A dyneema question...

[fryewe]

Perhaps this has been addressed in one of the may other threads on HPME lines, but if so, I've missed it, and am wondering...

I want to install new lifelines on my cockpit area, and started researching. The guidance I've found suggests that eye splices in those lines should be taken to a thimble or ring to assure the radius of the splice is no less that eight times rope diameter, because tighter radiuses weaken the connection significantly.

This complicates the making of the lines a bit.

As I was pondering this, it occurred to me that I've seen no such caution re soft shackles. Soft shackle nooses are generally capturing a shackle "body" whose diameter is no greater than 2x the line diameter, and the shackles are used in applications that experience a much higher fatigue cycle rate and possibility of line chafe.

I realize the shackles have breaking strengths greater than the rated strength of the line itself, but since dyneema lifelines are generally oversized re strength due to selecting a larger size than needed for comfort in grabbing the line, so lifelines should generally exceed strength needed.

Is the concern in one case and not the other simply because of application...the use of the lines as "life"lines?

What am I missing? Or can I simply take the splice to a SS shackle with a quarter inch or so radius without worry (doing routine inspections for chafe or deformation, of course)?

[savoir]

A lot of people use soft shackles improperly. You are right that the shackles do not like sharp bends. That is because half (or thereabouts) of the fibers are being asked to take all of the load while the other half are in compression. Around a larger radius object like a thimble all of the fibers can share the load.

Soft shackles are best used to attach to something more bulky such as a thimble or a clew grommet. If you want to attach to an object that is relatively thin, such as a padeye, then several turns of a thin lashing like 1/8" would prove more reliable.


If you are making Dyneema lifelines you should terminate each line around a thimble, then attach the thimble to the pulpit, a shackle or pelican hook.

[Training Wheels]

As long as the turning radius is equal to or greater than the diameter of the line, your spliced eye should be 100% of the breaking strength of the line.


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[Stumble]

Fry,

On my boats just spliced the lifelines to the forward stantion, then at the aft end spliced in a thimble, with a lashing making the connection between the thimble and the aft stantion. No muss, no fuss took about fifteen minutes a lifeline.

On dyneema the bending radium seems to not be as critical as was originally thought, and I am pretty sure that down to 1:1 D/d is considered acceptable. But still there is little to no downside to making it larger. The biggest issue seems to be throat angle, when a gradual angle is prefered over a sharp bend.

[fryewe]

Thanks for the responses.

I'm still playing around with dyneema splicing, and have some spare thimbles and rings laying about. I'll probably have a go at it both ways with a line or two and then go with what seems prudent.

I like the simplicity and strength of lashings, but also the convenience of pelican hooks on the lines.

Not launching until early June, so there's time to play around with it a bit.

[Training Wheels]

Use lashings rather than turnbuckles, and pelican hooks for the gates.


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[savoir]

I'll second that.