keel·son /ˈkɛlsən, ˈki(ə)l-/
  內龍骨
  Keel·son n.  Shipbuilding A piece of timber in a ship laid on the middle of the floor timbers over the keel, and binding the floor timbers to the keel; in iron vessels, a structure of plates, situated like the keelson of a timber ship.
  Cross keelson, a similar structure lying athwart the main keelson, to support the engines and boilers.
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  keelson
       n : a longitudinal beam connected to the keel of ship to
           strengthen it