A submersible is an underwater vehicle which needs to be transported and supported by a larger watercraft or platform. This distinguishes submersibles from submarines, which are self-supporting and capable of prolonged independent operation at sea.[1]
The first recorded self-propelled underwater vessel was a small oar-powered submarine conceived by William Bourne (c. 1535 – 1582) and designed and built by Dutch inventor Cornelis Drebbel in 1620, with two more improved versions built in the following four years.[4] Contemporary accounts state that the final model was demonstrated to King James I in person, who may even have been taken aboard for a test dive.[5][4] There do not appear to have been any further recorded submersibles until Bushnell's Turtle.
The first submersible to be used in war was designed and built by American inventor David Bushnell in 1775 as a means to attach explosive charges to enemy ships during the American Revolutionary War. The device, dubbed Bushnell's Turtle, was an oval-shaped vessel of wood and brass. It had tanks that were filled with water to make it dive and then emptied with the help of a hand pump to make it return to the surface. The operator used two hand-cranked propellers to move vertically or laterally under the water. The vehicle had small glass windows on top and naturally luminescent wood[clarification needed] affixed to its instruments so that they could be read in the dark.[citation needed]
Bushnell's Turtle was first set into action on September 7, 1776, at New York Harbor to attack the British flagship HMSEagle. Sergeant Ezra Lee operated the vehicle at that time. Lee successfully brought Turtle against the underside of Eagle's hull but failed to attach the charge because of the strong water currents.[citation needed]
Operation
Apart from size, the main technical difference between a "submersible" and a "submarine" is that submersibles are not fully autonomous and may rely on a support facility or vessel for replenishment of power and breathing gases. Submersibles typically have shorter range, and operate primarily underwater, as most have little function at the surface.[citation needed] Some submersibles operate on a "tether" or "umbilical", remaining connected to a tender (a submarine, surface vessel or platform). Submersibles have been able to dive to over 10km (33,000ft) below the surface.
Submersibles may be relatively small, hold only a small crew, and have no living facilities.
Different basic technologies used in the design of submersibles.
Atmospheric pressure
The Earth's atmosphere exerts a pressure on its surface, similar to how water exerts pressure due to its weight. Unlike water, however, the atmosphere is compressible because it is composed of gases. Consequently, the density of the atmosphere varies with height, with highest density at sea level. As a result, the maximum atmospheric pressure is experienced at sea level, gradually decreasing with increasing altitude.
To calculate atmospheric pressure, we consider the pressure exerted by a column of seawater 10 meters in height. Under average condition, the atmosphere can support such a column, resulting in an atmospheric pressure of 103,000 Newtons per square meter (N/m2).
Gauge pressure and absolute pressure When measuring gas pressures, including those experienced underwater, gauge pressure and absolute pressure are essential concepts.
Gauge pressure: A pressure gauge is typically calibrated to read zero when the gauge is at atmospheric pressure. This gauge records only the “difference of pressure” between the measured pressure and atmospheric pressure. If such a gauge is used underwater, it will indicate only the additional pressure exerted by the water. For example, if the gauge reads 120 bar, the measured pressure is actually 120 bar above atmospheric pressure, equivalent to 121 bar relative to vacuum.
Absolute pressure: At sea level the atmosphere exerts a pressure of approximately 1 bar, or 103000 n/m2. Underwater, the pressure increases by approximately 0.1 bar for every metre of depth. The total pressure at any given depth is the sum of the pressure of the water at that depth (hydrostatic pressure)and atmospheric pressure. This combined pressure is known as absolute pressure, and the relationship is:
To calculate absolute pressure, add the atmospheric pressure to the gauge pressure using the same unit. Working with depth rather than pressure may be convenient in diving calculations. In this context, atmospheric pressure is considered equivalent to a depth of 10 meters. Absolute depth (m) = gauge depth (m) + 10 m.
Depth measurement: Pressure monitoring devices
The pressure the is more important for structural and physiological reasons than linear depth. Pressure at a given depth may vary due to variations in water density.
To express the linear depth in water accurately, the measurement should be in meters (m). The unit “meters of sea water” (msw) is a by definition a unit for measurement of pressure.
Note: A change in depth of 10 meters for a change in pressure of 1 bar equates to a water density of 1012.72kg/m3[citation needed]
Single-atmosphere submersibles have a pressure hull with internal pressure maintained at surface atmospheric pressure. This requires the hull to be capable of withstanding the ambient hydrostatic pressure from the water outside, which can be many times greater than the internal pressure.
Ambient pressure submersibles maintain the same pressure both inside and outside the vessel. The interior is air-filled, at a pressure to balance the external pressure, so the hull does not have to withstand a pressure difference.
A third technology is the "wet sub", which refers to a vehicle that may or may not be enclosed, but in either case, water floods the interior, so underwater breathing equipment is used by the crew. This may be scuba carried by the divers, or a breathing gas supply carried by the vessel.
