“Found this digging around the mouth of a major Caribbean harbor (on my property). Did this come out of a cannon?”
"There’s a lot of cannonballs in the bottom of the ocean around the Caribbeans. They’ve been known to wash up on beaches from North America to South America. I have a friend that found one on a beach in South Carolina."
...film container. No mine has this particular imprint on the housing. For pressure you install AP or frog type device under, and pressurize with AT.
They are used all over to prevent damage to ships in general.
We use yokohama fenders while repairing the regular fenders on the jetty.