iain

AlpineK: that comes straight from the crooked river. sometimes it shows up a little brown in the spigots because the park ranger forgot to replace the dirty sock that is filtering out the dead cow parts.

can I nominate this for best cc.com troll?

I bet Dr. Karl Prusik would think otherwise. Though he probably doesn't care that much, as he wasn't engaging in all this geek crap and was actually out in the caves and hills.

An uncool sandbagging example would be when a friend of mine posted on here claiming the great gendarme variation on n. ridge of stuart is 5.7-5.8 tops, a set of hexes will get you up no prob. Sandbagging is perhaps more fun if it is a single pitch bolted line w/ little consequence.

The reason for the two 3-wrap prusiks on a rescue belay is more for shock-load heat dissipation across more nylon rather than raw grabbing power. You can catch a rescue load (usually considered 200kg) with a single 8mm 3-wrap prusik on 11mm static. Single prusiks functioning as "ratchets" on rescue loads are considered quite adequate. There is no reason to use anything but stock perlon for prusiks, rescue or recreational.

I'm not disagreeing with you, but you seem to think I am. I was just pointing out something that was interesting. Also, you can generate a pretty whopping force if you jerk a 3:1 with two people hauling. Try it sometime if you have access to a dyno. I'm not saying 5mm is inadequate. In fact, I thought I just demonstrated it was not.

look punks, I wear fleece and will continue to do so. Patagucci's R2 is about the perfect mountain garment.

It is interesting to note when prusiks do fail, it is in the entrance to the barrel of the hitch and not the knot. Makes you wonder if you really do get near twice your breaking strength out of them.

glad we got that sorted out

Are you saying a single strand of the prusik cord is experiencing T at that location because there are 2 strands of material? I could agree it is close to that. Otherwise, if you are pulling on a z-drag with force T, that prusik (as an entire unit) is experiencing 2T worth of force.

so do you chalk up when climbing the white cliffs of Dover? And while you are climbing there do you engage in a thick British accent and say things like "This Blessed Plot" etc.?

Stephen, I'm not sure if I understand you exactly, but the force on the hauling prusik in the standard "z-drag" would be 2T if you are pulling with T, as it is connected to a pulley. edit: whoops, slow reply Ideally, the prusiks will begin to slide to some extent before they will fail. Prusiks can even be used to act as a clutch, slipping on purpose to make sure the system is not overloaded. This is generally not necessary.

Sure you don't mean "imminent"?

spell czech might not hurt either.

eminent?

Sorry, I have no idea what pulley would work with 5mm. Perhaps someone can ring in with some experience with 5mm. 1150 lbs force equals about 5.1 kN, so it's in the same ballpark as the number I put down (that was from REI). That's the breaking strength of the material. But take a look at the prusik. Is all of the force being held by a single stand of that material? I doubt it's split perfectly 50:50 between the two strands, but neither is bearing the entire load. So if you said it could support 10.2kN (2 strands, each holding 50%), you're doing quite well in terms of safety margin. You have a knot in the line too, which, on average, reduces the cord strength by 1/3rd. So if you take that into account, you would have about 8.5kN to work with. You would have to generate over 8 times the force of your 1kN load to break that material. Pretty good margin of safety from strictly a material strength standpoint. Perhaps this is overanalysis, but maybe it helps (I hope I calculated that right!)

The prusik you use to haul with will experience a peak of force when the haulers start yarding on the rope, and your "progress capture" prusik will peak when the haulers quit hauling. These forces can be quite large if you have haulers who don't pull smoothly and continuously and just try to jerk the person up. However, you still have almost a 10:1 safety factor with the 5mm prusiks (assuming your subject, hanging in air, is putting about a 1kN force on the rope to begin with). That would be a 100kg person, or 220lbs, seems reasonable for your "average" climber with ton of gear. If you are heavy, maybe that is something to consider. But 10:1 is pretty conservative margin. There are only a few pulleys out there that will reliably mind prusiks made from 5mm. Something to consider.

dreamin, I believe. nice picture!

I dislike the posturing, when someone chimes in to say a particular hard route is "sweet" simply to say, yes, I have climbed it, behold me in all my glory. Route name-dropping.

It seems your "experiential learning" would be limited to things that are a part of the human experience. How do you teach someone concepts that exist beyond our immediate environment? Clay models? Dance around holding hands to form a benzene ring? It would be difficult to grasp things like quantum mechanics, organic chemistry, astronomy, etc without hitting the books. There are so many new concepts to absorb, and books are a very efficient way of inserting that knowledge in the brain.

w00t well there you go, thanks. w00t! w00t!

yeah! mid-atlantic ridge! take that!

A single strand of 5 mm cord has a breaking strength of 5.6kN or so. In a prusik, there are two strands holding a load, one with a knot in it, so a prusik with 5 mm cord should in theory hold about 9.4kN. In reality, there will be some movement as the prusik sets, etc. That's a pretty healthy margin for something that is basically supposed to support body weight and change. For an 8.1mm rope, 5mm seems like a reasonable choice to me. It would be illogical to trust 5mm prusiks on an 8.1mm rope, but not on an 11mm rope. That said, I use 6mm 5mm is pretty thin stuff and seems to wear out faster. If you are ever using prusiks to get over a rock edge, you will be happy to be using 6mm. You could just try seeing if 6mm will work on your 8.1mm ropes. Just buy some and try hanging on it, it's cheap. See what happens. 3-wrap it if need be. As the prusik material gets worn a bit, it will "stick" better too. -Iain