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THE ELECTRIC PLANT OF THE BATTLESHIP
Purpose. It is intended to describe the electric plant of a battleship and, because of the fact that it embodies the highest developments to date and marks another step in the adoption of electric propelling machinery, the particular plant of the battleship Tennessee is chosen for illustration.
Scope. The scope of this paper must necessarily be limited by the scarcity of dependable data available and limitations of space practically confine the discussion to the ship's propelling machinery. This is, at once, the most interesting and the only part for which data is now at hand.
Increase in Use of Electricity Aboard Ship.—The marked increase in the use of electricity aboard ship is worthy of mention. While the development has been contemporary with the increase in size of ships, it is not believed that the size factor alone has been responsible for this development.
The increase aboard ship has followed closely a similar increase ashore and, while the naval progress has not quite satisfied the more ardent advocates of electric propulsion, our navy is, nevertheless, in the vanguard, in fact, leading the world in this radical step forward.
For auxiliary and miscellaneous uses, the capacity of generators installed per ship has increased from about 100 kilowatts in the go's to about 1200 kilowatts in 1916; and now comes the jump from 14,000 kilowatts in the first electrically propelled battleships to the proposal of 150,000 kilowatts for the new battle cruisers.
The magnitude of such a proposal and its bearing on the particular subject under discussion warrants a review of the factors justifying the selection of this type of drive.
Type of Drive Comparatively Recent.-Active discussion of electric ship propulsion did not start until about ten years ago and real development was slow until about five years ago. The subject has been one of considerable argument and little has been taken for granted. Before the adoption of electric battleship propulsion there was an experience with about 12,000,000 horsepower of marine turbines, 3,000,000 horsepower of which were geared installations, so that the electric drive had the inertia of considerable precedent to overcome.
Factors Affecting Choice of Drive.—The choice of this type of drive appears most logical in ships of over 5000 horsepower, with especial advantages for battleships or other very large fighting ships. Approximately in their order of importance, the following factors have been considered in the adoption of type of drive:
6. Care and upkeep. Reliability.—No serious question has been raised as to the mechanical reliability of the individual parts of the system, the discussion centering on the hazards of control and operating cables and the action of water on the electrical apparatus. As, obviously, these hazards can be easily insured against to any reasonable degree desired, the advantages of the electric drive as regards reliability may be pointed out.
Greater reliability is attained owing to the facility with which power may be shifted between generators and motors, the installations being practically duplicates throughout. For instance, the breaking down of one turbine does not materially affect the ship, except at high speeds, say above 17 or 18 knots.
Difficulties with auxiliaries often affect operation and output as seriously as trouble directly with the main units. The flexibility of this drive and the ease with which load from all propellers can be shifted to the other main unit gives it a further advantage.
Since the permanent advent of the turbine in marine practice, the elimination of considerable blade trouble may be expected.
The blade distortion, occurring nearly always during backing, will not occur with the electric drive in which the main units are always turning in the same direction.
The elimination of racing further increases the reliability of this system.
Maneuvering Qualities.—Very superior maneuvering qualities are claimed. The control is well centralized and the operation of light parts only is necessary. The speed can be very accurately adjusted and maintained without undue effort on the part of the operators. This advantage is strikingly evident during heavy seas, when the prevention of propeller racing is automatic, being electrically under governor control, thereby eliminating mental strain on the operator and physical strain on the equipment.
Full power can be obtained astern and, as this is accomplished without reversing the main generators, the electric drive has, in this particular, a big advantage over the geared turbine installation.
While much greater rapidity of operation is claimed for this form of propulsion, it is thought wise to defer opinion in this regard pending further experience in more difficult service.
Economy.-Claims of great superiority of economy have been the subject of lively dispute, 20 to 30 per cent in favor of the electric drive and against reciprocating engines and direct-connected turbines being claimed. It is reasonably certain, however, that for a battleship where economy at two speeds, cruising and full, is necessary, the electric drive is considerably superior to the reciprocating and direct-connected turbine systems; and, at cruising speed is also superior to geared turbines. As most of the steaming is done at cruising speed, this is an important advantage. The table below shows comparative water rates at various speeds for all the types except geared turbines, data for which has not been found.
Pounds Steam per Effective Horse Prop:
Speed Ship Type
15 knots Florida Parsons Turb. 31.8
24.0 23.0 Utah Parsons Turb. 28.7
323 Delaware Recipro. Eng.
18.7 California Elec. Drive
17.3 15.2 15.0 16.4 175
power per Hour at
at 21 knots
The steam consumption of the Tennessee is shown graphically on Fig. 1.
Inherent advantages of the electric drive over the geared turbine are that the former uses only one turbine at low powers and has the double motor winding, the equivalent of two gear ratios. Not only does this permit of more efficient speeds for the turbines but it eliminates some of the element of compromise in the propeller. The handicap of the geared turbine with only one speed reduction is evident.
The turbines not only operate at more favorable speed but, also, more favorable load conditions, as at low speeds only one turbine is used, so that the load will always be twice that on direct-connected machinery.
The larger number of turbines and the friction and windage losses of the astern turbines incur further losses in the other types of drive, but these are not so large as the other factors above mentioned.
Space Occupied.—While the electric drive probably has little or no advantage over the geared turbine in the amount of space occupied (except for very large and high powered ships), the flexibility of arrangement has not only permitted highly desirable changes in the hull design to be made, with more effective use of space, but, military advantages of considerable weight have accrued to this type.
Weight.—The electric drive is probably heavier than geared turbines in the smaller sizes but for the largest ships now contemplated, the balance probably shifts.
Care and Upkeep.—These are related to reliability and the best of records have been made by ships with this drive. The high speed turbines, having smaller dimensions, are easily handled and repairs to turbine rotors have been made by the ships mechanics. As one engine room would be idle practically all the time, the engine room watch can be considerably reduced if not cut in two. A further advantage arises from the possibility of overhaul of one of the turbines, while still maintaining 17 to 18 knots.
It must not be assumed from the above favorable statements that the case of the electric drive affords no rebuttal, but, as this has been ably handled by its opponents, the newer drive will probably need all the support it can accumulate. There has been