Rappelling

Steve,

What's the manufacturers name of your shunt? If it's available online, please indicate where.

Regards,
JimK

That's a clever setup, Steve. I'm seriously thinking of buying the shunt (assuming my wife will let me spend more $$$ on climbing! ). Thanks for taking the time to post the pics.

Edit: Will this work with 1/2" arborist rope? And in the bottom picture, the lanyard you're pulling on is the shunt release?

Originally posted by RescueMan

Originally posted by Mutt
As far as fast rappells having a better chance of becoming uncontrolled drops - does anyone have any further experience or knowledge of this? I'm wondering if the risk is greater for static kernmantle rope, "undoubled", if that makes sense?

More rock climbers, cavers, and rescuers die on rappel than than on any other roped activity. It seems the more experience a climber has, the more cautious they are about rappeling.

A single strand of kernmantle rope, particularly if it's smaller than 1/2", will offer much less friction than doubled ropes.

And it's not hard to get a rappel device (particularly a fig 8) hot enough to melt rope.

- Robert

Okay, so with doubled 1/2" arborist rope, a mini-rack, and a drop of no more than 50 - 60 feet, I should be at less risk than climbers/cavers who are using single, small-diameter static kernmantle on long drops.

Correct me if I'm wrong, but wouldn't descenders be subject to the equivalent of a car's "brake fade" when they get hot? In other words, as the descender heats up, it provides less friction? Even on my fastest drops, with such a low height, the rack has never gotten too hot to touch. Could this be part of the problem for other vertical sports?

although the cord is the release i find it very sensitive, and tend to just release it fully and belay myselfoff the krab. I have a colleague who controls himself exclusively with the release however, just depends what you're most comfortable with.
This device is pretty cheap by the way, only £30 here in the uk.


to quote robert
It is designed for double ropes as small as 8mm or single ropes 10-11mm. It is designed to be used only on dynamic rope, slips at a relatively low force, and has a relatively weak body that will blow off the rope under serious shock loading.

This is true, however what is also true is that unlike rock climbing, in tree climbing you should never have any slack on your rope, in which case there should never be any reason for any shock loading whatsoever. This is down to the individual however. I never have any slack on my rope, but know people who do.
with regards to only being for use on dynamic rope i'm not sure thats accurate and can see no reason for it.


but anyway, hope you give it a try, its a great set up.

Originally posted by RescueMan
Brake fade from overheating is caused by glazing of the brake shoe friction material and is not applicable to descent devices.

Well, I don't know how much it's applicable to descenders, but the concept is the same: converting kinetic energy into heat through friction. As your brakes heat up, they lose efficiency. I would think this phenomenon would be true for descenders as well, but the loss of efficiency in a descender might be negligable at lower-than-rope-melting-point temps.

robert, do you know what load they had on the shunt to cause slippage?
I've been using my shunt now for over a year on 10.5 and never had it slip once.
by the way, have you tried the shunt with this set up?

I too learned Bob Wray's technique of placing a descender below the blake's. A couple of observations and perhaps a questions or two.

I would have never tried this as a beginner. Only after learning SRT and rapelling comfortably would I even try it. My initial reaction is why bother, just more stuff to rig. Then I tried it and just love it for the reasons Joe Maher described; smooth, fast, safe, less wear on the rope. I use the Petzl Stop as my primary descender.

After rigging my stop, I lock it off. I pull my blake's down and my bridge goes slack as I am now hanging on my descender. I loosen the blake's alot! It does not need to be tended as it just follows along. If I don't loosen it enough, it grabs and needs to be loosened more.

I have tested this very loose blakes a number of times. When rapelling FAST, it has always grabbed. I really like the Stop for this because it works just like the blake's hitch-let go to stop.

I can't figure out how you could rig a descender above the blake's hitch on the "haul rope". Unless sitting on a branch, this would be under tension and not allow rigging a figure 8 or other mechanical descender. Am I missing something?

On balance, I like it and carry my stop with me on every climb. Don't always use it, but I can.

Bob

I think this is the report on the Shunt and the Rocker:

http://www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf

Spend some time searching the HSE archives for info on karabiner research and info on tree climbing too. Very valuable stuff to learn.

There are two studies done with rap backups like the Shunt and Rocker. They came to almost opposite conclusions. BUT...the tests were done with different conditions. In one, the rope with the device attached was weighted. This is similar to having a long length of rope below the device.

Either test showed that both devices worked within a satisfactory range.

Like Robert is saying, the Shunt is not a general-duty too. Read up on it at Gary Storrick's site too. Read Petzl's info.

Tom

I'm going to ask the dumb question: My son and I are just recreational tree-climbers and have been using a Petzl Pirana descender (which is a figure 8 with a couple of extra "hooks" on it to lock down the rappel). Are we missing a safety technique here? We are usually descending at least 100' in the Old Growth Firs we climb and as long as we don't descend too fast, we have not had any problems with the heat build up.

wahoo,

I think this whole discussion revolves around using a descender in addition to or instead of a friction hitch in Double Rope Technique. The standard descent method is just to descend on the blake's hitch. Using a descender is a more complex variation. SRT as you do requires the descender, so I can understand why you thinking, what is the questions here?

Bob

The question remains, are we missing a safety procedure by only using the pirana descender? This seems like such a simple descent - very uncomplicated, safe and controlled..... Ben

The oft quoted article by Gary Storrick:

http://storrick.cnchost.com/VerticalDevicesPage/Misc/RappelSafetyPost.html


http://www.chockstone.org/TechTips/RapBackup.htm

I'm brand new to tree climbing and have learned a lot just reading these posts. I have developed, however, what I think is a good and safe way to descend with SRT. Actually, I just posted this on the General Discussion forum (didn't see this one in time).

Once I decide to come down, I hang from the top ascender (clipped in to my harness), pull up some slack from below the bottom ascender (the one for my feet) and hook my Figure eight into the line and the carabiner on my harness.

Then I lift myself with the foot ascender and loosen the top one. I never unhook the top ascender. I next hang via the Figure eight, loosen the bottom ascender so it's very loose (I could take it off, but didn't bother). Then I put my top hand on the top ascender to keep it from grabbing, and rappell down. No unhooking, never a chance to fall. This way I also have a backup (let go of the top ascender) in case I lose the descent controlling grip (the one below the figure eight).

I got the idea from reading about rock climbers rappelling. They always have a backup (often a prussik) above the descender to catch them if something goes wrong with the controlling hand or descender.

I used Bachman knots for both of my ascenders because they are easier to move up after being weighted than a prussik but I think any climbing knot would work.


Eric (newbee from Connecticut)

Try the autoblock knot below the descender, it will be easier to handle. Read the article I linked to, it is a ropework classic. Try them both and see how they are different.

You can get hung up on the upper one.
Id be wary of using that upperbelay with a toothed ascender, it may get a little sharp if you stop suddenly. A bachmann knot sounds like a much better way to go, and heaps cheaper as well!

Thanks for the link to the autoblock and prussik sites. Sounds like a great idea. Now I have something new to try. Always makes for a good weekend.

It's full foliage this weekend here in CT. Gonna have a great time in the trees.

Thanks again for the suggestion