Salvage diving

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US Navy diver dredging an excavation site during an underwater recovery operation, searching for personnel who went missing during WWII off the coast of Koror 180124-N-QA919-0008 (25209544777).jpg
US Navy diver dredging an excavation site during an underwater recovery operation, searching for personnel who went missing during WWII off the coast of Koror

Salvage diving is the diving work associated with the recovery of all or part of ships, their cargoes, aircraft, and other vehicles and structures which have sunk or fallen into water. In the case of ships it may also refer to repair work done to make an abandoned or distressed but still floating vessel more suitable for towing or propulsion under its own power. [1] [2] [3] The recreational/technical activity known as wreck diving is generally not considered salvage work, though some recovery of artifacts may be done by recreational divers.

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Most salvage diving is commercial work, or military work, depending on the diving contractor and the purpose for the salvage operation, Similar underwater work may be done by divers as part of forensic investigations into accidents, in which case the procedures may be more closely allied with underwater archaeology than the more basic procedures of advantageous cost/benefit expected in commercial and military operations.

Clearance diving, the removal of obstructions and hazards to navigation, is closely related to salvage diving, but has a different purpose, in that the objects to be removed are not intended to be recovered, just removed or reduced to a condition where they no longer constitute a hazard or obstruction. Many of the techniques and procedures used in clearance diving are also used in salvage work. [2]

Range of salvage activities

The US Navy considers the recovery of sunken or wrecked naval craft, submarines, human remains, critical items of equipment needed to determine the cause of a mishap, including classified and sensitive materials to be within the scope of their salvage and recovery operations. [2] Commercial salvors will generally undertake an operation if it is likely to be sufficiently profitable, taking into account the known hazards and risks.

Diving work associated with marine salvage operations

Where practicable, procedures which minimise the work needed to be done by divers are used, as diving is slow, labour-intensive, dangerous, expensive, often inefficient, and may require other work near the dive site to be interrupted during the dive. However it is the only way some tasks can be done, and for some it is the most efficient way to do them. [1] :Ch. 4

Survey of underwater damage

For stranded and floating vessels, a detailed hull survey includes the parts of the ship that are underwater. These will be external areas below sea level, and any internal areas that are flooded. If sea conditions or access are unsuitable for external survey, internal survey will have to be more comprehensive as the information about one side must be extrapolated to provide needed information about the inaccessible side. The diving survey includes: [1] :Ch. 2

The dive team should be briefed on all structural damage found inside the hull so that they can check for underwater damage in the same areas. When practicable the work of the divers should be minimised as diving is slow, labor-intensive, dangerous and expensive work. Tidal flow can change the conditions and limit diving operations, and also affect the condition of the vessel and seabed in the vicinity. Where scouring is likely it should be monitored by regular underwater inspections. Video records allow comparison to estimate the rate of scour or deposition. [1] :Ch. 2

Patching of damage

Underwater patching is almost always done by divers. As much patch fabrication and rigging as possible should be done out of the water to minimise diving time. Small leaks are generally sealed off and made watertight by wooden plugs and wedges, small wooden patches and concrete boxes, small steel plate patches or combinations of these, caulked and sometimes additionally sealed with epoxy resin or fibre-reinforced resins. Small steel patches for minor leaks are usually fitted with gasket material to seal against the damaged hull. Major patching is characterized by extensive diving work and includes detailed underwater surveys, measurements, and major underwater cutting and welding operations to prepare and fit the patch. [1] :Ch.10

Reinforcement and shoring

If a ship is pumped out while the deck is submerged the top of the deck is loaded by hydrostatic pressure and may require shoring to support the load. This is generally done by divers and is time-consuming and expensive. The load may also be compensated by compressed air in the space if practicable. [1] :Ch. 6

Installing cofferdams

A cofferdam is an enclosure built within a body of water to allow the enclosed area to be pumped out. [4] This pumping creates a dry working environment so that the work can be carried out safely. [1] :Ch.10

