Engineering Wonders of the World
Volume I

356 ENGINEERING WONDERS OF THE WORLD. and safety in the event of the vessel ground- ing. As, however, carrying all this weight in the bottom of the ship may render a vessel unduly stable and uneasy in her rolling, in some cases side ballast tanks have been fitted (M'Glashan’s patent), as shown in Fig. 11 ; Fig. 11.—HALF SECTION OF SIDE TANK STEAMER, while in the section shown in Fig. 8 triangular «paces at the corners of the deck are utilized for this purpose. As regards loading and discharging facilities, large hatchways must be provided in the decks, together with numerous winches, derricks, and cargo gear. Cabin accommodation in a cargo ship is very simple, and presents no difficulties in design. Very different, however, are the re- quirements in the case of a passenger vessel. Here everything must be done to secure the maximum amount of comfort for the pas- sengers. The arrangement of cabins and public rooms must facilitate decorative effect, and due attention must be given to the problems of ventilation, lighting, heating, cooking, water services, and other subsidiary matters too numerous to mention. In the case of warships, paramount interest centres in the provision of efficient armour and armament, in conjunction with high speed and the carriage of sufficient fuel to give the vessel a good radius of action. The problem of speed involves, in the first place, consideration of the “ resistance of the ship. This is due to two causes—“ skin friction ” and “ wave-making.” Frictional resistance is the re- Speed, .. p Resistance, suit, as its name implies, ot and the rubbing of the particles propulsion, of water against the vessel’s skin, while wave-making resistance is due to the formation of wave systems at the bow and stern. Various formulæ have been pro- posed for determining ship resistance, but all are more or less based upon the trials of existing ships ; and the only reliable method of determining the resistance of a new design with any certainty is the experimental tank method devised by the late Mr. W. Froude, to whom—in conjunction with his son and suc- cessor at the British Admiralty tank, Mr. R. E. Froude—our present knowledge of this subject is chiefly due. In addition to that owned by the British Government, experimental tanks have beon constructed by several foreign states, and also by two private shipbuilding firms in the United Kingdom—Messrs. William Denny and Brothers of Dumbarton, and Messrs. John Brown and Company of Clydebank. A view of such a tank is shown in Fig. 12. It will be observed from this illustration that a recording carriage is provided, which travels over the tank and for its full length, the model being attached beneath the carriage. The models are shaped out of paraffin wax by a special cutting machine, their length being 12 to 15 feet. The records obtained by towing a model at different speeds can be applied to any ship of the same form and proportions, no matter what her absolute dimensions may be. After determining a ship’s resistance, the next question to be decided is a suitable value for the propulsive, coefficient—that is, the ratio of the power usefully employed in overcoming the ship’s resistance (or, as it is termed, the effective horse-power) to the power