Good question. When you write a book, you have to be very conservative, so, based on these results, I'd probably say that a minimum setup would be a locker and a non-locker. But there is nothing here that convinces me, that for my own purposes, two non-locking quickdraws is inadequate.

Jay

25-foot route, and the leader is so inattentive that he has let 12.5 feet of slack build up in the rope.

WTF? Where do you get these people? Won't happen unless the belayer had swallowed 4-5 Valiums and had chugged some beer to put them down.

I recently caught a leader fall on trad/aid with the largest guy I've probably ever climbed with. Ivan goes at @ 250 and 6'7" or so. He popped a piece while fiddling in the next one, and the friggan fall still wasn't 12.5' or marginally so if that...well - it wouldn't have been except for rope stretch and me being pulled up.

If I am leading a group with n00b belayers and 400 lb. climbers, then my anchor will consist of 17 pieces and 23 lockers, backed up by every tree in the forest

So to come up with an upper bound on our fall factor we need to put a reasonable upper bound on belayer inattentiveness. On a top rope, the largest fall factors can occur when the climber falls from the anchor on a short route. So, let's say that the climber falls from the anchor on a 25-foot route, and the leader is so inattentive that he has let 12.5 feet of slack build up in the rope. The fall would then be 12.5 feet onto 37.5 feet of rope, for a fall factor of 1/3.

On a steep sport climb that only see a few laps before moveing on to next climb 2 draws fine. Less than overhanging with a group use and some pendulums use lockers.

With kids traversing all over the place the biners getting dragged back and forth there is a good chance of gates opening.

Just you and your palls doing a few loops on steep stuff a few draws perfect.

Birthday party that you are responsible for = 4 lockers and helmets for belayer and climber.

Overkill helps insure that you NEVER have to explain to mom why her kid is not coming home.

I think that most experienced climbers believe that if two carabiners with gates opposite and opposed are used for the master point of a top rope anchor, then neither carabiner needs to be a locker. However, over in this post, cleethree writes:


So, presumably, the reason that one biner should be a locker is to eliminate the possibility that both biners are simultaneously loaded with their gates open in a fall. Well, the worst carabiners that meet the CE standard have open-gate strength ratings of 6 kN, giving 12 kN, or 2700 lb, of open-gate strength when used in pairs. To see if this is enough strength, let's calculate the peak impact force in a wost-case top rope fall. Under common assumptions, the peak impact force on the anchor can be calculated as a function of the climber's weight, the fall factor, the UIAA impact force rating of the rope, and the friction between the rope and the anchor. In order to come up with a worst-case fall scenario, we'll use reasonable upper bounds for each of these parameters in our calculation. We'll also assume that the belayer is anchored and gives a static belay.

Upper bounds for impact force parameters

Climber's weight. The heaviest climber I have ever personally climbed with was a guy from the gym who weighed 290 lb. (I, who weigh 135 lb, belayed him, and it wasn't pretty, even on toprope, with me anchored.) Now, if someone who weighs 290 lb can toprope, it is likely that at some church outing or office "team-building" event somewhere, a 300+ pounder has or will get on a toprope. The two fattest people I have ever personally known were Jerry and Marvin from my karate class in high school. Jerry and Marvin were taking karate to lose weight. Jerry, the lighter of the pair, weighed 360 lb, and I think if he set his mind to it, he could struggle up an easy TR route. But Marvin, at 440 lb, just wouldn't get off the ground. So, I think that 400 lb is a reasonable upper bound on the climber's weight.

Fall factor. Fall factor, of course, is the length of the fall (before the rope begins to stretch) divided by the amount of rope out between the belayer and the climber. If the belayer has zero slack in the rope when the climber falls, the fall length will be zero, and hence so will the fall factor. But there often will be at least a small amount of slack in the rope, and if the belayer is inattentive, there could conceivably be a lot. So to come up with an upper bound on our fall factor we need to put a reasonable upper bound on belayer inattentiveness. On a top rope, the largest fall factors can occur when the climber falls from the anchor on a short route. So, let's say that the climber falls from the anchor on a 25-foot route, and the leader is so inattentive that he has let 12.5 feet of slack build up in the rope. The fall would then be 12.5 feet onto 37.5 feet of rope, for a fall factor of 1/3.

UIAA impact force rating. The largest permissible impact force rating for a dynamic rope under UIAA guidelines is 12 kN. We'll use that value.

Friction. Friction is calculated as a fraction of the tension in the climber's side of the rope. It's almost universally taken to be 1/3, so we'll use that value.

So, to recap, our parameters will be the following:

Climber's weight: 400 lb.
Fall factor: 1/3
UIAA impact force rating: 12 kN
Friction factor: 1/3

Now, we plug these values into my on-line impact force calculator¹, and here are the results we get.



The bottom line of figures, the force on the anchor, is what we're interested in. Depending on which impact force model is used, the calculated peak impact force is between 15 and 17 kN, which, regardless of model, is substantially greater than 12 kN, the combined open-gate strength of two UIAA-certified carabiners.

So, is the n00b right? Do we need a locker in the master point of a TR anchor after all?

Jay

¹ The impact force equations that this calculator uses are documented here and here.

In no stretch of any imagination will you ever get anywhere remotely close to 17 kN in a top rope fall.

First of all, no one makes a rope with an impact force of 12 kN, no one.

The highest I have seen is 11.1 kN...

...and the second highest I have seen is....

Second, 400 lbs. is an unrealistic number to use, 300 is more adequate...

...but even at that we are talking about a fraction of a percent of climbers who fit in that category.

Third, a fall factor of 1/3rd is also pretty unrealistic.

If the climber did truly take a factor .33 fall and weighed 400 lbs. he would hit the ground on anything less than a full rope length climb.

It’s possible but again we are talking about a fraction of a percent of examples.

When discussing safety parameters one must include the extreme examples in which the equipment can be used.

But there is a limit to it.

If you’re looking at scenarios that are in one hundred thousand of one percentile, you’re looking too far.

Take a look at the UIAA rating. They base their strength requirements on the assumption the climber is 80 kg.

After killing two expensive Helium draws on an extended sport climbing road trip (The draws were used on the top anchors for lowering etc - 2 somehow got a lot more wear than the others) I decided that having 2 DEDICATED "top anchor draws" was a good idea. I tweaked them to be IDEAL for clipping in, lowering and TRing if so desired.

They consist of: A 2' tripled up (trad draw) Blue Water sling. Very strong, burly and extendable incase you want to extend the anchor point over an edge etc. The "anchor biner" is a classic BD "Lightweight D". The narrow bar stock and nose on this biner is IDEAL for clipping into everything you'll find at an anchor but SPECIFICALLY for those anchors made of JUST CHAIN, washers and Bolts - no hangers. Then on the rope side I use a Non-Locking Oval on one and a LOCKING oval on the other. Nice, thick bar stock for long wear, smooth lowering and locking if needed. Plus, if I do lock the one and lower, another leader can still easily clip the non-locking one as they finish.

While some may decry the specialization here, it makes life SIMPLE when I grab my sling for sport days.

So the two slings are 6' long and tripled up to 2', right?