On a wooden battleship the cannons were literally tied in place so when the recoiled after being fired they would not smash into the gun crew on the other side of the ship. If a cannon broke its restraints it could maim the crew and break through the hull.
The very next line is “loose cannon, rock the boat – is that a mixed metaphor? Boats did have cannons. And if one got loose, it would cause the boat to rock…”
Except that actually makes sense.
On a wooden battleship the cannons were literally tied in place so when the recoiled after being fired they would not smash into the gun crew on the other side of the ship. If a cannon broke its restraints it could maim the crew and break through the hull.
The very next line is “loose cannon, rock the boat – is that a mixed metaphor? Boats did have cannons. And if one got loose, it would cause the boat to rock…”