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This is a follow up to a thread posted 9/5/09 by Solojourneys, regarding solo top roping. reference: http://www.trailspace.com/forums/climbing/topics/60204.html
I felt compelled to revive this thread because several of the postings therein described basically unsafe belay set up concepts, and wish to warn others why these belays are considered suboptimal, especially considering a bolted top rope anchor should offer ideal bomber pro, compared to most trad belay situations.
Solojourney describes a set up he alleges to be redundant, which is kinda true, but it falls considerably short if evaluated using SRENE (Solid, Redundant, Equalized, Non-Extending) criteria to construct anchors. To begin with, whenever Solo’s rope is weighted only one half of the system will be bearing weight, placing all that weight on just one of the two anchor bolts at any time. Thus no effort is made to equalize the burden among both anchors. Since the most common failure mode of anchors is the stone or a device's placement within the stone – not the equipment per se – Solo’s set up fails to provide security from the biggest liability of any belay set up.
Furthermore since the twin rope lengths are not joined together down-line from their attachment to the anchor bolts no provision is made to limit extention (the free fall that results when one anchor fails, before the other anchor receives the load on the other rope). If the bolts have any distance between them the shock loading of the back up rope can be as severe as that which caused the first anchor to fail, not exactly a desireable circumstance. Both of these issues can be mitigated somewhat if Solo takes the effort to unite both rope lengths with a figure eight below the bolts, preferably such that the angle between the rope lengths leading to the bolts form an acute angle of less than 40 degrees.
Lastly as Bill alludes in his comments to Solo, the self belay devices he describes do not allow the rope to feed through the device when engaged, thus any fall will create some level of shock when the rope is loaded thusly; he is better off using a Trango Cinch or similar device that permits some slippage of the rope through the device when initially shock loaded by a fall.
The variation of this top rope scheme described in the same thread by Tokyo Bill has all the liabilities of the system used by Solo; additionally the back up system (the rope with intermittent figure eight tie-ins, makes shock loading the back up rope a certainty. Worse, depending of the distance between these figure eight tie-ins, this set up possibly will result in a significant - up to factor-1 fall - something that should be avoided if possible.