Power storage for marine seismic vessel

A marine vessel having backup power storage in the event of primary power source failure. The invention applies to different marine vessels and is particularly suited to vessels used in marine seismic operations. A rotating mass energy storage provides stored energy which can be distributed to the vessel following primary power source failure. A pulsed generator charges the energy storage means, and the pulsed generator can comprise a homopolar generator or a compensated pulsed alternator. The primary power source can recharge the energy storage means, and a sensor and controller can control different functions related to the control and operation of the primary power source and the energy storage means

BACKGROUND OF THE INVENTION 
The present invention relates to the field of power systems for marine 
vessels and is especially useful for marine seismic exploration vessels. 
More particularly, the invention relates to a secondary power source for 
storing large quantities of energy and for selectively discharging such 
energy when a primary power source for the vessel is inoperative. 
Seismic exploration methods indicate the physical properties and spatial 
disposition of geologic formations underlying the earth surface. In land 
based seismic systems, mechanical vibrators or explosive charges initiate 
a pressure wave in earth materials. In marine systems, a seismic source 
array comprising air guns or other pressure source wave generators are 
towed by a vessel through the water. Source waves from a seismic source 
travel downwardly through the subsurface formations, and portions of the 
seismic wave energy are reflected, refracted and transmitted by geologic 
interfaces between subsurface geologic units. The returning reflected 
waves are detected by a sensor or sensor arrays located at a known 
position relative to the energy source. In marine seismic operations, the 
reflected waves are detected with towed sensors such as hydrophones or 
bottom cables positioned on the ocean floor. 
Seismic sensors in marine systems comprise transducers which convert 
pressure, velocity or acceleration into electric signals. The output 
signals are recorded and processed to indicate mechanical, acoustic and 
structure characteristics of geologic units. For example, the propagation 
time of a seismic wave reflected from a point is proportional to the depth 
of the reflection point. Travel times from multiple, spatially diverse 
source and receiver pairs facilitate construction of maps representing the 
spatial disposition of subsurface geologic units. 
Towed vehicles are typically neutrally buoyant and depend on water flow 
over control surfaces to maintain position in the water. If the tow 
vehicle should lose forward motion, the tow vehicle is uncontrolled and 
may sink. Such event can damage towed arrays and can sink the tow vehicle 
and the tail buoy marking the array tail-end. Even if the equipment does 
not sink, the submerged tow vehicle and towed array will comprise a 
navigation hazard. 
Numerous vessel propulsion systems have been developed for marine vessels, 
including gasoline engines, diesel engines, electric motors, and jet 
propulsion units as the primary sources of power. Secondary power sources 
permit vessel operation following failure of the primary power source. 
Otherwise, power failure can lead to irretrievable loss of the vessel, 
towed equipment and data acquired by the vessel. Existing secondary power 
sources for marine vessels typically comprise storage batteries such as 
silver/zinc batteries or auxiliary fuel-powered propulsion systems. 
Battery power sources are heavy and require recharge time and maintenance. 
Auxiliary power systems are subject to the same failure mechanisms 
experienced by the primary power sources, and may not provide reliable 
auxiliary power. Conventional batteries and conventional generators 
provide relatively low storage density for secondary power requirements. 
Accordingly, a need exists for an improved apparatus for storing and 
discharging large amounts of energy. The apparatus should be portable and 
should be capable of sustaining energy discharge over a defined time 
interval. 
SUMMARY OF THE INVENTION 
The invention provides a marine vessel having a hull and a propulsion 
system for moving the hull through water. The vessel includes a primary 
power source for engaging and for transferring energy to the propulsion 
system to move the hull through water, and a rotating mass energy storage 
means engaged with the propulsion system for storing energy and for 
selectively discharging said energy to operate the propulsion system. 
In different embodiments of the invention, a pulsed generator charges the 
energy storage means, and the pulsed generator can comprise a homopolar 
generator or a compensated pulsed alternator. The primary power source can 
recharge the energy storage means, and a sensor and controller can control 
different functions related to the control and operation of the primary 
power source and the energy storage means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Streamer arrays used in marine seismic exploration produce significant 
hydrodynamic drag acting against the tow vessel. Seismic streamer arrays 
between four and eight kilometers in length create between 2,000 to 5,000 
pounds of drag at about five knots. 
