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PROPELLING-POWER DEDUCTIONS FOR VESSELS EQUIPPED WITH OIL AND GAS ENGINES.
The general principle upon which the Panama measurement rules accompanying this report are based is that net tonnage should express, as nearly as practicable, the actual earning capacity of vessels—their space available for passengers and cargo. To give effect to this principle it is necessary that deductions made from gross tonnage in determining net tonnage should correspond as closely as is feasible with the spaces required for the crew, for navigation purposes, and for propelling power.
The largest deduction from gross tonnage is for the space occupied by the engine and fuel, and it is especially important that the deduction for propelling power should be made by applying a correct rule. This is not an easy problem to solve. Vessels are of many types, employed in widely different services. Moreover, vessels of the same size and speed and employed in the same service may be equipped with different kinds of engines, varying as regards the space they occupy and the kind and quantity of fuel used.
The marine engine is having a rapid development at the present time. The standard type of reciprocating steam engine is being improved; oil instead of coal is being used to generate steam; the turbine engine is being tried out in service; and new types of engines, such as the internal-combustion oil and gas engines, are being successfully employed in marine service. The substitution of oil for coal in the furnaces of steam engines lessens the space required for fuel, while the use of internal-combustion instead of steam engines largely reduces the fuel consumed and may somewhat reduce the size of the engine room.
In view of these facts it seems desirable to study the effects of oil fuel upon fuel space and the effects of internal-combustion engines upon the size and location of fuel compartments and upon the size of the engine room for the purpose of deciding whether the same rule for propellingpower deduction may properly be applied to vessels equipped with all types of engines. Consideration is first given to the relative fuel spaces required by coal-burning and oil-burning engines of like power. In order to make the discussion of internal-combustion engines clear to nontechnical readers, a brief description is given of the main kinds of oil and gas engines now in use for marine service.
The kinds of fuel that may be used in internal-combustion engines determine the sources of the supply of fuel for such engines, and the sources of supply may affect the location of the stations at which fuel may be secured and the amount that vessels must carry in actual service. Moreover, the nature of the fuel oil may determine whether it may or may not be stored in the double bottom or other portions of the ship that are not available for the stowage of cargo. It has accordingly been deemed necessary to present a short discussion of fuel oils used in internal-combustion engines.
The purpose of this chapter is to consider the relative space required for propelling power (including engine room and fuel compartments) by steam marine engines and by internal combustion marine engines, to ascertain the net saving in cargo space that results from equipping a vessel with an internal-combustion engine instead of with one driven by steam power, and to decide whether it is or is not advisable to make propelling power deductions from gross tonnage, in the case of vessels with internal-combustion engines, in accordance with a different rule than is applied in the case of ships with steam engines—to decide whether the use of oil and gas marine engines makes it desirable to supplement the Danube rule with a special rule applying only to the internal-combustion engines. The chapter also considers whether the substitution of oil for coal as the fuel for steam engines calls for a special rule for propelling power deduction.
Vessels using oil for fuel may be broadly classified as (1) oil-burning steamships; (2) vessels fitted with internal-combustion oil engines; and (3) vessels, equipped with internal-combustion gas engines. Each of these groups includes different types; but, from the standpoint of tonnage measurement as well as from the point of view of the principles of engine construction, the threefold classification indicates the essential differences. These three types of oilburning marine engines will be considered in turn.
I. OIL-BURNING STEAMSHIPS.
The number of steamships equipped with oil-burning engines is increasing rapidly. The latest vessels added to the American-Hawaiian Co.'s fleet, for instance, are equipped to burn oil; likewise the Pacific Mail Steamship Co. has equipped the four largest vessels of its fleet with facilities for using oil fuel, these vessels being used in the trans-Pacific service. Oil as a fuel is especially favored by the owners of tank steamers and in general it is to be expected that oil instead of coal will be used by a steadily growing share of ocean steamers.
All three of the rules applied in making deductions for propelling power were formulated with reference to engines using coal for fuel and no modification has been made in these rules because of the substitution of fuel oil for coal in the furnaces of a relatively large number of ocean vessels. Whether the same rules may fairly be applied in making propelling-power deductions for both oil-burning and coal-burning steamers ought to be carefully considered. The deductions for propelling power ought to approximate the space required for machinery and fuel in order that the net tonnage of vessels may correspond as nearly as practicable to the capacity of vessels for the accommodation of passengers and cargo.
The space occupied by the engines and boilers is practically the same whether coal or oil be used for fuel; indeed, some steamers are equipped to burn either coal or oil in the furnaces. Mr. R. P. Schwerin, the vice president of the Pacific Mail Steamship Co., which operates both oil-burning and coal-burning steamers, states that “the space required for engine and propelling machinery would very rarely be affected by the kind of fuel used, as practically the same machinery would be used in either case.” 1
Unless there is a material difference in the relative volume of the spaces required for coal and fuel oil, the deductions for propelling power may be made by applying the same rule both to oil-burning and coal-burning engines. The space occupied by engines and boilers being the same in the case of both kinds of steam engines, the question to determine is whether the application of the Danube rule to propelling power deductions in the case of oil-burning engines will unduly favor vessels equipped with such engines.
