The Collaborative International Dictionary of English v.0.48:

Chesses \Chess"es\, n. pl. [Cf. F. chassis a framework of
   carpenty.] (Mil.)
   The platforms, consisting of two or more planks doweled
   together, for the flooring of a temporary military bridge.
   --Wilhelm.
   [1913 Webster]

   Note: A singular, chess, is sometimes used. "Each chess
         consists of three planks." --Farrow.
         [1913 Webster]