A summary of sunken ship salvage methods

Abstract: The common methods currently salvage of steel, and its main characteristics and scope of application are introduced.

Keywords: sunken ship salvage underwater construction

At present, the methods for salvaging steel shipwrecks mainly include: salvaging pumping and salvaging in cabins, pumping and pumping in sealed cabins, pumping and drainage, lifting and salvaging ships, lifting floats and salvaging vessels, foam plastic salvage, and floating crane salvage. These fishing methods can be used alone or in combination.

A pumping chamber salvage law

Cabin pumping and salvage is the earliest and most widely used method of salvaging shipwrecks. It is still an effective method for salvaging sunken ships in shallow water. In addition, lift the sunken ship by means of eel lifting, etc., and some should be grounded. If the hatch or porthole is still underwater after the ship is stranded, it must be pumped by the sealed tank to float. In some areas or periods, because there are no salvage equipment such as salvage buoys, the pumping and salvaging method is also widely used. Because this salvage method requires only simple tools such as pumping, and sealing materials such as wood, wood, velvet It is easy to raise batts, battings, and cement, and the operators only need to have knowledge of seals. Therefore, during the Second World War and after World War II, most countries such as China, the United States, and the former Soviet Union used this method.

With the sealed pumping and salvaging method, the corrosion of the ship cannot be too severe. Otherwise, the strength of the hull is not enough to withstand the water pressure after pumping the tank. Bulk pumping should generally seal large tanks that are buoyant and easy to seal. If the top of the engine room is out of water, the engine room can withstand water pressure and sometimes seal it. The buoyancy of some cargo ships after pumping in the large tanks is sufficient to make them floating vessels. It is often not considered that the engine room is sealed. The tanks of the front peak tank, rear peak tank and deep oil tanker, although the volume of sealing is not large, but due to their limited buoyancy and the need to arrange pumping pipes, vent pipes, and pumping pumps, it is not easy to construct and generally does not cover.

Sealing is divided into two types: sealed type and sink type:

1 sealed seal

Sealed sealing is the main method of sealing the cabin. It uses thick planks or wooden beams to seal hatches, doors, windows, passages or holes, sealing wood and timber joints and wood and hatches, doors and windows. At the joints, the old cotton tires shall be wrapped with flannel as leakage-proof dunnage, which is easy to rot when the battings and rags are soaked in seawater for a long time, and may also be made of chemical fiber fleece, blankets, acrylic battings, and closed-cell foams. Such as sealing material.

For air vents and other vents, generally use a board to do the back cover, and use the hook bolts to hook the cabin floor, and then poured concrete in the wind bucket. The accelerator may be added to the concrete so as to have a greater strength in one or two days. If the time permits, the concrete should be pumped as much as possible after three days. The use of concrete to plug the wind buckets and vents is simpler than the use of wood plus velvet cloth and cotton tires, and watertightness and strength are better.

If it is a large hole a few meters long, it can be supplemented with steel plates and stiffeners. The method is: first draw the template in the shape of a hole, open the screw hole, and seal the edge of the plate with an under-water adhesive to cover the leak-proof pad (foam Rubber strips or foam strips) are then hoisted into the hole to be installed by divers.

Sealed airlocks are to be provided with a vent pipe and connected to the water surface so that air can be replenished in the tank during pumping. In order to observe the water level in the tank, a pressure gauge can be connected.

2 Caisson seal

The sunken tank is also called the caisson and is generally suitable for the sunken deck about 1m below the water surface . Otherwise, the project volume is larger than the sealed one. The method for constructing a caisson is to first construct a well circle on the surface of the water, and the well circle is generally arranged horizontally with wooden planks, and its size should be such that it can fit just outside the hatch. The lower part of the ring is pressurized with iron, and the bottom is made of batting, flannel or closed-cell foam to make the deck watertight. Well rings made with the help of divers are put into the hatches, and they are fastened to the hatches with hook bolts. The upper part of the bolts are placed on top of the wells.

Two- closure inflatable pumping method

If the distance between the sunken deck and the surface of the water exceeds 2m , the ventilating pipe mentioned above is used to seal the pumping water. The deck of the sunken ship may be collapsed due to unreliable water pressure. If you add a brace in the cabin, you may not be able to construct it due to too many brace bars. At this time, the cabin can be filled with compressed air to increase the pressure under the deck, and then pumping water. This method of pumping water from the floating sunken ship is called the sealed inflatable pumping method.

