Tying hollow block

Hi. I have a load of this and plan to turn it into prussiks. Two questions, any novel ways of sealing the ends after cutting, and what knot is best. Thanks 

David Coley wrote:

Hi. I have a load of this and plan to turn it into prussiks. Two questions, any novel ways of sealing the ends after cutting, and what knot is best. Thanks 

Can you add a picture of “this”?

David Coley wrote:

Hi. I have a load of this and plan to turn it into prussiks. Two questions, any novel ways of sealing the ends after cutting, and what knot is best. Thanks 

Interesting - I didn't know it was sold from spools. 

I assume you are talking about the Sterling Hollow Block?  The Sterling documentation states it shouldn't be used as your primary means of attachment to the rope.

1. Splice it, don’t knot it.

2. Be very aware of the failure modes of braided aramid if using it as anything but a below-the-device third hand. The newer (black) hollowblock is supposed to be less vulnerable to this, but braided aramid can self abrade leading to failure under very low loads without obvious damage.

@lecerfagile wrote:

I am a canyoneer based in southern Utah, and not a hunter. It's interesting to see folks applying the same techniques and equipment across varying disciplines. This forum popped up in a recent Web search for hollowblock info. I am impressed with the level of safety awareness on display in this thread, and thank you for helping spread the word about this often misunderstood product. FWIW, here's a short take from the canyoneering world:

While working as a canyoneering guide back in 2011, I witnessed a hollowblock fail under bodyweight: a few guides were hanging around the basement of the outfitter shop, doing rope maneuvers a foot or two off the floor (rope anchored to ceiling beams). At that time, the guides were using HollowBlocks as a multipurpose tool: mainly as a "third hand" (aka autoblock rappel safety / backup) but also (hypothetically) as a friction hitch (e.g. Prusik) for ascending rope, or other primary attachment. One of the guides was practicing a changeover maneuver (changing from rappel to ascent) and had a hollowblock as his upper attachment point to the rope (tied in a friction hitch of some kind, probably an autoblock). Anyway almost immediately after weighting it, it failed and he fell a couple feet to the floor. Ouch, but NBD. It shook us up b/c although the hollowblock was worn and fuzzy, it was a unit that was part of the guiding equipment cache and still in service. We quickly assembled a few more worn samples and tried to break them by applying bodyweight, and by simply pulling by hand. I was able to break one with my bare hands (and I'm not particularly strong in the upper body dept.)
https://saddlehunter.com/community/index.php?threads/important-information-on-sterling-hollow-block.17056/post-437242

Eli W wrote:

.... failure modes of braided aramid.....

Dang!!!  Thanks for the enlightenment.

Photo as requested 

David Coley wrote:

Photo as requested 

Where did you manage to find that?

Matthew Bell wrote:

Where did you manage to find that?

Sterling sells it for firefighting (for keeping track of position in zero visibility/ as a tagline, not for life safety loads)

https://www.rocknarbor.com/product/sterling-rit-900-6-8mm-hollow-braid/

That’s RIT 900, it’s flat from being spooled, but will return to round when loaded.  Shouldn’t be as much internal self abrading as the Hollow Bloc.

Brocky wrote:

That’s RIT 900, it’s flat from being spooled, but will return to round when loaded.  Shouldn’t be as much internal self abrading as the Hollow Bloc.

I don't think the issue with the hollow block is self abrasion rather the cycle fatigue of the technora. The RIT 900 is made from Twaron which is chemically very similar to technora. (Technora being derived from two diamines and Twaron being from only one) 

Check this study out specifically the "bending flex cycle test" results

https://user.xmission.com/~tmoyer/testing/High_Strength_Cord.pdf

I would expect Twaron to follow a very similar cycle fatigue degradation as technora. 

Not trying to sow FUD here but something to think about for sure. 

My custom samples of the Technora HollowBlock 2 are tied with a double fisherman’s bend with then ends taped. 

Eli W wrote:

1. Splice it, don’t knot it.

2. Be very aware of the failure modes of braided aramid if using it as anything but a below-the-device third hand. The newer (black) hollowblock is supposed to be less vulnerable to this, but braided aramid can self abrade leading to failure under very low loads without obvious damage.

The current hollowblock (hollowblock2) are made of a completely different fiber now. I don't think any of the information you posted is relevant at all.
Technora seems to hold knots just fine.
'aramid' is a nebulous term that encompasses nearly all fibers used in climbing soft goods.

It's a little worrying that posters are looking a braided tan cordage and making enormous assumptions about the cordage and the fibers it's made of. Without any actually certainty of what the cordage actually is. You cannot make a distinction between fibers types with a compressed image over MP.

Daniel wrote: 'aramid' is a nebulous term that encompasses nearly all fibers used in climbing soft goods.

Not in my realm.  I wonder why you would imply that people think aramid and nylon are the same thing.

Mike Gibson wrote:

Not in my realm.  I wonder why you would imply that people think aramid and nylon are the same thing.

I don't recall making that statement 

Eli W wrote:

1. Splice it, don’t knot it.

2. Be very aware of the failure modes of braided aramid if using it as anything but a below-the-device third hand. The newer (black) hollowblock is supposed to be less vulnerable to this, but braided aramid can self abrade leading to failure under very low loads without obvious damage.

Invisible damage is one of my biggest concerns in making DIY soft gear. I just don't know how it will weaken as it ages, because the available data may not reflect my usage patterns accuracy. So I've decided to commit to randomly break-testing some of my own pieces, every year.

The last few months, I've made a couple dozen slings (mostly trad pieces).. I tag & date everything, and I set up a calendar schedule going a few years out. The idea is to randomly pick out & break about 1-2 pieces a year, and measure how they hold up.

It's kind of a lot for a DIY garage project, but I couldn't think of another approach that would have a chance at detecting any significant weakness trends.

Matthew Bell wrote:

I don't think the issue with the hollow block is self abrasion rather the cycle fatigue of the technora. The RIT 900 is made from Twaron which is chemically very similar to technora. (Technora being derived from two diamines and Twaron being from only one) 

Check this study out specifically the "bending flex cycle test" results

https://user.xmission.com/~tmoyer/testing/High_Strength_Cord.pdf

I would expect Twaron to follow a very similar cycle fatigue degradation as technora. 

Not trying to sow FUD here but something to think about for sure. 

Twaron and Technora are both aramids, but Twaron is more closely related to Kevlar, both self abrade more than Technora, as stated in the study you referenced.The Hollow Block is specially braided to be flat, unlike most 12 strand hollow braids.  The Hollow Block is next to the RIT 900 below.

  Agree that splicing is the way to go, neater and retains more strength than knots.

I've never spliced. Might anyone have a link to a video suitable for this material, please. And the size of spikey thing I'd need. Thanks 

Please keep in mind:
* Its all sheath
* Its all structural

There is no core--no redundancy.

Its less about material, and more the construction of the hollow blocks. IE no core. You rap and fuzz up the sheath, well, the sheath is all you have for strength.

This is why I switched to the VT Prusik. It has a core. A load carrying part of it that isn't affected by abrasion.

Desert Rock Sports wrote:

Please keep in mind:
* Its all sheath
* Its all structural

There is no core--no redundancy.

Its less about material, and more the construction of the hollow blocks. IE no core. You rap and fuzz up the sheath, well, the sheath is all you have for strength.

This is why I switched to the VT Prusik. It has a core. A load carrying part of it that isn't affected by abrasion.

Speaking of redundancy this is what I use. Technora sheath with a nylon core

https://www.rocknarbor.com/product/ape-canyon-outfitters-6mm-trc-eye-to-eye-hitch-cord-23/