At the 1939 meeting of the Society of Naval Architects and Marine Engineers, Mr. N. J. Pluymert, naval architect of the Socony Vacuum Oil Company, read a paper entitled "Modern Tanker Design," wherein he described the evolu-tion of better, faster, more economical bulk oil carriers during the decade just closed. The first paragraph of this pa-per, as published in Pacific Marine Review for December, 1939, states:
"During the past eight or nine years many improvements have been made in the hull and machinery of tankers which have resulted in material benefits to the shipowner. The increased use of welding in hull construction has brought about a considerable reduction in steel weight, with a consequent increase in the vessel's deadweight. The change from low-pressure steam and diesel to high pressure steam-turbine drive has led to lighter machinery. In conjunction with these changes there has been a trend toward higher speeds and an increase in cargo deadweight."
The tankers reviewed in this paper covered five designs for steam propulsion, all approximating 500 feet overall length, all 37 feet molded depth, all increasing from 28' \W to 30' i3/' draft, and from 65' 9" to 68' molded beam.
It is interesting to note the conservative common-sense approach to the welding problem. The first design entered service in 1930 and was all riveted, using 970,553 rivets; the fifth design entering service in 1939 was largely wel-ded, using 122,055 rivets and 371,168 feet of weld.
Displacement tonnage grew from 20,316 in 1930 to 21,503 in 1939, while light weight of ship was reduced from 5900 to 4953 tons, thus showing a gain in deadweight capacity from 14,416 to 16,550 tons. At the same time, the designed propulsion power was increased from 3600 ihp reciprocating to 4000 shp turbine, with a consequent increase in trial speed at those powers from 12.28 to 13.7 knots. On actual average service the 1930 design gave 11.49 knots on 3084 ihp and consumed 32.95 tons of fuel per 24 hours, while the 1939 ship produced 14 knots sea speed on 4014 shp while burning 27 tons of fuel a day.
Machinery weights were greatly reduced over this series of designs. Propulsion machinery in the 1930 tanker weighed 810 tons and that for the 1939 vessel only 590 tons. Cargo pumps and piping weighed 180 tons on the earlier design and 80 tons on the latter.
Two tankers to the latest design of this series had been built by the Shipbuilding Division of Bethlehem Steel Com-pany on their Frear bracketless longitudinal system with fluted bulkheads. When these two, christened Mobilfuel and Mobilube, showed on trial and in service the results outlined above, they naturally attracted the attention of the U.S. Maritime Commission, who had then a large tanker construction program under contemplation.
Socony-Vacuum had ordered six more of these tankers from Bethlehem. The Maritime Commission proposed to the oil company that national defense features be incorporated in these six tankers on a cost cooperation basis. The U.S. Navy wanted 12,000 shp and 16 1/2 knots sea speed. Socony-Vacuum operation in the Beaumont ship canal made twin screws impractical. On conference, Mr. Pluymert agreed to adaptation of his design to include the na-tional defense features desired and expressed confidence that this could be done without "major sacrifice" of dead-weight capacity.
That he made good is amply proved by the recent trials of the Corsicana, first of their six tankers. She exceeded re-quirements in every particular, easily generating more than 12,000 normal shaft horsepower, and at that power ma-king a speed of better than 17 knots.
The principal characteristics of Corsicana are given herewith in comparison with those of Mobilfuel.
It will be noted from this table of characteristics that in Corisicana, as compared with Mobilfuel, the power of propul-sion machinery has been increased by 200 per cent and the speed by 22 per cent, with a sacrifice of less than one per cent in oil capacity.
To accomplish this remarkable result, the following steps were taken.
First, an analysis of the hull lines was made, and it was determined that the bow lines should be somewhat fined in order to make the required speed with economy.
Second, a careful survey of the machinery requirements indicated that the fore and aft space devoted to machinery would take care of the more powerful machinery without crowding. There was a slight reduction of the space available on the operating platform but not enough to in any way affect the handling of the throttle controls. In fact, there is more room on the Corsicana for the working of these controls than is provided on many of the world's noted steamships.
Third, a rearrangement of the spaces forward and aft of the cargo tanks and in the superstructure amidships pro-vided ample room for such national defense requirements as gun foundations, ammunition magazines, and addi-tional crew accommodations.
