Preventer Rigging -- Lessons from the Platino Disaster

[Kenomac]

Originally Posted by groundtackle

No affiliation but did personally use one of these during an oops gybe on a large vessel. It slows down the boom speed travel when a bow - boom end preventer is rigged. Simple, inexpensive and works.

https://dreamgreen.org/boom-brake

Chris

Regarding boom brakes:

Rigging a boom brake is a great idea on any sailboat under about 50ft, we had a Dutchman on our Hunter 450 that worked fantastic.

I tried unsuccessfully to mount the largest size Dutchman on our Oyster 53 a few years ago, and just couldn’t get it rigged properly... so I gave up and sold it.

On our 62, I just don’t think it would be possible, there’s no safe place to locate a boom brake or it’s rigging without endangering the cockpit occupants.

[groundtackle]

Kenomac, with your Oyster 53' obtaining a fair lead from the shrouds to boom position and be unobstructed may prove difficult with that higher cabin structure. Might be possible to dead end up the turnbuckle a little, worthy of thought with proper toggles. It doesn't shock load it just runs.
I've not found it necessary to lead the line aft to cockpit once the correct arc and line tension set. Never liked stepping over that line to shrouds when going fwd so only rigged it when required.
Talking with Don Green recently and he mentioned a larger unit in the works for bigger boats and loads.
Chris

[RaymondR]

Originally Posted by Kenomac

If a partially furled, loose footed mail sail was to backwind in 35 knot winds, the force of the sail on the boom would not be exerted on the outermost end of the boom, it would be somewhere near the middle.

Not necessarily.

If the furling mechanism is a cylindrical foil, around which the sail is wrapped, supported at it's ends then the loads will be transferred to the end bearings without any vertical or lateral loading or the outer boom housing.

I used a simplified model without addressing the loading on the boom by the vang. So if a vang is in use it will load the boom as a cantilever whilst the end applied preventer loads it as a column. And, if the main sheet is not fixed at the outer end this will also generate cantilever loading.

[Tillsbury]

Originally Posted by Kenomac

If a partially furled, loose footed mail sail was to backwind in 35 knot winds, the force of the sail on the boom would not be exerted on the outermost end of the boom, it would be somewhere near the middle.

Only if it were attached to a car at the clew that ran along the boom. Many in-mast furling arrangements are direct to the end of the boom, so that’s where the force is applied.

Although in the case of a gybe, the key point is where the sheet is attached. If the sheet is close to or at the end of the boom, then the preventer should be there too. Those are the forces you need to balance. Either way, a preventer attached to the end of the boom experiences the lowest loading and the best angle when taken to something suitably big at the bow (I.e. a decent cleat or Samson post, not a little padeye whether securely attached or not).

[Tillsbury]

Originally Posted by a64pilot

Now all this is pure supposition and not from years per experience, I went with a brake largely because the boat had one, that had never been used obviously.

I’m not certain, but I don’t think that it’s easy to find a boom brake for a boom that size. Most of the commonly available ones are only for considerably smaller boats.

[Dockhead]

The discussion has been focussed on the gear and how it is rigged. It's very useful to talk about this, but we shouldn't forget tactics. Plan "A" should definitely be not getting the main backwinded in the first place.


I don't sail deep with the mainsail in use at all beyond maybe F7. I will sail up to F8 with the wind somewhere on the beam, with the mainsail in use. It's not unusual for me to be using all plain sail with 30 knots of apparent wind, on a beamish reach. Like that we did a 218 mile day last summer en route between Faroes and England, a personal best.

I would be interested to hear how others address the risk of a Platino type event. We depend very much on the autopilot and do not indeed have someone behind the helm at all times even in strong weather. I'm not sure what the risk is of sudden and total autopilot failure like what Platino experienced. I've been through everything with my pilot in 10's of thousands of miles of sailing, and it has failed a few times, but always gradually. Low fluid, or an air leak, is indicated by gradual deterioration of course holding, which at a certain point starts to set off rudder response alarms.


I suppose hoses could burst or a breaker could flip off so maybe I should be being more careful.

[Kenomac]

Originally Posted by RaymondR

Not necessarily.

If the furling mechanism is a cylindrical foil, around which the sail is wrapped, supported at it's ends then the loads will be transferred to the end bearings without any vertical or lateral loading or the outer boom housing.

I used a simplified model without addressing the loading on the boom by the vang. So if a vang is in use it will load the boom as a cantilever whilst the end applied preventer loads it as a column. And, if the main sheet is not fixed at the outer end this will also generate cantilever loading.

Our main sheet on the 53 attaches to the boom 1 meter before the end of the boom, and there’s also a car which moves half way along the boom beginning from the boom end.

[RaymondR]

Originally Posted by Kenomac

Our main sheet on the 53 attaches to the boom 1 meter before the end of the boom, and there’s also a car which moves half way along the boom beginning from the boom end.

Boom furling or mast furling?

[Kenomac]

Originally Posted by RaymondR

Boom furling or mast furling?

We have a Hood in mast furling system.

[Breaking Waves]

Originally Posted by Dockhead

I don't sail deep with the mainsail in use at all beyond maybe F7.

