Design and Development of Submarine, Suitable Options for Bangladesh Navy

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Introduction

The idea of
travelling underneath the ocean waters inside a closed vessel has been around
for centuries. Some history says, Alexander the Great ventured below the waters
of the Aegean Sea inside a glass barrel around 333 B.C. The next record of a
submarine came more than 1900 years later. In 1578 AD British naval officer
William Bourne described a wooden frame vessel enclosed in waterproof leather;
which was rowed underwater. C Drebbel, a Dutchman patented his submarine, which
was bound by waterproof leather, invented in 1598, was powered by oars allowing
it to be rowed underwater and air was provided by tubes. His boat was
successfully tested in the Thames River and travelled at depths about 5 meters.
In 1904, the French built the Aigrette, the first submarine to use a gas engine
on the surface and an electric engine below. The US followed in 1911 with the
F-class Skipjack submarine. It was powered by diesel instead°ef gas engines.
During First World War (WWI), Germans and their U-boats proved the worth of the
submarine in the war theater. Germany was successful in submarine operation for
the sinking of 11 million gross tons of Allied ships. In 1938, Auguste Piccard
built his record- setting bathyscaphe Trieste. This 50-foot-long submarine
still holds the record for deepest dive, about 12,000 meters deep in the south
Pacific’s Marianas Trench.

Technology of Submarine

Submarines are
completely enclosed vessels with cylindrical shapes, narrowed ends and uspally
two hulls. The inner or pressure hull protects the crew from the immense water
pressure of the ocean depths and insulates the vessel from the freezing
temperature. The outer hull shapes the submarine’s body. The ballast tanks,
which control the submarine’s buoyancy, are located between the inner and outer
hulls. Modern nuclear and electric submarines are of single hull. Stability and
other submarine’s buoyancy are controlled by ballast tanks. Submarine’s size
& position are calculated by design technology. To stay in control and
stability, a submerged submarine must maintain a condition known as trim. It
means submarine’s weight must be perfectly balanced throughout the whole body.
Two trim tanks forward and aft help the submarine keep the accurate trim by
either added or expelled water from them as needed.

Once the submarine
is underwater, it has two controls mechanism used for steering. The rudder
controls side-to-side turning, or yaw. On the other hand diving planes, control
the submarine’s rise and descent, or pitch. There are two sets of diving
planes. The sail planes and the stern planes. Some modem submarines, like
Virginia class of US Navy (the latest nuclear submarines), make use of bow rather
than sail planes. In the above figure of a submarine, 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, radio and radar antennas are usually extended through the conning
tower. In the early days, submarine was operated from conning tower. A
periscope enables a submarine to see what is happening on the surface while
remaining underwater. With the advances in technology, the entire look and
operation of submarines change. In Virginia-class submarine, a series of
mirrors and lens are used to view above the surface where colour cameras send
visual images to large screen displayed in the ship’s control room.

Working Principles of Submarine To function underwater, submarines are built a bit differently than surface ships that float on water. To travel under the water, the submarines must be signed with certain basic laws of nature, including Archimedes’ policies and age laws. Whether a submarine is floating or submerging; Depending on the buoyancy of the ship. Buoyancy of submarine is controlled by the ballast tanks which are found between the submarine’s inner and outer hulls or some special arrangement of ballast tanks. The submarine resting on the surface has positive buoyancy. It means it is less dense than the water around it and subsequently will float. At that time, the ballast tanks are mainly full of air. To submerge the submarine, it must have negative buoyancy. Vents above the belt tank are open. Through the flood ports the wind blows in the sea and the submarine begins to sink. For the rebirth of the submarine, the compressed air simply forced the beach to be broken into pieces. To keep the submarine upright, her metacentric height remains positive.

