US3523514A

US3523514A - Salvage pontoon

Info

Publication number: US3523514A
Application number: US779378A
Authority: US
Inventors: Kenneth R Fishel
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1968-11-27
Filing date: 1968-11-27
Publication date: 1970-08-11
Anticipated expiration: 1987-08-11

Description

United States Patent [72] Inventor Kenneth R. Fishel Altadena, California [21] Appl. No. 779,378

[22] Filed Nov. 27, 1968 [45] Patented Aug. 11, 1970 The United States of America as represented by the Secretary of the Navy [73] Assignee [54] SALVAGE PONTOON 7 Claims, 5 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 1,240,180 9/1917 Arazoza 114/52 Primary Examiner Andrew H. Farrell Attorney-Justin P. Dunlavey and Ervin F. Johnston ABSTRACT: A salvage pontoon which has a. negative metacentric height during its lift phase so that if the payload becomes accidentally detached during the lift phase the pontoon will rotate and fill with water through its open bottom end for a safe ascent to the surface. The pontoon includes a lift tank which is open at its bottom and closed at its top. A negative buoyancy control tank and a positive buoyancy tank are mounted to the top portion of the lift tank. The pontoon has a negative metacentric height and positive buoyancy when the lift tank, positive buoyancy tank, and negative buoyancy control tank are dewatered.

Patented Aug. 11, v 3 3,523,514

FIG. 2. INVENTOR.

KENNETH R. FISHEL ERVIN F. JOHNSTON ATTORNEY."

SALVAGE PONTOON The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

In conducting salvage operations at sea, pontoons are frequently employed for retrieving large objects from the ocean floor. These pontoons are lowered by a surface ship to the site of the object to be retrieved and, after connection to the object, the pontoons are dewatered until there is sufficient positive buoyancy to raise the object to the surface of the ocean. In order to raise heavy objects, such as a sunken vessel, from the ocean floor it is necessary that these pontoons be quite large. Should one of these pontoons accidentally become disconnected from the object to be raised, the pontoon, because of its positive buoyancy, will begin a free ascent toward the surface of the ocean with increasing velocity if the air within the pontoon is free to expand. Should the surface support ship be in the path of the pontoon the result would most likely be disastrous. If the air is not free to expand within the pontoon differential, pressures can rupture the tanks. The falling debris would present a severe hazard to personnel on the bottom of the ocean.

The present invention provides a salvage pontoon which has a built-in safety feature to obviate the hazards of presently existing pontoons upon accidental disconnection from the object to be retrieved. To accomplish this purpose I have provided a salvage pontoon which includes a lift tank which is open at its bottom and closed at its top. Mounted to a top portion of the lift tank I have provided a negative buoyancy control tank and a positive buoyancy tank. During all operating phases of the salvage pontoon the negative buoyancy control tank is normally kept in a dewatered condition. When the lift tank and positive buoyancy tank are flooded thesalvage pontoon will descend, guided by a reaving line from the surface ship to the object to be retrieved. When the pontoon is in the vicinity of the object to be retrieved a lowering line from the surface ship positions the pontoon over the object so that the pontoon can be connected thereto. After the connections are made, the positive buoyancy tank is then dewatered, at which time the pontoon has a slight upward buoyancy to enable the divers to check the condition of the lift lines. The lift tank is then dewatered sufficiently to commence raising of the object. Should the pontoon become accidentally disconnected from the object during ascent l have provided the pontoon with a negative metacentric height so that the lift tank will rotate sufficiently to flood itself and prevent rapid upward movement of the pontoon. After flooding of the lift tank, the positive buoyancy tank remains dewatered and with its slight upward buoyancy, the pontoon will ascend slowly to the surface of the ocean so as to prevent any hazard to the surface ship, the object on the bottom, or personnel.

