Hi Agargoyle and B.P.,
[/edit] first of all, could you Agargoyle please post a picture of the so named Cramer Hitch? [edit]
I begin by noticing that the "Cramer", the Halter, the (slipped) Marlingspike Hitches and the (slipped) Champagne Knot are topologically the same knot (not in the sense that they are equivalent to the unknot, but in the sense that we can, by starting from one knot, obtain the others by simple moves without untying the knot).
[/edit] please, note that they work differently, in real/practical knotting the geometry of a knot is more important than its topology! [edit]
The Champagne Knot is shown also as a fig 8 marlinespike see (1, p.300-301), really they are both shown in the same page of that book (p.301).
The Marlingspike is usually shown as in ABoK#1789, but in ABoK#1186 (central figure) it looks like the Cramer (so we can call the Cramer a Slipeed Marlingspike (#1186) Hitch). The nipping loop and the rim of the bight (of the collar, I mean the point of contact of the Standing Part and the Running Part before it enters the nipping loop) should stay at the antipods, otherwise the nipping loop is not stable. And so if the Cramer is not stable it can vanish or can capsize into the Halter Hitch.
I think that the Cramer Hitch can show nipping loop instability (yes it can depend on the rope used, the pole, the movement of the Hitch (are you sure it is the best hitch for a fender, Agargoyle?)...). I think a better Cramer variant is shown in the first attached picture (it is based on a Figure 9 knot or better it is a twisted slipped Marlingspike Hitch) but you can obtain it from the standard Cramer by going around the Standing Part from the opposite side. (A more stable nipping loop is obtained with another twist but in that case we lose the quick release feature, because after releasing the slipped bight the rope remains under the wrap).
(I'm using the "figure something" terminology but it can be misleading!?).
Xarax has tied a similar hitch (not slipped) but with another purpose, he named it Bowline Hitch: look at the second picture.
Hope this helps.
Ciao,
s.
1.
http://books.google.com/books?id=miHrAAAAMAAJ&pg=PA300&lpg=PA300&dq=champagne-knot&source=bl&ots=nY1U-dk1V2&sig=ioady6BpwS6h1oYHqipvWxhIp9c&hl=en&sa=X&ei=G4gQT4a4DMbdtgfi6Ph0&ved=0CDwQ6AEwBA#v=onepage&q=champagne-knot&f=false from
http://igkt.net/sm/index.php?topic=3748.msg21765#msg21765