Surface Forces: <b>December 21, 1999</b>

December 21, 1999

The US Navy has decided to use an electric drive system in the DD21 destroyers. In such a system, there are no 200-foot-long shafts connecting the diesel engines to the propellers; instead, the engines drive generators, and wires carry the electricity to a motor located very close to the propeller. This idea isn't new; the US Navy was using it for battleships as early as 1900, but it never really worked out since there was no real savings in weight and the system was complex. What has made the difference now is new technology that allows the motors to run the propellers directly, rather than through the traditionally huge "reduction gears" used by all warships to date. This technology was developed recently and is being built into new passenger cruise ships. It provides a genuine reduction in weight, and several other benefits. It is far more quiet, a quality that is of interest to submarines and to the surface ships they try to torpedo. The diesel engines do not have to be at the bottom of the ship (a position required by the traditional propeller shafts), but could be higher up where they are safer from torpedo hits. The savings in weight and space could be used to add weapons or crew comfort, or to build a smaller and stealthier ship. Maintenance crews and costs could be cut by a third. One possible leap-ahead concept is that the engines could provide electric power for a host of new weapons (lasers, micro-wave beams) that require electricity rather than gunpowder or rocket fuel. Ships rarely maneuver at their highest speeds, and the last nautical mile per hour of speed costs far more horsepower than the first one. The unused speed (or even a couple of knots of speed that might have been handy) could be diverted into electricity for these new systems. Visionaries note that the starship Enterprise appears to use this system, relying on the warp drives for either high-speed cruising or for the power to raise shields and power the phasers. The Navy expects that electric drive will be used by all future warships, revolutionizing naval architecture. The big decision to be made is whether to build the DD21s with the latest electric drive designs, or to pour money into risky but promising new directions that could produce an even better drive system in a short time. One school of thought is not to risk money on technology that might not work, while the other is worried that the Navy could miss a whole generation of new technology (as it did when it ignored the development of stealth aircraft). --Stephen V Cole