An interesting feature of the machinery installation was a new design of the Foster Wheeler water tube boiler which flares out to take advantage of the greater beam available as the frames of the ship at the stern curve outward from the run to the propeller. The Foster Wheeler Company has named this design the "P" type in honor of Mr. Pluymert.
Corsicana was named for the oil town Corsicana, Texas, where oil was first discovered by Texans in 1894. Her five sisters will all be named for Indian tribes or chiefs whose names begin with the letter C. The names now selected are Caddo, Calusa, Ca-tawba, Colina and Conastoga.
These tankers are all to be equipped with the spacious de luxe crew accommodations now characteristic of Ameri-can cargo carriers.
The propulsion plant in each of these tankers comprises a pair of water tube steam generators supplying steam at 375 psi and 700° F. to a set of cross-compound, double reduction-geared turbines that are designed to deliver 12,000 shp at 105 rpm of the propeller shaft.
On the Corsicana and three of her sisters, the turbines, gears, main condensers and air ejectors were supplied by Westinghouse Electric and Manufacturing Co.; and on the other two the turbines are to be General Electric with Bethlehem condensers.
Furnished by the De Laval Steam Turbine Co. are: the motor-driven main and auxiliary circulating and condensate pumps servicing the condensers; the motor-driven lubricating oil service pumps; the main feed pumps and their tur-bine drive; the motor-driven fire pump; and the motor-driven main cargo pumps.
For cleaning lubricating oil, De Laval Unimatic oil purifiers are provided.
The deaerating feed water heaters of the surge tank type were furnished by the Elliott Company. These tanks are so installed as to give a good suction head on the main feed pumps.
General service heat exchangers, such as the lubricating oil coolers, the fuel oil coolers, the heater drain coolers, the evaporators, the distillers and the salt water heaters, are all from the Davis Engineering Corporation.
The steam generators furnished by the Foster Wheeler Corporation are equipped with: Todd variable capacity oil burners and oil heaters; Kinney fuel oil service and transfer pumps; Vulcan soot blowers: American Blower Corpora-tion forced draft blowers; and combustion control by General Regulator Corporation.
Torsion meters for measuring the shaft horsepower of the turbines and salinity indicators for testing the condition of the boiler feed water were supplied by McNab.
General Electric Company supplied the auxiliary power plant which includes in each ship: two 300-kw turbogene-rator sets; one 50-kw turbo-generator auxiliary set; two 25-kw motor-generator sets: a switchboard for distributing current for lighting, cooking and auxiliary power; and practically all the motors for driving the auxiliary machinery.
All deck machinery including the electro-hydraulic steering gear is by the American Engineering Co.
All electric motor controls are the product of Cutler-Hammer, Inc.
National Transit Pump & Machine Co. furnished for each ship the general service, engine room bilge, pump room bilge and three cargo stripping pumps. The general service pump and one cargo stripping pump are driven by Whiton turbines; the others are motor driven.
The rotary type ballast pump is by the Kinney Manufacturing Co., driven by a Whiton steam turbine.
All main cargo pumps are electric motor drive and are furnished by De Laval.
Steam pressure reducing valves and the steam whistle are by Leslie.
Galley range and much of the accessory equipment in the galley were installed by the Edison Electric Appliance Co.
Navigation Equipment on the bridge included: sounding machines and compasses furnished by Kelvin and Wilfred O. White Co.: complete master gyro compass and repeaters, course recorder and helm angle indicator furnished by the Sperry Gyroscope Company: and the Fathometer echo-sounding apparatus installed by the Submarine Signal Corporation.
Radio equipment on the Corsicana was furnished and installed by the Mackay Radio & Telegraph Company and consists of the following:
155-B Intermediate Frequency Main Transmitter, 300-watt power output.
156-A High-frequency transmitter, 200-watt power output.
149-A Emergency intermediate frequency transmitter, 50-watt power output, operated from emergency storage bat- tery source of supply.
101-B Auto Alarm equipment with 101-A radio control panel, including 103-A master antenna control switch, char-ging equipment, etc.
105-A Binnacle type direction finder, with automatic compensator, including loop and sense antenna.
117-B All-wave receiver (low, intermediate and high frequency marine bands all covered).
122-B Auxiliary stand-by intermediate frequency receiver.
123-B Emergency crystal detector receiver.
Complete main and auxiliary antenna systems.