Different types and sizes of underwater vessels are used for various purposes, from defence to research and exploration. They can venture into the abysmal depths of the ocean and can stay put for hours to days. They are suitable for sustaining life inside or being unmanned. Moreover, they can be self-powered or operated by secondary modes of power.
A submarine is the most prominent type of underwater vehicle. It is a self-propelled large underwater craft of single or multiple large pressure vessels with a dedicated propulsion and supply system. However, apart from submarines, there are other underwater vehicles as well.
Types of Underwater Vehicles
Based on occupancy, underwater vehicles are classified into the following types.
- Submarines
- Submersibles
- Autonomous Underwater Vehicles (AUVs)
Submersibles are smaller underwater crafts used for various underwater operations. Most are ‘not self-propelled’ and fully or partially dependent on an external operator, facility, support vessel, or submarine. However, several submersibles are also self-propelled. They are mainly used for research and exploration, sometimes adventure and commercial purposes. As surprising as it may sound, these submersibles were the precursors to submarines as humans have explored the world under the oceans and seas for centuries.
Now, let us look at the phrase manned or unmanned. As explanatory, crewed vehicles are the ones that are capable of carrying one or many people on board. On the other hand, unmanned ones operate without human occupancy. This brings us to another declassification of submersibles as manned or unmanned.
The first manned submersible was built 400 years ago by a Dutch scientist in 1620. Since then, humankind has been experimenting with these vessels. The famous “Bushnell’s Turtle” in 1775 was the first revolutionary manned submersible design recorded in history. The hull was simply an oval-shaped pressure vessel carved out of wood and brass.
The ballasting operations for sinkage and flotation were carried out through small tanks operated by a primitive hand pump. Two simple hand-operated cranks propelled the vessel. Small windows provided a good view, while many instruments had radium luminescence coating for seeing them in the dark.
It was constructed to fit explosives in enemy ship hulls and is still considered a pioneer in the domain of underwater vehicles. Even modern, colossal, heavily armed nuclear-powered naval assault submarines are indebted to this breakthrough invention.
Modern manned submersibles are called Human Occupied Vehicles or HOVs. However, they have some unique sub-types like:
Deep-Submergence Vehicles (DSVs): They are intended for critical deep-sea operations, military, and research, carrying crew, and are self-propelled. They are designed to withstand titanic pressures and conditions at extreme depths. Moreover, they have very high endurance and range. The oldest and the most famous DSV to date is the Alvin, owned by the US Navy and operated by the Woods Hole Oceanographic Institution, and active for almost 60 years! Other than being involved in a plethora of research and exploration expeditions, it was most notably used in scouring the sunken wreckage of the Titanic. It also has three sister prototypes that feature robust titanium hulls.
Bathyscaphes: These are free-diving, deep-sea manned submersibles. Their distinguishing feature is a sizeable top hull or float. Below it is a dome-like pressurized chamber for crew members. During diving, this hull or float is filled with extra ballast water, which allows the entire vessel to sink. There are dedicated tanks in the float, which are also filled with gasoline, helping in the sinkage, but this has a more significant role at higher depths.
At greater depths, the incompressibility of gasoline enables it to withstand a large modulus of external pressures. This gasoline is entirely removed at the surface, and the ballast water is adjusted accordingly for the desired flotation. Sometimes, the float may also have spaces for using iron pellets or shots as ballast which are released during ascent.
Though they can venture to a great depth, they have a limited capability for lateral movement. A small propeller or a fan is placed atop the float. The inherent tendency of lateral movement due to underwater currents helps move up to a few meters within the site of interest. They are often towed to the launch point at the surface using guide ropes or towing lines.
They are considered advanced improvements over Bathyspheres, unpowered and primitive vessels used for deep-sea explorations in earlier days.
Unmanned Submersibles are smaller as they do not carry a crew. Remotely Operated Underwater Vehicles ROVs are the most common types of unmanned submersibles. They operate from the surface or shore using tether lines or cables. Power cables or chords connected to the control point supply electricity to the vessel. Depending on the configuration, they can operate at various depths and move at all degrees without any problem, accounting for their flexibility.
Autonomous Underwater Vehicles or AUVs are essentially the same as ROVs with one significant difference, control. As the name suggests, they can move independently without cables or tethering along with a time-to-time direct user control mode. They run on systems pre-programmed by the operator.
So, instead of conventional submersibles, they are more like unmanned, autonomous, underwater robots that can propel themselves. They are considered a massive breakthrough for research and military applications over the last few years. Sizes are highly variable, ranging from the size of a portable gas cylinder to larger ones measuring 10 to 20 meters.
The carrying capacity of an Autonomous Underwater Vehicle (AUV) is directly related to its size and is determined by its payload capacity.
There are different types of submersibles based on their designs:
1. Single atmosphere submersibles: These have a single pressurized hull that is both watertight and airtight, allowing the crew to be maintained under atmospheric conditions. These submersibles need to withstand high external hydrostatic pressure while maintaining lower internal pressure, making them complex and expensive to design and build.
2. Equal pressure submersibles: These maintain equal pressure internally and externally, resulting in lower net pressure on the hull. They are designed with simpler configurations compared to single atmosphere submersibles.
3. Wet Sub: In this configuration, the vessel is partially exposed to water, with specific equipment and systems enclosed. Occupants are exposed to the marine environment, requiring SCUBA equipment and breathing apparatus similar to deep-sea divers.
Submarines are the most advanced underwater vehicles and come in various types:
– U-Boats: Developed during the World Wars, U-boats were crucial components of naval warfare. They had a unique design resembling ships and could operate both on the surface and underwater.
– Midget Submarines: Small submarines used for military purposes, carrying a limited crew and capable of launching torpedoes, bombs, and mines.
– Human Torpedoes: Small submarines with a single diver or operator for launching torpedoes. They were popular during the world wars but phased out with the development of larger submarines.
– Conventional Submarines: Symmetrical, cylindrical, self-propelled vehicles used for military and commercial purposes.
Modern submarines can be categorized based on propulsion systems, such as conventional diesel, diesel-electric, nuclear, air-independent, and steam-powered submarines. Submarines can also be classified based on their utility, including naval/defense, commercial, civilian, and research purposes.
Overall, submarines provide a unique underwater experience, with different types and designs catering to various applications and requirements. With the following content: