Dyneema to supplement standing rigging?

[BAD ORCA]

Mostly thinking out loud here and was curious if this is done or heard of being done to help prevent a dismasting offshore?

People now use Dyneema for standing rigging in place of cables due to its strength, but got me wondering...if you wanted the ultimate rigging strength to help prevent a dismasting, couldnt you just zip tie 1/4 or 5/16" dyneema rope to you stainless cable rigging and secure it to the mast and deck (robustly) to help add significant strength to the stainless rigging, if you were going offshore for extended periods and expected bad weather and knockdowns?

Im no engineer, but it seems like it would add minimal windage and weight ( if secured very well) for a hefty increase in rigging strength.

It would obviously take some engineering to get it hooked up correctly but does this sound like something that would be feasible for an offshore boat, or possibly cause more problems than it solves?

I've heard stories of people loosing their rig just from a lower shroud breaking. It seems if there was a dyneema rope attached to the shrouds to absorb the sudden loss of a shroud, it could buy enough time to save the rig in a worse case scenario, but again im no engineer so i dont know the technical numbers/stresses involved.

According to some charts, 5/16 dyneema has north of 13k pounds of breaking strength. In comparison, 5/16 stainless rigging is somewhere in the neighborhood of 8K. Thats similar to 1/4 Dyneema.

Thanks, im not thinking of buying a spool to start attaching to my shrouds, just curious about the feasability and to hear any opinions...

[SailingHarmonie]

Would not work. it is virtually impossible to share the load between two wires, even if they have the same stress vs strain relationship, which metal and dyneema cables most certainly do NOT.

If you want a stronger rig, just use bigger wires. Or just switch to all dyneema. A properly sized dyneema rig is always significantly stronger than a metal one. Dyneema needs to be sized not based on its strength, but rather on its stretch at normal rigging loads. So dyneema rigs always end up being larger diameter than the metal ones they replace.

Now, just because the cables themselves are stronger does NOT mean the rig is less likely to fail. Rigs do not come down because the wire was not strong enough. They come down because a component failed.

[thomm225]

My backstay is looking a bit worn after 20 plus year so last time I was up the mast I ran a polyester line around the second outer pin on the mast head then back to a secure point on the stern.

This doubled polyester line will be the backup for the backstay.

Specs says tensile strength for a single polyester line is 4800 lbs. and I have it doubled.

Soon I'll go up and install the new backstay.

Breaking strength on new the 1 X 19 3/16 SS backstay wire is 4700 lbs. so a little less that the polyester line.

[Benz]

It's impractical, not only because of attachment considerations, but because you're adding windage and complications. If you're concerned about wire strength, go up a size all 'round, and make sure your chainplates are in good shape.
Or go to an all-dyneema system, engineered to give you peace of mind.
I'd rather have one system that is reasonably foolproof that backups on backups.
If your existing rig is too old for comfort, and you can't afford to upgrade, it's best to stay close to shore until you can secure a confidence-inspiring rig.

[hberg]

Neat question! Thanks for writing it I love what ifs. I've considered similar when sailing hard & imagining fixes to worse case scenarios like a stay going down (due to whichever fail point) with a long journey ahead. Adjust point of sail and then jury rig a fix right...and how easy of a fix of the spare dyneema you have is already rigged eh...Another exoskeleton of a rig to share the load does sound tricky with the different materials (and lots of holes for attachments in the mast close together can't be good...) but what if the backup rig was loaded slightly less?

For this case I think it plays out like this: one stay or shroud breaks and then load is placed on backup dyneema. Assuming the boat was tuned correctly and the dyneema backup was not under load until the break, the dyneema stay will not be tensioned properly relative to the rest of the rig of course, and by design. The mast is not straightv

I wonder if the difference in tension between the OG and backup stay would be enough to cause big enough detriment to the security/stability/what not of the boat IN AN oh **** scenario. For long term times obvi to be avoided

[Nekton73]

How will you terminate and attach the dyneema to your hull and mast? If it uses the same chainplates, tangs and pins as the existing rigging then really you are only protecting against stay failure. If you make completely new and separate attachments for everything then you would have the redundancy you are seeking.

