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i think of the double eyed split tail friction hitches we
use as all very similar; this giving a key to easily remembering them.
They all employ a top coil (4 uninterrupted turns around host lifeline)
that will give pretty sure stop, but too powerfully so might bind. So we
precede them with another choking grab (except VT family uses a gauntlet
of braids to bend lifeline like rappelling rack to not pass full loading
to the coil) to limit loading to the coil and keep it in it's productive
powerband of slide and grip without seizing.
These descend in DdRT and not SRT. For the hitch must be unladed to slide
smoothly. The load switches to the saddle termination leg of DdRT, as you
slide hitch on other leg of support. This works just like the hitch leg of
support was failing or stretching, and the other line/leg takes the
loading, thus freeing up hitch to slide. SRT doesn't have another leg of
support to transfer loading too; so hitch tends to grab tighter, rather
than slide in descend mode.
A Distel just takes the leg to top of the coil, and brings
it below to serve this previous grab that buffers loading to the coil. A
Schwab simply reverses this grab; so that a Distel is kinda like a 4/1
Clove, while a Schwab is a 4/1 Cow type configurations. The self tending
class of hitches, take 1 leg as buffer similarly, but then also that choke
tightens down on the other leg too, so that the loading to the coil is
buffered at the top and bottom of the coil, and just not to 1 leg of the
coil. Without this innovation, the hitch seems to grab when moving up and
needs to be tended by hand or device.