Okay, I had my coffee and made another UCR
. It actually held without slipping, even with me bouncing a bit in the hammock.
What differed this time was that I made the bury 18" long, a bit under 8 fids for the 7/64 AmSteel I'm using.
So, an 8" bury failed and an 18" bury succeeded. I'll experiment with bury length to find the tipping point.
The idea I alluded to in my previous post was to put the slippery half hitch at the tailing end of the bury, rather than as a stopper at the head end. Though it seems counter-intuitive, I think it ensures that both ends of the bury are initially under tension which, in turn, induces the compression whereby the bury grips the inner line.
It may also be that part of this morning's success with the 18" bury was to 'milk' the length of the bury prior to loading the line, making sure that the bury and the enclosed line made good contact so the constrictor could bite.
There is obviously some threshold length for the bury. I believe that a short bury could still be made to hold by using a hitch at its tail -- slippery half hitch, rolling hitch, sailor's gripping hitch, etc, etc. I'm not sure what the active mechanism is. Perhaps the tailing hitch merely needs to compensate for the friction deficit of the short bury. I lean, though, toward my initial idea -- that the hitch ensures initial tension at both ends of the bury.
Hope that makes sense, but I am open to correction and education.