submarine hw

1. Submarines
Deepankshi Yadav
V- B
Roll No -12

2. What is a submarine?
 Submarines are a special type of watercraft that can
operate underwater.
 Then first working submarine was built in 1620 by
Cornelius Drebbel. It was propelled by oars.
 Submarines are used by the military as part of navy
forces, protecting aircraft carriers, performing
reconnaissance and carrying out other tasks.
 Submarines are also used in other areas such as
marine research, undersea exploration and salvage
missions.

3. Construction of Submarines
 Submarines are completely enclosed
vessels with cylindrical shapes,
narrowed ends and two hulls. The
inner hull protects the crew from the
immense water pressure of the ocean
depths and insulates the sub from the
freezing temperatures. This hull is
called the pressure hull. The outer hull
shapes the submarine's body. The
ballast tanks, which control the sub's
buoyancy are located between the
inner and outer hulls.
 Once the submarine is underwater, it has two controls used for steering. The
rudder controls side-to-side turning and diving / sail planes control the sub's rise
and descent.
 Submarines use ballast tanks to hold water, allowing them to submerge when
necessary
 it has a tall sail that rises out of the submarine's hull. Inside this fin-shaped sail is the
conning tower ("conn" means to direct the steering of a vessel). The periscope
and radio and radar antennas are usually extended through the conning tower.
 A periscope enables a submarine to see what is happening on the surface while
remaining underwater. Only the end of the periscope must break the water. The
periscope is made with mirrors and lenses that reflect and bend images down a
long tube to the eye of a Sailor.

4. How does it work?
 A submarine resting on the surface has positive
buoyancy, which means it is less dense than the water
around it and will float. At this time, the ballast tanks are
mainly full of air.
 To submerge, the submarine must have negative
buoyancy. Vents on top of the ballast tanks are
opened. Seawater coming in through the flood ports
forces air out the vents, and the submarine begins to
sink.
 The submarine ballast tanks now filled with seawater is
denser than the surrounding water. The exact depth
can be controlled by adjusting the water to air ratio in
the ballast tanks. Submerged, the submarine can
obtain neutral buoyancy. That means the weight of the
submarine equals the amount of water it displaces. The
submarine will neither rise nor sink in this state.
 To make the submarine rise again, compressed air is
simply blown into the tanks forcing the seawater out.
The submarine gains positive buoyancy, becomes less
dense than the water and rises.
surfaced submerging
submerged surfacing

5. Facts on submarines
 The word ‘submarine’ was first used in the 17th
as an adjective meaning ‘underwater.
 Some submarines can remain submerged for
months at a time.
 German U-boats sank more than five thousand
merchant and fishing ships during the conflict.
 The standard submarine was about two
hundred feet long and displaced several
hundred tons.
 Militaries use submarines to patrol ocean
waters and to attack enemy ships during
wartime. Military submarines are usually very
large and may carry more than 100 people.