The Collaborative International Dictionary of English v.0.48:

Keelhaul \Keel"haul`\, v. i. [imp. & p. p. Keelhauled; p. pr.
   & vb. n. Keelhauling.] [3d keel + haul: cf. LG. & D.
   kielhalen, G. kielholen. ] [Written also keelhale.] (Naut.)
   To haul under the keel of a ship, by ropes attached to the
   yardarms on each side. It was formerly practiced as a
   punishment in the Dutch and English navies. --Totten.
   [1913 Webster]