Inflatable pumping operations are not complicated, but they require a lot of experience, or they are prone to accidents. If the pumping is insufficient, pumping will start, and the sunken deck will be collapsed. However, if there is too much inflation, the pressure in the cabin will increase rapidly and exceed the pressure outside the cabin, which will blow off the sealing material on the sealing board, causing the cabin to leak.

Three- pressure drainage drainage method

Pressurized drainage and salvage method is to press the compressed air into the tanks and eliminate the buoyancy of the water in the tanks. The method is suitable for salvaging oil tankers that have turned over the sea floor. If the shipwreck has good airtightness and there are longitudinal compartments, it is easy to control the lateral stability, it can be uncavitated or not substantially sealed, and it is not necessary to lift the ship (big wire rope at the bottom of the ship) and salvage pontoons. Simply insert the inflation tube first. Inflatable cabin, you can pontoon. If the rear cabin of the shipwreck is damaged, it is difficult to accumulate air in the engine room and the weight of the sunken ship is heavy, the lifting tail of the buoy should be added; if the seabed is silt or quicksand, chimneys, superstructures, etc. are deeply buried in the mud. With large waves and deep water, it is difficult (or even impossible) to pass through the nacelle under the nacelle. You may consider filling the nacelle with closed-cell foam and other floats to compensate for the lack of buoyancy at the rear of the ship.

The use of pressurized drainage and salvage method should pay attention to the stability of the ship. Due to the presence of one or two vertical partition walls, the tanker is divided into left and right tanks or left, right, and right tanks, and the stability is better. The large tanks of other freighters are usually not divided into left and right, so the free surface of inertia is large and the stability is very poor. It is necessary to use buoys or ships to assist in righting in order to overcome the lack of stability.

Four ship lifts and salvage

The lifting and salvage of ships is also called barge lifting and salvaging. It is used to lift or lift the sunken ship to other places by the buoyancy of the engineering ship or barge, and can also be used for the rescue of ships stranded or hitting the reef.

The following points should be noted when barges are lifted and salvaged:

( 1 ) Float as much as possible in the slow flow, and calculate how much flow rate can control the float, so as to avoid surprises and accidents.

( 2 ) It is advisable to leave the ship at the bottom before the lowest tide. When the shipwreck just left the ground, it relieved the pressure of the sunken ship on the sea bottom. There would be air bubbles overflowing from the bottom of the ship to the water surface. When the sunken ship is salvaged, it should avoid using the method of the lowest tide to tighten the pulley and the high tide and the sunken ship to float. Because the ship is often lifted due to accidents. If it does not move, the tide is rising again, the pulley is overstressed, the winch cannot be loosened, and a serious accident occurs.

( 3 ) The reserve buoyancy of the ship's carry-lift shall be 20% to 40% of the salvage weight , and the actual reserve buoyancy that should be provided depends on the specific circumstances.

It is relatively easy to raise salvage materials and tools for ship lifting and salvage, and it is applicable to inland rivers, small waves, coastal areas with good weather conditions and offshore areas. For a long time in the past, domestic and foreign countries have used this method to lift a large number of shipwrecks, and some countries have used double-type salvage vessels to lift submarines or small warships that had crashed in the sea prior to the promotion of fishing floats. With the widespread use of salvage buoys, this method has rarely been used for coastal salvage, but this method is still one of the methods that can be considered in shallow water areas such as rivers, seas, and bays, or in areas with small winds and waves.

According to different fishing modes, the ship lifting and salvaging methods can be divided into unilateral lifting and salvaging, top lifting and salvaging, top lifting and salvage, lifting and salvaging, lifting and salvaging, and girder salvage.

1 Unilateral lifting method

Unilateral lifting and fishing, also known as clip lifting and short stubble, is one of the more widely used methods for ship lifting. One or more pairs of engineering ships (or barges) are arranged parallel and symmetrically on the waters on both sides of the sunken ship, sandwiching the sunken ship, and then connecting the sunken ship with a pulley on one side of the sunken ship (large steel cable) or sunken ship. The hanging cranes (some of the shipyards have welded the submarines and landing crafts), and use a winch to lift the sunken ship.

2 lifting and fishing

Lifting and salvaging is to use one or more pairs of flat-headed squares to weigh the ship against the wrecks, or to lift the roofs of the shipwreck with construction work. The winch and the tackle block are arranged on the engineering bridge deck, and the bottom of the sunken ship is connected with the tackle block, and then the winch is used to lift the sunken ship. When the two sides of the sunken ship and the sunken ship are refuted, pressurize the water in the projected hoppers to reduce the trim. The method is easy to operate, and general engineering refutators are equipped with this equipment to cope with emergencies. A project with a length of more than 30 meters and a width of more than 9 meters can be lifted up to about 40 tons . Therefore, it is more practical to use a roof lift method for salvaging small shipwrecks.

