GB2068299A - Method of salvaging sunken vessels - Google Patents

Abstract

A sunken vessel is raised by introducing into the hull of the vessel liquified nitrogen which evaporates rapidly to displace water from the vessel and to absorb sufficient heat to cause the formation of ice on the vessel. The ice closes or partly closes any apertures in the vessel. <IMAGE>

Description

SPECIFICATION Method of salvaging sunken vessels This invention relates to the general field of salvaging sunken vessels which involves an operation of raising a sunken vessel to the surface of the water in which it has gone down. The term "vessel" is used herein in the very broad sense of meaning any sunken object which may require a salvage operation to be performed in any place, and while the main field of application of the invention is likely to be that of marine salvage in oceans, coastal waters and inland waters, it will be understood that there can be various other instances where the need arises to raise a sunken object which is itself not a ship, boat or like craft in the generally understood sense.

For example, there are various installations associated with the operations of obtaining oil and natural gas at sea where an accident can occur which calls for an object to be salvaged and it will be appreciated that the method of the present invention is applicable to such cases.

Hence, the term "vessel" is to be taken as covering any object which may require salvaging from water, being an object which is not wholly solid and which has an external shell structure (hereinafter referred to as the "hull") with an interior space or a number of separate interior spaces.

There has been a proposal for a method of raising a sunken vessel (U.K. Patent No.

162513) which suggested introducing liquified air into the interior of the vessel with the object of forming masses of ice of celluiar structure containing a quantity of gas to give the buoyancy required to raise the vessel.

There is no evidence that any attempt was ever made to put this proposal into practice.

The object of the present invention is to provide a method of raising a sunken vessel using liquified gas in a new, or improved, manner.

According to the invention I provide a method of raising a sunken vessel comprising introducing a liquified gas into an interior space within the hull through an aperture in the hull which is an existing aperture, or is one which has been prepared, the liquified gas being one such that at the pressure and temperature prevailing in the water in and surrounding the vessel the liquified gas will be instantaneously transformed into gas at a rate in terms of volume per unit of time which is sufficiently in excess of the rate (in the same terms) of escape of gas through any available aperture in the hull (including the said aperture) for the gas within the hull to increase the buoyancy of the vessel to a state to cause the vessel to rise to the surface of the water and float thereon.

In practise, a sunken ship or boat may have a number of apertures in its hull such as hatches, doors, portholes, bilge outlets, waste outlets and the like which are open and there may also be holes produced by circumstances leading to the sinking. Thus the method of the invention may include the sealing, or partial sealing, of some or all of such apertures to reduce the total aperture area of escape available to the gas to that which is required for the buoyancy state to be achieved as above described.

Nevertheless, in the case of a relatively small vessel such as a yacht or motor boat such sealing may be found to be unnecessary providing the vessel was not severely holed when it sank.

The liquified gas which is used should be one which has a high volumetric ratio of transformation from the liquified state to the gaseous state and also one which is non-toxic.

Gases which could give rise to explosion or fire hazard should be avoided.

A good example of a suitable working substance for this method is liquid nitrogen (which has been used successfully in performing the method of the invention in practice).

Liquid nitrogen is readily available commercially at reasonable cost and carries no toxic, fire or explosive hazards. The ratio of transformation at atmospheric temperature and pressure is of the order of 1 to 700, which is to say that one cubic foot of liquid nitrogen will give rise to approximately 700 cubic feet of nitrogen gas. Thus, for a salvage operation, the volume of liquid nitrogen which has to be stored and transported is small compared with the volume of gas which it can produce.

Liquid nitrogen is given as one example; there are other liquified gases which may be used provided that the gas chosen has a critical temperature which is below the temperature of the water in which the method is being performed.

Taking the example of liquid nitrogen for further explanation of various aspects of the method, the liquid nitrogen may be carrid in a surface salvage ship being stored under pressure in insulated containers from which it is conveyed to the sunken vessel through one or more insulated supply pipes. If a suitable aperture is not already available in the hull for any supply pipe then an aperture can be cut by a diver, or by remotely controlled cutting apparatus, and the end of the pipe connected to the aperture with a suitable adaptor. It will be appreciated that any such connection of a supply pipe to an existing or prepared aperture does not have to be a fluid tight connection because, during the performance of the method, it will not matter if some of the displaced water and some of the gas produced from the liquid nitrogen is allowed to escape through said aperture.

The pressure required to convey the liquid nitrogen down to the sunken vessel and to introduce it into the hull can be brought about by self-pressurisation of the liquid nitrogen container created by causing the liquified gas to absorb heat from the atmosphere or the water at the surface. A suitable pump or pumps may be provided to pump the liquid nitrogen down when the depth of the operation requires.

To illustrate the sort of conditions which can apply in practice the following example is given of one practical test which was carried out to successfully raise a sunken 40 ft. ketch from a depth of about 40 ft. of water:-- the liquid nitrogen was provided stored under pressure in a commercially available insulated container and was introduced into the hull through a 3/8" diameter insulated pipe with the end of the pipe being manually inserted through an aperture in the hull. A control valve in the pipe was opened for a very short period of time (a fraction of a minute) and it was observed that the vessel very rapidly rose to the surface due to the very rapid formation of a large volume of nitrogen gas inside the hull.