[BAD ORCA]

Originally Posted by Benz

It's impractical, not only because of attachment considerations, but because you're adding windage and complications. If you're concerned about wire strength, go up a size all 'round, and make sure your chainplates are in good shape.
Or go to an all-dyneema system, engineered to give you peace of mind.
I'd rather have one system that is reasonably foolproof that backups on backups.
If your existing rig is too old for comfort, and you can't afford to upgrade, it's best to stay close to shore until you can secure a confidence-inspiring rig.

Well. its non of that. I thought i said pretty clearly i was just curious not because im trying to cheap out on proper rigging repairs. Adding heavier cables must be much more of a penalty in weight and windage and pure Dyneema does not sound like a wise idea for an offshore boat. One single swipe of a sharp object and you could sever a Dyneema shroud in an instant.

Maybe i didnt explain myself clearly but think of it like this, and in the context of offshore sailing, not coastal cruising.

Your offshore and caught in a severe storm, the potential for multiple knockdowns is a real possibility. Most well made/rigged boats may be able to take one or two, maybe more im not sure but, consider many cant or dont and loose their entire or partial rig.

Let assume you had 1/4 or 5/16" dyneema lines attached to the shrouds but not under any tension, very slightly slack just enough to absorb the shock of a shroud that suddenly snaps. The metal rigging does all the work on a normal day, the dyneema is just there and attached to absorb the shock of a sudden breaking cable.

Again im no engineer so i dont know what those forces and loads would be for each cable. Im sure there are a ton of factors involved for each individual rig. My thinking was that it was there as a backup device.

A righting boat that has been knocked down with sails up must put and exponential amount of stress on the rig with sails filled with water. My guess is that this is what probably breaks most masts, correct me if im wrong, im learning. If the standard rig had dyneema to absorb the load (only under a severe stress moment) maybe that would be the difference between a lost rig and a saved rig, this is the angle im approaching this from.

It still may be unfeasible but i just wanted to clarify my thought process. I appreciate your opinion.

[thomm225]

Originally Posted by Nekton73

How will you terminate and attach the dyneema to your hull and mast? If it uses the same chainplates, tangs and pins as the existing rigging then really you are only protecting against stay failure. If you make completely new and separate attachments for everything then you would have the redundancy you are seeking.

That's why polyester line is better as a backup since you don't need to use attachments as with normal rigging.

My backup polyester line went up and over the outer pin on the mast head and was tied to the bronze chainplate. It was doubled 3/8 polyester line which has about twice the strength of my 3/16 1 x 19 wire rigging.

It was a backup to my back stay.

My backstay is attached to the inner rear pin on the mast head.

My new backstay will be attached to the rear outer pin.

All I have left to do is go up and attach it.

[BAD ORCA]

Originally Posted by hberg

Neat question! Thanks for writing it I love what ifs. I've considered similar when sailing hard & imagining fixes to worse case scenarios like a stay going down (due to whichever fail point) with a long journey ahead. Adjust point of sail and then jury rig a fix right...and how easy of a fix of the spare dyneema you have is already rigged eh...Another exoskeleton of a rig to share the load does sound tricky with the different materials (and lots of holes for attachments in the mast close together can't be good...) but what if the backup rig was loaded slightly less?

For this case I think it plays out like this: one stay or shroud breaks and then load is placed on backup dyneema. Assuming the boat was tuned correctly and the dyneema backup was not under load until the break, the dyneema stay will not be tensioned properly relative to the rest of the rig of course, and by design. The mast is not straightv

I wonder if the difference in tension between the OG and backup stay would be enough to cause big enough detriment to the security/stability/what not of the boat IN AN oh **** scenario. For long term times obvi to be avoided

Thats exactly what i was thinking. In my reply to Benz i mention its not really meant to share the load of the standard rigging in a normal every day sail, its just set so its ever so slack. The metal rigging does all the work on a normal day, the Dyneema (which is piggy backed directly onto each individual shroud) rig is just there to HOPEFULLY absorb the forces of a sudden snapping cable OR in a maybe better case set so that it starts to absorb the excess stress of a cable at its limits of being stressed. The Dyneema would be tensioned in a way where it starts to absorb the load just when the standard rig is at its max stress.

This is obviously very impractical for most boats as they will never be subject to multipple knockdowns. My thinking was purely for ocean crossing boats or boats that plan high lattitude sailing and know they will have to deal with severe weather regularly.