When all or part of the main deck of a sunken ship is submerged, flooded spaces cannot be dewatered until all openings are sealed or the effective freeboard is extended above the high water level. In salvage, one method of doing this is to build a temporary watertight extension of the entire hull of the ship, or the space to be dewatered, to the surface. This watertight extension is a cofferdam. Although they are temporary structures, cofferdams have to be strongly built, heavily stiffened, and reinforced to withstand the hydrostatic and other loads that they will have to withstand. Large cofferdams, are normally confined to harbor operations. [1] :Ch.10

Complete cofferdams cover most or all of the sunken vessel and are equivalent to extensions of the ship's sides to above the water surface. [1] :Ch.10

Partial cofferdams are constructed around moderate-sized openings or areas such as a cargo hatch or small deckhouse. They can often usually can be prefabricated and installed as a unit, or prefabricated panels can be joined during erection. When partial cofferdams are used, it may be necessary to compensate for hydrostatic pressure on the deck by shoring the decks. With both complete and partial cofferdams, there is usually a large free surface in the spaces being pumped. [1] :Ch.10

Small cofferdams are used for pumping or to allow salvors access to spaces that are covered by water at some stage of the tide. They are usually prefabricated and fitted around minor openings. [1] :Ch.10

Diving work on cofferdams often involves clearing obstructions, fitting, and fastening, including underwater welding, and where necessary, caulking, bracing and shoring the adjacent structure. [1] :Ch.10

Attachment and rigging of lifting or hauling gear

Inspection of ground tackle

Setting up for dewatering with compressed air

Wrecking in place

Planning of salvage diving operations

Information gathering

Detailed information of the layout and structure of the vessel to be salvages and the type and location of cargo are useful for planning and essential for the actual salvage operation. Information acquired during the planning stage can greatly facilitate the actual operation. [2]

If the vessel is to be raised, details of the cause of sinking and the extent of damage is required.

Useful information can be gathered from ships plans, cargo manifests, loading plans, interviews with witnesses and survivors, photographs and official reports of similar accidents. [2]

Planning of the salvage operations

The choice of salvage systems depends on the specific conditions of the job. Divers can work efficiently in shallow water, but the practicality decreases rapidly with depth and has an absolute limit determined by current technology. They bring the advantages of human vision, judgement and high dexterity manipulative skills, but these are offset by depth limitations, dive duration, risk, support requirements and cost. Manned submersibles and atmospheric diving suits can go deeper than ambient pressure diving without decompression obligations, and have advantages of human vision and judgement, and when working without tethers have good maneuverability, but dexterity is compromised, and cost is high. Tethered unmanned ROUVs eliminate the risk to human life of manned systems and are available with a wide range of capabilities which can be matched to the operational requirements, and are not limited by operator fatigue. [3] :Ch.1

Searching for objects and wreck sites

Underwater search and recovery operations are used to locate, identify, observe and recover specific objects from the seafloor. Typically, search and recovery operations are conducted as two distinct phases - the search includes detection and identification of the target and, in some cases, direct inspection. Operations are generally planned to suit expected conditions, but plans should be sufficiently flexible to allow for changes to suit actual conditions. [3] :Ch. 2

Search equipment

The equipment available for underwater searches ranges from simple equipment like grapples and draglines to complex acoustic technologies and magnetic field sensors.

