We were abseiling into a cave (about 15 metres height) using a rope hanged by its middle from an anchor:
_ /o\ | | | | | | | | | |
My experience on abseiling is mostly from climbing, where I descend on both strands. But my friend said that one should do it on one strand (it's understandable because it was a very stiff static rope). So we made a knot on the rope. Then she connected to one strand, leaving the other completely free, and descended.
_ /o\ \ / & / \ | | | | :) | | | | |
Later, someone else told me that one should connect the descending device to one strand, and the prusik to the other.
So, my question is: should one connect the prusik to the same or the other strand, and why?
Also: if using two different strands, should one also tie a knot on the rope?
(side note: we used the setup with one free strand to practice building a hauling system. It was very easy to retrieve the free strand for that purpose. Is this a significant consideration when deciding how to connect the prusik?)