Does rigging stretch over time?

[roaringgirl]

A split-off from another thread. As I understand it, rigging wire does get longer when you apply stress to it but will go back to its original length when that stress is removed, unless the stress is so large it goes beyond the plastic limit, in which case the wire will permanently deform (and work-harden). The plastic limit for the wire normally used for rigging is around 60% of the yield stress on yacht rigging, Selden (https://support.seldenmast.com/files/1605537330/595-540-E.pdf) advises tightening to somewhere in the range 15-25% of the yield stress (depending on rig type). So we should be nowhere near permanently deforming the wire. A supplier of 1x19 rigging wire (Stainless Steel Wire Rope Technical Information | S3i Group) says:

Stretch in Wire Ropes​

Stretch is a characteristic of all wire ropes; constructional stretch initially (as the individual wires 'bed down') and then as conventional elastic stretch.

This permanent stretch can be as much as 0.1% for a 1x19 strand.

---

Elastic Stretch​

Once a cable has bedded down it will obey Hookes Law; elastic stretch will be proportional to the load applied. Resistance to this stretch is determined by the modulus of elasticity.

and yet... some forumites real-life experience is that wires have stretched so far the bottlescrews can't tension them properly. So... what's going on?!

 

[neilf39]

Usual case is the boat deforms. In some cases deck compression occurs. Doesn't take that much.

 

[LittleSister]

. . .
and yet... some forumites real-life experience is that wires have stretched so far the bottlescrews can't tension them properly. So... what's going on?!

Some forumites' experience is not governed by the rules of physics, I suspect!

 

[penberth3]

A split-off from another thread. As I understand it, rigging wire does get longer when you apply stress to it but will go back to its original length when that stress is removed, unless the stress is so large it goes beyond the plastic limit, in which case the wire will permanently deform (and work-harden). The plastic limit for the wire normally used for rigging is around 60% of the breaking strain, on yacht rigging, Selden (https://support.seldenmast.com/files/1605537330/595-540-E.pdf) advises tightening to somewhere in the range 15-25% of the breaking strain (depending on rig type). So we should be nowhere near permanently deforming the wire. A supplier of 1x19 rigging wire (Stainless Steel Wire Rope Technical Information | S3i Group) says:


and yet... some forumites real-life experience is that wires have stretched so far the bottlescrews can't tension them properly. So... what's going on?!

Is it too late to ask for a ban on the expression "breaking strain"? It turns me into a grumpy old man, every time!

 

[roaringgirl]

Is it too late to ask for a ban on the expression "breaking strain"? It turns me into a grumpy old man, every time!

Is yield stress better?

 

[LittleSister]

Some forumites' experience is not governed by the rules of physics, I suspect!

Or perhaps their stainless steel rigging self-identifies as some other material?

 

[Refueler]

There are a number of factors that happen after setting up rigging ... as I am sure OP and most are aware of :

1. Rigging settles, basically all those joints / connections etc. move slightly till they settle in final position - meaning that day or so after rigging - you need to go round and check tension again ... nip up where its slacked slightly.
2. Deck / keel compression altering the mast height slightly.
3. Longitudinal deformation of the boat structure.
4. The rigging wires themselves 'stretching'as the lay works. There are two levels to this ... temporary stretch where most will retract and permanent where most will not retract - decided by the amount of tension applied.

#4 is interesting as we all know of option in chandlers of buying 'pre-stretched' or non pre-stretched rope. Not so common with wire.

 

[lustyd]

There’s another explanation too. On my old boat the previous owner had replaced several bottle screws but not the wire. The new bottle screws were longer so obviously the rig was slack. Took me a while to work that out as I assumed the boat/deck had issues. Unfortunately if you don’t know why it’s slack you can’t (sensibly) just change wire length and pray.

 

[Praxinoscope]

I check the rigging tensions before lift in and again about 7 days after lift in when the boat is afloat, usually there is a minor amount of adjustment needed (about 30kg addition on the backstay and cap shrouds) to bring the tensions back to my preferred settings.

