Forces in a Guided Rappel

[ratagonia]

Many of us who use guided rappels fairly often have always wondered
what kind of forces are generated using this technique. I had the
opportunity to measure a guided rappel last week, and here's what we
found.

I went training with the other ZAC guides in Water Canyon last
Friday, March 7, 2008. We set up a guided rappel for the last big
rappel in the canyon. The rap is 90 feet high, and the rock that
forms the bottom of the rap is about 80 feet away. My 155 foot rope
just barely makes it.

For both guide and rappel lines, we used Bluewater Canyon Pro 8.0 mm
ropes. The Dynamometer was set up between the bottom anchor and the
bottom of the rope. The Dynamometer was a 4000 lb model, and had
ticks at every 25 lbs, and a max-load hand. The rope was tensioned
(only moderately tight) at the bottom using a Voodoo system.

We sent one 150 lb person down the guide line. Normally, I would
tighten the system a foot or two at the top, at this point, but in
this case I decided against it, so we could see where different
weights of people ended up. Next we sent a 120 lb person down, then
another 150 lb person. I then tightened it up reasonably snug from
the top, using a 1:1 counterweight and tying a block in with a couple
inches of slack.

Results

My 190 lbs on the guided rappel generated a maximum load of 625
lbs. Maximum force was reached at the very bottom of the rap, just
before stepping onto the sand. Most people tend to bounce more at
the very bottom, also, which probably contributed to the max load.

Discussion

This was much lower than I had previously suspected, as being about
5X bodyweight. 5X is probably still a good, conservative upper limit.
This 45 degree overall angle (roughly) would produce higher loads
than most guided rappels I have done (which seem to be for the most
part, steeper).

Application of Results

The geometry of each guided rappel will be somewhat different. This
guided rappel with a 45 degree overall run only generated 3.5X
bodyweight. Shallower angles are likely to produce lower forces.

The BW Canyon Pro rope is considered to be highly static, thus we would expect that using almost any other rope would result in more rope stretch, and therefore lower loads. (A high level of staticity is usually considered desirable when setting a guided rappel).

Tom

[oldno7]

very interesting information, thanks for posting.

[Deathcricket]

Forgive my ignorance being a noobie and all. But besides pussies who dont want to get wet, what's a valid reason to use a guided rappell? Never used one before and just wondering. They sound like a pain to set up from what I hear.

That, and you can't do any "stunts" on them :)

Seriously though, why?

[ratagonia]

Forgive my ignorance being a noobie and all. But besides weanies who dont want to get wet, what's a valid reason to use a guided rappel? Never used one before and just wondering. They sound like a pain to set up from what I hear.

That, and you can't do any "stunts" on them :)

Seriously though, why?

Good reasons for setting up a guided rappel:

1. Showing off your sophisticated canyoneering technique.
2. For comfort, or to manage heat, keeping people out of the water can be a good idea.
3. To pass an obstacle, such as a pothole (can be a very elegant and quick solution).
4. To speed things up (in some cases MUCH faster, especially with noobs).
5. To pass a tricky or dangerous obstacle, especially in Class C (flowing water) canyons. Larger, heavier people have a distinct advantage in technical swims and hydraulics. The biggest (Brian Cabe, if available), most competent can go down first and get the bottom anchor, and only Brian has to deal with the nasty hydraulic.
6. It's more FUN that way.
7. Can be easier on the environment - fewer footprints on the sensitive mosses.
8. Because everyone can do stunts on a guided rappel!
9. Keeping Tom dry and warm might be a good thing for the entire group!
10. Very good for moving injured canyoneers down rappels.

Tom

[stefan]

that's for posting this, tom

[m cabourne]

With regard to Tom's reasons

2) I once found it an advantage on a long cold swim at the end of the day to minimize exposure time in the water. It did mean the first one down had to carry lots of rope and those that followed needed to pass several knots on the tag line.

8) Zip line comes to mind, although you can "splat" the bottom anchor.

Mike C.

[Randi]

With regard to Tom's reasons

2) I once found it an advantage on a long cold swim at the end of the day to minimize exposure time in the water. It did mean the first one down had to carry lots of rope and those that followed needed to pass several knots on the tag line.

8) Zip line comes to mind, although you can "splat" the bottom anchor.

Mike C.

Hey Mike! Welcome to Bogley (formarly known as UUTAH). Nice to see another Californian on board! : )

~Randi

[Iceaxe]

8) Zip line comes to mind, although you can "splat" the bottom anchor.

We once set a zip line for the exit to Zero G. And the only reason for doing it was it made for a cool stunt.

