Posted: Fri Jan 15, 2010 5:32 am
Autoxfil wrote:The test was performed with a solid anchor (which a self arresting rope-mate is certainly not),
which also implies, though, that in glacier travel minimizing the impact force on the belayer is important. The forces may not reach high values simply because the belayer is swept off his (her) feet (or rendered unable to self arrest) before that happens.
Besides, 24 m of rope may be too many for a party of three traveling with a 50 m rope, unless they have a separate rope for rescue. This implies that the forces seen in the field may be closer to the upper bounds seen in those experiments.
Autoxfil wrote:and used a solid "crevasse edge". If a crevasse has enough snow to let you get partway across, the rope will cut deeply, absobing a lot of energy.
Your best bet in that case is to tie knots in the rope. Take also into account that friction works in two ways. One the one hand, it dissipates energy; on the other hand, it causes stress and strain along the rope to be non-uniform. Overall, the rope stretches less in the presence of friction.
Autoxfil wrote:when using a dynamic hip or boot/ax belay to bring up a seconding climber rope stretch is not the primary means of force-control anyway.
As far as belaying the second goes, you could use Dyneema and it would make no difference as long as you left no slack.
One advantage of a less stretchable rope is that it is more efficient in pulley systems. In cases when the climbers have to stay far away from one another (big crevasses), less stretch may in fact help. Overall, though, I'm not convinced low-stretch is always the answer, even when lead belaying is not called for.