 

[rotrax]

I have much experience of Motorcycle Bowden Cables, making thousands in my career and sending many to restorers and collectors all over the world.

I had one customer who complained of "Stretch" in his cables I made for him using his NOS pre war outer cable for authenticity.

I did simple destructive testing using my large Churchill press, finding the soldered nipples failed long before there was any stretch in the inner cables.

His "Stretch" was the outers compressing, giving the same effect. That never happened to the same extent with my prefered Taiwanese outer, but did happen.

My counterbored and soldered brass nipples failed with eleven times more force than could possibly have been applied through the handlebar and foot controls.

About the same force, in fact, as new genuine Yamaha cables failed. These were bought for comparison. These had hydraulicaly formed nipples.

 

[Refueler]

I have much experience of Motorcycle Bowden Cables, making thousands in my career and sending many to restorers and collectors all over the world.

I had one customer who complained of "Stretch" in his cables I made for him using his NOS pre war outer cable for authenticity.

I did simple destructive testing using my large Churchill press, finding the soldered nipples failed long before there was any stretch in the inner cables.

His "Stretch" was the outers compressing, giving the same effect. That never happened to the same extent with my prefered Taiwanese outer, but did happen.

My counterbored and soldered brass nipples failed with eleven times more force than could possibly have been applied through the handlebar and foot controls.

About the same force, in fact, as new genuine Yamaha cables failed. These were bought for comparison. These had hydraulicaly formed nipples.

UGH !! Bowden cables .... Husqvarna / Jonsered have a sadistic streak when it comes to Lawn Tractors .... they use a proprietary Bowden to engage grass cutter ..... the top lever part relying on a plastic part to accept the Bowden toggle .... so you have a double failure ... the toggle fails ... after a while the plastic bit fails ....

 

[KREW2]

There is a painstaking way of tensioning rigging without a loos gauge. I believe it works on the theory that stainless wire does stretch under tension, but will revert back to its original length when the tension is removed.
It involves a taping a ruler or a piece of doweling to the wire above the top of the swaged fitting. As you tighten the bottle screw you use a vernier to measure the stretch until it has reached the required length.

 

[rotrax]

UGH !! Bowden cables .... Husqvarna / Jonsered have a sadistic streak when it comes to Lawn Tractors .... they use a proprietary Bowden to engage grass cutter ..... the top lever part relying on a plastic part to accept the Bowden toggle .... so you have a double failure ... the toggle fails ... after a while the plastic bit fails ....

You have lost me - what is a Bowden toggle?

I suspect you mean nipple.

My nipples NEVER failed. I made many of the antique ones myself from brass bar.

 

[Refueler]

You have lost me - what is a Bowden toggle?

I suspect you mean nipple.

My nipples NEVER failed. I made many of the antique ones myself from brass bar.

I am no cable creator ... but when I here word 'nipple' on a cable - I think of the pear or round shaped ends fitted to cables. The barrel shaped - remind me of Toggles on Duffelcoats .... or Seagull outboard starter cord ...

 

[rotrax]

I am no cable creator ... but when I here word 'nipple' on a cable - I think of the pear or round shaped ends fitted to cables. The barrel shaped - remind me of Toggles on Duffelcoats .... or Seagull outboard starter cord ...

A nipple of the type you describe is known as a barrel nipple.

Failure of such a nipple in a plastic lever might be if hygroscopic plastic was used which has swollen, stopping the nipple articulating smoothly oin the bore. This would cause the cable to bend, fatiguing the cable strands. A Bowden type cable should ALWAYS have a straight pull at each end, with freely articulating nipples.

 

[roaringgirl]

There is a painstaking way of tensioning rigging without a loos gauge. I believe it works on the theory that stainless wire does stretch under tension, but will revert back to its original length when the tension is removed.
It involves a taping a ruler or a piece of doweling to the wire above the top of the swaged fitting. As you tighten the bottle screw you use a vernier to measure the stretch until it has reached the required length.

The Loos gauge for wire >8mm is cost prohibitive, making the strain measurement method the only practical solution for most owners of larger rigs.