#racing_boat  a boat propelled by oarsmen and designed for racing
  supertype:  #small_boat__smallboat  a boat that is small
  subtype:  #racing_gig  a light narrow racing boat for two or more oarsmen
  subtype:  #racing_shell__shell  a very light narrow racing boat
     subtype:  #racing_skiff__single_shell  a shell for a single oarsman
     subtype:  #scull  a racing shell propelled by one or two oarsmen pulling two oars

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