  • Echo-sounders can provide a continuous record of depth under the ship during a search, which can reveal obstacles that might damage towed transponders. They have a narrow beam and poor resolution, and would only be likely to find large targets. [3] :Ch. 2
  • Side-scan sonar uses acoustic transducers which scan a fairly wide swath to each side of the vessel or towed unit. Large areas can be covered in each pass. There is a narrow band directly below the transducer that is not covered. The image produced can have a fairly high resolution and can identify seabed texture an artifacts above a moderate size. The image produced can be interpreted visually to identify a wide range of three-dimensional shapes, and is fairly efficient in covering large areas. The effective resolution depends mainly on the operating frequency, with higher frequency giving greater resolution but shorter effective range and narrower width of seabed covered in each pass. A 500 kHz system might effectively scan a swath of 50 to 100m with the possibility of detecting a target of the order of 1m diameter, while a 30 kHz system might find a shipwreck in a swath of up to 5 km wide, depending on depth. The data may be viewed in real time and recorded for further analysis. [3] :Ch. 2
  • Multi-beam sonar
  • Towed pinger locators are passive acoustic search systems that only receive a signal from an acoustic beacon, Aircraft that fly over the sea carry such a beacon on the flight data recorder in case they are lost at sea. They do not always have directional resolution and may need several passes to locate the target accurately. [3] :Ch. 2
  • Magnetometers can detect variations in magnetic field that may be caused by masses of ferromagnetic material - iron and steel - and cables carrying electric current. Since ships usually contain a fairly to very large amount of ferromagnetic material, this equipment is quite effective for locating shipwrecks. They are also useful for resolving ambiguous targets in areas of high topographical variation, and can detect targets buried under sediment. [3] :Ch. 2
  • Optical Imaging Systems. can be used for underwater searches if the visibility is good enough. In deep water they need to carry their own light source. They can be used in combination with side scan sonar, to help with identification of an object as it is found.

Remotely operated vehicles are platforms that can carry sensors underwater and maneuver them in proximity to the object. They are limited to operating in relatively small areas because the support ship must loiter almost directly over the ROV and the umbilical limits the system's maneuverability. An ROV can be very effective at locating small isolated targets in a known debris field, and visually identifying a target in good visibility. [3] :Ch. 2

Search patterns

The effectiveness of a search can be expressed by how thoroughly and efficiently the search area is examined. Systematic examination of the search area is achieved by following a predetermined pattern that suits the conditions of the search. [3] :Ch. 2

  • Parallel grid search: The most common pattern for a towed sensor search, using parallel straight line search tracks. Adjacent tracks use sufficient overlap to compensate for errors in the path, width variations in the scanned swath and losses in resolution at the extreme edges. The turn between each leg of the search must allow the towed array to stabilise depth and lateral position before the new leg scan, and this can take a significant part of the search time. A towed array should preferably be towed roughly parallel to the depth contours as this reduces the need for depth changes on each leg. [3] :Ch. 2

Salvage work

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. Protecting the environment from spillage of oil or other contaminants is also a high priority. Most salvage is carried out by specialist salvage firms with dedicated crew and equipment. [5]

Salvage diving techniques

Scuba is not authorised for most salvage work by commercial or naval operators due to relatively high risk in comparison to surface supplied techniques, though naval operations may use scuba for non-penetrative work in good visibility and relatively shallow depths. [2]

The choice between surface oriented and saturation diving is based largely on depth and the amount of decompression anticipated.

Underwater work techniques used in salvage diving work

Hazards common to salvage diving

Salvage diving platforms and support vessels

Support equipment and ROVs

Organisations

In 1978, the U.S. Navy Special Operations Officer (1140) community was established by combining Explosive Ordnance Disposal (EOD) and Expendable Ordnance Management officers with Diving and Salvage officers. "The combination gave a breadth and depth of professionalism to Navy salvage that had not been possible before." [6]

List of notable salvage operations involving divers

See also

Related Research Articles

An overhead or penetration diving environment is where the diver enters a space from which there is no direct, purely vertical ascent to the safety of breathable atmosphere at the surface. Cave diving, wreck diving, ice diving and diving inside or under other natural or artificial underwater structures or enclosures are examples. The restriction on direct ascent increases the risk of diving under an overhead, and this is usually addressed by adaptations of procedures and use of equipment such as redundant breathing gas sources and guide lines to indicate the route to the exit.

