this is a tuna line radio marker buoy
lost long ago and far away by a Korean fishing boat (fishing ship, in truth).
The cover bolts needed a good drink of penetrating oil,
but in the end they succumbed to
the will of my spanners.
A depressing thought that no doubt every time
one of those huge dry cell 24 volt batteries is replaced,
the old dud is heaved overboard…
after all, why should fishermen bother about
polluting the ocean?