Apparatus for and method of interconnecting and controlling units of a power train for maximum flexibility and economy in operating auxilliary marine vessels

A plurality of diesel motor AC generator units, or power producing units, connected in parallel to provide a AC power pool that is rectified and voltage controlled by a plurality of silicon control rectifiers, or power control units, for activating any of a plurality of DC shunt wound motors, or power using units, singly and in combination to drive any plurality of propellers and auxilliary equipment in minimum numbers at maximum loads and effect a fuel economy of at least 18% over reduction-gear driven vessels.

BACKGROUND OF THE INVENTION 
The invention relates generally to power trains for powering auxiliary 
marine vessels, and more particularly to diesel electric power trains 
having silicon voltage control rectifiers for vessels subject to a wide 
range of loads, uses and space limitations. 
In the prior art power trains for the purposes noted lacked flexibility of 
operation and control, and within such limitations often operated at less 
than maximum efficiency. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a power train for auxiliary 
marine vessels that is controllable by a plurality of power control units 
in forward and reverse directions from zero to maximum r.p.m. (revolutions 
per minute). 
Another object of the invention is to provide a power train as stated above 
comprising a plurality of power producing and power using units that have 
respectively different performance characteristics that are 
synergistically complementary to supply a variety of loads at respectively 
maximum unit efficiency. 
Yet another object of the invention is to supply a standby for each power 
producing, using and control unit to prevent a failure of one from 
interfering with the flexibility and control for the full efficient use of 
said power train. 
A further object of the invention is to provide a power train that is 
susceptable to division for an installation of maximum convenience and 
space saving. 
A final object of the invention is to provide a method of synergistically 
complementing the maximum advantages of power producing and power using 
units and eliminating the respective disadvantages of both.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a typical power train 9 of the invention comprises two 
main diesel motor AC generator units, or power producing units 10, 
connected in parallel and to a smaller auxiliary diesel motor AC 
generator, or power producing unit 12, through a transformer 14. A third 
diesel motor AC generator, or power producing unit 10', shown in phantom 
may be added to the power train if desired. 
The output of power producing units 10 is rectified and voltage controlled 
by power control units 16 comprising four silicon control rectifiers 17 
and four variable current controls 18. The silicon control rectifiers 17 
are connected through magnetic contacts 19 to shunt wound DC motors, or 
power using units 20. Current through the shunt field windings 21 is 
regulated by said current controls 18 mounted between the output of said 
power producing units 10 and said field windings or coil 21. Main 
propulsion motors 20 respectively receive the output of a power control 
unit 16, the propulsion motors being mounted in pairs to drive respective 
main propellers and propeller shafts 24 either singly or jointly through 
respectively common gear boxes 26. Single motors 20 are provided to drive 
main auxiliaries such as a bow thruster 28 and a tow winch 30 
respectively. These motors are connected each alternatively to a pair of 
silicon control rectifiers 17 and each to a variable current control 18 to 
provide standbys in case of a failure of one. 
Referring to FIG. 2, the performance characteristics of a diesel engine is 
shown to be that torque and horsepower rises with rpm until a maximum for 
all three is reached. Since the diesel of the disclosure cannot safely be 
run above 900 rpm, the torque and horsepower at this speed is maximum at 
100%. 
Referring to FIG. 3, the performance characteristics of a shunt wound DC 
motor is shown to be that torque is constant at 100% from zero through 
100% of the base revolutions/minute, the horsepower rising with the rpms 
to maximum at 100% of the base rpms as voltage to the motor is increased. 
Thereafter rpms can be increased up to 200% of the base rpms without 
damage by reducing shunt field current. In this mode horsepower remains 
constant at 100% and the torque varies downward as shown in FIG. 3. 
Referring now to FIG. 4, a tug and tow performance curve shows that with 
5578 shaft horsepower, the tug and tow will make 10.7 knots with propellor 
speed of 145.7 rpms. Now referring to FIG. 5, it is seen that when running 
free, the tug of FIG. 4 is limited by its gear reduction drive to a 
propeller speed of 150 rpm to use only 3330 shaft horsepower of the 5578 
shaft horsepower available to make 14.63 knots. It is seen in comparison, 
that the electric drive of the invention with one engine of 2600 shaft 
horsepower can drive the tug 13.9 knots with both propellers at a speed of 
140 rpm using all available shaft horsepower, which is only 0.73 knots 
less than the reduction gear drive does with two engines. If two engines 
are used in the electric drive of the invention which can increase its 
motor, shaft and propeller speeds without damage by reducing the motor 
field current, it is seen that at 168 rpm all available 5200 shaft 
horsepower is used to drive the tug 15.7 knots. 
Referring now to FIG. 6, the fuel consumption curve of a diesel engine 
shows that fuel consumption per brake horsepower/hour decreases as the 
load increases to its rated capacity. Thus in the case of FIG. 5 for the 
gear reduction drive tug only 3400 brake horsepower of the 5750 available 
is used, that is about 60% for a fuel consumption rate of 0.409 
lbs/bph/hr. or 197.2 gallons/hr. Whereas the invention using one engine 
utilizes the full 2875 brake horsepower available to consume only 0.392 
lb/bhp/hr. or 158.3 gallons/hr. In free running, the electric drive of the 
invention will use 734 gals. per day less to travel the same distance, 
that is, less about 18%. Even if the power train of the invention has 
about 10% loss against 3% loss in the gear reduction drive power train, or 
a net of 7% loss, nevertheless there is a fuel economy gain of 18%, plus 
half the lubricating oil and half the engine time expended for 8% slower 
time for the trip. 
Referring to FIG. 7, a further comparison is made as in FIG. 5 but with 
diesel engines of lesser brake horsepower in two and three engine 
installations. 
In addition to economy of operation the power train of the invention lends 
itself to a further economy in the use of limited space available on an 
auxiliary marine vessel. Thus power producing units may be mounted forward 
to better trim the vessel without an addition of ballast when loaded or 
working, and the power using units may be mounted aft to shorten propeller 
shafts and save the space required by longer ones. Power control units may 
be mounted wherever convenient, their mass and space being negligible. 
It should be understood, that the invention units can be separately and 
jointly connected in any arrangement in number and function so that power 
using units can be run independently of each other off of one producing 
unit through one or more power control units, or vice versa.