Thanks for asking this! Was wondering myself.
Have a stupid question to ask along with this. Is it possible/feasible to set a snare on a drowning rig?
No different than any other trap. Just attach the end to the drowning lock. It'll work best if you can use as short of a snare as possible to still get your desired loop size. a 40" snare would work most all the time.
Good tip there. When I make snares for open water drowning, I include a drowning lock
on the snare cable positioned so that it
will slide toward the loop.
Now when I make the set, as ADC says you just attach the snare to the drowning lock on your drowner cable. In addition, I attach a heavy window sash weight to the drowner lock on the snare itself. Two sash weights if small. These are just set on the bottom.
The beaver gets into the snare, can't go up the bank any further, then turns and swims to deep water. The snare tightens and drags the sash weights as the drowner lock on the drowner cable slides towards deeper water with the beaver. As the beaver goes deeper, those sash weights slide right up to the snare loop.
What I find interesting when snaring beaver in open water is the lack of struggle marks on the bank as opposed to a foothold held beaver that temporarily reaches the bank. A foothold held beaver will have deep struggle marks on the bank 'til it turns to open water, that is, IF it goes up the bank first, which doesn't happen too often. The snare-held beaver will simply walk up the bank 'til the snare tightens, discover its held, then turn to swim out away from the entanglement it finds itself in.
Anyway, for what it's worth.