My boyfriend and I do top rope climbing quite regularly in our indoor climbing centre. On attempting a harder route, he slipped and fell, reaching the ground.
I am trying to understand what went wrong.
Here are the details of that climb:
We are approximately the same weight, he is a couple of Kgs more than me but normally never lifted higher than toes when he falls. The route he was working on was 14.5m, which he was 3m high at the time of the fall.
From previous routes set this rope is stretchy. I normally don't give much slack, however, he is a fast climber so it can be a little difficult to keep up. Probably irrelevant, but when he fell he seemed to bounce backwards towards me which left me quite shocked and possibly not applying as much pressure as I should have done.
My main question is, is it normal to fall to the ground in these conditions or is there something I could have done to prevent this?
If you're top roping on a 14.5m climb, 10% stretch* in the 29m of rope between you will be up to 2.9m. In practice there's less rope than that between you, but if there's a little slack in the rope on a climb of that height, the fall could easily hit 3m.
The only way round it is to keep more tension on the rope in the first few metres.
As you're already aware ropes stretch under load, the longer the rope, the further it will stretch. You have to be very careful close to the ground on long climbs as the fall distance could be within the stretch on the rope.
* 10% stretch is the maximum permitted elongation with a static load of 80kg. This is a dynamic situation, so the value can only be used as a guide.
Not aiming to repeat what Separatrix has said; So assuming he's going to be hitting the floor just because of the stretch, you want to minimise slack.
To do this, firstly you want to see if there's a way that you can pull the slack in faster. There's many way to do this and I'm sure you're aware of them all so I won't list how to belay faster.
Secondly, if he's going to do something that he feels is a risk and he isn't happy with the amount of slack, it's up to him to call it out. He was on a harder route, so should've been concious that he was likely to fall, thus gone slower to ensure that the slack was taken up.
Finally, if you can see that there's a load of slack, and you can't pull it in fast enough, tell them they're at risk and to stop/slow down.
I can't emphasise the last one enough. The person belaying has to do everything they can to protect the climber; and if that means the climber has to get comfy somwhere and wait for the belayer to do something, then that's what needs to happen.
Rope stretch is definitely a factor, but something I always do when I am unsure is I sit on the rope before climbing. What I mean is to have the belayer take in any loose rope, and then let your body weight fall until the rope is keeping you from sitting on the ground. The knot will tighten and all of the little loose ends will also tighten and remove most of the unexpected slack that can occur. That leaves you being as tight as possible to the climber.
You did slow his fall.
Assume 15 meters of rope to the top then 12 meters back to him for a total of 27 meters. Stretch = 3/27 = 1/9. So just over 10%. And that assumes no slack in the line.
When you are top roping you can use a less stretchy rope as there should be not dynamic type falls where you need the stretch.
You failed to specify whether the rope was installed in the gym or you brought your own (and presumably led the pitch) and whether this gym allows leading routes with the installed ropes.
If this is purely a top-roping gym with preinstalled ropes, it's quite likely that the ropes are static ropes which tend to have about 4% stretch as opposed to dynamic ropes more in the 12-15% range under load.
That can make for a considerable difference already.
"He seemed to bounce backwards towards me" sounds like you were standing at an angle. For the first pitch, it's usually better to stand slightly to the side (if the climber isn't right below the anchor, the side not getting the pendulum swing) so that neither your climber will drop on your head nor will the rope angle make it likely to drag you from your position significantly (consequently feeding a commensurate amount of rope) without your weight providing a direct counterforce rather than just a bit of inertia.
Standing at an angle also tends to mask slack a lot: slack is the amount of rope that can go through before the rope becomes taught. Some people think "slack" means the rope sloping downwards from the belay device before going up again. While that is a big red flag: the more you stand at an angle, the more slack you can have (even if you could stand your ground on a fall) without it being terribly conspicuous.
When the line/route is significantly overhanging or sideways, it's much preferable to stand below the toprope anchor rather than near your climber when those positions differ.
And when a grounder is to be feared, be prepared to haul in the last bit of rope tight, then jump down (the locality may only provide for actually sitting down, but that's still better than nothing).
Besides technically identifying where the slack came from, don't lose the simple moral: the belayer actually has to work pretty hard in the first few meters of the top rope route to keep the rope taut. Belaying top-rope is not a freebie. The quality of the belay still matters. Outdoor, on longer routes, a top rope belayer has a bit more stretch to work against, and has to manage terrain problems as the route ascends.
On short, indoor routes you likely have a dynamic rope (stretchy) that is also quite old and worn and has a lot of friction. So it will slow you down, and the friction will cause you to think the rope is taut even though slack is building. You have to muscle it through to avoid this.
Plus, you should communicate this through with your partner. Gravity does not know the difference between a slow belayer and a fast climber. Climbing is a team sport. The belay is part of the climb. Assessing the environment of the belay is part of the belay. Let's say it's rope drag, which is my guess. Then in the future if you notice rope drag, your partner needs to know that big moves early in the climb can lose full protection. This is okay, but you should acknowledge and agree to this risk ahead of time.