What is "cable buoy"

Buoy \Buoy\ (bwoi or boi; 277), n. [D. boei buoy, fetter, fr. OF. boie, buie, chain, fetter, F. bou['e]e a buoy, from L. boia. ``Boiae genus vinculorum tam ferreae quam ligneae.''
--Festus. So called because chained to its place.] (Naut.) A float; esp. a floating object moored to the bottom, to mark a channel or to point out the position of something beneath the water, as an anchor, shoal, rock, etc.

Anchor buoy, a buoy attached to, or marking the position of, an anchor.

Bell buoy, a large buoy on which a bell is mounted, to be rung by the motion of the waves.

Breeches buoy. See under Breeches.

Cable buoy, an empty cask employed to buoy up the cable in rocky anchorage.

Can buoy, a hollow buoy made of sheet or boiler iron, usually conical or pear-shaped.

Life buoy, a float intended to support persons who have fallen into the water, until a boat can be dispatched to save them.

Nut buoy or Nun buoy, a buoy large in the middle, and tapering nearly to a point at each end.

To stream the buoy, to let the anchor buoy fall by the ship's side into the water, before letting go the anchor.

Whistling buoy, a buoy fitted with a whistle that is blown by the action of the waves.

n. (context nautical English) An empty cask employed to buoy up the cable in rocky anchorage.