Ratlines and Dynex?

[Joe Henderson]

Dear John,

What do you mean "Dyneema hates compression"

Is it as bad as Kevlar?

Have we all been wrong about the toughness of this material?

The ability of this fibre to accept tight radiuses and fairly sharp deflections, while being hammered to death, is what has enabled us to utilize it in the many and varied ways that have come to be accepted in the canon of rigging. Soft shackles spring to mind for instance.

I have never bothered in the slightest about bend radii.

How do you reconcile 'Dyneema hates compression" with the widely accepted use of larkshead/cow hitch attachments of snap shackles etc. and the use of the material in spinnaker braces with nothing more than a bit of leather around the eye that takes the clip, not to mention the nip in the pole beak or the working of the brace through the dead eye on the sheer.

I understand that the loading of standing rigging is a somewhat different scenario, but I have found that bend radius, within reason, is more a function of choosing the correct thimble to fit in the turnbuckle and tang rather than any perceived weakness or vulnerability in the material.

Even years ago, when I was making shrouds out of Kevlar 68, I found that as long as the eyes were competently and securely formed round a proper thimble the bend raduis had no effect on the strength and durability of the stay, even after several seasons on a trailer sailer catamaran.

If the fibre is sized for standing rigging according to generally accepted methods for mitigating stretch, then the breaking load is so high compared to the working load that any reduction due to being turned around a thimble is, to my way of thinking, largely irrelevant.

The fact that there is double the material ( albeit loaded in slightly divergent way around the thimble) also tends to instill confidence.

Do we need to modify our thinking re lanyards around pins for shroud attachment, for instance?

Regards,

Joe Henderson, Henderson Rigging.

[Joe Henderson]

Dear John Franta,

You may have missed my question in June regarding " Remember Dyneema hates compression"

We have now completed several standing rigging jobs using Dynex around thimbles( Both re-rig and new build, not to mention the thousands of running gear terminations we have done in Dyneema/Spectra ) and if we are missing something I would dearly like to know so I can contact our clients about any potential problems.

Regards,

Joe Henderson.