The Bottom Line Trumps Security
A key technology necessary
to create acoustically silent submarines is the production of the precisely machined
massive propellers that provide the motive force. Cavitation, a phenomenon that
generates air bubbles in regions around the propeller where the local pressure is
lower than the vaporization pressure of water, generates noises that sound like
fingers snapping, and is a major betraying sonar signature of submarine models.
Cruising at great depths where pressure is higher helps mask the effect, but the
time submarines are most vulnerable are when nearer to the surface. The good news
it that finite element computer modeling has produced shapes capable of eliminating
the cavitation, but extremely precise machinery is required to craft the 20-foot-plus
diameter, 40-ton-plus behemoths. Such technology would provide significant advantage
to the Navy. The bad news is that a few years back Toshiba, who was contracted by
the Navy to build the milling machines to do the job,
the technology to Russia, thereby undermining the effort.