yes, i know, lol...
however, i intended these to reflect 'dummy' mines, which were historically used, to hamper/slow down mine-clearing ships...
from our 'know-it-all'
friend, Wikipedia:
Dummy mine[edit]
Plastic drums filled with sand or concrete are periodically rolled off the side of ships as real mines are laid in large mine-fields. These inexpensive false targets (designed to be of a similar shape and size as genuine mines) are intended to slow down the process of mine clearance: a mine-hunter is forced to investigate each suspicious sonar contact on the sea bed, whether it is real or not. Often a maker of naval mines will provide both training and dummy versions of their mines.
be assured, i did not take Wiki's word for it, and asked some retired naval officers, one of them being my own father, whose first command was a minesweeper, and they confirmed the use of these dummy mines, as well
of course, these won't drift as the others might, but for a purely visual purpose, they're okay, i guess....