Ever since I learned how to make multi-point trad anchors, I have been taught to make pre-equalized anchors. I’ve constructed my anchors in a way that each piece of protection shares the load as equally as possible. This has been a practice that I carried over to bolted anchors. In Europe I was taught that the only redundancy a single bolt needs is to be connected to a back-up bolt. This connection could be as simple as a quick draw or a runner connected to a “master carabiner” that is attached to both bolts. This method does not distribute the load between the two bolts, it merely uses the second bolt as a back up in case the first one fails. At first I was reluctant, but the Europeans insisted. Is this method safe?
A single modern bolt is rated to 25 KN. Belaying 2 followers at about 1 KN per fall should not come close to the bolt’s failure point if a proper belay is used. If both climbers fell at the exact same on a tight top belay, around 2 KN would be put on the anchor, 1/12 of the strength of a single bolt. For this purpose, it seems that a single bolt would be completely sufficient as an anchor.
More force is put on an anchor when it is being used to belay a leader fall. In testing that Petzl did HERE they found that a factor 1 fall produced 6 KN on the anchor. That is 1/4 of the strength of a single bolt. Although that is not even close to the bolt’s rating, it is close enough for me to want the redundancy of a second bolt in care of more severe falls or poor bolt quality.
The question is then, which type of anchor is better at withstanding a leader fall? Does a pre-equalized anchor effectively distribute upward force? It is all about the direction of the next piece of protection for the climber. There seems to only one scenario in which a pre-equalized anchor can effectively distribute the weight of the upward pull of belaying a lead fall. That scenario would be if the bolts were in a horizontal line and the next piece of protection is straight up from the anchor. In any other scenario, it seems as if the force of belaying a lead fall would be put on whichever single leg of the multi-point anchor that captures the force first. In that case it doesn’t matter if the anchor was equalized or not.
The more I thought about and used this method, the more comfortable I became with it. It seems to come down to personal preference and the speed it takes to construct because in practice there is not much difference between the two anchor styles. For trad anchors I will always pre-equalize my anchors. However, I might be using this method for quickness and efficiency when using bolted anchors.