Submersible

A submersible is a small craft.

It needs a big ship to carry it. It cannot stay at sea alone.

Some have people inside. Others are robots with no people.

They go very deep. They can see the bottom of the sea.

They can also fix things. They help find old ships.

It is a way to explore the deep blue water.

A submersible is a special underwater vehicle. It is not the same as a submarine. A submarine can stay at sea for a long time. A submersible needs a large ship to carry it. It also needs a ship to give it power.

Some submersibles have people inside. We call these human-occupied vehicles, or HOVs. Other submersibles are robots. These are called remotely operated vehicles, or ROVs. An ROV stays connected to a ship by a thick cable. This cable is called an umbilical. It gives the robot power and sends video back to the ship.

Submersibles use buoyancy to move up and down. Buoyancy is a force that pushes up on things in water. If a craft is heavy, it sinks. If it is light, it floats. Most submersibles try to stay in the middle. This is called neutral buoyancy.

These tools help us explore the deep ocean. They can find old shipwrecks. They can also fix things on the sea floor. Some can even dive to the very bottom of the ocean.

A submersible is a special vehicle used to travel under the water. It is different from a submarine. A submarine can travel alone for a long time. A submersible needs a larger ship to carry it and support it. It often needs that ship to provide power or breathing gases. Some submersibles carry people inside. These are called human-occupied vehicles, or HOVs. Other submersibles are robots. These are called remotely operated vehicles, or ROVs. They stay connected to a ship by a thick cable called an umbilical. This cable sends power and video back to the crew on the ship.

Submersibles move up and down using a way it works called buoyancy. Buoyancy is an upward push from the water. To go down, a craft must have negative buoyancy. This means the craft is heavier than the water it pushes away. To go up, it needs positive buoyancy. This means the craft is lighter than the water it pushes away. Most submersibles try to stay in the middle. This is called neutral buoyancy.

They can use tanks to change their weight. They can also use heavy weights that they drop to float up fast.

People have been building underwater vessels for a long time. In 1620, an inventor named Cornelis Drebbel built a model. It was powered by oars. Later, David Bushnell built a vessel called the Turtle in 1775. It was made of wood and brass. It used hand pumps to move up and down. It even had small glass windows. Sergeant Ezra Lee used it in New York Harbor in 1776. He tried to use it during the American Revolutionary War.

Exploring the deep ocean is a very big job. The bathyscaphe Trieste was the first to reach the bottom of the Mariana Trench in 1960. In 2012, James Cameron used the Deepsea Challenger to reach the bottom of the Challenger Deep. Another vessel called the Limiting Factor has visited the deepest points in all five oceans. This craft was made by Triton Submarines. It cost $37 million to build. It has helped people find old shipwrecks in the Philippine Trench.

Submersibles help us learn about the world in many ways. Scientists use them for oceanography to study the sea. They also use them for underwater archaeology to find old things. Some submersibles are used for tourism so people can see the ocean. Others are used to fix equipment on the sea floor. Even robots like ROVs help by repairing oil platforms. They can even look at the wreck of the Titanic. These machines let us see places that are too deep for humans to swim.

A submersible is an underwater vehicle designed for specialized tasks beneath the sea. It is important to distinguish a submersible from a submarine. A submarine is a self-supporting vessel capable of long, independent operations at sea. In contrast, a submersible requires a larger watercraft or platform for transport and support. These support vessels often provide essential resources like power or breathing gases.

Because they rely on external support, submersibles typically have a shorter operational range. They are designed to function primarily underwater rather than on the surface.

Submersibles are categorized by how they are operated and whether they carry people. Human-occupied vehicles, or HOVs, allow a small crew to travel inside the craft. These vessels may be small and lack living facilities for long stays. Other types are uncrewed, such as remotely operated vehicles (ROVs) or unmanned underwater vehicles (UUVs). An ROV is often connected to a surface ship by an umbilical. This umbilical is a thick cable that provides power and communication. Operators on the ship use this connection to see sonar or video images.

Autonomous underwater vehicles (AUVs) are a different type of uncrewed system. These are robots that travel through the water without continuous input from an operator.

Moving through the water requires mastering the physics of buoyancy. Buoyancy is the upward force, or up-thrust, that a liquid exerts on an object. According to Archimedes' principle, this up-thrust equals the weight of the liquid the object displaces. Submersibles manage three states of buoyancy to control their depth. Negative buoyancy occurs when the vehicle's weight is greater than the up-thrust, causing it to sink. Positive buoyancy happens when the vehicle is lighter than the displaced water, causing it to rise. Most submersibles aim for neutral buoyancy, where weight and up-thrust are equal. This allows the craft to remain stable at a specific depth.

To control these states, engineers use several technical systems. Pilots use variable buoyancy pressure vessels, known as trim tanks, for fine adjustments. For larger changes near the surface, they use ambient pressure ballast tanks. These tanks are fully flooded during underwater operations. Some submersibles also carry high-density external ballast. This can be released in an emergency to help the vessel float back to the surface quickly. For movement, many crafts use marine thrusters or pump-jets. These provide agile mobility and allow the use of manipulator arms. These arms are dexterous tools that the crew can use to handle objects on the sea floor.

Operating at great depths also requires managing extreme absolute pressure. Absolute pressure is the sum of the water's weight, called hydrostatic pressure, and the atmospheric pressure above. At sea level, the atmosphere exerts about 1 bar of pressure. For every meter of depth, the pressure increases by approximately 0.1 bar. To protect the crew, engineers design different types of pressure hulls. Single-atmosphere submersibles maintain internal pressure at surface levels. This requires a very strong hull to withstand the massive external pressure. Ambient pressure submersibles maintain the same pressure inside and outside the vessel. A third type is a "wet sub," where water floods the interior and the crew uses breathing equipment.

The history of underwater travel began with early, simple designs. In 1620, Dutch inventor Cornelis Drebbel built an oar-powered vessel. Later, in 1775, American inventor David Bushnell created the Turtle. This was the first submersible used in war during the American Revolutionary War. The Turtle was made of wood and brass and used hand-cranked propellers. It featured tanks that filled with water to dive and emptied with a hand pump to surface. On September 7, 1776, Sergeant Ezra Lee operated the Turtle in New York Harbor. He attempted to attach explosive charges to a British ship, but strong currents prevented him from finishing the task.

Modern exploration has reached the most extreme points on Earth. The bathyscaphe Trieste was the first to reach the bottom of the Mariana Trench in 1960. In 2012, James Cameron reached the Challenger Deep using the Deepsea Challenger. Another notable vessel is the DSV Limiting Factor, manufactured by Triton Submarines. This craft was commissioned for $37 million and has visited the deepest points in all five oceans. It has also been used to find shipwrecks in the Philippine Trench at depths of 7,200 and 7,300 meters. Today, submersibles are vital for oceanography, archaeology, tourism, and repairing offshore equipment like oil platforms.