stiffened by longitudinals of various types. To these, the outside plating is secured, the garboard strakes being adjacent to the keel plates. An inner bottom is fitted on large ships; this extends to the armor shelf on battleships and monitors, and to the shelf plates on other vessels. The double bottom extends fore and aft to a greater or less degree from the midship section, depending upon the particular type of ship; it is subdivided into small cells by water-tight frames and longitudinals, so that leakage shall be reduced to a minimum if the ship touches bottom. The frames near bow and stern are spaced more closely than elsewhere to provide local strength, and breast hooks, ram plates, transoms, and counters are fitted for like reasons. Sheathed ships are fitted with outside plating to which is fastened outside wood planking below the water-line; composite ships have no outside plating but have wood planking which is fastened to the frames; in both cases this planking is coppered to lessen fouling, great precautions being taken to prevent injury to the steel hull from galvanic action. Bulkheads are used to vertically subdivide the ship's interior into water-tight compartments for the preservation of buoyancy and stability; non-water-tight bulkheads are also fitted to provide stowage and living spaces. Decks are primarily used to provide shelter, working spaces and living quarters; secondarily, to horizontally subdivide the hull into a still greater number of water-tight compartments. Those used for the latter purpose are of steel, and may or may not be covered with planking or linoleum. Other decks are planked and calked only, but deck stringers and tie plates are used to stiffen the deck beams, which are also supported by stanchions in addition to the bulkheads. All of these are absolutely necessary to ensure the ship's structural strength. To secure accessibility to all parts of the ship, numerous hatches, doors, scuttles and man-holes are provided; these are water-tight where necessary, and are always fitted for battening down on upper decks. Warships are provided with protective decks of steel, to protect the propelling machinery and other objects below the waterline; even on gunboats it is not uncommon to find a steel watertight deck, which assists in preventing loss of stability if the outside plating should be penetrated near the water-line. STEERING GEAR: The rudder of a warship is unusually large and the steering gear unusually strong, in order that such a vessel may be under more perfect control than is considered necessary in merchantmen; and in the later designs of warships the after deadwood is cut away and the rudder partially balanced to still further increase the manoeuvring qualities. The rudder is arranged so that it can be unshipped in dry dock. The rudder stock is made of special forged steel, its size depending upon the speed and size of the ship and the rapidity with which it is necessary to put the helm hard over when the ship is at her maximum speed. The rudder frame is usually of cast steel, which is filled in with wood and covered with steel plating. On most ships, the weight of the rudder is taken on a suitable carrier within the ship, firmly supported by the hull structure and so arranged that the stuffing box and gland attached to the rudderpost casting may be accessible, as shown on Plate 5. With sheathed or composite ships, copper alloys are used instead of steel for rudder post and rudder. To the rudder head, the rudder cross-head or the tiller is firmly secured. Sometimes both are fitted, as shown on Plate 6. It frequently occurs that the run of the ship is so fine that it is necessary to fit a secondary cross-head placed further forward, in order to provide space for the steering gear and its connections, the two cross-heads being connected by suitable rods. It is not uncommon, where space permits, to use a straight tiller or quadrant which is connected to the steering mechanism by chain or wire rope. The rudder is thus turned through an angle of about 35 degrees on each side of the centre line, hard-over stops being fitted to the rudder post and the rudder frame to limit the amount of travel should accidents occur to the steering mechanism. The motive power is usually steam or hydraulic, hand power being always provided for use in cases of complete break down. The application of air and electricity is still in the experimental stage. Where a rudder cross-head is used (Plate 6), the steam engine. turns a shaft having a right and left-handed thread which drives two nuts connected to the cross-head by side rods. By turning the engine in one direction the nuts recede from each other and the cross-head turns in one direction, and by turning the engine in the reverse direction, the nuts approach each other and the cross-head is turned in the reverse direction. When hydraulic |