Did the OP say that he had seen this "barrel" on other sailboats?

I've been studying the picture and something occured to me. The ends appear
flat. Like a drum.
If it were for liquid storage, a rounded shape would be stronger,
particularly on a rocking boat with liquid sloshing back and forth within
it.

I wonder if the "barrel" is really a drum, installed on this particular boat
in honor of the "Drum of Drake" legend and boat name.

Eisboch