bottom; hence, it is known as a flat keel. Its usual shapeis that of an I-beam. All other parts used in constructingthe hull are attached, either directly or indirectly, to thekeel.The athwartships structure consists of transverseframes and decks. The decks run outboard from the keelto the turn of the bilge (where the bottom turns upward).Here, they are attached to the transverse frames, whichthen extend upward to the main deck.Frames running parallel with the keel are calledlongitudinals. From the turn of the bilge up the sidesthey are also called stringers. The network of floors andlongitudinals resembles a honeycomb (known ascellular construction), which greatly strengthens thebottom of the ship. When plating covers thehoneycomb, double bottoms are formed. The spacebetween the inner and outer bottoms (known as tanks) isused for liquid stowage. Planks laid upon the tank topsare called ceilings. The forward end of the keel, which isextended upward, is called the stem. The after end of thekeel has a similar extension called the sternpost. Thepart of the stem above water is the prow; the forwardedge of the stem is the cutwater.The interior of a ship is divided into compartmentsby vertical walls, called bulkheads. Bulkheads run bothtransversely and longitudinally. Most bulkheads aremerely partitions; but spaced at appropriate intervals,they are transverse watertight bulkheads. Thesebulkheads extend from the keel to the main deck andfrom side to side to provide extra stiffening and topartition the hull into independent watertight sections.Large ships have a series of longitudinal side bulkheadsand tanks that provide protection against torpedoes.Usually, the outer tanks are filled with oil or water, andthe inner tanks (called voids) are empty. The innermostbulkhead is called the holding bulkhead. If a torpedowere to hit the ship, the outer tanks, although ruptured,would absorb enough energy from the explosion that theholding bulkhead would remain intact, thus preventingflooding of vital spaces.The plates that form the ship’s hull are calledstrakes. Strakes are fastened to the framework inlongitudinal rows. The keel forms the center strake.Strakes are lettered, beginning with the A strake oneither side of the keel and extending up to the main deck.Some of the strakes also have names. The A strake iscalled the starboard strake; the strake along the turn ofthe bilge is the bilge strake; the uppermost strake is thesheer strake. A protecting keel running along thebottom near the turn of the bilge is called a bilge keel.Its purpose is to reduce rolling of the ship. (A shiprolls from side to side; it pitches when it goes up anddown fore and aft; it yaws when the bow swings toport and starboard because of wave action.)The upper edges of the sides, where the sheerstrakes join the main deck, are called the gunwales(rhymes with funnels). The foremost part of the ship,where the gunwales join the stem, is known as the eyesof the ship. The port and starboard quarters are locatedwhere the gunwales curve inward to the sternpost.The water level along the hull of a ship afloat is thewaterline. The vertical distance from the bottom of thekeel to the waterline is the ship’s draft. Freeboard is thedistance from the waterline to the main deck. Figures8-2 and 8-3 show various parts of the hull and deck.DecksThe floors of a ship are called decks. They divide theship into layers and provide additional hull strength andprotection for internal spaces. The undersurface of eachdeck forms the overhead (never the ceiling) of thecompartment below. Compartments are the rooms of aship. Some compartments are referred to as rooms, such8-3Student Notes:Figure 8-2.—The hull.Figure 8-3.—The weather deck.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
