Underwater search and recovery

Underwater search and recovery is the process of locating and recovering underwater objects by divers.cite book |author=PADI |title=PADI Search & Recovery manual. ASIN: B000YPP84E |year=2003 |publisher=PADI |location=United States |isbn= | ] Although most underwater search and recovery is done by commercial divers as part of professional marine salvage operations, search and recovery diving is also frequently undertaken as part of recreational diving, and most diver training organisations have dedicated training courses on the subject. Search and recovery is generally considered a more hazarous 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 and cave diving, both of which are considered highly hazardous). [http://www.padi.com/padi/en/kd/searchandrecovery.aspx] ]

Underwater search and recovery used to form a mandatory component of the Advanced Open Water Diver 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.

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.

earch

Underwater searches, much like above water searches, are designed around specific search patterns. The most common forms of underwater search patterns are:
* Circular search
* 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 is either a snorkeller 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 magnometers or hand held sonar may be used.

Types

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, 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. Usually 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.). The classic example of this would be an archaelogical search, say, for dinosaur bones in a river bed known for them.

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 15 pounds. Anything heavier represents a material change to the diver's bouyancy 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 used with 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. This risk, when, controlled with the possibilty of rapid ascent following the freeing of the object from suction caused by it resting upon the sea bed can seriously compromise the safety of the recovery team if done improperly. Lift bags can be rated up to 200 pounds.

Significantly larger objects usually require specialised commercial lifting equipment, either a winch attached to a boat or platform, or specialised equipment to seal and inflate sunken vessels.

See also

* Underwater navigation
* Underwater archaeology

References

Footnotes

Further reading

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