which we had already uncleated and acted as a brake).the boat stood up, and we proceeded to remove the mainsail while motoring onward.

This happened at midnight.

But the point is a moderately sized preventer did not break even though the force on the backwinded sail was enough to knock the boat entirely down.

So, I guess it depends on the boat and the sizes of everything, but not all gybes apparently will break the gear.

One lesson: Be ever so aware of wind direction while sailing down wind, the wind vane is best.

Second lesson: the preventer must be on a winch so it can be eased.

Third lesson: The preventer must be sized according to the size of the boat and the mainsail and boom.

Forth lesson: As has been said, a boom brake might have made this a more gentle gybe.

One thing I am thankful for: My boat is an old IOR race boat which has very heavy duty fittings particularly on the sail handling gear including the mainsheet system and the traveler. Stuff rarely breaks on this boat.

Sorry for the duplication

[RaymondR]

Originally Posted by SteveSadler

JMH If you disagree, at least provide a reason other than no no no!
Shock loads are why things break, as in the case here, elasticity greatly lessens the load.
Didn't you use a nylon snubber on your anchor chain so many years ago? Do you remember why?
Finally, lets keep your personal insults out of the forum, they and their authors aren't welcome here.

Goes back to Newtons second law of motion: Force equals mass by acceleration.

The mass of the swinging boom (For calculation purposes considered to be concentrated at it Moment of Inertia) is decelerated by having taken up all the slack in the main sheet. At this time the deceleration of the swinging boom commences (The acceleration is negative) The deceleration is measured as velocity change ie. distance divided by time, divided by the time when velocity equals zero.

The second division by time is the killer in that if you make it very small the force gets very high. A bit like the difference between decelerating your car by jumping on the brakes versus doing it by running into a brick wall. By doing it using the brakes over a few seconds you only experience a couple of G,s of force but by doing it over a few microseconds using a brick wall you experience hundreds, or even thousands, of G,s of force.

[fxykty]

They weren’t going downwind, they were on a broad reach. Two sails (headsail and main) is reasonable on that point of sail. Read the report before commenting.

I stand by my earlier comment that they would likely have been just fine had the autopilot not failed. Granted, it seems they were complacent about the building conditions (likely due to being very early in the passage), but I’m sure they would have successfully shortened sail and continued fine.

One of the things the report makes clear is that even with crew who are individually experienced, it’s very important to review and practice the standard operating procedures for safety and emergency events prior to a passage. Clear lines of command are required as well.

[wingssail]

Originally Posted by waterman46

...Also, it was stated by some that there might be an optimum point on the boom to minimize preventer stress. In fact the stress will always be least when preventer is rigged to end of boom. And the bow is best place to run it from....

Yes, I agree, the end-of-boom attachment results in much less load on the preventer, and passing it to a block or cleat at the bow gives a good angle. I don't understand comments that attachments such as 1/3 back from the gooseneck is best. This dramatically increases the load.

And, if you are rigging a preventer for sailing with the boom much closer to the centerline, to control boom movement, such as in reaching in waves which otherwise would swing the boom back and forth, the preventer must be led to the deck nearly midships to get any kind of angle. From any point on the boom to the bow, while the boom is more closely sheeted inboard, results, again, in a bad angle and higher loads.

[wingssail]

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.

I've always thought the reason to use non-stretchy sheets was to keep the shape and trim of the sail during increases or puffs of wind.

Even if the sheet stretches, the force of stretching it will be conveyed to the boat, and pull the boat. And when the puff passes and the line recovers, isn't that continuing to pull the boat.

So I think it is a sail shaping and trimming reason more than converting wind into boatspeed.

[wingssail]

Originally Posted by waterman46

Y

...But I still wonder why it did not seem to occur to the crew, that they could have stabilized that boom instantly by either releasing the topping lift and/or rigid vang, as case may be, to dump aft end of boom on deck whete iy could be easily tied down.

On many boats the boom vang system holds the boom up to nearly horizontal and the allowable travel is not enough to let the boom down to the deck.

And on boats with a hydraulic boom vang the gas pressure in the vang cylinder will hold the boom up, and full on mainsheet pressure won't pull it much more than a 1ft. After that it is in danger of breaking.

[wingssail]

Originally Posted by fxykty

Though I totally agree changing to low stretch/ high strength lines to reduce line diameters, reduce windage, and (sometimes) improve handling. Similar motivations as changing out blocks for low friction rings and hard shackles for soft shackles. Where it makes sense.

smaller diameter lines also have less friction so more of your force on the tail of the line goes to pulling it in (or out)

[RaymondR]

Having wandered over to a marina fairly full of large expensive boats and the sizes of the booms on them with in-boom furling I think that were I to contemplate owning one of them I'd want something better engineered than a spur of the moment arrangement with lines running everywhere. Hydraulic dampers and inertia reels are old technology.

[pbmaise]

Originally Posted by accomplice

The report wisely points out that sheeting angle and position matters.

I am still trying to figure out a good way to rig our preventers so they can be set from the cockpit.

Advantage trimarans!

I noted in one reply the bow cleat was employed. On my trimaran's I employed the stern cleat and ran one end of the preventer line to the cockpit where the preventer was secured on a winch.

The other end of the preventer line ran forward to a large block attached to a 1" galvanized shackle on the backstay chainplate.

A block was not needed on the stern cleat since the cleat itself had a large smooth turning radius.

With this setup it was possible to release one preventer, jibe or tack, and set the other preventer without leaving the cockpit.

I employed a preventer no matter which way the wind was coming from.

[jmh2002]

Originally Posted by pbmaise

Advantage trimarans!

I'm pretty sure that my next boat for cruising will be a catamaran, with 2 masts, and no booms. This will also mean that the sails will all be smaller and therefore easier to handle.