History of Submarine Development

Initially,
submarines depended on human’s energy to move. Submarine designed by Drebbel was
tested on the Thames River in 1620 and carried the King of England on one of
its dives. It used oars to move itself along. In the mid-1770s, David Bushnell
built a submarine Turtle that used hand and foot cranks for propulsion. This
one-person submarine was the first used in war and exhausted its operator
within a few minutes. It was the first to use diving planes to control depth. But,
due to the large and bulky size of the boiler, he failed. In the 1860s, the
Confederates built steam-powered submarines and were never completely
submerged. The first submarine in the US Navy, the USS Holland, used a gasoline
engine while on the surface and an electric engine while submerged. The
electric engine could recharge while the gasoline engine was being used. The
electric engine allowed the submarine to travel underwater for a few hours, at
a decent speed. The engine was relatively small, but the batteries were large,
bulky and heavy. Finally, steam and gasoline engines were phased out by
less-volatile diesel engines. In 1904, the French became the first to build a
submarine Aigrette, which used a diesel engine on surface and an electric
engine while underwater. The US followed the trend building its first
diesel-powered submarine, the F-class Skipjack, in 1911.

These two
innovations gave submarines the ability to remain submerged for weeks or
months, and enabled impossible voyages such as USS Nautilus’ crossing of the
North pole beneath the Arctic ice cap in 1958. Most of the naval submarines
built since 1960s in the US and the USSR/Russia have been powered by nuclear
reactors. The limiting factors in submerged endurance for these submarines are
logistic supply and crew morale. In 1959, the first ballistic missile
submarines were put into service by both super powers as part of the Cold War
nuclear deterrent strategy.

Use of Submarine

Submarines were
first widely used during World War I (1914-1918). Now- a-days, Military usage
includes attacking enemy surface ships or submarines, aircraft carrier
protection, blockade running, ballistic missile submarines as part of a nuclear
strike force, reconnaissance, conventional land attack (by using a cruise
missile), and covert insertion of special forces. Commercial/ civil uses for
submarines include marine science, salvage, exploration and facility inspection/maintenance
etc. Submarines can also be modified to perform more special functions such as
search-and-rescue missions or undersable cable repair. Submarines are also used
for tourism and underwear archeology.

Modem submarines are cigar-shaped, sometimes called a “teardrop hull”. It reduces the hydrodynamic drag when submerged; but decreases the sea-keeping capabilities and increases drag while surfaced. Since the limitations of the propulsion systems of early submarines, their hull designs were compromised. Late in WWII, when technology allowed faster and longer submerged operation, hull designs became teardrop shape to reduce drag and noise. Today, in a modem military submarine, the outer hull is covered with a layer of sound-absorbing rubber, or anechoic plating, to improve stealth capacity. Usually the pressure hulls of deep diving submarines are spherical instead of cylindrical. This allows a more even distribution of stress over the hull at the great depth. All post WWII; Soviet/Russian heavy submarines are built with a double hull structure. American and most other Western submarines switched to a single-hull approach. They still have light hull sections in the bow and stem, which house main ballast tanks and provide a hydro-dynamically optimized shape. But the main cylindrical hull section has only a single plating layer. The double hulls are being considered for future submarines in the US to improve payload capacity, stealth and range. Picture shown below is the nuclear submarine USS Greeneville in dry dock.

The submarine hull
usually known as pressure hull is generally constructed of thick high strength
steel with a complex structure. WWI submarines had hulls of carbon steel, with
a 100-metre maximum depth. During WWII, high-strength alloyed steel was
introduced, allowing 200-metre depths. High-strength alloy steel remains the
primary material for submarines today. To exceed that limit, a few submarines
were built with titanium hulls. Titanium can be stronger than steel, lighter,
and is not ferromagnetic. Titanium alloys allow a major increase in depth and a
Russian Alfa-class submarine successfully operated at 1,300 meters. However,
the high cost of titanium construction led to the abandonment of titanium
submarine construction as the Cold War ended.

Power and Propulsion

First submarines
were human propelled. The first mechanically driven submarine was French
Plongeur in 1863,that used series for slow speed and in parallel for high
speed. During the WW II, German Type XXI submarines were designed to carry
hydrogen peroxide for long-term, fast air-independent propulsion (AIP). Today
several navies use AIP. Notably Sweden uses Stirling technology, where engine
is heated by burning diesel fuel with liquid oxygen from cryogenic tanks.
British Vanguard class submarine uses pump- jet propulsion instead of
propellers.