3 top hoisting method

The method of lifting the sunken ship by jacking and floating crane is called top hoisting. Generally, two sets of tackles are arranged on the deck of the floating crane (cradle carrier). The tackle connects the two bottoms of the ship in the sunken ship. The two bottoms of the sunken ship are connected to the hooks of the floating cranes, and then the pulleys are tightened synchronously. The hooks lifted the sunken ship, which increased the lifting force of the floating crane and reduced the lateral force of the bottom of the ship to the shipwreck. For example, a 400t floating crane could only be hoisted by 400t , and the total lifting weight of the 400t floating crane could be increased to 600t .

The top-lift fishing method is generally constructed by a single boat. If the lift of a single boat is not enough, two boats can also be used for top-lifting at the same time. However, special attention should be paid to safety. The permissible top lifting force of the floating crane should be appropriately reduced to prevent the two floating cranes from being affected. Uneven power. Salvaging small shipwrecks can be replaced by booms instead of floating cranes.

4 lifting and fishing methods

Rafting and fishing is a method of salvaging smaller wrecks using large engineering ships or engineering refutations (usually 2000t ). A number of booms were erected on one side of the engineering vessel, a tackle block was arranged on the transverse deck at each boom, and then it was moored on the side of the sunken ship. The tackle on the boom connected to the bottom of the shipwreck and the tackle on the deck. Connect the shipwreck to the bottom of the ship, then use a winch to tighten the tackle and lift the ship. Prior to winch lift, it is generally ballasted with water in side tanks and double bottoms on the other side of the engineering vessel to reduce its yaw. In order to reduce the collision between the engineering ship and the shipwreck, the engineering ship should roll about 3 ° to the side of the shipwreck . The actual allowable inclination should be determined according to the stability of the engineering ship and the buoyancy of the reserve.

5 Raise and salvage

Lifting and salvaging is also called barge boating. The project was moored over the sinking ship in the direction of the sunken ship, and then the tackle blocks hanging on both sides were connected to the bottom of the ship under the sunken ship. Then the pulley was tightened to lift the ship. In this method, the masts and other components higher than the sunken deck are to be cut first. If you want to make the sunken deck out of water in order to pump floating pontoons, you must use high tide to settle on the beach. When you leave the beach, it is best to take a toll on the shoal, and then the project evacuation should be immediately evacuated from the top of the sunken ship to avoid accidents on the sunken ship during the ebb tide. If there is insufficient tidal range, and the shipwreck deck is still unable to produce water after the beach has been exposed to dry tide, the shipwreck must be towed out of the water.

If this is the case, it should be delayed on the beach where the slope is small and the bottom friction is small. Some small vessels have been salvaged by this method, which are less frequently used due to poor safety and more salvage methods.

6 girder type fishing method

The girder salvage, also known as the baffle, is generally arranged with a pair of project scuttles juxtaposed on top of the sunken ship. Each pair of project bridges is constructed with a large beam consisting of large wooden beams. The wooden beams are clamped with angle irons and bolts and can be unloaded after use. under. The large beam is composed of three layers. The lower beam is a long beam with two wooden beams butt-joined to each other, and two individual wooden beams are on the beam. Each of the two large beams forms a group, where the rigid crossbars are placed on top and the crossbars are covered with a piece of angle iron in order to suspend the upper block in the block. The slippery car was connected to the bottom of the ship that had been drawn underneath the sinking ship, and then the pulley was tightened to raise the shipwreck. In order to reduce the inclination of the project and increase the bending moment of the girder due to the inclination, a ballast platform can be built outside the outer block of each project, and sand and other ballast can be used in the platform. As the girder is above the sunken ship, when setting the bottom of the ship and the position of the girder, a neutral position such as a chimney or a chimney etc. should be left when the water is discharged to allow the deck to discharge water.

Due to the improvement of fishing equipment and the need for more rafts for girder-type salvage, this method has rarely been adopted.

Five pontoon lifting and fishing method

The use of fishing buoy buoyancy to lift the floating sunken ship is called buoy lifting and fishing. In the mid-1950s, China began salvage the wreck with the Yangtze River estuary and coastal fishing buoy.

Salvage buoys are available in hard and soft shells: Hard shells are made of steel plates or wood, steel shells are made in China, and the former Soviet Union made some wooden shell buoys in the Second World War. Because the wooden shell buoys are not durable, Has been eliminated. Soft buoys are generally made of rubber and nylon.