When an object is immersed in a liquid, it displaces the liquid, pushing it out of the way.
Once the object is partially immersed, pressure forces exerted on the immersed parts are equal to the weight of water displaced, Consequently, objects submerged in liquids appear to weigh less due to this buoyant force. The relationship between the amount of liquid displaced and the resulting up-thrust is known as Archimedes' principle, which states:
"when an object is wholly or partially immersed in a liquid, the up-thrust it receives is equal to the weight of the liquid displaced."[citation needed]
Buoyancy and weight determine whether an object floats or sinks in a liquid. The relative magnitudes of weight and buoyancy determine the outcome, leading to three possible scenarios.
Negative Buoyancy: when the weight of an object is greater than the up-thrust it experiences due to the weight of the liquid displaced, the object sinks.
Neutral Buoyancy: if the weight of an object equals the up-thrust, the object remains stable in its current position, neither sinking or floating.
Positive Buoyancy: when the weight of an object is less than the up-thrust, the object rises and floats. As it reaches the liquid's surface, It partly emerges from the liquid, reducing the weight of the displaced liquid and, consequently, the up-thrust. Eventually, the reduced up-thrust balances the weight of the object, allowing it to float in a state of equilibrium.
Buoyancy control
During underwater operation a submersible will generally be neutrally buoyant, but may use positive or negative buoyancy to facilitate vertical motion. Negative buoyancy may also be useful at times to settle the vessel on the bottom, and positive buoyancy is necessary to float the vessel at the surface. Fine buoyancy adjustments may be made using one or more variable buoyancy pressure vessels as trim tanks, and gross changes of buoyancy at or near the surface may use ambient pressure ballast tanks, which are fully flooded during underwater operations. Some submersibles use high density external ballast which may be released at depth in an emergency to make the vessel sufficiently buoyant to float back to the surface even if all power is lost, or to travel faster vertically.
Deep-diving crewed submersibles
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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 1,200m (3,900ft).
Some submersibles have been able to dive to great depths. The bathyscapheTrieste was the first to reach the deepest part of the ocean, nearly 11km (36,000ft) below the surface, at the bottom of the Mariana Trench in 1960.[citation needed]
China, with its Jiaolong project in 2002, was the fifth country to send a person 3,500 meters below sea level, following the US, France, Russia and Japan. On June 22, 2012, the Jiaolong submersible set a deep-diving record for state-owned vessels when the three-person sub descended 6,963 meters (22,844ft) into the Pacific Ocean.[6]
Among the most well-known and longest-in-operation submersibles is the deep-submergence research vessel DSVAlvin, which takes 3 people to depths of up to 4,500 metres (14,800ft). Alvin is owned by the United States Navy and operated by WHOI, and as of 2011 had made over 4,400 dives.[7]
James Cameron made a record-setting, crewed submersible dive to the bottom of Challenger Deep, the deepest known point of the Mariana Trench on March 26, 2012. Cameron's submersible was named Deepsea Challenger and reached a depth of 10,908 metres (35,787ft).[8]
Commercial submersibles
Private firms such as Triton Submarines, LLC. SEAmagine Hydrospace, Sub Aviator Systems (or 'SAS'), and Netherlands-based U-boat Worx have developed small submersibles for tourism, exploration and adventure travel. A Canadian company in British Columbia called Sportsub has been building personal recreational submersibles since 1986 with open-floor designs (partially flooded cockpits).[9][10][11][12]
A privately owned U.S. company, OceanGate, also participated in building submersibles, though the company fell under scrutiny when their newest submersible imploded underwater with no survivors.[13]
Small uncrewed submersibles called "marine remotely operated vehicles," (MROVs) or 'remotely operated underwater vehicles' (ROUVs) are widely used to work in water too deep or too dangerous for divers, or when it is economically advantageous.
Remotely operated vehicles (ROVs) repair offshore oil platforms and attach cables to sunken ships to hoist them. Such remotely operated vehicles are attached by an umbilical cable (a thick cable providing power and communications) to a control center on a ship. Operators on the ship see video and/or sonar images sent back from the ROV and remotely control its thrusters and manipulator arm. The wreck of the Titanic was explored by such a vehicle, as well as by a crewed vessel.[citation needed]
↑ "Human Occupied Vehicle Alvin". NDSF Vehicles. Woods Hole Oceanographic Institution. Archived from the original on 3 January 2012. Retrieved 27 November 2011.
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.
Alvin (DSV-2) is a crewed deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts. The original vehicle was built by General Mills' Electronics Group in Minneapolis, Minnesota. Named to honor the prime mover and creative inspiration for the vehicle, Allyn Vine, Alvin was commissioned on June 5, 1964.
Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.
