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Underwater search and recovery is the process of locating and recovering underwater objects, often by divers, but also by the use of submersibles, remotely operated vehicles and electronic equipment on surface vessels. Most underwater search and recovery is done by

professional divers A professional is a member of a profession or any person who works in a specified professional activity. The term also describes the standards of education and training that prepare members of the profession with the particular knowledge and skil ...

as part of commercial

marine salvage Marine salvage is the process of recovering a ship and its cargo after a shipwreck or other maritime casualty. Salvage may encompass towing, re-floating a vessel, or effecting repairs to a ship. Today, protecting the coastal environment from s ...

operations, military operations, emergency services, or law enforcement activities. Minor aspects of search and recovery are also considered within the scope of recreational diving.

Professional search and recovery

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The scope of professional search and recovery includes the following applications: *Marine archeology - search for artifacts of historical interest and importance, and where applicable the recovery of such artifacts for study. *Marine salvage - search for lost material of value and recovery thereof *Environmental protection - search for environmentally undesirable material and disposal thereof *Forensic S&R - search for and recovery of material relevant to police investigations *Emergency S&R - Search for and recovery of victims of accidents and disasters *Military S&R - Search and recovery related to military operations and material *Scientific S&R - search for objects of scientific interest, recovery of instrumentation and samples

Recreational search and recovery

Search and recovery diving is also frequently undertaken as part of

recreational diving Recreational diving or sport diving is diving for the purpose of leisure and enjoyment, usually when using scuba equipment. The term "recreational diving" may also be used in contradistinction to "technical diving", a more demanding aspect of ...

, and most diver training organisations have dedicated training courses on the subject. Search and recovery is generally considered a more hazardous speciality diving course.For example, PADI regards search and recovery as one of only three speciality which require the student to already be certified as an Advanced Open Water Diver before commencing (the other two being

ice diving Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...

and

cave diving Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other ...

, both of which are considered highly hazardous

/ref> Underwater search and recovery used to form a mandatory component of the

Advanced Open Water Diver Advanced Open Water Diver (AOWD) is a recreational scuba diving certification level provided by several diver training agencies. Agencies offering this level of training under this title include Professional Association of Diving Instructors (PADI ...

training course for many North American diver training agencies,For example, it was a mandatory part of the PADI Advanced Open Water Diver course until 1989 which, in addition to learning basic search and recover skills, also assisted in teaching students to cope with

task loading In underwater diving, task load indicates the degree of difficulty experienced when performing a task, and task loading describes the accumulation of tasks that are necessary to perform an operation. A light task loading can be managed by the opera ...

. Although the scale, value and equipment used in commercial and recreational search and recovery are enormously different, the basic premise remains the same in each case.

Search

Diver search

Underwater searches, much like above water searches, are designed around specific search patterns. The most common forms of underwater search patterns are: *

Circular search Underwater searches are procedures to find a known or suspected target object or objects in a specified search area under water. They may be carried out underwater by divers, manned submersibles, remotely operated underwater vehicles, or autonomous ...

* Jackstay search * Expanding square search * "U" pattern search The patterns are usually performed by divers in pairs or teams below the water, but they can also be conducted by use of a tender who may be a

snorkeller Snorkeling ( British and Commonwealth English spelling: snorkelling) is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped breathing tube called a snorkel, and usually swimfins. In cooler waters, ...

at the surface, a person on a towing boat, or a person located on the shore. In simple search operations, the patterns will usually be conducted by the divers simply looking visually for the object. In more sophisticated search operations, underwater

magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...

s or hand held

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...

may be used.

Types

US Navy 100708-N-4776G-203 Explosive Ordnance Disposal Technician 3rd Class Jonathan Sokol conducts training on a AN-PQS 2A hand held sonar

Diver training traditionally divides searches into two categories, ''specific'' and ''non-specific''. A ''specific'' search is an attempt to locate a known object in a known area where it was believed to be lost even if the time period is undefined, and the search terminates upon the location of the object. The classic example of this would be an item lost overboard from a boat, which needs to be recovered. A ''non-specific'' search is a search for either a type of object or anything valuable within the dive locale. The discovery of a relevant object does not usually terminate the search until the entire search area has been covered, or the search terminates early for other reasons (air supply, no decompression limits, etc.).

ROV searches

Searches using non-visual methods

* A

is a device that measures

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

magnetic dipole moment In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnet ...

. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. Magnetometers can be used as

metal detector A metal detector is an instrument that detects the nearby presence of metal. Metal detectors are useful for finding metal objects on the surface, underground, and under water. The unit itself, consist of a control box, and an adjustable shaft, ...

s: they can detect only magnetic (

ferrous In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...

) metals, but can detect such metals at a much greater distance than conventional metal detectors which rely on conductivity; they are capable of detecting large ferrous objects over considerable distances. *

Side-scan sonar Side-scan sonar (also sometimes called side scan sonar, sidescan sonar, side imaging sonar, side-imaging sonar and bottom classification sonar) is a category of sonar system that is used to efficiently create an image of large areas of the se ...

dragline A dragline excavator is a piece of heavy equipment used in civil engineering and surface mining. Draglines fall into two broad categories: those that are based on standard, lifting cranes, and the heavy units which have to be built on-site. ...

is a line which is towed ether across the bottom, or at a depth controlled by floats and weights, or hydrodynamically, by paravanes or otter-boards, that is intended to snag the target, indicating its position. * Cadaver dogs

Recovery

Recovery techniques depend upon the type and size of the object. Smaller objects, such as a coin or camera, can simply be carried up by the diver. Training agencies vary in what they specify to be the maximum weight that can be safely carried up unassisted, but normally the limit is set around . Anything heavier represents a material change to the diver's buoyancy control, and may put the diver at risk from an uncontrolled ascent if contact with the object is lost during ascent. Medium-sized objects are normally recovered using a lifting bag, and students are trained in lifting bag technique. The most common hazard is entanglement with lines whilst filling the lifting bag from the diver's

alternate air source In underwater diving, an alternative air source, or more generally alternative breathing gas source, is a secondary supply of air or other breathing gas for use by the diver in an emergency. Examples include an auxiliary Diving regulator#Demand ...

. This risk, when coupled with the possibility of rapid ascent following the freeing of the object from suction caused by it resting upon the

sea bed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most ...

, can seriously compromise the safety of the recovery team if done improperly. Lift bags can be rated up to several tons, but these are beyond the capacity of most recreational divers. A cubic metre of air per tonne at ambient hydrostatic pressure is needed. This is not practicable for cylinders carried by the diver (the most common scuba cylinder size has a total capacity of at surface pressure.) Significantly larger objects usually require specialised commercial

lifting equipment Lifting equipment, also known as lifting gear, is a general term for any equipment that can be used to lift and lower loads. Types of lifting equipment include heavy machinery such as the patient lift, overhead cranes, forklifts, jacks, buildin ...

, either a winch attached to a boat or platform, or specialised equipment to seal and inflate sunken vessels.

References

Footnotes

{{Underwater diving, prodiv Underwater diving procedures Emergency services