The Collaborative International Dictionary of English v.0.48:

Coamings \Coam"ings\, n. pl. [Cf. Comb a crest.] (Naut.)
   Raised pieces of wood of iron around a hatchway, skylight, or
   other opening in the deck, to prevent water from running
   bellow; esp. the fore-and-aft pieces of a hatchway frame as
   distinguished from the transverse head ledges. [Written also
   combings.]
   [1913 Webster]