An object of the present invention is to overcome the aforementioned problems of prior art salvage pontoons;

Another object is to provide a salvage pontoon which, upon accidental disconnection from an object to be retrieved from the ocean floor, will not impose any serious hazards to a surface ship and its personnel or personnel working at the bottom of the ocean;

A further object is to provide a salvage pontoon which, upon accidental disconnection from an object to be retrieved from the ocean floor, will automatically flood itself so as to prevent an explosion of the pontoon or a hazardous upwardly ascent thereof;

Still another object is to provide a salvage pontoon which can be simply flooded and dewatered to cause the pontoon to assume buoyancy conditions which facilitate safe and easy operation of the pontoon.

Other objects and many of the attendant advantages of this invention will be readily appreciated as it becomes better understood by reference to the description and accompanying drawings which follow.

FIG. 1 is a schematic side view of a surface ship lowering the salvage pontoon for connection to an object to be retrieved from the ocean floor;

FIG. 2 is a diagrammatic view of the various operational phases of the salvage pontoon;

FIG. 3 is a vertical cross sectional view of the salvage pontoon;

FIG. 4 is a side view of another embodiment, i.e. a horizontal salvage pontoon; and

FIG. 5 is a view taken along plane V-V of FIG. 4.

Referring now to the drawings wherein like reference numerals designate like or similar parts throughout the several views, there is shown in FIG. I a salvage pontoon 10 which is being lowered by a surface ship 12 for the purpose of retrieving an object, such as a mine 14 from the ocean bottom. The pontoon 10 is being guided in its descent by a reaving line 16 and is being lowered by a lowering line 18. FIG. 1 corresponds to view A of FIG. 2.

As shown in FIG. 3 the salvage pontoon 10 may include a lift tank 20 which may be a large hollow cylinder which is open at its bottom 22 and closed at its top 24. Mounted to the top portion of the lift tank 20 and preferably as near the top thereof as practicable, are a negative buoyancy control tank 26 and a positive buoyancy tank 28. In order to achieve this uppermost location of the latter two tanks, I have found it desirable to seal the top of the lift tank 20 with the negative buoyancy control tank 26 and locate the positive buoyancy tank 28 immediately therebelow. In order to optimize a maximum mass and pressure strength for the positive buoyancy tank 28, I have selected a toroidal shape which, in the same manner as the buoyancy tank 26, may be symmetrical about the longitudinal axis of the lift tank 20. For a purpose which will become apparent hereinafter, the negative buoyancy control tank 26 and the positive buoyancy tank 28 are constructed with a large mass while the mass of the lift tank 20 is kept at a minimum. All of these tanks may be constructed of steel.

In order to guide descent and ascent of the salvage pontoon 10 the pontoon may be provided with a hawse pipe 30 which extends along the longitudinal axis of the lift tank 20 and through all three of the

tanks

26, 28, and 20. The hawse pipe 30 receives the reaving line 16 which extends between the surface ship 12 and the mine 14 and, upon connection to the mine 14, will receive a lift chain 32, shown in view B of FIG. 2. The lift chain 32 is stopped at the top of the negative buoyancy control tank 26 by a flower pot stopper 34. A padeye 36 may be connected to the top of the negative buoyancy control tank 26 for receiving the lowering line 18 from the surface ship. As shown in FIG. 3, lateral bracing members 38 may be provided between the hawse pipe 30 and the interior of the lift tank 20 for stiffening this tank at its bottom end 22 and a location intermediate the ends of the lift tank.

In order to flood and dewater the positive buoyancy tank 28 inlet and

outlet tubes

40 and 42 may be provided with

control valves

44 and 46 respectively. In order to flood and dewater the lift tank 20, an inlet and outlet pipe 48 may be provided which may be also connected to the valve 44. The valve 44 may be a three position valve so that an operator can selectively open either the positive buoyancy tank 28 or the lift tank 20 or close off both of these tanks. If desired, a valve 50 may be provided for the negative buoyancy control tank 26 so that this tank can be pressurized to withstand pressures in deep ocean environments. In all operating phases of the of the lift tank 20 during slow ascent of the pontoon and mine. combination.

