Propulsion Machinery      The propulsive power installation is undoubtedly the most complete of any yet installed in a veseel of the tanker type, and should in service prove most efflcient and economical. The main propulsive power consists of two, single-acting, 2-cycle, 6-cylinder Bremer-Vulkan M.A.N. motors, constructed under license from the Maschinenfabrik Augsburg Nurnberg by the Bremer-Vulkan Schiffbau and Maschinenfabrik.      Many improvements based on the recommendations made by the Marine Department of the Standard Oil Company (New Jersey) were incorporated in the design, that organization having had an exceptionally extensive experience in the operation of diesel motors, particularly the Fried Krupp and Sulzer 2-cycle single-acting types, and were thus able to advance many ideas, the adoption of which has greatly improved the motors for the C. O. Stillman, not alone as regards strength, reliability, and ease in operating, but also as regards simplicity in design and accessibility for overhauling. The motors thus evolved and constructed are designated Type K 6 Z 70/20 Bremer-Vulkan 1926, the symbols K 6 Z 70/120 meaning model K, six power cylinders of 70 cm. diameter, stroke 120 cm., and each has the following general dimensions and characteristics: Diameter of power cylinders .......................... 70 cm. = 27.5” Stroke ..........................................................  120 cm. = 47.24" Normal revolutions per minute ............................................90 Shaft horsepower at 90 R.P.M. 2150 at 56.2 pounds M.E.P. Engine Tests      The first of the motors completed was thoroughly shop tested during the months of October, November, and December, 1926, and January, 1927, and from observations and tests made during that period it is evident that the care taken in design and construction has resulted in a most satisfactory diesel unit. The motor was first tested using a high gravity diesel oil as the fuel; then with standard diesel oil; and later with bunker fuel oil Grade C. Two grades of diesel oil were easily handled, but the bunker fuel oil grade C had to be subjected to purification by centrifuging, and the fuel oil pump and all fuel pipes from the strainers to the fuel injection valves had to be heated to about 150 degrees Fahrenheit to obtain the most satisfactory viscosity of this fuel. The operation of the engine using the purified bunker fuel oil grade C was just as satisfactory as with the diesel oils, but the period of test was not of sufficient duration to afford comparable data regarding relative wear upon the cylinder liners and piston rings. The only alteration made to the motor by reason of and during the tests was that made to the lubricating oil grooves in the main bearings; it was found during the first days of operating the motor that the grooves as originally provided did not afford a proper flow of the lubricating oil, the pressure circuit of oil being through the main bearing seats to the bottom half bush, into the crank shaft bore and by way of the crank web to the crank pin, through the crank pin and brasses up through the connecting rod bore to the crosshead lubricating oil pumps.      The engine was tested direct coupled to a Heenan & Froude dynamometer, and for determining the brake horse power of the motor the dynamometer water flow and the inlet and outlet temperature of the water flow were accurately determined, the results of brake and calorimetric values being quite uniform, with only negligible differences. During January 12, 13, and 14, a 36-hour test of the motor while operating at full and partial loads was conducted, and subsequently a 3-hour overload test was run.      From these test results it is apparent that the motor developed a normal output of 2150 brake horsepower when operating at 90 revolutions per minute, and under these conditions consumed 0.41 pound of fuel oil per brake horsepower, the mechanical efficiency attained being 0.75.      The motor was tested with overloads up to 30 per cent, and for revolutions up to 125 per minute, at which overloads and revolutions there was no perceptible vibration, and the combustion was entirely satisfactory. Due to the capacity limitations of the dynamometer the motor was not tried at greater powers or at higher revolutions than the foregoing. The lowest revolutions at which the motor was tested was about 25 revolutions per minute. The test results were considered to be quite satisfactory, especially in view of the fact that the actual flywheel for the unit had not been installed, only a light temporary one, to accommodate the turning gear and the rotor of the dynamometer and affording a means of taking care of the torque fluctuations. The maneuvering gear proved to be very reliable and easily manipulated, a false maneuver being practically impossible. The amount of air required for starting is exceptionally small. From tests made, using two starting air flasks of 185.4 cubic feet total capacity and 583 pounds per square inch initial pressure, the motor was completely reversed and put into action 15 times without replenishing the air in the test flasks, which air at the end of the 15 reversals had a pressure of 114 pounds per square inch.      As the motorship C. O. Stillman is to be equipped with six such starting air bottles, and the air is to be stored at 924 pounds per square inch pressure, the installation should be sufficient for at least 50 successive starts, without refilling the flasks. Each attached compressor is of sufficient capacity to afford the full load injection air requirements of two motors. With full load on one motor during tests. the suction side of the first stage of the compressor was throttled about 45 per cent.      The attached scavenging pumps are of greater capacity than required for full load operation of the motor, having an excess capacity of about 45 per cent, figured on scavenging pump-power cylinder stroke volume. With the M.A.N. patent port scavenging a scavenging air excess of 25 per cent of the power cylinder stroke volume is deemed a sufficient surplus. The excess scavenging air is quite advantageous in that exhaust gas temperatures are comparatively lower and the motor’s maneuvering qualities are bettered. Each of the two scavenging pumps is provided with two equalizing pipes having a hand operated slide valve and so arranged that the equalizing pipes may be entirely opened or partially closed as required, to afford the most favorable conditions of scavenging air and exhaust gas temperatures. As the C. O. Stillman is to be equipped with exhaust gas boilers, this ready control of the exhaust gas temperatures is essential.