Weird Venice: Ever Wondered About Those Ropes....
(And I just happened to have a Venetian rope phonephoto!!)
Actually, I recently asked a sweet young vaporetto boatman what they called this knot. Nothing, he said... it's just a regular knot.
If you could see the way they can securely tie up a waterbus to the boatstop on the fly, and then release it with practically just a flick of the wrist, you wouldn't think it was so regular!