The invention provides an alternative energy source for maintaining vessel 
speed in the event of primary power failure. Depending on the array 
configuration, a modest speed between one and two knots should prevent 
sinking and should provide adequate steering control. Assuming one hundred 
horsepower is required to pull 4000 pounds of drag at five knots, ten 
horsepower could pull the same equipment at a speed of about 1.6 knots. 
Although the original velocity is not maintained, the reduced propulsive 
power would provide control to the tow vehicle and towed arrays. 
If the primary energy supply ceases operation, the uninteruptible 
propulsion system of the invention is activated to supply motive force to 
keep the tow vehicle and towed arrays under control at a reduced power 
output. The energy required to produce ten horsepower for thirty minutes 
is 13.4 megajoules. In one embodiment of the invention which stores energy 
in a rotating mass, a solid cylindrical mass of 500 kg having a radius of 
0.25 meter rotating at 1000 rpm has a specific energy approximating 170 
w-hr/kg. Rotating the same mass at 2000 rpm produces a specific energy 
approximating 685 w-hr/kg. Rotating the same mass at 3000 rpm produces a 
specific energy approximating 1542 w-hr/kg. By selecting the mass, radius 
and rotational frequency, an energy storage device can be designed for 
specific applications and energy requirements for a marine vessel. 
The invention is particularly advantageous over conventional storage 
devices having limited energy storage capabilities. A lead-acid battery 
can store specific energy in the range between 25-35 w-hr/kg, an advanced 
lead-acid battery can store between 35-40 w-hr/kg, a nickel-metal hydride 
battery can store between 50-60 w-hr/kg, a lithium-ion battery can store 
between 80-90 w-hr/kg, and a lithium-polymer battery can store 
approximately 100 w-hr/kg. As demonstrated by these storage capabilities, 
the invention is capable of storing significantly more energy than 
chemical storage devices in the same mass and volume because the energy 
density of the storage is significantly greater. 
The invention provides a high-powered pulsed generator as an energy storage 
mechanism or signal generator for a marine vessel. As used herein, the 
term "pulsed generator" includes homopolar generators, compensated pulsed 
generators, and other forms of rotating mass energy storage devices. A 
pulsed generator provides multiple functions of storing energy and of 
discharging such energy. One form of pulsed generator uses passive 
compensation where a continuous conducting shield is at rest relative to 
the field excitation. The static exciting field diffuses through the 
shield and induces a voltage in the spinning armatures. The alternator may 
include a stationary, rotating, or counter-rotating compensating coil, and 
numerous configurations of such pulsed generator devices exist. 
One embodiment of the invention uses compensated pulsed alternators as the 
pulsed generator because such devices can be designed to produce hundreds 
of pulses per second or to produce a single pulse similar to a homopolar 
generator. Pulsed generators can be operated in series or in parallel. The 
invention is particularly suited for seismic exploration but is also 
applicable to other marine vessels where failure of the primary power 
supply was undesirable. The term "water" means all applications having 
water as a mass for supporting a vessel hull and includes open water, 
marshes, tidal regions, rivers, estuaries, and man-made impoundments. 
Referring to the drawing, a schematic diagram for one embodiment of the 
invention is illustrated. A pulsed generator such as compulsator 10 is 
illustrated as being engaged with a converter shown as transducer 12. 
Transducer 12 is engaged with vessel hull 14 and converts the energy 
discharged from compulsator 10 into an energy form capable of transmission 
to the electric motor 16. Transducer 12 is positioned between hull 14 in 
contact with a selected propulsion means such as drive train 18. A primary 
power source such as engine 20 is also engaged with drive train 18 for 
providing the power to move hull 14. 
Drive motor 22 provides energy to recharge compulsator 10 after energy has 
been discharged from compulsator 10, and controller 24 can be engaged with 
compulsator 10 to manage the energy discharge and recharge. Sensor 26 can 
detect the operation of primary power source 20 and can generate a signal 
for transmission to controller 24. Using input from sensor 26, controller 
24 may dynamically modify the output of compulsator 10 and of transducer 
12 to produce the desired energy discharge. 
Drive train 18 can comprise shaft 28 and propeller 30 or can comprise jets, 
compressed air discharge ports, ballast or flotation controls, or other 
types of systems. Such systems can move hull 16 vertically, horizontally, 
laterally, or axially within the water. Rudder 32 can provide steering 
control, and controller 24 can be integrated with the working components 
of the vessel. 
