The Collaborative International Dictionary of English v.0.48:

Garboard \Gar"board\, n. (Naut.)
   One of the planks next the keel on the outside, which form a
   garboard strake.
   [1913 Webster]

   Garboard strake or Garboard streak, the first range or
      strake of planks laid on a ship's bottom next the keel.
      --Totten.
      [1913 Webster]

WordNet (r) 3.0 (2006):

garboard
    n 1: the first wale laid next to the keel of a wooden ship [syn:
         garboard, garboard plank, garboard strake]