A remotely operated underwater vehicle (ROUV) or remotely operated vehicle (ROV) is a free-swimming submersible craft used to perform underwater observation, inspection and physical tasks such as valve operations, hydraulic functions and other general tasks within the subsea oil and gas industry, military, scientific and other applications. ROVs can also carry tooling packages for undertaking specific tasks such as pull-in and connection of flexible flowlines and umbilicals, and component replacement.
An underwater environment is a environment of, and immersed in, liquid water in a natural or artificial feature, such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.
Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' principle is a law of physics fundamental to fluid mechanics. It was formulated by Archimedes of Syracuse.
Diving physics, or the physics of underwater diving is the basic aspects of physics which describe the effects of the underwater environment on the underwater diver and their equipment, and the effects of blending, compressing, and storing breathing gas mixtures, and supplying them for use at ambient pressure. These effects are mostly consequences of immersion in water, the hydrostatic pressure of depth and the effects of pressure and temperature on breathing gases. An understanding of the physics behind is useful when considering the physiological effects of diving, breathing gas planning and management, diver buoyancy control and trim, and the hazards and risks of diving.
A diving weighting system is ballast weight added to a diver or diving equipment to counteract excess buoyancy. They may be used by divers or on equipment such as diving bells, submersibles or camera housings.
A deep-submergence vehicle (DSV) is a deep-diving crewed submersible that is self-propelled. Several navies operate vehicles that can be accurately described as DSVs. DSVs are commonly divided into two types: research DSVs, which are used for exploration and surveying, and DSRVs, which are intended to be used for rescuing the crew of a sunken navy submarine, clandestine (espionage) missions, or both. DSRVs are equipped with docking chambers to allow personnel ingress and egress via a manhole.
Kaikō was a remotely operated underwater vehicle (ROV) built by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) for exploration of the deep sea. Kaikō was the second of only five vessels ever to reach the bottom of the Challenger Deep, as of 2019. Between 1995 and 2003, this 10.6 ton unmanned submersible conducted more than 250 dives, collecting 350 biological species, some of which could prove to be useful in medical and industrial applications. On 29 May 2003, Kaikō was lost at sea off the coast of Shikoku Island during Typhoon Chan-Hom, when a secondary cable connecting it to its launcher at the ocean surface broke.
The Scorpio is a brand of underwater submersible Remotely Operated Vehicle (ROV) manufactured by Perry Tritech used by sub-sea industries such as the oil industry for general operations, and by the Royal Navy and the United States Navy for submarine rescue services. Originally developed by AMETEK Straza of El Cajon, United States, they were subsequently developed by Perry Tritech. Although the design of the original Scorpio is over several decades old, it forms the basis for a current generation of Scorpio-branded ROVs. Scorpio ROVs are named in a sequence following the order of manufacture, such as "Scorpio 17" or "Scorpio 45" which refer to specific ROVs.
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of breathing gas for the occupants.
An underwater glider is a type of autonomous underwater vehicle (AUV) that employs variable-buoyancy propulsion instead of traditional propellers or thrusters. It employs variable buoyancy in a similar way to a profiling float, but unlike a float, which can move only up and down, an underwater glider is fitted with hydrofoils that allow it to glide forward while descending through the water. At a certain depth, the glider switches to positive buoyancy to climb back up and forward, and the cycle is then repeated.
Marine salvage is the process of recovering a ship and its cargo after a shipwreck or other maritime casualty. Salvage may encompass towing, lifting a vessel, or effecting repairs to a ship. Protecting the coastal environment from oil spillages or other contaminants from a modern ship can also be a motivator, as oil, cargo, and other pollutants can easily leak from a wreck.
A radio-controlled submarine is a scale model of a submarine that can be steered via radio control. The most common form are those operated by hobbyists. These can range from inexpensive toys to complex projects involving sophisticated electronics. Oceanographers and military units also operate radio-controlled submarines.
Diving equipment, or underwater diving equipment, is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
The following outline is provided as an overview of and topical guide to underwater diving:
The following index is provided as an overview of and topical guide to underwater diving:
Diving support equipment is the equipment used to facilitate a diving operation. It is either not taken into the water during the dive, such as the gas panel and compressor, or is not integral to the actual diving, being there to make the dive easier or safer, such as a surface decompression chamber. Some equipment, like a diving stage, is not easily categorised as diving or support equipment, and may be considered as either.
A variable-buoyancy pressure vessel system is a type of rigid buoyancy control device for diving systems that retains a constant volume and varies its density by changing the weight (mass) of the contents, either by moving the ambient fluid into and out of a rigid pressure vessel, or by moving a stored liquid between internal and external variable-volume containers. A pressure vessel is used to withstand the hydrostatic pressure of the underwater environment. A variable-buoyancy pressure vessel can have an internal pressure greater or less than ambient pressure, and the pressure difference can vary from positive to negative within the operational depth range, or remain either positive or negative throughout the pressure range, depending on design choices.
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