With the general development of the large gas engine there has come a natural tendency to apply it as a motor to nearly every variety of machinery demanding the effort of mechanical energy. It is to be expected, therefore, that the combustion motor, in more than one type, should be applied to the propulsion of boats: not only for driving the small, high-speed pleasure craft, but also vessels of larger size and less pretensions as to speed.
An article by Herr C. Stein in recent issues of the "Zeitschrift des Vereines Deutscher Ingenieure " reviews the practical applications which have been made of gas engines for propelling commercial vessels, and although the subject is in an early stage of its career it already demands attention and review.
The earliest attempts to use internal combustion motors for marine service involved the carrying of compressed illuminating gas, a freight boat called "L'Ide" having been so equipped to run between Havre, Rouen and Paris in 1885. The gas was compressed to 100 atmospheres, there being 80 tanks, each holding 22 cubic meters of gas, the total volume of gas carried being 1800 cubic meters. The 40 h. p. engine consumed 450 litres of gas per h. p. per hour, giving a speed of 10 kilometers per hour for 100 hours, or a ration of 1000 kilometers. The gas tanks themselves weighed 26,000 kilograms, and Herr Stein computes that this weight, if replaced by a tank of petroleum, would supply fuel for 1200 hours, or twelve times the period obtained with compressed gas.
By the use of modern benzine or gasoline motors the question of fuel is readily solved, and some very successful motors of this type have been made for marine use.
All such motors involve certain modifications to be made in the propelling machinery in use for steam propulsion, and these points are very fully discussed in Herr Stein's paper. Thus the gas engine is not easily reversed, and should be operated regularly at its normal speed, the speed changes being controlled by other means than by varying the velocity of the engine.
Reversals are effected either by changing the angle of the propeller blades, or by the use of reverse gearing, changing the direction of revolution of the propeller shaft. The shifting propeller blades are not found to work well for larger powers than 100 horse power, although this method is satisfactory for small boats. Herr Stein illustrates several arrangaments of clutches for reversing the propeller shaft, some of these being combined with a pivoted tail shaft, so that the propeller can be raised out of the water when proceeding under sail.
The use of gasoline motors for marine service is necessarily limited, and hence the practicability of employing producer gas becomes a matter of interest. The development of the suction gas producer offers opportunity for the arrangement of a complete power gas plant for such a service, and Herr Stein describes such an equipment on a freight boat on the Elbe. This boat, the "Lotte," is 41 metres long, 4.6 metres beam, drawing 2 meters with a load of about 240 tons. This boat is fitted with a pair of balanced gas engines, the cylinders having the vis-a-vis arrangement, the suction gas producer being placed in an adjoining compartment, in order to protect the moving parts from the heat and dust. The engines develop about 100 h. p., this sufficing to propel the boat at a speed of about six kilometres per hour against the current. Experiments with this and other boats propelled by suction gas power show that the cost of transport falls as low as 0.64 pfennig per ton kilometre, or about 0.25 cents per ton mile, as against 1 pfennig for steamboat transport, and 3.2 pfennig on the railway.
The suction producer is especially applicable for use on shipboard, since an unlimited supply of water is available for condensing the impurities, tar, aud other volatile matter in the gas, and there is also ample opportunity for keeping the cylinders of the motors properly cooled. In general the conditions for operating the internal combustion motor are far more favorable on shipboard than on road vehicles. The question of weight is not of such controlling importance, and hence the various parts may be of ample strength. The difficulties from dust and dirt are absent, while the working parts may be made readily accessible. At the present time the larger sizes of gas engines have not been applied to marine propulsion, but for the propelling of boats of moderate size at the speeds common for ordinary river transport the engines now available have already proved their capability and high economy.
The Diesel motor has also been applied to marine propulsion, and it has the especial advantage of using heavy oil, petroleum and similar fuels directly in the cylinder, without requiring any carburetter.
Gas engine propulsion for boats may be said to be yet in its infancy, but the results thus far attained have been most encouraging, and there is every reason to believe that the use of internal combustion motors on shipboard will become widely extended.