Instead of the liquid nitrogen being supplied from a salvage ship on the surface, a tank or tanks of the liquified gas may be lowered, or taken down, to the sunken vessel for the operation of introducing the liquid nitrogen into the hull to be carried out either by direct control by divers in the vicinity of the sunken vessel or by remote control means operated from the surface. Depending upon the depth of the sunken vessel, the pressure required for introducing the liquid nitrogen may be obtained by self-pressurisation of the nitrogen container by allowing the liquid gas to absorb heat from the surrounding water, or pumping means may be provided to produce the required pressure.

In another aspect of the invention use is made of the refrigerating property of a liquified gas, such as liquid nitrogen, in that the latent heat of the change of state from liquid to gas is taken from the surrounding water and thus produces sufficient fall of temperature to cause the formation of ice. The formation of ice can be controlled and utilised for certain purposes as hereinafter described and as referred to in my prior application No.

8003791.

Some of the water in the hull of a sunken vessel and immediately to the outside of the hull can be frozen to seal up any apertures which would allow too great a volume of gas to escape from the interior of the hull and any such aperture which is too large to be effectively sealed by the formation of ice alone may be sealed by using known methods and apparatus for repairing holes in structures under water. Alternatively an aperture may be partially covered by a grid or framework which would provide a suitable base for the formation of ice to complete the sealing of the aperture. In view of the fact that gas is to be allowed to escape during the raising operation, it may not be necessary to provide completly fluid-tight sealing of all apertures.

The accompanying diagrammatic drawing which illustrates a section through the hull of a sunken vessel is intended to show, by way of example, how the formation of ice may be used in carrying out the salvage method according to this aspect of the invention.

Prior to the introduction of the liquid nitrogen, the interior space 10 of the hull 11 is provided with a suitable number of vent pipes, such as indicated at 12, each extending upwardly and inwardly into the space 10 from a position near the bottom of the hull and these are for the purpose of allowing for the escape of water and gas during the operation.

If the pressure of gas escaping through the vent pipes 1 2 is not sufficient to prevent the openings of the pipes becoming iced up, then suitable heater units may be incorporated in the pipes to assist in preventing ice formation which would block the pipes.

If a suitable aperture is not already available then one is cut in the hull at a position such as indicated at 1 3 for the insertion of the supply pipe 14 to introduce the liquid nitrogen into the interior space 1 0. Ice is formed on the inside and the outside of the hull in the shape of films as indicated at 1 5 and 1 6 and the formation of ice is allowed to continue until a desired thickness has been achieved.

These films of ice 1 5 and 16, in addition to sealing up any excess apertures, also serves to strengthen the deck and other parts of the hull where the ice forms. Ice also forms in a layer in the lower part of the interior space 10, as indicated at 17, below which is a space 1 8 which may be occupied by water or the whole of space 1 8 may be ice.

The precedure as set out above is repeated in each separate interior space of the vessel, according to the design thereof, and as soon as the formation of ice has sealed any apertures to the extent that the rate of escape of the gas is less than the rate of formation of the gas from the introduction of the liquid nitrogen, then the vessel will rise to the surface. The bulk of ice formed in the lower part of the compartments 10 will assist in stabilising the vessel as it rises to the surface and assist in preventing it from capsizing when reaching the surface.

Depending on the construction and lay-out of the vessel it may be sufficient to introduce the liquid nitrogen into some only of the separate interior spaces instead of dealing with the whole of the interior of the hull.

As with the vent pipes 12, the region in the immediate vicinity of the supply pipe 14 may be kept free of ice formation by the use of a heater if the pressure of the gas being produced is not sufficient to prevent ice being formed in this region.

According to a further aspect of the invention, liquified gas may be converted to the gaseous state at the surface above a sunken vessel and then passed through high pressure piping down to the vessel or, where a container or containers of the liquid gas is taken down to the vicinity of the vessel, the conversion to gas may take place outside the vessel with the gas being conveyed by high pressure piping into the vessel.

Claims (5)

1. A method of raising a sunken vessel comprising introducing a liquified gas into an interior space within the hull through an aperture in the hull which is an existing aperture, or is one which has been prepared, the liquified gas being one such that at the pressure and temperature prevailing in the water in and surrounding the vessel the liquified gas will be instantaneously transformed into gas at a rate in terms of volume per unit of time which is sufficiently in excess of the rate (in the same terms) of escape of gas through any available aperture in the hull (including the said aperture) for the gas within the hull to increase the buoyancy of the vessel to a state to cause the vessel to rise to the surface of the water and float thereon.

2. A method according to Claim 1 wherein apertures in the hull are at least partially blocked by ice formed by transfer of heat from sea water to the gas produced in the vessel from said liquified gas.

3. A method according to Claim 1 or Claim 2 wherein water is displaced from the interior of the vessel in a generally downward direction through vents provided in the vessel.

4. A method of raising a sunken vessel substantially as herein described with reference to and as illustrated in the accompanying drawing.

5. Any novel feature or novel combination of features disclosed herein or in the accompanying drawing.