The drawing illustrates a marine vessel adapted to seismic operations 
wherein hull 14 is independently moveable in the water. Fuel tank 34 
provides storage for primary power source 20, radio/modem 36 is engaged 
with antenna 38, and UPS 40 and exhaust 42 are integrated within mast 44 
which extends above the water surface. 
A pulsed generator such as compulsator 10 can comprise a high power 
electric storage device and signal shape generator suitable for 
transmitting energy to electric motor 16. Compulsator 10 can comprise an 
electric generator having one or more phases which produce an alternating 
current, and this current is transmitted over the period represented by 
the discharge of energy from compulsator 10. 
Compulsator 10 is capable of storing significantly more energy in less 
weight and space than electrical capacitor banks or batteries. 
Consequently, the energy density of compulsator 10 is extremely high as 
significant energy is stored per unit volume of space. In addition to the 
energy storage density, pulsed generators produce very high current of 
long duration and relatively low voltage compared to the high electric 
potential of short duration delivered by capacitor based energy storage 
systems. The rotating mass energy storage provided by compulsator 10 also 
eliminates the toxic hazards associated with the use and disposal of 
conventional batteries. 
Homopolar generators store energy in the inertial form of a spinning rotor 
or flywheel. Electrical contacts such as brushes slide at high speed on 
the outer periphery and axial shaft of the rotor to collect the generated 
current. Homopolar generators store inertial energy in the rotor/flywheel 
as the rotational velocity of the rotor/flywheel is increased. A homopolar 
or pulsed generator converts inertial energy into electric energy which is 
dissipated in the form of heat and work by a converter such as electric 
motor 16. As current begins to flow through the rotor and brushes, Lorenz 
forces decelerate the rotor and the stored kinetic energy is converted to 
one or more electric pulses to provide a secondary power source for hull 
14. 
Solid copper-graphite brushes have been developed to conduct electrical 
currents ranging up to hundreds of thousands of amps, and compulsators 
have been developed with a power density above 1000 kW/kg. Pulsed 
generators have been used to weld metal, power solid state lasers, and 
fire electromagnetic guns. Other compulsator applications include 
simulation of micro-meteorites impacting space vehicles, sintering 
operations, hypervelocity spraying of dense metal coatings, and the 
ignition of lean mixtures in automobile engines, however compulsators have 
not been used for secondary energy supply storage in vessels. 
The construction of various compulsators and compulsator improvements is 
described by U.S. Pat. No. 4,200,831 to Weldon et al. (1980), in U.S. Pat. 
No. 4,841,217 to Weldon et al. 1989), in U.S. Pat. No. 4,858,304 to Weldon 
et al. (1989), in U.S. Pat. No. 4,935,708 to Weldon et al. (1990), in U.S. 
Pat. No. 5,530,309 to Weldon (1996), the disclosures of which are 
incorporated herein by reference, and by other sources. 
Pulse generators are commercially available from Parker Kinetic Designs, 
Inc. of Austin, Tex., and are available in representative sizes ranging 
between 6.7 megajoules ("MJ") at 1.5 MA and 60 MJ at 1.5 MA. A 10 MJ 
homopolar generator has an effective capacitance of 2,000 farads, a peak 
discharge current of 1,500,000 amps, and maximum terminal voltage of 100 
volts DC. A 60 MJ device has equivalent series capacitance of 333 farads, 
equivalent parallel capacitance of 12,000 farads, peak discharge current 
of 9,000,000 amps, and maximum open terminal voltage of 600 volts DC. A 60 
MJ device comprises six pulsed power supplies which can be connected to a 
common bus system to furnish the capability to interconnect individual 
generators and to form various parallel and series combinations. Drive 
motor power is provided by a common 2400 horsepower high pressure 
hydraulic system. 
The invention provides a unique system for providing power to remote 
vehicles, and eliminates the need for heavy batteries conventionally used 
in power back-up systems. The absence of large storage batteries 
eliminates environmental problems associated with leaking batteries and 
hazardous disposal issues. The invention reliably provides high current, 
long lasting secondary power for maintaining minimal vessel speed and 
control following loss of a primary power source. 
Although the invention has been described in terms of certain preferred 
embodiments, it will be apparent to those of ordinary skill in the art 
that modifications and improvements can be made to the inventive concepts 
herein without departing from the scope of the invention. The embodiments 
shown herein are merely illustrative of the inventive concepts and should 
not be interpreted as limiting the scope of the invention.