As shown in phase A of FIG. 2 the salvage pontoon 10 is provided with a positive metacentric height and negative buoyancy when the lift tank 20 and the positive buoyancy tank 28 are flooded and the negative buoyancy control tank 26 is dewatered. The salvage pontoon still has positivemetacentric height but has positive buoyancy when the lift tank 20 is flooded and both the positive buoyancy tank and negative buoyancy control tank are dewatered. This would be similar to phase A of FIG. 2 except the positive buoyancy tank 28 is dewatered and the pontoon has a slight upward buoyancy. The salvage pontoon 10 has a negative metacentric height and positive buoyancy when the lift tank 20, positive buoyancy tank 28, and negative buoyancy control tank 26 are dewatered. This condition is essentially shown in phase C of FIG. 2 where the negative metacentric height is causing the pontoon to rotate so as to flood the lift tank 20 upon accidental disconnection between the pontoon and the mine 14. ln order to achieve a good metacentric height it is desirable to locate the negative buoyancy control tank 26 and the positive buoyancy tank 28 as close to the top of the lift tank 20 as possible and to provide these tanks with a heavy mass while the lift tank 20 is provided with a relatively light mass.

ln the operation of the salvage pontoon 10 the positive buoyancy tank 28 is flooded at the surface of the ocan by opening

valves

44 and 46 and the lift tank 20 is flooded by then closing the positive buoyancy tank 28 and utilizing valve 44 to open the pipe 48. The pontoon will then assume a vertical position. Water may be introduced into these tanks by a hose (not shown). As shown in FIG. 1 and in phase A of FIG. 2, the pontoon 10 is then guided down the reaving line [6 by the lowering line 18 until the lift chain 32 has passed through the hawse pipe. When the pontoon 10 is in the immediate overhead vicinity of the mine 14 the lift chain 32 is stopped at the top of the pontoon by a flower pot stopper 34. A diver on the floor of the ocean then opens both

valves

44 and 46 to the positive buoyancy tank 28 and dewaters this tank by a pressure hose from the surface ship (not shown). This causes the salvage pontoon 10 to assume a slight positive buoyancy and take a slight strain on the lift chain 32 so that personnel can check to ensure that the connections have been properly made. The lowering line 18, and reaving line 16 are then removed. The diver then opens all valves 51 below the desired water level in lift tank 20, and utilizes valve 44 to open the lift tank, and applies pressure by a pressure hose from the surface ship (not shown) to sufficiently dewater the lift tank 20 so that the salvage pontoon l and the mine 14 commence their ascent towards the surface of the ocean. It should be noted that in this phase, the pontoon alone may have a negative metacentric height but the pontoon and mine system combination maintains a positive metacentric height, and pontoon rotation is prevented by the lift chain 32 through the hawse pipe 30.

As shown in phase C of FIG. 2, should the lift chain 32 accidentally become disconnected from the mine 14 the salvage pontoon will continue its ascent and because of the rapidly expanding air in the lift tank 20 any water remaining therein will be forced out through its bottom. This will quickly establish or increase the negative metacentric height of the salvage pontoon 10 so that the lift tank 20 will rotate and become flooded with water as shown in phase D of FIG. 2. When the lift tank 20 is flooded the salvage pontoon once again assumes a slight positive buoyancy and a positive metacentric height so that it will gradually ascend to the surface of the water as shown in phase E of FIG. 2. lt should be noted that by maintaining the negative buoyancy control tank 26 in a dewatered condition at all times that an operator need only be concerned with flooding or dewatering the positive buoyancy tank 28 for the desired buoyancy control purposes.

Because of the relatively light construction of the lift tank 20 it may be replaced if it becomes seriously damaged during operation. Repairs of presently existing pontoons have not been too successful. Another advantage of the pontoon 10 is that once the object to be retrieved has been brought to the surface of the ocean the bottom end 22 of the pontoon can be capped with the lift tank 20 sufficiently dewatered for towing the object to a desired destination.

