The Collaborative International Dictionary of English v.0.48:

Undecked \Un*decked\, a.
   1. Not decked; unadorned.
      [1913 Webster]

            [Eve] undecked, save with herself, more lovely fair
            Than wood nymph.                      --Milton.
      [1913 Webster]

   2. Not having a deck; as, an undecked vessel.
      [1913 Webster]