China's steel shell pontoons have 800t (refers to the lift weight), 500t , 250t , 200t , 100t and 60t . Soft buoys are generally small, stereotyped products are two kinds of 5t , 10t , used to salvage small ships. During the Second World War, some countries had produced rubber pontoons of 30 tons or more. In the early 1970s , the salvage department in Guangzhou had made 100t and 200t rubber salvaging pontoons, which were used exclusively in sunken tanks to increase buoyancy. Although the soft buoys have small buoyancy, they are easy to transport and can be transported by planes, helicopters, etc. to urgently needed sites.

Most of the floating buoys on the floating pontoons are placed on the sunken and sunken sides of the sunken ship. The woven ropes or nylon rope covers cover the rims. The rims of the buoys are connected to the steel cable rings.

Steel buoys are generally placed on both sides of the sunken ship. The diver's weight is placed on the bollards of the pontoon by the diver, and then it floats up and floats.

The reserve buoyancy of the buoys should be 20% to 40% of the salvage weight .

Floating float lifting and salvaging methods can be further divided into direct salvage method, gradual salvage method and polyline fishing method:

1 direct salvage

The method of using a pontoon to lift and sink the sunken ship continuously is called a direct salvage method. Lifting floats generally do not take up at the same time from the float, because it is difficult to parallel from the floating point, and due to water flow and other reasons, the site is difficult to grasp and scheduling. The steps of the direct salvage method are: first place the buoys and tie them properly, then one end floats and floats, and finally all floats. While one end of the sunken ship is out of water, a part of the buoy is also out of the water, which increases the stability of the float.

Regardless of the way it floats, the maximum permissible trim angle should be within 15 ° when the sunken ship rises and the sunk depth exceeds 1/3 of the sunken ship . It is possible to increase the trim angle by more than 15 °. In this case, a step-by-step approach should be adopted. Polyline fishing method.

The slower the sinking speed of the sunken ship, the better, but after the sunken ship leaves the sea floor, the adhesion force disappears, the gas in the buoy tank expands, the acceleration occurs, and the floating speed increases. The speed should not exceed 3m /s , or else the deceleration must be controlled by the control buoy.

2 step by step fishing method

If the sunken ship floats vertically, it can be taken gradually. Gradually salvaging is to control the pontoon before and after the sunken ship, and control the buoy to stop floating when the effluent starts, so that the trim angle can be controlled within the specified range, and then the pontoon is suspended and the pontoon is suspended, the sunken ship is laid down, and the control float is closed. Throw until it can float with the direct salvage method described above.

The general steps of the salvage method are: ( 1 ) Before floating, firstly put and tie up the pontoon; ( 2 ) One end floats first, control the buoy first, and float one end; ( 3 ) The other end is also floated, two The buoy is fully exposed at the water surface; ( 4 ) The pontoon is unloaded with the buoy suspended and then floated by direct fishing.

3 fold line fishing method

If the sunken ship is deep in water, it is not advisable to float directly with a buoy once again, and it is not appropriate to use salvage gradually. In this case, the polyline method can be used. The so-called fold line salvage method is to make the sunken ship form a zigzag line. The fishing line should be based on the relative relationship between the depth of the water and the length of the sunken ship. When floating, the control pontoon at the top of both ends of the sunken ship is first discharged, and then the sunken ship continues to rise in the semi-floating state at the original place. The last line of salvage fishing is a floating stage. Each buoy is controlled by a single streamer. When the sunken ship rises and the control buoy loses almost no buoyancy, the streamer is towed to the control pontoon to prevent it from colliding with the sunken ship or colliding with the shipwreck. Before towing the wreck, the control buoy must be dismantled. The advantage of folding line fishing is to float from the spot, saving time compared to the gradual salvaging method. The disadvantage is that wind waves easily cause the upper and lower control buoys to collide with each other. Due to the deep water, if the cable is broken, slipped off, or the float leaks or sinks, the consequences are serious.

Six- seat inflatable buoy and foam fishing method

Inboard buoyancy equipment is used to put buoyant instruments or materials such as rubber buoys, diesel barrels, wood, bamboo, and foam blocks into a sunken ship, and use its buoyancy to lift a sunken ship. Inboard buoys are generally used for small ships that do not require large buoyancy, and they can also be used as auxiliary buoyancy for other salvaging methods. Foam plastic boat salvage, is the use of foam light weight, can remove sunken ship cabin water buoyancy float to float, using this method requires that the foam is a closed-cell type, that is, the bubbles in the plastic are closed, water is difficult to penetrate.