[Randi]

You forgot one: Propelling young children down the canyon efficiently and quickly! : )~ MEOW MEOW, MEOW!

Good reasons for setting up a guided rappel:

1. Showing off your sophisticated canyoneering technique.
2. For comfort, or to manage heat, keeping people out of the water can be a good idea.
3. To pass an obstacle, such as a pothole (can be a very elegant and quick solution).
4. To speed things up (in some cases MUCH faster, especially with noobs).
5. To pass a tricky or dangerous obstacle, especially in Class C (flowing water) canyons. Larger, heavier people have a distinct advantage in technical swims and hydraulics. The biggest (Brian Cabe, if available), most competent can go down first and get the bottom anchor, and only Brian has to deal with the nasty hydraulic.
6. It's more FUN that way.
7. Can be easier on the environment - fewer footprints on the sensitive mosses.
8. Because everyone can do stunts on a guided rappel!
9. Keeping Tom dry and warm might be a good thing for the entire group!
10. Very good for moving injured canyoneers down rappels.

Tom

[Brian in SLC]

Forgive my ignorance being a noobie and all. But besides pussies who dont want to get wet, what's a valid reason to use a guided rappell?

Perhaps there are some types of ignorance that are unforgivable...

-Brian in SLC

[Deathcricket]

Also I apologize for the derogatory term. Even "weenies" maybe is a little strong. Everyone should know their limits and not get in "over their head". If i got into a canyon and something was beyond me, I'll be the first to ask for help. But I don't understand taking the "easy way" intentionally, like a guided rappell would offer. If the canyon is too hard, there are easier ones to practice on. When I get in a canyon I want undertow, potholes, water slamming me in face, and whatever else the canyon wants to throw at me. Thats part of the challenge right? If someone was to offer me a guided rappell it would be like a cheat. At least for me.... Ok you do the hard part and I'll glide down and avoid the nasty obstacle, lol.

But, I can also "understand" wanting to see a beautiful canyon but not wanting the dangers or even getting cold/exposure. But for me personally the experience would be lessened without the challenge. So if people want to make the trip easier, that's cool. Everyone has their own idea what is fun. For me it's the physical challenge and figuring out obstacles. I'll even take a downclimb over a rappell if it looks safe enough. For others it could be the nice scenery, hanging with friends/family, using technical skills to setup a guided rappell, or even bragging rights (yeah i did that canyon). It's all good!

So my "tone" wanting to impose my personal belief that you should experience the canyon and not bypass "hard parts" is just my personal opinion and nothing more. Just was curious if there were other reasons besides making the canyon easy is all.

[ratagonia]

Also I apologize for the derogatory term. Even "weenies" maybe is a little strong. Everyone should know their limits and not get in "over their head". If i got into a canyon and something was beyond me, I'll be the first to ask for help. But I don't understand taking the "easy way" intentionally, like a guided rappell would offer. If the canyon is too hard, there are easier ones to practice on. When I get in a canyon I want undertow, potholes, water slamming me in face, and whatever else the canyon wants to throw at me. Thats part of the challenge right? If someone was to offer me a guided rappell it would be like a cheat. At least for me.... Ok you do the hard part and I'll glide down and avoid the nasty obstacle, lol.

But, I can also "understand" wanting to see a beautiful canyon but not wanting the dangers or even getting cold/exposure. But for me personally the experience would be lessened without the challenge. So if people want to make the trip easier, that's cool. Everyone has their own idea what is fun. For me it's the physical challenge and figuring out obstacles. I'll even take a downclimb over a rappell if it looks safe enough. For others it could be the nice scenery, hanging with friends/family, using technical skills to setup a guided rappell, or even bragging rights (yeah i did that canyon). It's all good!

Just was curious if there were other reasons besides making the canyon easy is all.

Hey Brian, sounds like we have a volunteer to rap into the Whirlpool of Death. You're off the hook.

http://www.climb-utah.com/Zion/kolob1.htm

's'okay if you want to not avoid any of the hard stuff. Perhaps it's not 'hard', just unpleasant. We can set up the guideline slack so we give you a good face shot and a thorough tumbling in the washing machine before dragging your sorry buttocks out of the froth.

Someone does not HAVE to go first. In Imlay, there are TWO "throws to a guided rappel". You want to prove the macho of your huevos, launching out on a thrown bottom anchor tends to produce a large amount of pucker!

And of course, the primary reason for doing a guided rappel: Chicks Dig It! You can go first, do the freezing cold swim and allow the ladies to gently float across the pool, high and dry. Mucho macho points.

Tom