NAVAL ARCHITECTURE deals with the designing and development of the nautical qualities of ships as distinguished from their construction, which belongs to shipbuildng. The existence of naval architecture as an art prob ably dates back to the first development of man, but its elevation into a science can scarcely be recognized until the 19th century, as a part of the advance in all mechanical sciences during that period. During the 18th century, and even earlier, some Continental mathematicians had devoted attention to the subject and developed various theorems concerning floating bodies which were likewise applicable to ships. Throughout this period the French were the acknowledged leaders in the development of knowledge relating to such matters. So much was this the case that it seems to have been not unusual for other countries to reproduce the models of French men-of-war, thereby admit ting the excellence of the French type and pay ing deserved tribute to the labors of the naval architects of that country.
Perhaps the most notable attempt, however, to place naval architecture upon a logical anal scientific basis, prior to 1800, was that of the famous Swedish naval architect, Chapman (1721-1808), who, during his long career, achieved special eminence in his profession and wrote a number of treatises relating to various features of naval architecture. One hundred years ago each nation, and, indeed, each master builder, carefully guarded as valuable secrets the methods and theories pertaining to the sci ence of naval architecture, which had been de duced from experience or which had been handed down by those who had conducted previous investigations. This state of affairs, indeed, extended well into the 19th century, but with the rapid development of iron shipbuilding, which started about the middle of that century, came a rapid advance in naval architecture and dissemination of knowledge upon the sub ject, until, to-day, in the leading shipbuilding countries of the world will be found schools de voted to this subject; and the products of the naval architect's skill differ only in compara tively minor respects, whether turned out from British, European, American or Japanese ship yards.
The primary object of the vast majority of i all ships is to-day, as throughout the past, trans fortahon, and the problem is only affected in its details in order to conform to the require ments of the articles carried, be they men, mer chandise, or, in the case of men-of-war, armor, armament and other appliances for rendering the vessel efficient as a fighting machine. The foregoing statement is quite as true of the hum ble 10-knot collier, which will carry in coal twice the weight of her hull, machinery and outfit, as of the trans-oceanic passenger liner which carries a comparatively small amount of cargo but a large quantity of bunker coal to enable it to make a high speed, and provides luxurious accommodations for numerous pas sengers. It is true also of the man-of-war, which carries a proportionately large crew and a fair amount of cargo in the shape of consum able stores, coal and ammunition, besides a considerable weight of armor, heavy arma ment, and the necessary military adjuncts re quired by the special service upon which em ployed. Considering, then, all ships as bearers
of burdens, there are two essential characteris tics which they must show: They must be able to go from point to point at an appropriate speed and with all reasonable safety for ship, cargo and crew. Ability to keep the sea under all the usual conditions of its intended service is indis pensable for every ship, and we will now con sider briefly the detailed factors entering into the problem.
Buoyancy.— When a ship is entirely water borne, the weight of water which it displaces is exactly equal to the weight of the ship itself and everything contained in it. To float at all, the volume of the enveloping surface of the ship must be greater than the volume of water which equals in weight the displacement of the ship.Clearly, for safety, there must be a margin, or reserve of buoyancy, in the ship over and above the buoyancy equal to its weight. The percentage of reserve buoyancy varies widely according to the type of vessel, passing from approximately zero in the case of diving, or submarine, boats (when in condition to dive), to as much as 100 per cent or more in the case of passenger vessels with large deck areas and high sides. In certain types of men-of-war, notably the large cruiser class, the percentage of reserve buoyancy is also very high. In the case of men-of-war, the reserve buoyancy is practically fixed by the design; but, in the case of merchant vessels, and particularly cargo car riers, which are subject to overloading, the re serve buoyancy is now practically determined by the marine insurance companies. The business of insuring ships and their cargoes is a large and important one, but is carried on by a com paratively small number of very powerful com panies or associations, and these companies, for their own protection, have a well-equipped, scientific and technical staff and have prescribed conditions affecting the safety, or seaworthiness, of ships, which must be complied with in order to obtain insurance at a reasonable rate. In England, the Board of Trade, which is the de partment of the government charged with au thority over matters relating to shipping, has acted in conjunction with the large insurance companies in laying down requirements for re serve buoyancy, these authorities being still further assisted' by representatives of the na tional associations of naval architects. The actual amount of reserve buoyancy required varies somewhat with the size and type of ves sel, and likewise with the character of the serv ice, the maximum amount being required for vessels engaged in winter service in the north Atlantic Ocean. Speaking broadly, the objects aimed at in the load-line requirements are to obtain the greatest possible carrying capacity, compatible with safety of the vessel under all conditions of weather, after making provision for minor casualties which might still further reduce the reserve of buoyancy.