Weapons and Armament

The success of
submarine is directly linked to the development of the torpedo, invented by
Robert Whitehead in 1866. His invention is essentially the same now as it was
140 years ago. To increase combat endurance most WWI submarines functioned as
submersible gunboats, using their deck guns against unarmed targets. With the
arrival of ASW aircraft, guns became more for defense than attack. The ability
of submarines to approach enemy harburs covertly led to their use as
minelayers. Modern submarine-laid mines are designed to be deployed by a
submarine’s torpedo tubes. After WWII, both the US and the USSR experimented
submarine that launched cruise missiles and anti-ship missiles such as Exocet
and Harpoon. Ballistic missiles can also be fired from a submarine’s torpedo
tubes, such as Tomahawk. Germany is working on the short-range IDAS (missile)
which is launched from a torpedo tube and can be used against ASW helicopters
as well as surface ships and coastal targets.

Sensors and Communication

A submarine will
have a variety of sensors determined by its missions. Modern military
submarines rely almost entirely on a suite of passive and active sonar to find
their enemy. Active sonar relies on an audible “ping” to generate
echoes to reveal objects around the submarine. Passive sonar is a set of
sensitive hydrophones set into the hull or trailed in a towed array, generally
several hundred feet long. Hull mounted sonar is employed to back up the towed
array, and in confined waters. Submarines also cany radar equipment for
detection of surface ships and aircraft. Commercial submarines rely on small
active sonar sets and viewing ports to navigate. Military submarines have
several systems for communicating with distant command centres or other ships,
such as; VLF (Very Low Frequency) radio for shallow depth and ELF (Extremely
Low Frequency) for greater depths. To communicate with other submarines a sonar
telephone is used.

Crew and Navigation

Typical nuclear
submarines have 80 to 120 crew. Non-nuclear or diesel-electric or AIP submarine
typically have 20 to 30 crews. The conditions on a submarine can be difficult
because crew members must work in isolation for long periods of time without
family contact. Submarines normally maintain radio silence to avoid detection.
Operating a submarine is dangerous, even in peacetime and many submarines have
been lost in accidents. Submarine crew need dedication, strong will power and
good team work. Staying, eating, sleeping and all other day to day activities
by the crew in a submarine are highly organized and systematic. Unnecessary
movement and making noise by the crew of a submarine is highly restricted.
Early submarines had a few navigation aids. But modern submarines have a
variety of navigation equipment. Modern military submarines use an inertial
guidance system for navigation while submerged, but drift error unavoidably
builds up over time. To counted this, the Global Positioning System is
occasionally used to obtain an accurate position.

The periscope allowing a view to the surface is only used occasionally in modem submarines. The most modem submarines have photonics masts rather than hull-penetrating optical periscopes. These masts must still be hoisted above the surface, and employ electronic sensors for visible light, infrared, laser range- finding, and electromagnetic surveillance. The most benefit to hoisting the mast above the surface is that while the mast is above the water, the entire submarine is still below the water and is much harder to detect visually or by radar or by ASW helicopter.

System and Support

With nuclear power,
submarines can remain submerged for months at a time. Diesel submarines must
periodically resurface or snorkel to recharge their batteries. The most modem
military submarines generate breathing oxygen by electrolysis of water. Fresh
water is produced by either an evaporator or a reverse osmosis unit. The
primary use for fresh water is to provide feed water for the reactor and steam
propulsion plants. It is also available for showers, sinks, cooking and
cleaning purpose. Seawater is used to flush toilets, and the resulting
“black water” is stored in a sanitary tank until it is blown
overboard by using a special sanitary pump. Water from showers and sinks is
stored separately in “grey water” tanks, which are pumped overboard
by using the drain pump.

Conclusion

Submarines have one of the largest ranges of
capabilities in any vessel, ranging from small autonomous (one- or two-person)
vessels operating for a few hours, to vessels which can remain submerged for 6
months such as the Russian Typhoon class (the biggest submarines ever built in
history). A conventional submarine operating on batteries is almost completely
silent, leaving only the noise from crew activity. AIP submarines, conventional
diesel-electric submarines with some kind of auxiliary air-independent
electricity generator become more popular as military arsenal. Commercial
submarines usually rely only on batteries. Diesel-electric submarines have a
stealth advantage over their nuclear counterparts. Some nuclear submarines such
as the American Ohio class can operate with their reactor coolant pumps
secured, making them quieter than electric submarine. Escape suits can be used
by the crew to abandon the submarine while in accident. Submarine is a costly
affairs and its operation is extremely challenging and courageous. But military
submarine is the worthy naval asset to deter any potential enemy with any
capacity.

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