Self belay impact forces

Question - I started setting routes at my local gym and they have us use a self belay with semi static ropes when we're setting routes with the grigri clipped to the belay loop and the 'climbers end' also clipped to the belay loop cause they don't believe in tying in... It just kind of freaks me out to take even 1-2 foot falls while trying moves because the catches even for a 1 ft fall are almost painful. Is the fall impact force a legitimate safety concern or am I just being a pansy

If you're talking about a worn out, over stretched rope when you say semi-static, plus youre doubling it up, sure that's going to result in some very abrupt stops. its not the most ideal scenario and as far as safety i would personally want some sort of backup, mainly bc of the static scenario and the single point (belay loop only).

Painful? Hell ya, i'm sure it is painful. if your lower back isn't starting to get sore after a few dozen or so drops like that id be really surprised.

is there just no one available to belay while you set routes?

edit to add: honestly, its your body and your safety ultimately. when you say "they have us use.." and its a system youre clearly not comfortable with, id say its a concern worth raising. there are as many ways to self belay as there are people that have had to do it for one reason or another. petzl has a complete line up of safety products specifically geared toward rope-suspended systems. pick the one most applicable to what youre doing and see if theyre ok w you using it. then you just have to work out if theyll buy the gear as gym equipment or buy it yourself and just bring it in with you to use there.

If the gym has bombproof floor anchors, secure the "belayer's end" of the rope to that and run your Grigri up the "climber's end". The extra rope length in play will significantly reduce peak loads. Keep slack to a minimum and hope for the best.

Do what John says. Thats what I do when setting too.

According to Beal, semi-static rope is built to safely catch a fall of up to fall factor 0.3. This means that it is safe to take a 3 foot fall with 10 feet of rope out. Safety in this case is likely referring to force that it will put on your body, not force at which the rope will break. So a 4 foot fall on ten feet of rope will likely leave the rope in tact, but really hurt.

In your situation, the rope is doubled up, so each strand is only getting half of your weight. This means that the impact forces will likely be doubled (edit - brenta below points out that it would actually be the square root of 2, so 1.4x instead of doubled) on both your body and the anchor because the rope will only stretch half as much and therefore won't absorb as much shock.

As I see it, you have three options:
1. As Gunkiemike said, if you can connect one end to a floor or other anchor, you will greatly reduce the fall factor (and the impact forces on your body).
2. Use a dynamic rope
3. Get something dynamic like a dynaclip to reduce the shock loading.

If it hurts, you're putting your body at risk by doing it on a repeated basis. Man up if it's once a year. Complain if it's daily. Since it's in between, I'll leave that up to you.

ill say it again. its not so much about specific methods. if any subject has been sufficiently beat to death on mp, its one of how to self belay (along with discussion of all elenors aliases).

the bigger issue here the "they have us use" part which implies they are telling the op as well as other route setters to use this method. the gym owner/manager folks need to be put on front street about this first. then you can start working on a best method.

AdamHertzberg wrote:According to Beal, semi-static rope is built to safely catch a fall of up to fall factor 0.3. This means that it is safe to take a 3 foot fall with 10 feet of rope out. Safety in this case is likely referring to force that it will put on your body, not force at which the rope will break. So a 4 foot fall on ten feet of rope will likely leave the rope in tact, but really hurt. In your situation, the rope is doubled up, so each strand is only getting half of your weight. This means that the impact forces will likely be doubled on both your body and the anchor because the rope will only stretch half as much and therefore won't absorb as much shock.

Greg D wrote: No. That's not how it works.

A doubled-up rope is stiffer than a single strand, but the force is proportional to the elongation (in the ideal case) which is less if you double up the rope. If you do the math, which is quite doable in the ideal case, you find that the force goes up not by a factor of two, but by a factor of square root of two. That gives you a ballpark figure for the real case, which is more complex to analyze due to damping, nonlinearities, the alignment of the planets, and what have you.

Thanks for the correction brenta. So really you end up with 1.4x (square root of 2) the forces in the theoretical world instead of 2x. I think it's still correct to say that the system is still no longer designed to take a 0.3 factor falls because more force than recommended is transferred to the body.

Also, is there a good site out there that deals with climbing math. I find it interesting, and I certainly don't want to clutter up general climbing forum with a topic that bores most. I explored going into an aerospace degree in college and some of the stuff came back to me when I started climbing, but I'm quite rusty as evidenced by my last few posts.

A toothed ascender such as a minitraxion strips the sheath of a rope at 4 KN

An ushba, which is the most popular tr solo device in squamish, cuts the rope at 5.5 KN

Consider how many times u hear about a stripped sheath or cut rope by the device on TR solo and that will give u a rough idea of the upper limit

Unless you do something REALLY stupid of course

;)

Thanks for all the replies guys, I guess I'm not gonna die - bearbreeder that is a good way to look at it indeed.

I've done it the gunkiemike way and short falls haven't been painful.