Underwater divers may be employed in any branch of an armed force, including the navy, army, marines, air force and coast guard. Scope of operations includes: search and recovery, search and rescue, hydrographic survey, explosive ordnance disposal, demolition, underwater engineering, salvage, ships husbandry, reconnaissance, infiltration, sabotage, counterifiltration, underwater combat and security.

<span class="mw-page-title-main">Cofferdam</span> Barrier allowing liquid to be pumped out of an enclosed area

A cofferdam is an enclosure built within a body of water to allow the enclosed area to be pumped out or drained. This pumping creates a dry working environment so that the work can be carried out safely. Cofferdams are commonly used for construction or repair of permanent dams, oil platforms, bridge piers, etc., built within water.

USNS <i>Grapple</i> Rescue and salvage ship

USS Grapple (ARS-53) is a Safeguard-class rescue and salvage ship in the United States Navy. Her home port is Norfolk, Virginia. On 13 July 2006 Grapple was decommissioned from US Navy service and converted to civilian operation by Military Sealift Command. She was redesignated as USNS Grapple.

<span class="mw-page-title-main">Navy diver (United States Navy)</span> US Navy personnel qualified in underwater diving and salvage

A United States Navy diver may be a restricted fleet line officer, Civil Engineer Corps (CEC) officer, Medical Corps officer, an Unrestricted Line Officer who is qualified in Explosive Ordnance Disposal (EOD) Warfare (1140) or an enlisted who is qualified in underwater diving and salvage. Navy divers serve with fleet diving detachments and in research and development. Some of the mission areas of the Navy diver include: marine salvage, harbor clearance, underwater ship husbandry and repair, submarine rescue, saturation diving, experimental diving, underwater construction and welding, as well as serving as technical experts to the Navy SEALs, Marine Corps, and Navy EOD diving commands.

<span class="mw-page-title-main">Marine salvage</span> Recovering a ship or cargo after a maritime casualty

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. Salvors are normally paid for their efforts. However, 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 and in these instances, governments or authorities may organise the salvage.

USNS <i>Salvor</i> Safeguard-class rescue and salvage ship

USNS Salvor (T-ARS-52) is a Safeguard-class rescue and salvage ship, the second United States Navy ship of that name.

USNS <i>Safeguard</i> Lead ship of her class

USNS Safeguard (T-ARS-50), formerly USS Safeguard (ARS-50), is the lead ship of her class and the second United States Navy ship of that name.

USS <i>Pigeon</i> (ASR-6) Minesweeper of the United States Navy

The first USS Pigeon (AM-47/ASR-6) was a Lapwing-class minesweeper of the United States Navy. She was later converted to a submarine rescue ship. She was named for the avian ambassador, the pigeon.

USS <i>Preserver</i> US Navy salvage ship

USS Preserver (ARS-8) was a Diver-class rescue and salvage ship commissioned by the U.S. Navy for service in World War II. She was responsible for coming to the aid of stricken vessels. Preserver was laid down by Basalt Rock Company in Napa, California, 26 October 1942, launched 1 April 1943, sponsored by Mrs. Walter F. LaFranz, and commissioned 11 January 1944.

<span class="mw-page-title-main">Underwater search and recovery</span> Locating and recovering underwater objects

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.

USNS <i>Sgt. Jack J. Pendleton</i> Cargo ship of the United States Navy

USNS Sgt. Jack J. Pendleton was a Lt. James E. Robinson-class cargo ship constructed during World War II as a Victory ship and named the SS Mandan Victory. The Mandan Victory was placed into service by the War Shipping Administration's Emergency Shipbuilding program under cognizance of the U.S. Maritime Commission.

USNS <i>Grasp</i> Safeguard-class rescue and salvage ship

USNS Grasp (T-ARS-51) is a Safeguard-class rescue and salvage ship, the second United States Navy ship of that name.

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 underwater vehicles, or from the surface by other agents, including surface vessels, aircraft and cadaver dogs.

