176
The Last Resource
syntatic foam packing which also contains a number of aluminium
buoyancy spheres.
Alvin dives by ooding its main ballast tanks while two trim
tanks, one near the bow and the other in the stem, set the craft at a
nose—down angle of up
to about 30° to assist the dive. The trim
tanks, lled half with mercury and half with oil, are connected so
that oil pumped from the top of one tank to the top of the other
forces the heavy mercury from the bottom of that tank back into
the rst one. The two side propellers may also be used to speed up
the dive. When the mission is completed the submersible returns
towards the surface, using either or both the oil—lled bags for
additional buoyancy as well as the side—propellers. To complete its
ascent, the main ballast tanks are ‘blown’. Unfortunately, in 1968
Alvin made an unscheduled dive when it sank empty in 4,500 feet
of water.
In comparison with conventional submarines, all research submersibles (except converted submarines such as the Soviet Savary—
anka) are exceedingly small. Since buoyancy is determined by the
ratio of volume to weight, this smallness inevitably brings with it
restrictions and compromises. The deeper a submersible goes—and
many of them go deeper than conventional submarines—the
Stronger must be the hull in order to resist the increased external
pressures. If the same materials are used in its construction, the
thickness of the hull and consequently its weight will increase with
every extension of the operating depth. Considerable research has
"
therefore gone into ways of improving the pressure hull. The results
account for the widespread use of spherical chambers, a shape
which offers the greatest known resistance to pressure, and the use
of materials with a high strength to weight ratio such _as titanium,
bre—reinforced plastics, cast glass and super—strength steels in their
construction.
A further requirement of modern submersibles is et compact
power pack. Most submersibles are electrically propelled and the
limited supplies of power which they can carry is generally reected
in their slow underwater speed; very few submersibles cruise
underwater for very long at speeds much above two knots. To
double their speed would take about eight times more power, which
with present batteries is not possible. Probably one of the best
sources of power for these low horsepower units is the silver—zinc
battery with its high energy to weight ratio. Unfortunately, this
The Last Resource
syntatic foam packing which also contains a number of aluminium
buoyancy spheres.
Alvin dives by ooding its main ballast tanks while two trim
tanks, one near the bow and the other in the stem, set the craft at a
nose—down angle of up
to about 30° to assist the dive. The trim
tanks, lled half with mercury and half with oil, are connected so
that oil pumped from the top of one tank to the top of the other
forces the heavy mercury from the bottom of that tank back into
the rst one. The two side propellers may also be used to speed up
the dive. When the mission is completed the submersible returns
towards the surface, using either or both the oil—lled bags for
additional buoyancy as well as the side—propellers. To complete its
ascent, the main ballast tanks are ‘blown’. Unfortunately, in 1968
Alvin made an unscheduled dive when it sank empty in 4,500 feet
of water.
In comparison with conventional submarines, all research submersibles (except converted submarines such as the Soviet Savary—
anka) are exceedingly small. Since buoyancy is determined by the
ratio of volume to weight, this smallness inevitably brings with it
restrictions and compromises. The deeper a submersible goes—and
many of them go deeper than conventional submarines—the
Stronger must be the hull in order to resist the increased external
pressures. If the same materials are used in its construction, the
thickness of the hull and consequently its weight will increase with
every extension of the operating depth. Considerable research has
"
therefore gone into ways of improving the pressure hull. The results
account for the widespread use of spherical chambers, a shape
which offers the greatest known resistance to pressure, and the use
of materials with a high strength to weight ratio such _as titanium,
bre—reinforced plastics, cast glass and super—strength steels in their
construction.
A further requirement of modern submersibles is et compact
power pack. Most submersibles are electrically propelled and the
limited supplies of power which they can carry is generally reected
in their slow underwater speed; very few submersibles cruise
underwater for very long at speeds much above two knots. To
double their speed would take about eight times more power, which
with present batteries is not possible. Probably one of the best
sources of power for these low horsepower units is the silver—zinc
battery with its high energy to weight ratio. Unfortunately, this