Читать книгу Inventors at Work, with Chapters on Discovery - George Iles - Страница 30

Table of Contents

Thirty to sixty years ago much of the world’s commerce was borne by clipper ships. In all likelihood as good lines as ever went into a vessel of this kind were displayed in the Young America, outlined on page 58, built in 1853 for California and East India trade. She once ran from New York to San Francisco in 103 days, and from San Francisco to New York in 63 days, records which have never been excelled. Her deck length was 235 feet; her depth of hold 25 feet, 9 inches; her moulded beam was 40 feet, 2 inches; her displacement was 2,713 tons. The lines worthiest of remark in her design are the diagonals and buttocks, together with her easy entrance and run. Most clipper ships were fuller forward than aft; this had two advantages: first, when forward burdens, anchors and the like, tended to an undue settling down at the head, it was well to increase the buoyancy forward; second, towing experiments prove that a form slightly fuller forward than aft offers less resistance than the reverse. This shape was hit upon by the old-time designers, doubtless as a result of many a shrewd experiment.

In the early days of steamships, hollow or somewhat concave water lines forward were in favor. Experiments with models have demonstrated that for boats so full in section as to be nearly square, it is best to have forward lines which are straight or nearly so. Recently it has been shown that at high speeds, with a midship section nearly semicircular, resistance is a little lessened by very slightly hollowing the water lines forward.

If a steamer is to have the utmost speed, as the Kaiser Wilhelm II, outlined on page 60, her design will be very unlike that of a vessel required to carry as much cargo as possible at a moderate or low speed, as in the case of the steamship sketched on page 61. The dimensions of the Kaiser Wilhelm II are:—length over all, 706¹⁄₂ feet; beam, 72 feet; depth, 29 feet, 6¹⁄₄ inches; displacement, 29,000 tons; speed, 23¹⁄₂ knots; indicated horse power, 38,000. As we compare with her details of form the general features of our cargo carrier, page 61, we observe in this freighter the full form of its water lines, its almost straight and blunt entrance forward; we also notice that the lower part of the bow has been cut away to avoid a reversal of curves which would create an eddy with its consequent increase of resistance. Further we may remark the squareness of the midship section, which means carrying capacity at its maximum, together with the long parallel middle body, little resisted by the water, ending aft in buttocks and water-lines quickly turned. This is a twin-screw ship: of length 358 feet, 2 inches; beam, 46 feet; draft, 23 feet; depth from shelter deck, 34 feet, 8 inches; displacement, 8,270 tons; speed, 9 to 10 knots.

STEAMSHIP KAISER WILHELM II.

Length over all, 706 feet, 8 inches. Beam, 72 feet. Draft, 29 feet, 6.3 inches.

Displacement, 29,000 tons. Indicated horse-power, 38,000. Speed, 23.5 knots.

Enlarged illustration (60 kB)

TWIN-SCREW CARGO STEAMER.

Length, 358 feet. Beam, 46 feet. Draft, 23 feet. Displacement, 8270 tons.

Enlarged illustration (61 kB)

U. S. TORPEDO-BOAT DESTROYER.

Length over all, 246 feet. Beam, 22 feet, 3 inches. Displacement, 489 tons.

Speed, 30 knots.

Enlarged illustration (34 kB)

A good designer has an easy task in drawing lines for a freighter in which the weight of hull, machinery and coals may be only 40 per cent. of the displacement, leaving 60 per cent. for earning space. Contrast this with an Atlantic flyer, where but 5 per cent. may remain for cargo. Here the designer’s problems are difficult indeed, and the chief way out of them is to enlarge his ship as much as he dares, for the bigger his vessel, its form and speed unchanged, the less will be its resistance as compared with displacement. But to an increase of size there are hard and fast bounds; first, those imposed by the shallowness of channels and harbors; while the depth of a ship is thus restricted, its length may be somewhat extended with safety and gain; to increase of beam there are distinct and moderate limits, to overpass them means that the ship will follow the wave contour of a heavy sea so closely as to have a quick, jerky and dangerous motion.

Cross-sections of ships