Our sail selection has always depended greatly on the length of the sail. I could probably accurately divide it into three buckets - a day sail, a 2 or 3 day sail and longer than that. On shorter lengths, you can pay more focused attention, and the value of extra boat speed is greater (getting into to harbor before night for instance). On ocean passages (greater than 3 days) we basically developed a 'comfortable pace' where things were always under control and mistakes could not bite us too hard. This will depend on sea state and steadiness/gustiness in addition to wind speed - flattish water is ofc easier to be comfortable on than turbulent cross seas. It also would depend on anticipated wind trajectory - if it's going up we were more conservative early than if it was forecast to drop. But generally in a F7 at 140 true angles that would usually be a #3 jib - perhaps full unless it was gusty - we would be making great boat speed with great steering balance and it would be very easy to reduce area.

I'm not sure what the risk is of sudden and total autopilot failure like what Platino experienced.

Generally you 'should not have' gradual deterioration on a passage - you should have taken care of that before the passage. You 'should have' known that the oil level was dropping or seen some oil below the ram, or felt the ram rod being extra slick . . . and fixed it. OFC that is in a perfect world, and sometimes it happens . . . but equally a gradual decline should not end up like this one did - you should realize it and do something about it, from just start topping up the oil regularly to swapping out the ram for a spare.

Sudden failures are more troublesome. As mentioned in a post above, there are several ways that can happen. Fluxgate failure has been the most common one for me and I always carry a spare fluxgate. It would probably make sense to (and be easy to) protect the autopilot breakers from accidentally being flipped - but I have never seen it done.

As you say, tactically better to sail with a sail plan and a sail area which is decently resistant to catastrophic failure if a failure or mistake happens. And to be situationally aware of what's happening with the boat - so, for instance, you identify things gradually failing before they go to hell.

None of the technical problems on Platino were all that difficult to have avoided. Nothing particularly clever was needed. Simple routine procedure would have avoided the autopilot failure. Simple proper design and installation of the preventer would have avoided that failure. Some decent engineers needed to be consulted for the new traveler installation, with an awareness of the huge boom weight. This level of simply doing things right and properly is also critical to preventing accidents.

breaking wave

[RaymondR]

Originally Posted by Kenomac

We have a Hood in mast furling system.

That's why your boom has a car on it for the mainsail tack. Boom furled main sails don't have the car.

[Breaking Waves]

On sail selection . . . it helps to have learned offshore sailing with a wind vane. That gear forces you to use relatively balanced and not too aggressive sail plans. But that is a rapidly declining background.

Many autopilots can have their steering aggressiveness adjusted. Many people crank that up, so the pilot steers straight, even when it has to compensate for unbalance or over aggressiveness. It would probably be better, at least for offshore work, to crank that down instead, so any lack of balance or over-aggressiveness is immediately apparent in the steering/course and can be corrected at the root rather than covered up by the pilot.

[jmh2002]

^^^ Yeah, (and even though somewhat off topic) don't forget that all those rudder movements are detrimental to boatspeed, and consume even more power from the battery bank too.

Reminds me of sailing once with a non performance minded skipper, reaching, and I kept asking how much helm he was using because he seemed to be fighting the wheel. So I kept easing the main, and the boat kept going faster, ask again, ease some more, boat faster still.

He couldn't understand how I was reducing the sail power but increasing the boatspeed.

Well, dragging the rudder sideways through the water is NOT helpful...

So a balanced sail plan is important in more ways than one and monitoring the rudder angle indicator, even just by manually eyeballing the wheel or tiller, should be standard procedure.

[philaw]

I've just read a big chunk of the report, and as a novice its striking to me, not the mistakes that were made, but just how much you need to get right. If 57mm padeyes hadn't been fitted by accident instead of 76mm ones, those people might still be alive. They had a ton of cat 1 gear for MOB situations, but couldn't deploy any of it. They had quality harness life jackets, but the MOB wasn't wearing one. It seems like you need to know the breaking strength of all the components in your rig, including the complicating effect of knots and blocks, and the numbers involved are staggering. A traveller meant to cope with static loads of 2,268kg got broken!? And the mainsheet was flying around the cockpit with these loads, like a cheese wire?! Amongst other things, maybe the boat was just too damn big for them.

[Kenomac]

Originally Posted by Breaking Waves

None of the technical problems on Platino were all that difficult to have avoided. Nothing particularly clever was needed. Simple routine procedure would have avoided the autopilot failure. Simple proper design and installation of the preventer would have avoided that failure. Some decent engineers needed to be consulted for the new traveler installation, with an awareness of the huge boom weight. This level of simply doing things right and properly is also critical to preventing accidents.

breaking wave

Of course, very easy for you to write... after the fact and behind the fair weather comfort of your computer keyboard.

Stuff happens out there... even when people do everything the correct way. Qualified marine technicians and engineers signed off on every part of the refit, the experienced crew had no way of knowing what was about to come their way.

Rather than toss stones of blame, everyone should learn from what happened to lessen the possibility of a repeat. I’ve personally, learned from the tragedy and hope I’m ready for the day when something similar might come my way. Oh wait... it did, but I was just more fortunate... nobody got hurt.