KEEL Another  structural  member  of  a  ship  is  the keel, which runs the length of the ship’s bottom from  the  stem  to  the  stern  post.  It  acts  as  a backbone,  performing  a  function  similar  to  that of the human spine. The keel of a metal ship does not project below the bottom as does the fin keel of a sailboat, but lies entirely within the ship. It consists of plates and angles built into an I-beam shape. The lower flange of the I-beam structure is the flat plate keel that forms the center strake of the bottom plating. The web of the I beam is the center vertical keel. The height of the center vertical keel varies from about 2 feet in small ships to nearly 7 feet in large ships. The upper flange of the I beam is called the rider plate. If the vessel is  fitted  with  an  inner  bottom,  the  rider  plate forms the center strake of the inner bottom plat- ing. At the ends of the vessel, the keel is joined to the stem and stern posts, which complete the backbone.  The  keel  accepts  the  major  portion  of load  during  dry-docking  of  the  ship. FRAMING Two sets of stiffening members called frames help  the  shell  plating  resist  the  pressure  of  water, wind, and waves. Transverse frames extend from the keel outward around the turn of the bilge and up the sides like the ribs of the human skeleton. Closely spaced along the length of the ship, they define  the  form  of  the  ship.  Longitudinal,  also called longitudinal frames or stringers, run parallel to  the  keel  along  the  bottom,  bilge,  and  side plating.  They  tie  the  transverse  frames  and bulkheads together along the length of the ship. When  two  sets  of  frames  intersect,  openings in one set must be cut to make way for the other. Those which are not cut are known as continuous frames.  When  smaller  frames  butt  into  larger frames without being continuous, they are called intercostal  frames.  Therefore,  ship  construction requires  two  methods  of  framing.  One  method uses  continuous  transverse  riblike  frames  with intercostal  longitudinal  between  them  or sufficient   plating   thickness   to   eliminate longitudinal members altogether. In this method the transverse frames are spaced about every 2 feet along the length of the ship. Ships built by this method  are  known  as  transversely  framed  vessels. Most merchant cargo ships and wooden ships are built in this fashion. The alternate method uses many  continuous  longitudinals  along  the  length of  the  ship  with  the  transverse  frames  spaced farther  apart.  Ships  built  by  this  method  are known  as  longitudinally  framed  ships.  Most  naval ships  are  built  this  way.  The  plating  loaded  on the  short  edges  of  longitudinally  framed  ships  has a  higher  buckling  strength  to  resist  the  loads. Therefore,  although  the  construction  for  longi- tudinally  framed  ships  is  the  more  difficult method, ships built by this method are stronger for  a  given  weight. BULKHEADS The   interior   of   the   ship   is   divided   into compartments  either  by  vertical  bulkheads  (walls), which are watertight, or joiner bulkheads, which are  not  watertight.  Structural  bulkheads,  which are watertight, also divide the ship into compart- ments but give the ship contour, shape, rigidity, and  strength  as  well.  They  may  be  transverse bulkheads  extending  athwartships  or  longitudinal bulkheads extending fore and aft. They not only subdivide  the  ship,  but  tie  the  shell  plating, framing, and decks together in a rigid structure. Transverse  bulkheads  are  numbered  to  correspond with  the  transverse  frames  at  which  they  are located. DECKS The  compartments  of  a  ship  are  further divided  by  a  series  of  decks  and  platforms  into tiers.   The   floor   of   a   ship’s   compartment   is normally called the deck, and the ceiling is called the  overhead. The decks of most ships consist of rectangular steel plates, similar to the shell plating, joined into strakes. The plates in the outermost strake of deck plating,  called  stringer  plates,  are  connected  to  the shell  plating.  Transverse  and  longitudinal  deck beams and deck girders on the underside of the deck strengthen the deck plating. These beams and girders  usually  consist  of  I  beams  or  T  beams fastened  to  the  shell  frames  by  triangular  steel brackets. Decks above the waterline usually are arched  (cambered)  so  that  they  are  higher  at the  centerline.  The  camber  aids  in  drainage  of water. The  name  of  a  deck  depends  on  its  position in   the   ship   and   its   use   or   function.   Decks extending from side to side and from stem to stern are  complete  decks;  decks  occurring  only  in certain  portions  of  the  vessel  are  partial  decks. The uppermost complete deck is the main deck. 17-3