In considering this question, it is especially important to bear in mind that the fairness of the application of the Danube rule for propelling power deductions—the deduction of actual propelling machinery space plus 75 per cent—is in no way affected by the fact that the fuel oil is carried in double-bottom compartments while coal is carried in bunkers. When doublebottom compartments are used to stow oil, such compartments are included in gross tonnage, just as bunker spaces used for coal are included. Propelling-power deductions made under the Danube rule, it will be recalled, are in nowise affected by any increase or decrease in gross tonnage, the Danube rule being superior to the Board of Trade percentage rule in this regard. The fairness of the deductions made under the Danube rule depends solely upon the relation of the volume of the spaces occupied by fuel and the volume of the spaces occupied by machinery. The specific question, and the only one to be considered in determining whether the Danube rule should be applied to propelling power deductions in the case of oil-burning steamers, is whether the space occupied by fuel oil is so much less than the space required for coal as to call for a modification of the Danube rule. Regarding the relative spaces actually occupied by fuel on coal and oil burning steamers, Mr. Schwerin states that:
Theoretically, oil fuel would occupy approximately 50 per cent of the space required for coal fuel. On this coast (the Pacific) we usually allow 4 barrels of oil per ton of coal. Taking coal at 42 cubic feet per ton and oil at 5.61 cubic feet per barrel, the actual space occupied would be as 42 is to 22.44. In other words, the oil would occupy 53.4 per cent of the space occupied by the coal. On the Atlantic coast, where better coal is obtained, 41 barrels of oil per ton of coal would probably be more accurate. On this basis the oil fuel would occupy 60 per cent of the space required for coal. On the other hand, with oil the entire space is filled, while with coal certain pockets are naturally void and the space between the floors of the ship is not filled with coal. Therefore it would be fair to assume that even with the best quality of coal the actual space required for oil would amount to about one-half the space required for coal.
i From letter dated Apr. 4, 1913.
The secretary of Lloyd's Register of British and Foreign Shipping, in a letter written June 28, 1913, estimates that "steam-engine vessels using oil" require, for similar voyages, fuel spaces of about 62 per cent of the fuel spaces needed by “steam-engine vessels using coal.”
Inasmuch as the space occupied by fuel oil need not be more than about 60 per cent of the space required for coal, it is evident that the application of the same power-deduction rule to both oil-burning and coal-burning steamers favors the oil-burning vessel to an appreciable extent. It should be noted, however, that the Danube rule favors the oil-burning vessel less than does the Board of Trade percentage rule, because of the fact that the stowing of fuel oil in double-bottom compartments causes those compartments to be included in gross tonnage. A vessel of the same size would have a comparatively greater tonnage under the British measurement rules if equipped with oil-burning steam engines than if equipped with coal-burning engines. The 32 per cent deduction for propelling power when made by the percentage rule is thus greater for vessels having smaller fuel compartments.
Under the Danube rule the relatively favorable treatment accorded oil-burning, as compared with coal-burning, steamers is frequently less than would appear to result from the difference in the spaces required for oil and coal fuel. When all or a portion of the fuel oil is carried in the double-bottom compartments, the net tonnage of the oil-burning steamer is increased by the tonnage of the space occupied by fuel-oil compartments. Theoretically, the vessel's cargo capacity would be increased by the number of tons added to the net tonnage of the vessel by the stowage of oil in double-bottom compartments instead of in tanks taking up a part of the vessel's hold. In actual practice, however, the increase in cargo capacity does not equal the space added to the net tonnage by including in the tonnage the volume of the double-bottom compartments used for oil. Ordinarily there is some gain in cargo space, but in some instances there is none. This is due to the fact that the space occupied by coal bunkers-space not required when oil is used for fuel-is not always usable
II. VESSELS WITH INTERNAL-COMBUSTION OIL ENGINES-PRINCIPAL TYPES OF ENGINES.
The oil-burning engine differs from the coal-burning engine merely in the use of oil instead of coal to develop steam in its boilers. Both are steam engines of the same type quite unlike the internal-combustion oil engine which consumes the fuel in the cylinders, its power being derived not from steam generated in boilers but from the combustion of oil upon its injection into the cylinders.
The type of internal-combustion oil engine at present most widely in use is the Diesel engine, which was first put into practical service in Germany in 1897. Dr. Rudolf Diesel, the inventor of the engine, had been experimenting for some time, an experimental engine having been completed in 1893. He had, indeed, applied for a patent in the United States in 1891, and one was granted July 16, 1895. The first Diesel engines were for stationary service, but marine engines were constructed in 1902–3. Since 1903, thousands of stationary Diesel engines have been constructed and sold throughout the world; and in November, 1911, there were, according to Mr. Diesel, 365 vessels equipped with Diesel marine engines. The number of vessels fitted with these engines is increasing.
The Diesel oil engine differs in principle from a gas engine, it being an internal-combustion engine, while the gas engine is an internal-explosion engine. The Diesel principle is to burn the oil in the cylinder; while the principle of the gas engine is to convert the fuel oil or coal into
gas which explodes in the cylinder.
1 R. Diesel, Present Status of the Diesel Engine in Europe, pp. 1 and 7.
2 Power, Mar. 11, 1913, p. 338.