Replying to the earlier point on the Somerville, firstly a minor administrative bobble, that the top-page search engine didn't return the entry, secondly, that I've just discovered it's widespread adoption throughout the Shibari community, because it merges a cuff with a bowline and will not turn over.
The current general method of tying is illustrated
here.
I'm half wondering whether it actually rates as the founding member of a new class of knot. Previously, shibari used a turned-over version of a reef knot, wrapped around the cuff: the Somerville then mated the loop of a bowline with it. The reason for this is because the bight is often used as a pulley (OK, hush, it's their necks - sometimes literally, I was taught it by an professional aerialist, the closest you'll get to a button-boy these days, so I'm fairly certain she knows her stuff), and so the knot is subject to forces in all directions on both standing and running ends from any and all angles, often amplified, which is to me the definition of a turn-over waiting to happen. Turn-overs on human limbs can be disastrous (in fact, no sooner taught than it was being used as a neck sling!), as they either fall apart (slightly better) or tighten (which can be dangerous).
It's a very recent (around 2009): some of the earlier thinking is
here, explaining its development. The use of the terms "single" and "double" columns are generalisations: a single column can be the torso, or a limb, a double column connects two of them, for example, disabling the subject by securing their arms, crossed, behind the back.
And as ever, in such delicate matters, a formal reminder is necessary: the activity must be sensible, sane, and consenting, and the rigger must have medical shears close to hand to release the subject without question if they use an emergency code of their predeclared choice (they usually use 6mm dia hemp, and a test is to trim the end of the rope, which precludes stoppers: in preparing the rope, wrap the point of cut with 2" gaffer tape, which is so strongly glued it'll neither roll not unstick, and cut it in half). Also, specialist medical training in the path of the nerves is essential, as some run very close to the more obvious binding points: this emphasises the value of such bindings, which secure without constriction. Generally, the use of knots is abhored as unnecessary: most ties use friction and tension, however one knot is essential at the ends of each line. Perhaps the most widely-used knot is the lark's head, used at the midway bight of the extension blight just above thumb-knots in the tail of the existing line, to extend it: shibari lines are almost always doubled at the midway point.