I got the idea reading Bernard Moitessiers book. In it he explains that he just loops cable around his mast over a wood block. The attachment of said dyneema would be tricky but i imagined it simply looped around the mast at the tops (to prevent more holes) and attached at the base ? Im not sure how that would be done. It may require new hardware designed to attach multiple cable to one chainplate. I havn't really though through the engineering. That would be a whole other topic of discussion.

[BAD ORCA]

Originally Posted by Nekton73

How will you terminate and attach the dyneema to your hull and mast? If it uses the same chainplates, tangs and pins as the existing rigging then really you are only protecting against stay failure. If you make completely new and separate attachments for everything then you would have the redundancy you are seeking.

I really just imagined it as a stay failure backup device. The Dyneema would get looped around the mast or somehow simply attached at the tops and connected to the existing chainplates, assuming they are well made/beefy chainplates. At some point if the chainplates are not up to the task, the strongest cables ever to exist would be useless.

[BAD ORCA]

Originally Posted by thomm225

That's why polyester line is better as a backup since you don't need to use attachments as with normal rigging.

My backup polyester line went up and over the outer pin on the mast head and was tied to the bronze chainplate. It was doubled 3/8 polyester line which has about twice the strength of my 3/16 1 x 19 wire rigging.

It was a backup to my back stay.

My backstay is attached to the inner rear pin on the mast head.

My new backstay will be attached to the rear outer pin.

All I have left to do is go up and attach it.

I was wondering if polyester with a little stretch and give would be even better than Dyneema?

[Benz]

Stangely enough, my Dyneema lower shrouds are on loops around the mast, but they rest on bolsters engineered for the load. And my mast has no sail track--it's a round section, so the loops don't interfere with a hoist.
But as for adding Dyneema loops on top of or around existing wire fittings, they'd add a lot of bulk aloft, as would whatever they need to rest on, and would need a means of tightening them alow--you'd want pretty decent tension if they were to hold the rig up after a wire broke from the forces of a rollover.
Wouldn't it be better to engineer a system that could survive a potential rollover, and then do your utmost to avoid rolling over?
People have suggested before on this forum the addition of a second set of shrouds in case one breaks, and the universal concensus is always that it's better to go up a size rather than deal with two parallel systems.
My opinion is that if you're buying Dyneema strong enough for rollover survival, you should just make the entire rig out of it and feel good.

[BAD ORCA]

Originally Posted by Benz

Stangely enough, my Dyneema lower shrouds are on loops around the mast, but they rest on bolsters engineered for the load. And my mast has no sail track--it's a round section, so the loops don't interfere with a hoist.
But as for adding Dyneema loops on top of or around existing wire fittings, they'd add a lot of bulk aloft, as would whatever they need to rest on, and would need a means of tightening them alow--you'd want pretty decent tension if they were to hold the rig up after a wire broke from the forces of a rollover.
Wouldn't it be better to engineer a system that could survive a potential rollover, and then do your utmost to avoid rolling over?
People have suggested before on this forum the addition of a second set of shrouds in case one breaks, and the universal concensus is always that it's better to go up a size rather than deal with two parallel systems.
My opinion is that if you're buying Dyneema strong enough for rollover survival, you should just make the entire rig out of it and feel good.

Thanks Benz, those are good points i will have to look into it a bit more.

[wholybee]

If you have a backup stay, of any material, that is parallel to the main stay but not tensioned, is going to be subjected to huge shock loads if the main stay fails. It will not survive. I'm not a structural engineer, but the breaking strength of 5/16 wire is 10-12k lbs. A shock load might be 5x that. So, you are subjecting 50k lbs to your backup shrouds and chainplates that normally only see somewhere around 3k lbs.

Even if the shock load was only 1.5x the breaking strength of the failed shroud, I don't think the dyneema would survive, and if it did you might rip the chainplates off the boat.

I think a better bet would be to upsize the existing shrouds and inspect them and do whatever you can so they won't fail in the first place.

[notoldbilbo]

Don't forget the problem - not confined to Dyneema - of utilising a too-small 'tight bend' radius, overstressing small groups of fibres which fail quickly-sequentially.
Rope engineers call this inter alia the 'D:d' ratio. That's why traditional rigging had 'thimbles' and why top tech rigging people Colligo Marine produce/recommend much the same for their high-tech rigging solutions.
Of course, experienced riggers know all about this problem....