Preventer Rigging -- Lessons from the Platino Disaster

[Kenomac]

Originally Posted by Dockhead

Yes, the SailKote works really well. During this coming winter I will have the sails laundered and refurbished and professionally coated with the stuff. A "must" for in-mast furling, I think.

Another addition would be the installation of a hydraulic backstay tensioner and hydraulic boom vang if you’re concerned about sail shape. Both of our boats have these features which I believe can alter sail shape much more than a Dyneema sheet. You should seriously consider them. The backstay tensioner provides a significant amount or mast bend which is quite noticeable.

But for the most part.... we have a sail assisted powerboat due to the light summer winds here in Western Greece.

[jmh2002]

Originally Posted by Kenomac

Another addition would be the installation of a hydraulic backstay tensioner and hydraulic boom vang if you’re concerned about sail shape. Both of our boats have these features which I believe can alter sail shape more than a Dyneema sheet. You should seriously consider them. The backstay tensioner provides a significant amount or mast bend which is quite noticeable.

Are you really suggesting that, when cruising, you would be constantly tensioning and easing the hydraulic backstay and vang in the puffs, to set the sail shape and make up for the polyester sheet stretching each time?

Yes we used to do this on the race boats, but I find it hard to believe anyone will be constantly doing this when cruising.

Yes those two adjustments can change the sail shape.

No they are not a substitute for Dyneema sheets.

So by all means use the hydraulics to help set the sail shape. But that won't stop the polyester sheet stretching and the sail shape changing constantly.

It's two different things.

[Dockhead]

Originally Posted by Kenomac

Another addition would be the installation of a hydraulic backstay tensioner and hydraulic boom vang if you’re concerned about sail shape. Both of our boats have these features which I believe can alter sail shape much more than a Dyneema sheet. You should seriously consider them. The backstay tensioner provides a significant amount or mast bend which is quite noticeable.

But for the most part.... we have a sail assisted powerboat due to the light summer winds here in Western Greece.

Well, I have a powerful vang -- Selden boomkicker gas strut type, with multiple purchase, run to a powerful electric winch. I like hydraulic vangs, but my vang is perfectly adequate, and I use it constantly. On this boat, I actually use the vang even when the boom is over the traveler and the mainsheet is working vertically, because it gives precise control in one dimension which does not vary if I ease the sheet for whatever reason.



But it is not a substitute for proper sheets -- we're talking primarily about jib sheets, and I presume you don't have a vang on your jib . And even with respect to the mainsail, the vang does not control the sail in that dimension.


Mast bend is also not a substitute for proper sheets.



Polyester sheets belong in the same trash bin where you put your old blown out dacron sails. You'll thank me later for this tip!

[cyan]

Originally Posted by Dockhead

I went from 16mm poly to 14mm racing dyneema with considerably higher breaking load than the 16mm poly. From memory, the stretch is something like 5 times less at the same load in tonnes (not % of breaking). The difference is truly night and day.

Really good point- you need apples-to-apples.
Cannot compare at 30% of breaking strength, as that number typically goes radically upward moving from poly to dyneema, even when going smaller in diameter-- you are no longer working in the same strain zone as a % of breaking strength, and it's non-linear.
I think the math actually showed close to 8 times less stretch for the same load when we went from 14mm poly to 12 mm dyneema on sheets. Feels like zero now.
(FYI, the old poly is now a preventer. Might re-think: the stretch is fine in my book, but the age?...)

[dfelsent]

Stiff sheets and halyards make a boat more controllable. I’ve raced and cruised plenty and there is a big difference in how a boat feels in gusts. High tech all the way. Control. Not about performance.

Sometimes self tailing winches require fat lines to work. There are composite lines that offer a fat outer diameter combined with enough strength and low stretch.

For a preventer my choice has been part dyneema part poly. Lower stretch but some give. Dyneema strop from the end of the boom to the gooseneck where it is stored. Then tie a poly line from the bow to the strop. Or shackle it.

Same as a mooring pendant. Dyneema/nylon. Or an anchor rode. Chain/nylon.

Strength and stretch. Pick where you want to be.

[ErnestV]

Originally Posted by Dockhead

It's really important to have the preventer on quite tight so that the boom can't swing and build up momentum and create a snatch load. Then all bets are off.

Right. I have a preventer line going from cockpit port to two massive blocks on the bow and led back to cockpit starboard. With this arrangement I am able to attach the boom end to the lee part of the preventer line, then brutally tightening it with the mostly unused winch on the weather side.
I had a crash gybe this year in a force 8 due to AP malfunction, and the only thing that happened was that it forced the boat to round up to the then-to-be new weather side. No damage.

[allene222]

I am sorry if this has been discussed as I did not read all 16 pages. I have two points to add.

