I have some like the Blackswans. Made them myself from black water pipe and a T. They work good in locations where you don't have a lot of overhanging limbs to tie to. I used to fish oxbows and would set them over a stickups in water deep enough to fish. Fish will tangle line sometimes. I have also used them like jugs. Slight breeze and anchor. Put them out and let them drift. I also took 1/2in water pipe insulation and put around bottom ring for extra flotation.
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Charlie Weaver USN/ENC 1965-1979