By blocking the rope, you will be rappelling on only one strand of rope, keeping the other strand free in case of an emergency.
Reduces or eliminates the twisting that occurs with two ropes, thus making rope retrieval easier.
Allows adjustable positioning of an edge protection pad on the free rope.
Allows re-ascending without re-rigging the rope.
A 'biner (carabiner) block is set up using a carabiner to block the rope on one side of the anchor so one strand is fixed. You can use a clove hitch on the "backbone" of the carabiner to do this. Obviously, the carabiner has to be bigger than the rappel ring or screw link that the rope is passing through.
You can also use a knot to block the rope. Tie a figure eight knot on a bight and clip the carabiner into the loop as a safety. If you also clip the biner through the inside of the knot itself, the knot will be easier to untie later.
In this photo, a carabiner has been inserted through the figure eight knot and into the bight. It is there to make the knot easier to untie once you retrieve your rope.
The last photo illustrates a variation of a knot block. The rope can still be retrieved. When the rope strand on the right is pulled, the carabiner slides down the rope.
This system works, but should not be used when the rope is in current. The force of the water can twist the two ropes together, making retrieval difficult or impossible.
Critical lesson learned - knot block is not always the same as a biner block...
My partner and I learned this the (almost) hard way - we were most comfortable with the knot block, even though we had just learned the biner block.
On our first canyon with our new 8mm Canyon Pro rope - we set a knot block (figure 8) in a rap ring, and as my partner descended, I watched the knot pull through - a combination of small diameter rope and a larger than normal rap ring (or quick link; can't remember for sure).
Fortunately for us, there was a low angle place for my partner to stop while I reset the block using a biner block.
Fortunately for me, the movement occurred before I followed my partner - I outweighed him substantially, and was therefore even more likely to pull the knot through. I probably wouldn't be writing this elsewise.
We never again used a knot block with the Canyon Pro.
The biner block also seems like it will clean on the rope pulldown more often than a figure 8 knot block...
It's fun to watch the looks on peoples face the first time they see a clove hitch on a biner. I can't count the number of times I've heard, 'Is that safe' or 'do you use that a lot' over my shoulder after I tie it.
Knots are fine if the rope dia./kont/and rap ring all match up but a biner is so much less work.
One drawback on the biner block is that it may snag on retrieval if the canyon wall surface is craggy or rocky. In this case everyone in the group goes down on one strand and maintains all the benefits that Rich mentioned, and the last person undoes the knot, retrieves the carabiner and goes down on the two strands being careful to separate them to avoid twisting.
Question about the biner block -
Doesn't it damage the biner when you pull the rope after rappeling and it bounces off the rock on the way down? One of the fundamental rules of climbing is to always retire dropped gear - repeatedly using a biner that has been effectively dropped over and over again makes me a little nervous. Any comments?
Question about the biner block -
Doesn't it damage the biner when you pull the rope after rappeling and it bounces off the rock on the way down? One of the fundamental rules of climbing is to always retire dropped gear - repeatedly using a biner that has been effectively dropped over and over again makes me a little nervous. Any comments?
There are quite a few "fundamental rules" of climbing that have been passed along based on old information that is not necessarily applicable today.
Back in the days when everyone used steel carabiners, it was advised to retire them if they were dropped because they may have been fractured. Most of us are now using aluminum carabiners. Aluminum is more malleable than steel, so much less prone to fractures.
Not suggesting you keep using your aluminum carabiner after dropping it 100 feet. But when you pull a 'biner block down, it isn't free-falling and crashing against the rock. It is being dragged across the rock and/or falling WITH the rope. It's rare to hear more than a light "click" if it actually hits the rock.
Aluminum carabiners are subject to micro cracks from impact too. If you drop one any great distance it's probably a good idea to retire it.
But when you're pulling your rope using a 'biner block, the 'biner never falls any great distance. At the beginning of the pull the 'biner is at the top of the drop. By the time the end of the rope pulls through the rapid at the anchor and the rope falls, the 'biner is only a few feet off the ground if not already in your hand.
Aluminum carabiners are subject to micro cracks from impact too. If you drop one any great distance it's probably a good idea to retire it.
This is another one of those areas requiring judgement calls. I've seen people drop a carabiner a few feet and become frantic about it. I've seen others drop them dozens of feet -- ping, ping, ping as it bounces off the rocks -- then pick it up and clip it back to their gear loop.
What's the advice coming from gear manufacturers nowadays? Was I wrong to state that aluminum is less prone to fracturing than steel?
This is another one of those areas requiring judgement calls. I've seen people drop a carabiner a few feet and become frantic about it. I've seen others drop them dozens of feet -- ping, ping, ping as it bounces off the rocks -- then pick it up and clip it back to their gear loop.
What's the advice coming from gear manufacturers nowadays? Was I wrong to state that aluminum is less prone to fracturing than steel?
Neither the steel used in carabiners or the aluminum alloys are subject to micro-cracking. There may be over-heat treated steel or titanium alloys that exhibit it, but the theory of micro-cracking only came up when they started using fancy ceramics for jet engine turbines.
You can drop your carabiners thousands of feet onto granite, and if they still open and close smoothly, they are fine to use. If you feel uncomfortable with this advice, then go ahead and retire them, or send them to me.
Can I prove this? There is an engineering argument - aluminum alloys (might be exceptions, but 7075-T6 is not one of them) and ordinary steel alloys (as used in carabiners) are not the type of material that exhibits micro-cracking. There is an evidence argument - while working at Black Diamond for 12 years, we NEVER saw a carabiner that exhibited any form of micro-cracking or loss of strength from being dropped (while still functional), including quite a few dropped the full height of El Cap (3000 feet). But no, I cannot PROVE that all biners over all time will never exhibit loss of strength.
And just to cover all the bases, carabiners dropped from outer space, on re-entry, will heat up substantially which will screw up the heat treating. There will likely be ablation of material off the outside also, so I advise against using biners that are dropped from outer space. Those should definitely be retired.
Perhaps Brian knows of some examples of hidden micro-cracking in conventional alloys.
Critical lesson learned - knot block is not always the same as a biner block...
lucky indeed...
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