speedline attachment krabs/crabs

[TIMON]

Going back to using the revolver carabiners....

 

 

In light of the tandem speeds limitations (20m/s), on a devise specifically designed for its task of carrying loads along a line, how does the revolver endure?

 

I have a feeling that by using it for a speedline attachment, premature failure of the 'pulley' is likely. Has anyone used them regularly for a long time without problems?

 

 

The instructor on our CS 41 has done a great deal of research with kit, ropes, etc so you could be pretty confident that he wouldn't be shelling that sort of cash out on kit that wasn't going to last.

[Gary Prentice]

Fair point, but it would be nice to hear some first hand experience of 'in the field' use - before I/we shell out ourselves:biggrin:

 

A carabiner in normal use has a 10 yr lifespan, so realistically say you expect five. Using a normal carabiner in a speedline role could you expect 12 months of use before wear became unacceptable? ( say using once or twice a week)

 

Would the revolver be the same, more or less. It would need to be more to justify the additional cost - unless using it reduced rope wear to the extent that rope replacement was figured into the calculation.

 

 

I've my accountancy head on this morning:biggrin:

[TIMON]

Well we just bought a load yesterday so I'll PM you in 10 years :)

[Gary Prentice]

Well we just bought a load yesterday so I'll PM you in 10 years :)

 

I'll explain to our lads that their speedline kit will have to be delayed subject to the results of further research:thumbup:

[daltontrees]

I'll explain to our lads that their speedline kit will have to be delayed subject to the results of further research:thumbup:

 

I was lucky to get a load of fairly cheap swing-cheek pulleys a few years ago, and I use them in preference to krabs when either the piece is heavy or the zipline is at a shallow angle.

 

You just need to feel the heat of a krab immediately after zipping something big in a shallow line to realise how much of the potential energy that has been n converted to frictional heat has been absorbed by the metal. It's never going to melt steel but it could be enough to cause microscopic recrysytallisation and the start and propagation of hairline cracks. I wouldn't really be worried about them wearing through, you cluld easily see whether that is happening, it would be brittle failure if they take a bit of a twist or a jerk.

 

Aluminium doesn't hav ethe density or structure to absorb this amount of energy, and aluminium has been known to crumble when heated.

 

Overthinking these things as I can't help doing, I have a sort of formula in my heads as to when to use steel krabs and when to use pulleys. It depends on how much of the potential energy will have to eb absorbed by friction. Big conifer limbs have a lot of drag, and air resistance takes up a lot of their energy on teh way down. They don't seem to heat up krabs the same as the equivalent weight of bare wood. Pulleys bring the pieve down quicker, and more of the energy is absorbed on the final impact (the piece hitting the ground), meaning less needs to be absorbed by the rope and the krab/pulley.

 

We had fun a couple of months ago zipping down a big Douglas Fir, the guys set up 'skittles' of ringed up wood on the lawn and when I zipped the next bit off I tried to judge the sling length just right so that I took out the skittles. On the very last shot before we switched to chogging down, I got a perfect 'strike'. One of the guys filmed it on his phone, I keep meaning to get it from him.

[Gary Prentice]

Over think, over-thinking, over-thinking:confused1:

 

 

I've ordered a load of steel krabs - to be going on with, but would still like a definitive answer as to suitability of something like this: ISC captive eye snap hook 3 way (aluminium) Thoughts anyone?

[TIMON]

Over think, over-thinking, over-thinking:confused1:

 

 

 

 

 

I've ordered a load of steel krabs - to be going on with, but would still like a definitive answer as to suitability of something like this: ISC captive eye snap hook 3 way (aluminium) Thoughts anyone?

 

 

I remember being told on my LOLER course that steel caribiners didn't have a use by date providing the gates still functioned.

 

With regards the captive eyes, how were you thinking of attaching the slings? If it was by way of a simple girth hitch then surely a simple 3 way would save money?

[daltontrees]

Over think, over-thinking, over-thinking:confused1:

 

 

I've ordered a load of steel krabs - to be going on with, but would still like a definitive answer as to suitability of something like this: ISC captive eye snap hook 3 way (aluminium) Thoughts anyone?

 

definitive? no such thing!

 

Captive eyes are going to be a pain in the proverbial, they can't just be clipped to a sling. I just take up a set of slings of various lengths and a set of krabs. If you're doing every branch is a whorl of 6 and clipping them all before starting a saw, you will need at least 2 lengths of sling, maybe 3. If you use captive eyes you'll juyst be constreaining your choice.

 

And those things are aluminium. For me that's a no-no for zipping.

[Gary Prentice]

I like the captive eye, similar to new tribes kit, in that secures the sling (larks footed) in position. As to using Ali connectors, loads of kits do, and apart from premature issues is there any other reason not to?

[mistahbenn]

$6.95 I use these...