PAASCH, H. From Keel to Truck, Marine Dictionary (4th ed., Paris, 1905).

PREBLE, G. H. A Chronological History of the Origin and Development of Steam Navigation, 1543-1882 (1883).

Report of Royal Commission on Tonnage. Reports from Commissioners, Vol. 49 (c-3074) (London, 1881).

SEATON, A. E. A Manual of Marine Engineering (12th ed., 1895).

SMITH, A. R. "Shipbuilding," in Twelfth Census of the United States, X, part iv, pp. 209-39 (1902).

SMITH, J. RUSSELL. The Ocean Carrier (1908).

SPEARS, J. R. Story of the American Merchant Marine (2d ed., 1915).

United States (Bureau of Corporations). Transportation by Water in the United States, I, chap. ii (1909).

-(Commissioner of Navigation). Annual Reports.

WALTON, THOMAS. Present-Day Shipbuilding (London, 1907).
Know Your Own Ship (London, 1909).
WHITE, SIR W. H. A. A Manual of Naval Architecture (5th
ed., London, 1900).

ZIMMERMANN, E. W. Foreign Trade and Shipping, part II, chap. ii (1917).

CHAPTER IV

MOTOR VESSELS AND UNRIGGED CRAFT

Vessels with internal-combustion oil engines, 48. Diesel marine engines, 48. Vaporizer marine engines, 52. Vessels with internal-combustion gas engines, 52. Those operated with refined oils, 53. Those operated with producer gas, 53. Unrigged craft, 54. Inland and seagoing barges, 54. Tank barges, 56. Rafts, 56. References, 57.

THOUGH the self-propelled vessels operating on the high seas are mainly equipped with steam engines, an increasing number have in recent years been fitted with internal-combustion engines. Indeed, but few technical improvements at present are receiving more current mention in maritime journals than those concerning motor vessels. These vessels may be grouped into two general classes: (1) those fitted with internal-combustion oil engines, and (2) those propelled with internal-combustion gas engines.

VESSELS WITH INTERNAL-COMBUSTION OIL ENGINES

The type of internal-combustion oil engine at present most widely in use is the Diesel engine which was invented by Dr. Rudolf Diesel, and first put into practical use in Germany in 1897. Thousands of stationary Diesel engines have been constructed and sold throughout the world since then, and considerable progress has been made in the introduction of Diesel marine engines. Since 1902-03, when the first Diesel marine engine was built, and particularly since 1905, when the first reversible engine of this type was constructed, many improvements have been made and numerous variations have been introduced by the several marine engine manufacturers who have undertaken their construction. In 1911 it was stated that 365 vessels were equipped with Diesel

engines,1 and since then the number has doubtless risen above the 400 mark.

Diesel-engined vessels are not to be confused with oilburning steamers, which merely substitute oil for coal as a means of generating steam in boilers. Diesel oil engines dispense with boilers, the oil being injected directly into the cylinders. Neither are they to be confused with gas motor vessels, the engines of which depend upon the explosion of gas made out of light oils or coal. Diesel oil engines depend upon the burning of oil in the cylinders. Crude petroleum, tar or creosote oils, the residual mineral oils which remain at the refineries after the lighter oils have been distilled, and a wide variety of other oils may be injected into the cylinders in the form of spray where it is ignited, not by an electric spark or other local ignition, but by the high temperature resulting from the compression of air in the

Direct-Reversible Diesel Two-Stroke, Single-Acting Engine for TwinScrew Motor Vessel

cylinders. Air compressors are used to convert the oil into a spray and to start the engine, and cooling appliances are required to cool the cylinders, valves and piston bearings.

1 R. Diesel, Present Status of the Diesel Engine in Europe, 27: Oil tank vessels 20, tugs 40, motor sailing vessels 10, merchant vessels 50 to 60, fishing vessels 15, submarines 140, other war ships 40, small marine craft 20, and miscellaneous craft 20.

Three principal types of Diesel marine engines have been developed: (1) The four-stroke cycle engine which requires four strokes of the piston to complete a cycle, the third being the working stroke. (2) The two-stroke single-acting engine which is equipped with a scavenger pump and is so constructed that two strokes complete a cycle, the second being the working stroke. (3) The two-cycle double-acting engine which differs from the single-acting engine chiefly in that each stroke is a working stroke, the cylinders being virtually double and the oil being injected alternately at each cylinder end. The four-stroke and two-stroke single-acting engines are at present in most general use, and the rivalry between the various firms which construct them is the best indication that their respective merits have not been finally determined.

The principal advantages claimed for Diesel marine oil engines as compared with marine steam engines are as follows: (1) They make possible a reduction in the size of

Twin-Screw Cargo Vessel Monte Penedo. Fitted with Two-Stroke
Single-Acting Diesel Motors

the engine room, although the peculiar tonnage measurement
rules of various maritime countries frequently induce vessel
owners to forego this advantage.1 (2) They result in the
reduction of fuel spaces, for the oil they use is less in vol-
ume than is the coal required by a steamer of equivalent
horse power, and the oil may be stored in compact tanks
and in the vessel's double bottom instead of in large spaces
in the hold, such as are required for coal bunkers. (3) They
1 See chapter ix, pp. 120, 121; also Johnson, Measurement of Vessels
for the Panama Canal, 153.

increase the vessel's deadweight capacity and available cargo space.1 (4) On routes where oil is readily available, or where the scarcity of both oil and coal makes it advisable to take on large quantities of fuel at the starting point, the Diesel oil engine is relatively more economical. (5) Diesel engines may be started at any time and within a very short time, no extensive preparations being required to get up pressure and power.

Diesel marine oil engines have, however, had to contend with various obstacles, and their adoption in the future will at most be gradual. Just as in the early years of ocean steam navigation coaling stations had to be established throughout the world, so now fuel oil stations must be established on all the main ocean routes. Doubt that necessary quantities of serviceable oil are available at reasonable prices would especially deter ocean-going tramps from being generally equipped with Diesel engines, for they need to sail wherever a cargo awaits transportation. Then, too, the cardinal

Four-Stroke, Direct-Reversible Diesel Marine Engine

virtue of a marine engine-particularly in case of passenger vessels-is absolute reliability, and the maritime world needs to be convinced that the Diesel engine possesses this quality. The early difficulty concerning the reversing of Diesel engines 1 For detailed statement see Johnson, Ibid., 155-56.