Leaving a brood wake astern, S.S. Mission Purisima makes a sharp turn. She is first of a fleet of "mission" tankers to be built by Marinship, and is the yard's tenth T-2. The first nine were delivered to the Navy.
( All phofos Marinslnp )
MANY T-2 tankers are being built by the U. S. Maritime Commission at various American yards. These tankers are of the single
screw U. S. M. C. design, which originally called for 12,000 shp in geared turbines and a sustained sea speed of 16 1/2 knots. As now being built in large numbers, they are powered with steam turbo-electric drive to avoid the bottleneck delay in the manufacture
of large helical gearing. The most available power plant was a combination giving 6000 normal shaft horsepower, and the bulk of the T2 tankers now under construction are being powered with that capacity steam-electric drive, which gives this tanker hull a good turn of speed, as tankers go.
This unusual shot shows the bow of one of the "mission" tankers plowing through the waters of San Francisco Bay.
However, the first group of tankers being built at Marinship are powered with steam-electric machinery that has a normal rating of 9000 shp and a maximum continuous operation rating of 10,000 shp. Trial results of these vessels are not published, but they are sufficient to allow the builders to make the claim that these are "the fastest commercial tankers being built today.“
Since we have frequently published complete details of T-2 tankers, we shall confine this article to a short description of the power plant on these ships, and to mention of the subcontractors and vendors to whom Marinship gives credit for helpful cooperation in making the construction record which, early in April, brought that yard the U. S. M. C. Tanker Champion Flag.
One of the new highspeed tankers shown during trials in San Francisco Bay.
The steam is generated in two Babcock & Wilcox design two-drum water-tube type oil-burning boilers operating under forced draft and having incorporated superheater and economizer. The heating surfaces in each hoiler, including water walls, are 6350 sf for the boiler, 675 sf for the superheater, and 1680 sf for the economizer. Furnace volume is 573 cf.
Steam conditions are 600 psi and 325° F. at superheater outlet, and each boiler has a capacity to produce 43,000 pounds of superheated steam and 4500 pounds of desuperheated steam per hour. These boilers operate with Bailey type feed-water regulators and under Bailey automatic combustion controls.
Steam arrives at the throttle of the propulsion turbine at 590 psi and 815° F. temperature. This turbine is a General Electric 14-stage machine the first wheel being fitted with a double row of Curtis blades and all the other rows being fitted with Rateau blades. At its normal rating, this turbine turns 3600 rpm with 1 1/4 inch absolute pressure at the exhaust to produce 6890 kw electric energy of 3-phase. 60-cycle alternating current at 3500 volts and an unity power factor.
The turbine is directly connected to the General Electric generator, and both are capable of running continuouslv at a speed of 3715 rpm for a maximum rating of 7650 kw. 3 phase, 60 cycles, 3610 volts, at unity power factor. The set will operate at 110 per cent normal rating speed, or 3860 rpm.
The Mission Purisima pulls away from her berth of the oulfittinq docks. The 16,500-ton tanker set a new construction record for
the tenth T-2 built in any shipyard with a total elapsed time of 166 days from keellaying to delivery.
This generator supplies current directly through suitable control apparatus to the propulsion motors, of which there are two types in these Marinship tankers. The first type is a 70-pole motor with a normal rating of 9000 shp at 103 rpm, and the second type is a 60-pole motor with the same rating at 120 rpm. Both of these motors will operate continuously at 10.000 shp output.
The generator and the motor each have a separate closed system of air ventilation fitted with surface air coolers, and their operation, without heating at the above ratings, depends on a flow through these coolers of 165 gpm (generator) and 175 gpm (motor) of sea water at an inlet temperature not exceeding 85° F.
The propulsion motor is located on the lower flat of the machinery space and is directly connected to the propeller shaft. The two boilers are on the upper flat directly above the motor, and the turbo-generator set is on the upper flat forward of the boilers on the port side. Abreast of the main generator set and on the starboard side of the upper flat, two auxiliary turbo-generator sets are installed.
These sets are each composed of a General Electric turbine running 5645 rpm, connected through a helical single-reduction gear set to three generators in line, running 1200 rpm.
The generators on each set are: a 400-kw, 450-volt auxiliary generator for lighting and auxiliary power services: an 85-kw, 110-v.d.c. exciter for field current for the main propulsion generator and the main propulsion motor; and a 55-kw. 120-volt d.c. exciter
for supplying power to the excitation bus for all auxiliary motors.
To save time and labor of machinists power machinery unit is preassembled and placed into the ships in a single compact piece.
View aft from the midship deckhouse of S.S. Mission Purisima shows auxiliary cargo space, mainmast and poop deck wifh king post prominent in the foreground.
View of the main propulsion motor, showing main feeder lines (upper leff), which carry 3600 volts from steam furbine driven qenerators.
View of the main steam turbine, showing steam inlef (upper riqht) and automatic operating equipmenf for the unit (center) .