bility for certain types of missions. In the 

 simplest example, the All Ocean Industries'' 



vehicle employs two 12-volt lead-acid batter- 

 ies inside its pressure hull; the total cost of 

 this power package is somewhere around 

 $70. Cost and reliability are so intertwined 

 that it is impossible to evaluate one without 

 the other using the present yardsticks of 

 evaluation. Confidence or reliability in a 

 power system is achieved through demon- 

 strated performance. For this reason the 

 lead-acid battery (in use since 1901 in U.S. 

 Navy submarines) is irresistible. For other 

 systems (fuel cells, thermoelectric genera- 

 tors and other batteries) to attain this de- 

 gree of confidence they must demonstrate 

 their reliability, but without a concentrated 

 research and development program which 

 will both demonstrate reliability and de- 

 crease purchase cost, it is difficult to foresee 

 a near-future competitor to lead-acid batter- 

 ies. 



In the final analysis, the nature, location 

 and total power output of a submersible's 

 power system are compromises of design and 

 operational trade-offs. Without compromis- 

 ing occupant safety, sound arguments can be 

 advanced for systems internal to the pres- 

 sure hull as well as external. Both solutions 

 are accompanied by disadvantages for which 

 there is no optimum solution in one submers- 

 ible. Perhaps future developments will help 

 to alleviate this problem, but for the present 

 let us examine the power sources with which 

 submersible builders have dealt: Batteries, 

 fuel cells and nuclear reactors. Though not 

 having a "self-contained" power source, sur- 

 face-powered vehicles such as GUPPY and 

 KUROSHIO II satisfy all other require- 

 ments of a submersible; hence, aspects of 

 their cable-supplied power systems are 

 briefly described. 



BATTERIES 



Batteries generate power through the flow 

 of electrons from a negative (anode) to a 

 positive (cathode) electrode immersed in a 

 conducting (electrolyte) medium (usually a 

 liquid). The basic electrochemical unit (an- 

 ode, cathode, electrolyte) is called a cell; the 

 finished, boxed unit is the battery and it may 

 consist of one or many cells. After a period of 



time, the flow of electrons from anode to 

 cathode (discharging) will weaken, and, for 

 further use, the electron flow must be re- 

 versed by recharging to bring the cell back to 

 its rated strength. Cells that can be re- 

 charged for many cycles are called second- 

 ary cells; cells that cannot normally be re- 

 charged — e.g., where the electrodes are de- 

 pleted — are called primary cells. Secondary 

 cells are the major suppliers of power in 

 submersibles. Primary cells are frequently 

 used to furnish emergency power or power to 

 ancillary components such as pingers or 

 transponders. Our main concern here is with 

 secondary cells or batteries, of which three 

 types have been used in submersibles: Lead- 

 acid, nickel-cadmium and silver-zinc. The 

 classification of batteries is derived from the 

 substance comprising the electrodes (silver- 

 zinc, nickel-cadmium) or from the substance 

 comprising the electrodes and electrolyte 

 (lead-acid). The electrolyte in the silver-zinc 

 and nickel-cadmium batteries is alkaline. 



While there is a lack of repoi'ted studies 

 aimed at improving the performance and 

 packaging of secondary batteries, there are 

 several excellent reports detailing the char- 

 acteristics of these power sources in the ma- 

 rine environment and other analyses exist 

 which compare the advantages and disad- 

 vantages of one source against the other. 

 The author has relied heavily on these stud- 

 ies to provide a state-of-the-art summary of 

 the characteristics and properties of second- 

 ary batteries for deep submergence. A sec- 

 ond topic — the means used to protect these 

 sources from seawater and pressure — is 

 dealt with under Protection and Pressure 

 Compensation. 



Characteristics 



In 1968 the National Academy of Sciences 

 published a report (5) on energy system re- 

 quirements and technology for undersea ap- 

 plications which cited the following advan- 

 tages and disadvantages of conventional bat- 

 teries relative to other energy sources. 



Advantages: 



a) Basically simple construction where all 

 components are self-contained within 

 the battery. 



319 