<span class="mw-page-title-main">Army engineer diver</span> Armed forces occupation

Army engineer divers are members of national armies who are trained to undertake tasks underwater, including reconnaissance, demolition, and salvage. These divers have similar skills and qualifications as professional divers. Army divers use both surface supplied "Hard hat" and SCUBA to perform their missions. In the United States Army, they are members of the Corps of Engineers. In the British Army, they may be Royal Engineer Divers or Commando Engineer Divers.

Underwater work is work done underwater, generally by divers during diving operations, but includes work done underwater by remotely operated vehicles and crewed submersibles.

<i>Safeguard</i>-class rescue and salvage ship United States Navy salvage and rescue ships

The Safeguard class is a class of Towing, Salvage and Rescue Ship under the United States Navy.

<span class="mw-page-title-main">Underwater survey</span> Inspection or measurement in or of an underwater environment

An underwater survey is a survey performed in an underwater environment or conducted remotely on an underwater object or region. Survey can have several meanings. The word originates in Medieval Latin with meanings of looking over and detailed study of a subject. One meaning is the accurate measurement of a geographical region, usually with the intention of plotting the positions of features as a scale map of the region. This meaning is often used in scientific contexts, and also in civil engineering and mineral extraction. Another meaning, often used in a civil, structural, or marine engineering context, is the inspection of a structure or vessel to compare actual condition with the specified nominal condition, usually with the purpose of reporting on the actual condition and compliance with, or deviations from, the nominal condition, for quality control, damage assessment, valuation, insurance, maintenance, and similar purposes. In other contexts it can mean inspection of a region to establish presence and distribution of specified content, such as living organisms, either to establish a baseline, or to compare with a baseline.

Submarine rescue is the process of locating a sunk submarine with survivors on board, and bringing the survivors to safety. This may be done by recovering the vessel to the surface first, or by transferring the trapped personnel to a rescue bell or deep-submergence rescue vehicle to bring them to the surface. Submarine rescue may be done at pressures between ambient at depth, and sea level atmospheric pressure, depending on the condition of the distressed vessel and the equipment used for the rescue. Self-rescue of submarine personnel by buoyant free ascent at ambient pressure is considered submarine escape. Survivors may require recompression treatment for decompression illness.

<span class="mw-page-title-main">Underwater cutting and welding</span> Metalworking techniques used by underwater divers

Underwater cutting and welding are metalworking techniques used by underwater divers in underwater construction, marine salvage and clearance diving applications. Most underwater welding is direct current wet stick welding, and most underwater metal cutting is immersed oxygen-arc and shielded metal-arc cutting, though other technologies are available and sometimes used. These processes are mostly applied to steel structures as that is the most common arc-weldable material used in the underwater environment.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 U.S. Navy Salvage Manual (PDF). Vol. 1: Strandings, Harbor Clearance and Afloat Salvage S0300-A6-MAN-010. United States. Navy Department. Supervisor of Salvage and Diving. 31 May 2013.PD-icon.svg This article incorporates text from this source, which is in the public domain.
  2. 1 2 3 4 5 6 US Navy (2006). US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. Retrieved 2008-06-15.
  3. 1 2 3 4 5 6 7 8 9 10 U.S. Navy Salvage Manual (PDF). Vol. 4: Deep Ocean Operations S0300-A6-MAN-040 0910-LP-252-3200. United States. Navy Department. Supervisor of Salvage and Diving. 1 August 1993.PD-icon.svg This article incorporates text from this source, which is in the public domain.
  4. Chisholm, Hugh, ed. (1911). "Cofferdam"  . Encyclopædia Britannica . Vol. 6 (11th ed.). Cambridge University Press. p. 649.
  5. Urbina, Ian (December 28, 2015). "Maritime 'Repo Men': A Last Resort for Stolen Ships (Published 2015)." The New York Times". The New York Times.
  6. Evans, James M. (1993-04-01). U. S. Navy Special Operations (1140) Community Diving and Salvage Functional Area. Research rept. Aug 1992-Apr 1993 ADA278438 (Report).