VE no. 6 wire, n = 97% 
into motor 
no. 2 wire, n = 99% 
Volts, DC 
0 10,000 20,000 
Depth (feet) 
Figure 6. Voltage gradient for three one-wire DC systems. 
Comparing the two systems, the AC system seems to be preferable, 
even though it is less compact and efficient than the DC system. The AC 
system is less susceptible to shorting since an insulation breakdown in one 
line results in a no voltage leakage and a breakdown in two separate lines 
would not be disastrous to the system (Figure 1). Also, as previously stated, 
the AC system is less susceptible to corrosive deterioration. Finally, induction 
motors can operate completely submerged while a DC motor requires com- 
mutation, necessitating a sealed, oil-filled commutator. 
Comparison of Hydraulic Systems 
Two working fluids, oil (conforming to MIL-S-5606) and filtered 
seawater, were considered in the hydraulic calculations. The oil was inves- 
tigated only in a closed (recirculating) system, while the seawater was 
considered in both a closed system and in an open system exhausting near 
the ocean floor. 
The performance of the closed oil system (Figure 7) was calculated, 
using Moody’s curves for friction factors (Moody, 1944) and the friction 
factor equation 
Ne 
Us as ( =) (4) 