FIGS. 4 and 5 illustrate another embodiment of the present invention which is a salvage pontoon 52 which can be operated for lifting purposes in a horizontal position. The pontoon 52 includes a lift tank 54 which is closed at its top and is open at its bottom by lightening holes or openings 56. Connected to the top inner surface of the lift tank 54 is a negative buoyancy control tank 58 which may extend along parallel to the longitudinal axis of the lift tank 54. The control tank 58 may be provided with a valve 60 for pressurizing this tank for deep ocean work. This tank will normally be in a dewatered condition during all operating phases of the salvage pontoon 52 in the same manner as previously described for the salvage pontoon 10. A pair of positive buoyancy tanks 62 may also be mounted within the lift tank 54 adjacent the inner surface thereof and the exterior surface of the negative buoyancy control tank 58. The positive buoyancy control tank 62 may also extend along parallels to the longitudinal axis of the lift tank 54 As shown in FIG. 5 the

tanks

58 and 62 are preferably located in the uppermost position with respect to the lift tank 54 and further are preferably constructed of a heavy mass while the lift tank 54 is constructed of a relatively light mass. ln this manner, the salvage pontoon 52 will assume a negative metacentric height when the

tanks

58 and 62 and the lift tank 54 are dewatered. Flooding and dewatering of the positive buoyancy tank 62 may be achieved by pairs of inlet and

outlet valves

64 and 66 respectively. Flooding and dewatering of the lift tank 54 may be achieved by inlet and outlet valve 68. The relationship of the metacentric height and the buoyancy of the salvage pontoon 52 is the same as previously described for the salvage pontoon 10, except that the salvage pontoon 52 is provided with two positive buoyancy tanks 62 rather than the one positive buoyancy tank 28 disclosed for the salvage pontoon 10. Because of the horizontal aspect of the salvage pontoon 52, it is desirable to utilize two hawse pipes 70 which are spaced apart along the longitudinal axis of the lift tank 54 and which may extend through both the negative buoyancy control tank 58 and the lift tank 54.

The operation of the salvage pontoon 52 is essentially the same as previously described for the salvage pontoon l0. During ascent of the salvage pontoon 52 and the payload, the negative buoyancy control tank 58 and the positive buoyancy tanks 62 are dewatered and the lift tank 54 is dewatered sufficiently for lifting purposes. Should the pontoon 52 become accidentally disconnected from the payload the pontoon 52 will rotate about its longitudinal axis so that the lift tank 54 will flood through its openings 56. When the lift tank 54 is flooded the pontoon will then upright itself and will ascend gradually toward the surface of the ocean without hazard to the surface ship. Once the salvage pontoon has surfaced with the payload to be retrieved, towing of the payload by the surface ship 12 can be immediately commenced since the salvage pontoon 52 is in a desired horizontal attitude for towing purposes.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. lt is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as speciflcally described.

I claim:

1. A salvage pontoon comprising:

a lift tank which is open at its bottom and closed at its top; a negative buoyancy control tank and a positive buoyancy tank mounted to the top portion of the lift tank;

the pontoon having a positive metacentric height and negative buoyancy when the lift tank and positive buoyancy tank are flooded and the negative buoyancy control tank is dewatered;

said pontoon having a positive metacentric height and positive buoyancy when the lift tank is flooded and the positive buoyancy tank and negative buoyancy control tank are dewatered; and

said pontoon having a negative metacentric height and positive buoyancy when the lift tank, positive buoyancy tank, and negative buoyancy control tank are dewatered. 2. A salvage pontoon as claimed in claim 1 wherein: lift tank is elongated; and

the negative buoyancy control tank and the positive buoyancy tank are both substantially symmetrical about the longitudinal axis of the lift tank. 3. A salvage pontoon as claimed in claim 2 wherein:

the negative buoyancy control tank seals the top of the lift tank. 4. A salvage pontoon as claimed in claim 3 wherein:

the positive buoyancy tank is in the form of a toroid and is located immediately below the negative buoyancy control tank.

5. A salvage pontoon as claimed in claim 4 wherein:

each of the lift tank and the positive buoyancy tank are provided with an inlet; said inlets being interconnected to a common valve.

6. A salvage pontoon as claimed in claim 4 including:

a hawse pipe extending through all three tanks.