Anchor 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.
   [1913 Webster]

   {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.
      [1913 Webster]