Auto-block: Dyneema Vs HollowBlock

Theories support that Dyneema does not go well with heat and therefore should not be used as an auto-block when rappelling. Therefore an hollowblock should be the preferred way. Any thoughts on this?

That is accurate for repeated use, or use a piece of 6mm cord.

Definitely do not use Dyneema for friction hitches or the like. Melting point is somewhere around 277F which is pretty low and can easily be reached due to friction while rappelling. You can use other material just be sure and know the pros/cons. For example, Nylon has a much higher melting point (above 400F) but one should take special precaution to which type of friction hitch is used as it is also a slicker material. The easiest solution is to just buy a hollow block or prusik loop that was designed for friction hitches.

I think Dyneema is fine for a prusik, for some uses. I wouldn't use it on a rappel or lower because it's moving faster (generating more heat) than if you're ascending a rope, holding a rope in place or most other uses for a friction hitch.

I would use dyneema in a friction hitch to ascend a line in an emergency, but for rappelling a 6mm cord or manufactured alternative (e.g., hollow block) will withstand heat better.

I don't carry prussiks specifically for self rescue in a multi pitch rock climbing context. Between my gri gri, Reverso, hollow block, and dyneema slings (alpine draws from the rack, plus x1 double length and x1 triple length that live on my harness for anchors), I feel pretty confident I can improvise my way out of sticky situations.

I personally would not use Dyneema for ascending a rope. Why introduce significant amount of wear and tear on a piece of gear like that? After a few uses I would only trust that piece of gear for situations with very minimal forces and would not trust it with my life. You are basically creating a very specialized piece of gear that could be replaced with something more robust and trustworthy. Obviously emergency situations would change things but for general use I dont see the need.

Jacob Rankinwrote:

After a few uses I would only trust that piece of gear for situations with very minimal forces and would not trust it with my life. 

the forces involved in ascending a rope ARE very minimal forces. agree that a dyneema sling shouldn't be the go to for a 3rd hand, but ascending a rope seems fine.

Also, more heat is generated in your dyneema sling when you take a fall on it than you ever will ascending a rope. somewhere on the interwebs is a video from richard delaney showing the amount of heat generated in a figure 8 knot as it's loaded, but i can't seem to find it. spoiler alert, it's more than you would think...

bottom line, if you trust a dyneema sling as an anchor, you should trust it for rope ascension.

I honestly am not too concerned about heat during ascension as much as I am frequency of abrasion. It just seems like unnecessary risk for something that can be easily avoided. I already have a 6mm cord for my third hand so why would I not just use that as my friction hitch for ascending?

Anybody using an aramid sling for an autoblock? I don’t own any so I’m not certain if this is practical with its stiffness. 

Chris Cwrote:

Anybody using an aramid sling for an autoblock? I don’t own any so I’m not certain if this is practical with its stiffness. 

sterling hollow block is aramid

Jacob Rankinwrote:

I honestly am not too concerned about heat during ascension as much as I am frequency of abrasion. It just seems like unnecessary risk for something that can be easily avoided. I already have a 6mm cord for my third hand so why would I not just use that as my friction hitch for ascending?

Because for ascending a rope under tension you need 2 hitches.

In the super-rare situation where I would need to ascend a rope under tension, I'd use my hollow block for my waist hitch and a dyneema sling in a Kleimheist/Bachmann as my foot prussik. If I'm ascending a rope that's not under tension, I'd use my gri gri at my waist and strop hitch a dyneema sling to the hollow block for my foot to step up.

But again, these are solutions to an extremely rare emergency situation. There is no "general situation" where I am doing this kind of improvisation in a free climbing context. If I were in the regular habit of ascending lines like an aid climber I'd just use proper ascenders.