A very rough sketch of an idea I had some time ago.
Maybe there would be added a swim ring for additional support of the upper body and make the additional air chambers longer for better suport.
The longer the tail the more air chambers

The why and how to use would be:
Why: to keep the possibly long tail from entailing in something under water (rocks, corals, etc)
How to use: the user should wrap its tail around itself, combining the additional air chambers for a great surface area and then either paddle towards shore or wait until being tugged out from the water, Or, if the user can actually swim somewhat using the surface bound tail to swim towards shore without getting it entangled.