clangingsymbol said:
I would be interested in knowing two things
First, you mention:
I imagine (assuming you are right handed) you rapped the rope around you so that the rope either did a loop around you and you are still using your right hand as a brake, or, the rope is forming a “U” so that the rope comes down through your ATS and around the right thigh, under your softer back side and up your left thigh to your left hand (which you are now using as a brake hand), and back down to the ground from there. Or, was there a different scenario in play?
Second, you mention:
What was the method of applying the fireman’s? I have applied a fireman many times with no issue…meaning when I pull on the rope, the rappeller is no longer able to move! Both for fun (to frustrate a friend while rapping…stopping them cold in their tracks…sometimes only inches off the ground) and as an example, teaching newbs how it works and what happens when I do it. I have also used it to pull people across a water feature, keeping them dry by pulling with all my might and then allowing them to pull against me to move along the rope and bypass the water horizontally. Most recently, this was done at the bottom of the first (I think it is the first) rap in Spry to some of my less experienced friends. I have also done it in Behunin and had it done to me in Punch Bowl down in the Superstition Wilderness outside of Phoenix, just because I was a sissy and didn’t want to get wet (little did I know the water was coming in Punch Bowl!!! But it was fun practice!!!).
Hoping to learn.
Brian Click to expand…
hank moon
Note: the stiffer the rope, the less relevant the Capstan equation. For most U.S. canyoneering ropes, rope stiffness is significantly more important than diameter as a factor in rap-device friction. Diameter is one of the least-important factors, though it generally offers a better grip and affects stiffness to some extent.
Jeff Randall
Exactly, Hank. If you get a very stiff rope that will not feed through a rap device then you are basically locking the rope up before it ever makes full contact. While Capstan Equation is still relevant, rope stiffness is a major factor when matched to some devices. My tests have been using rope and/or cord with basically the same amount of stiffness, in other words all things being equal except for diameter. I didn’t believe the Capstan Equation when I was first told about it, but after a lot of testing I’m a convert to the science behind it. It will blow your mind but it works.
Jeff Randall
I have the testing to prove what I typed. In fact, I have done extensive testing on this. But before we start showing all the test data, please research the Capstan Equation.
550 Cord with a Nylon sheath requires almost exactly the same amount of downward force through a descender (or around an object) to hold a load as a 7/16″ rope with nylon sheath to hold the same weight. Diameter has next to nothing to do with holding force around an object. Holding force comes from the coefficient of friction between the two materials contacting each other and the radians of contact they make – the Capstan Equation.
I will agree the more points of contact we make between the rope and the device, the more friction we have but that is simply because we are increasing the radians of contact between two materials. It’s the same way a rappel rack works. By shoving the bars closer together you increase the amount of contact the rope makes on the bars, thus increasing friction.
Again, this is not just some theory I created. It is an actual scientific equation.
rick t
disagree with jeffs suggestion about the relevance of rope thinness or thickness. the “radians of contact” , the first factor he mentions, are a direct function of the ropes thickness. The fatter the rope the more, wider, or greater contact it has on the descender, and on a skinnier rope these points of contact are obviously smaller. The number of contact points also directly affects the level of friction, increasing the areas of friction, which is why we now use canyoneering specific rappel devices with additional arms or legs or fins, as opposed to the old ATC.
garthkevin1
Thanks guys, makes sense now.
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garthkevin1
Okay, longer rappel more rope weight. So am thinking correctly that the rope is thinner from the weight? Hence the need for more friction?
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Jeff Randall
The more rope weight beneath the rappel device, the more friction you have on the device due to the weight of the rope pulling down like your brake hand does. The less rope weight beneath the rappel device, the more your brake hand would have to apply pressure to increase friction in the rappel device.
The actual science behind the required amount of weight below the device to hold yourself from falling is the “Capstan Equation” – an equation that figures the radians of contact the rope has on the rappel device as well as the coefficient of friction between the rope material and the rappel device material at the points of contact, thus giving you a ratio of force required to hold a load in equillibrium. It has very little to do with the diameter of “thinness” of the rope.
Kuenn
You are thinking incorrectly.
It means you start out with less friction on your rappel device.
See Tom’s post above, “On a 300′ rappel, I tend to make two adjustments. You have to start out pretty loose to get it to self-feed on the upper 100′, then add friction about 100′ down, then add more another 100 feet down.”
Think of it in terms of a bottom (fireman’s) belay. You have someone pulling down on your rope, his name is “rope weight”. This increases the friction variable when you start your long rappels. It decreases as you go down because Mr. Rope Weight is loosing weight below as you descend.
There are several posts for this topic on this forum. Here’s one for starters.
Wayne L
My group did Englestead last summer. My friend and I practiced rappelling in his barn using extra friction created by passing the rope through a carabineer attached to the leg loop and another attached near the ATC. It seemed reasonable until I started the 300 ft. rap and hadn’t figured the weight of so much rope hanging below. I was disappointed about having to feed the rope for the first 200 feet, but I was so thankful that none of us lost control and got hurt or died. I was afraid to pull the rope out of the upper carabineer during the rap, so just left it there. Next time I think it would be better to just put it through the leg loop carabineer and have the upper carabineer as a backup in case I needed more friction.
Kuenn
Good on y’all for practicing prior to going. Folks should do that more often.
Remember too, simulating rope weight is quite simple during practice sessions. At 8.34 lbs per gallon of water – hanging a milk jug or two of water on the rope does the trick. Now you’ve got the equivalent of 300′ rope weight on a 20 foot practice rap.
(Weight for 300′ of 8.3 canyon fire = 1.38 gallons of water)
ratagonia
Having to feed it is not a good thing. It usually causes it to bounce on each feed, which saws the rope where it crosses an edge. I cut halfway through a rope on a rappel a couple years ago – thankfully @Brian in SLC noticed something was funny an pulled up the rope and reset it before following me down. I suspect this is how the ropes get coreshot on the final rap of Not Imlay.
On a 300′ rappel, I tend to make two adjustments. You have to start out pretty loose to get it to self-feed on the upper 100′, then add friction about 100′ down, then add more another 100 feet down. Can do this with an ATC-XP: Start with single biner low friction side; at 100′, clip into a carabiner on the off-side leg loop, so the rope zigs, then crosses my lap; at 200′, add more by clipping into a biner up by the rappel device, creating a Z Rig. It helps (no matter what device) to extend your rappel using two carabiners or a 12″ sling.
Important to practice at home. The off-side leg loop biner is gotten by rotating your hips to get the biner to the rope, rather than trying to bring the rope to the biner. (You can then control the friction by rotating your hips.)
Practice at home. But your garage practice does not simulate the hand and body fatigue you will experience on the real thing, and does not simulate the flush of adrenaline at the top and the loss of stimulus when that fades about half way down.
Tom
2065toyota
Or just upgrade to new and improved equipment and buy a CRITR.
Yes, an ATC or other devices with attachments work, but why make it more dangerous and more difficult than it needs to be.
ratagonia
If I may pipe in…
People have a variety of personal preference in how much friction they rappel with. Personally, I like to have enough friction that it requires very little engagement to control the descent, but not so much as to require feeding the rope into the device. I know bottom belays are very effective when performed on me, even when I blow it initially and set less friction than I want.
If one likes it loose, requiring quite a bit of control from the brake hand, then a bottom belay might be not very effective.
We are all happy that Cesar had a bottom belay going, and that it worked, though perhaps not as easily as one would hope.
Tom