Page 249 - NAVAL SCIENCE 3 TEXTBOOK

NAVAL WEAPO N S AND AIRC RArl 255

that little more can be done to change substantially the acolls-
tic characteristics associated with a ship's hull. Research is ongo-
ing to develop a screw shape that would reduce cavitation, at least
to some degree. For now, however, underwater ship noise C;.ll1 be
reduced onl), by slowing the speed of the ship. using special noise-
reducing mountings for machinery that must operate, and shut-
ting down nOllvital noise-producing machinery.
i'vlinesweeping is done by trawrsillg a mined area with
mechanical sweeps that set moored mines ;.tdrift by cutting their
mooring c,tbles, and with influence sweeps that simulate the nec-
essary chill"acteristics to C<lllse detonation of influence mines. The
sweeps Gill be dragged through the area either by minesweeping
ships or, in some cases, by it helicopter. Ivlinesweeping helicopters
were developed in the 1970s, and have been extensively used as
sweeping \'Chicles in most mine-clearing operations conducted by
The MCM 1 Avenger mine countermeasures ship.
the U.S. Navy since.
The Navy's primary mine countermeasure force is the four-
Though these measures can greatly reduce the magnetic sig- teen-ship AI'ellger-c1ass of mine countermeasures ships built dur-
nature of a steel-hulled ship, some residual magnetic fietd is ing the 1980s. They are made of wood sheathed in fiberglass, and
always generated by aU steel vessels. Consequently, minesweeper can find, c1assii)', ilnd destroy moored and bottom mines. They
hulls are built of wood, fiberglass, aluminulll, or other nonmag- have both conventional minesweeping geM and newer devices
netic materi.lls. Stich as remotely operated underwater vehicles to seek out and
Very little can be done to protect a ship from acoustic mines. destroy mines. The Navy's new littoral combat ships also have i\
minehunting capability.
iVlost underwater noise generated by ships is caused by the move-
ment of the screw blades with respect to the water. This effect is
called ({lI'if{/tioll beCi.lUSe of the bubbles of water vapor that arc
Mine Hunting
formed and collapse at sonic or subsonic frequencies around the
tips of the blades. Some noise also is produced b)' water flowing j\·line hUllting is the methodical detection, location, and neutral-
over sharp surfaces on the hull and by machinery inside the ship. ization of mines. It involves searching an area with mine-detecting
Beyond the Alb{/core hull design of lluclear submarines, it appears gear to locate mines and then removing them by the llse ofdi\'ers or

A mine countermeasure Sea
Stallion helicopter tows a
magnetic minesweeping sled
past an Egyptian merchant
ship while sweeping the Suez
Canal during Operation Nimbus
Star in 1974. The canal had
been closed for seven years by
Egyptian mines laid during the
Arab-Israeli wars of the 19605.