Inboard foam plastic fishing can be divided into two types:

The first type is underwater foam foam fishing ( FIS foam fishing) . It is to inject a variety of chemical agents into the shipwreck, foaming it and creating a bubble floating ship. The chemicals used are generally of the urethane type. The method is to mix the chemical reagents respectively from the quantitative pump into the underwater spray gun (spray nozzle), and chemical reaction occurs to foam, after overflowing the nozzle or nozzle. Cured into a foam, block or whole fixed floating in the sunken cabin on the top, and some floating to the top or contact with the cabin structure, equipment, etc. and then completely solidified, and condense into one. When the foam condenses with the cabin components, the cleaning work after the float is time-consuming. The advantages of the amino-type foams are: good underwater condensation, no free liquid level in the tank, favorable stability after the floating of the sunken ship, and reduced work for sealing the hatches. Some use expandable polystyrene granules, which are injected into the tank from the conveying pipe, and then heated with steam so that the granules are foamed and float in the upper part of the tank to generate buoyancy, but they are not as strong as the urethane type. Blocking, sometimes detrimental to the stability of the wreck.

The second is the recovery of water-foamed foam plastics, also known as ERS foam fishing. The foamable foam is made into granules. When used, the plastic granules are heated and foamed like popcorn on an engineering ship or on the shore, and then transported by a jet pump through a pipeline to a sunken tank, and after being foamed in a workshop. Globular, and then transported to the shipwreck, the material used is mostly expandable polystyrene. The advantage is that the sunken ship is easier to clear after it floats, and the foam ball can be used repeatedly, but the preservation and transportation are troublesome and the storage cost is high. In addition, the ball flows freely in the sunken ship, which is unfavorable to the stability of the sunken ship. The sealing is more demanding than the FIS method.

With foamed foam, it is necessary to prevent the overflow of the foam, and it is required that the strength after sealing can withstand the pressure of the foam on the sealed area.

The proportion of foam increases with water depth, and the deeper the water is, the lower the buoyancy is. At present, it is generally used to salvage shipwrecks, such as boats that sink on reefs, shallow water areas near piers, and breakwaters.

Seven floating crane salvaging ship

It is a method of lifting a shipwreck directly out of the water with a floating crane. Compared with other salvaging methods, the advantages are fast and effective. Currently the world from the weight of large floating crane vessel gradually increased, with the development of the ocean, floating crane ship crane force is increasing, a lot more than 2000t floating crane ship has even appeared in more than 10,000 tons of heavy lifting floating crane vessel. Some of China's major ports and salvage and salvage departments in the sea generally have 500 tons of floating cranes. The Shanghai Salvage and Salvage Bureau has 2,500 tons of "Dali". The Guangzhou Salvage and Fishing Bureau and the Bohai Petroleum Department all have 900 tons of floating floating cranes. The floating crane is generally a parallel double main hook hook. Due to its close distance, the maximum lifting force may not be exerted until there is no large balance beam. The balance beam is longer, the hook is suspended on the beam, and the beam is lifted. Due to the limited length of the beam, the buoyancy cannot be distributed within a sufficient length of the shipwreck, and the lifting force is concentrated, so that the shipwreck cannot withstand such a large longitudinal bending moment. Therefore, this method is only suitable for salvaging small shipwrecks. Some floating cranes are double-framed and their stress is better.

Some small warships, such as small submarines, landing craft, torpedo boats, etc., are welded on the ship's gang. When the construction is completed, the sunken ship can be lifted out of the water simply by placing a sling on the hanger. For a large sunken ship or a merchant ship without a hanging ship, a certain number of ship bottoms are to be drawn under the ship's ship.

It is prudent to use a plurality of floating cranes to hang a sunken ship. Since the overload of the floating crane itself is extremely limited, even overloading is not allowed. If there is a suspended floating vessel, the steel cable breaks or loses the lifting force when lifting. The original hoisting weight suddenly increased to other floating suspended boats near the side where the hoisting boat was lost, and could not be evenly distributed to all the floating hoisting ships. Therefore, the lifting force of each floating hoisting boat should be uniform and synchronized when lifting. , And there must be a considerable reserve of lifting power, the size of the reserve lifting capacity to be able to cope with when a floating crane loses its power when the other floating gondolas can withstand. Because the stability of the floating cranes is generally poor, some of them are overturned due to changes in the position of the retracting force within the rated lifting force. Some harbour operations use floating cranes, and empty ships or moored in the harbor will be a little Storms and overturning; individual floating cranes hung in Hong Kong and were overturned due to the sudden slippage of cargo. Therefore, special attention should be paid to the stability of the floating crane to ensure the safety of the project construction.

Source: "Guangdong Shipbuilding" 2006 the first period.