Submersible facts for kids

A submersible is a special kind of underwater vehicle. Unlike a submarine, which can travel long distances on its own, a submersible usually needs a bigger ship or platform to carry it and help it operate. Think of it like a small car that needs a big truck to get it to its starting point.

Submersibles come in many forms. Some are designed for people to ride inside, called Human-Occupied Vehicles (HOVs). Others are uncrewed, meaning no one is inside them. These are often called remotely operated vehicles (ROVs) or unmanned underwater vehicles (UUVs).

People use submersibles for many different jobs. They help scientists study the ocean (oceanography), explore old shipwrecks (underwater archaeology), and discover new parts of the deep sea. They are also used for tourism, fixing equipment underwater, finding and bringing up lost items, and even filming underwater.

History of Underwater Vehicles

The idea of traveling underwater is very old! The first recorded self-propelled underwater vessel was designed by a Dutch inventor named Cornelis Drebbel in 1620. He built a small boat that could be moved by oars underwater. He even showed it to King James I, who might have even gone for a test dive!

Later, during the American Revolutionary War in 1775, an American inventor named David Bushnell created the first submersible used in war. It was called Bushnell's Turtle. This oval-shaped vessel was made of wood and brass. It could dive by filling tanks with water and surface by pumping the water out. The operator used hand cranks to move it up, down, or sideways. It even had small glass windows and special glowing wood to help the operator see the instruments in the dark.

The Turtle was first used on September 7, 1776, in New York Harbor. Its mission was to attach explosives to a British warship called the HMS Eagle. Sergeant Ezra Lee operated the Turtle and managed to reach the Eagle's hull. However, strong water currents prevented him from attaching the explosive device.

How Submersibles Work

Retired modern submersible Star III of Scripps Institution of Oceanography

The main difference between a submersible and a submarine is that submersibles are not fully independent. They often need a support ship to provide power, breathing gases, and other supplies. Submersibles usually have a shorter range and spend most of their time underwater, as they don't work very well on the surface. Some submersibles stay connected to a support ship by a "tether" or "umbilical" cable, which provides power and communication.

Submersibles can dive incredibly deep, some going more than 10 kilometers (about 6 miles) below the surface! They are usually quite small, holding only a few people, and don't have living areas like larger submarines.

Many submersibles have excellent movement abilities. They use propellers or special water jets to move precisely in any direction.

Understanding Pressure and Buoyancy

When you go deep underwater, the water pushes on the submersible with a lot of force. This force is called pressure. The deeper you go, the greater the pressure.

Dealing with Pressure

There are different ways submersibles are built to handle this pressure:

• Single-atmosphere submersibles: These have a very strong outer shell, called a pressure hull. Inside this hull, the air pressure stays the same as it is on the surface. This means the hull must be strong enough to resist the huge pressure from the water outside.
• Ambient pressure submersibles: In these submersibles, the pressure inside is kept the same as the pressure outside. This means the hull doesn't have to withstand a big difference in pressure. The inside is filled with air at a very high pressure, matching the water pressure outside.
• Wet subs: These vehicles might be open or enclosed, but water fills the inside. The crew wears scuba gear or uses a breathing gas supply from the vessel to breathe underwater.

Buoyancy: Floating or Sinking

Ictineu 3 is a crewed submersible with a large semi-spheric acrylic glass viewport and is capable of reaching depths of 1,200 meters (3,900 feet).

When an object is placed in water, it pushes some of the water out of the way. The water pushes back with an upward force called buoyancy. This idea is explained by Archimedes' principle, which says that the upward push an object gets is equal to the weight of the water it pushes aside.

Buoyancy and the object's weight decide if it floats or sinks:

• Negative Buoyancy: If the object's weight is more than the upward push from the water, it will sink.
• Neutral Buoyancy: If the object's weight is equal to the upward push, it will stay at the same level in the water, neither sinking nor floating.
• Positive Buoyancy: If the object's weight is less than the upward push, it will rise and float on the surface.

Controlling Buoyancy

To move up and down underwater, submersibles need to control their buoyancy.

• When operating underwater, a submersible is usually neutrally buoyant, meaning it's balanced and can stay at a certain depth.
• To go down, it can become negatively buoyant.
• To go up, it can become positively buoyant.

Submersibles use special tanks called trim tanks to make small adjustments to their buoyancy. For bigger changes, especially near the surface, they use ballast tanks. These tanks are filled with water to make the submersible heavier (negative buoyancy) and emptied to make it lighter (positive buoyancy). Some submersibles even carry heavy weights that can be dropped in an emergency. If all power is lost, dropping these weights makes the submersible light enough to float back to the surface.

Deep-Diving Crewed Submersibles

Some submersibles are built to go to the very deepest parts of the ocean.

• The bathyscaphe Trieste was the first to reach the deepest known part of the ocean, the bottom of the Mariana Trench, in 1960. It went almost 11 kilometers (about 6.8 miles) down!

• China developed the Jiaolong submersible. In 2012, it set a deep-diving record for government-owned vessels, going down 6,965 meters (22,844 feet) into the Pacific Ocean.

• One of the most famous and long-serving submersibles is the Alvin. It can carry three people and dive to depths of up to 4,500 meters (14,764 feet). The United States Navy owns Alvin, and it has made thousands of dives since it started operating.

• In 2012, filmmaker James Cameron made a record-setting dive to the bottom of the Challenger Deep, also in the Mariana Trench. His submersible, named Deepsea Challenger, reached a depth of 10,908 meters (35,787 feet).

Commercial Submersibles

Many private companies build small submersibles for different purposes, like tourism, exploration, and adventure travel. Companies like Triton Submarines and U-boat Worx create these vehicles. There are even companies that build personal submersibles for recreation.

One company, OceanGate, also built submersibles. However, their newest submersible, the Titan, sadly experienced an implosion underwater in 2023, and there were no survivors.

Marine Remotely Operated Vehicles (ROVs)

Small uncrewed submersibles are called "marine remotely operated vehicles" (MROVs) or "remotely operated underwater vehicles" (ROUVs). These are used a lot for jobs in water that is too deep or too dangerous for human divers, or when it's simply cheaper to use a machine.

ROVs are often used to repair offshore oil platforms and attach cables to sunken ships to help lift them. These ROVs are connected to a control center on a ship by a thick cable called an umbilical cable. This cable provides power and allows the operators on the ship to see video and sonar images from the ROV. They can then control its thrusters and robotic arms from far away. For example, the famous wreck of the Titanic was explored by both crewed submersibles and ROVs.

Images for kids

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  Retired modern submersible Star III of Scripps Institution of Oceanography

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  Ictineu 3 is a crewed submersible with a large semi-spheric acrylic glass viewport and is capable of reaching depths of 1,200 meters (3,900 feet).

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