1) I did the calculations at one point and having a preventer going from boom end to bow cleat and then back to the cockpit so you can release it if needed pretty much has to be dyneema. There is just too much stretch at the angles involved to use anything else. As I recall, polyester would not even prevent a gybe it would have so much stretch. For reference, there is a line stretch calculator on L-36.com where you can put in lengths and forces and see the stretch in inches for various lines. https://L-36.com/line_stretch.php

2) A tip I got from Stan Honey is to use dynamic climbing line on the traveler control line. That gives some give to any accidental gybe so that things won't break. Any motion on the traveler will not change sail shape and easing some fraction of an inch in a puff might even be a good idea. The problem I have is that I need to remove it when not in use because it is not UV safe.

We suffered an accidental gybe a few weeks ago. The guy at the helm was trying to avoid another boat during a pre-start. The traveler was not centered so the dynemic line didn't have enough length to help and it partially pulled the control block off the deck. Still trying to figure out a better way to rig it.

Allen

[ErnestV]

Originally Posted by allene222

There is just too much stretch at the angles involved to use anything else.

Allen, I had an old polyester line rigged at the event I described just before. And stretch is exactly why I try to grind the hell out of the preventer using the genoa winch.
Obviously I succeeded in pre-stretching the line sufficiently.

[Captain Max1]

Just curious, I assume they were reefed, but how much? I wouldn’t have much sail up in 48 k.

[Dockhead]

Originally Posted by ErnestV

Allen, I had an old polyester line rigged at the event I described just before. And stretch is exactly why I try to grind the hell out of the preventer using the genoa winch.
Obviously I succeeded in pre-stretching the line sufficiently.

Yes, but then you add the load you've put on with the winch, to the load from any accidental jibe. Nor does a loaded line stretch less than an unloaded one. On the contrary, it will stretch more and more until it breaks.


I'm not sure this is a productive approach.

[allene222]

Originally Posted by ErnestV

Allen, I had an old polyester line rigged at the event I described just before. And stretch is exactly why I try to grind the hell out of the preventer using the genoa winch.
Obviously I succeeded in pre-stretching the line sufficiently.

Glad it worked out. I stand corrected. I might point out that pre stretching doesn't change the distance the additional force will stretch the line assuming it obeys Hooke's law. It probably doesn't so I would expect pre stretching to be a good idea as it will take out slack and perhaps some construction stretch. But from a pure elastic stretch standpoint, pre stretching won't stop the line from continuing to stretch.

Of course, Dyneema will change properties when pre stretched and it becomes a different animal but that is another topic.

Years ago I rigged my boat with a line from mid boom to the rail as a preventer. We forgot to release the preventer as the trimmer brought in the mainsheet and it pulled the bottom off the boom. The boom had some issues that allowed this to happen but that led me to get a big fat Dyneema line that went end boom to bow to cockpit as my preventer.

[ErnestV]

Originally Posted by Captain Max1

Just curious, I assume they were reefed, but how much? I wouldn’t have much sail up in 48 k.

Yes, sure, we had the first reef in as we were planning to travel on this tack for about 7 hours.

[Jaimesan]

Isn't it just risky at 35 kn with messy seas to go downwind with autopilot and with mainsail expecting a preventer to control the situation?
Seems a headsail and sitting by the helm was the safest option, and probably the most comfortable considering the risk of crash gibing.
Sometimes experienced sailors push it a bit too much.
Sad to read the report.

[exMaggieDrum]

Granted I haven't read the report (yet but I will) nor all the 11 pages of replies, but one thing I have grown to love is to sacrifice sail area for a high boom that won't kill someone in a gibe. Every time I have been on deck sweeping booms I have been nervous as hell even for controlled gibes. As well as for just trying to walk around the cockpit with the gibe squared away with the mainsail stowed.



Certainly this dramatically lessons the power available which will lessen max speed, and there probably some boat engineering dynamics that make a lower boom better. For cruising I would vote for safety rather than max speed. On long passages (long being more than a few hours) the crew become complacent even understanding that going downwind is inherently dangerous to the rig if not to the crew.

[Kenomac]

Originally Posted by exMaggieDrum

Granted I haven't read the report (yet but I will) nor all the 11 pages of replies, but one thing I have grown to love is to sacrifice sail area for a high boom that won't kill someone in a gibe. Every time I have been on deck sweeping booms I have been nervous as hell even for controlled gibes. As well as for just trying to walk around the cockpit with the gibe squared away with the mainsail stowed.



Certainly this dramatically lessons the power available which will lessen max speed, and there probably some boat engineering dynamics that make a lower boom better. For cruising I would vote for safety rather than max speed. On long passages (long being more than a few hours) the crew become complacent even understanding that going downwind is inherently dangerous to the rig if not to the crew.

Another case of commenting prior to reading the report.

The boom did not kill the crew member, the balled up main sheet whipping across the traveler plane and striking the crewmember as he crossed over the traveler is what killed him.

Best to read the report rather than comment first next time, the boom was well above their heads.