System For Retrieving Anchor Chains

Abstract

This invention relates to a system for retrieving the anchor chain which has been cut loose from an anchored vessel. A buoy, filled with water to make in non-buoyant, is attached to the anchor line. If it becomes necessary to sever the anchor line from the ship, the anchor line and flooded buoy both drop to the ocean floor. When it is desired to retrieve the anchor line, a gas generating device, made a part of the buoy, is actuated to drive the water out of the buoy. The now buoy rises to the surface and brings the end of the anchor chain with it.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is concerned with retrieving an anchor line which has been cut or cast off from an anchored vessel floating on a body of water. More particularly, the invention is concerned with a retrieving system incorporating in the anchor line a buoy made non-buoyant but containing means actuatable from the surface for making the buoy buoyant.

2. Setting of the Invention

The need for oil and gas has caused men to explore water-covered areas which may be productive of oil and gas. Some of these wells are drilled from fixed platforms. A fixed platform is merely a drilling deck platform supported above the water by piles extending down into the water bottom. In deep water this is not economical and such structure becomes difficult to erect. Therefore, many wells in water-covered areas are drilled from floating drilling vessels. In most drilling vessels, a drilling derrick is mounted over a vertical passage in the vessel through which drilling operations are conducted. A riser pipe, which is a large diameter pipe, e.g., 20 inches in diameter, extends from this passage in the drilling vessel to the subsea well. Drilling operations are conducted through this riser pipe.

It becomes important that the ship stay in a relatively fixed position, i.e., that it not wander too far from a position directly above the well being drilled. At present, the most common method of anchoring a drilling vessel is by the use of anchoring lines or cables extending from the ship to anchors set in the ocean bottom. Sometimes in severe weather it is necessary to release these anchor lines from the ship without much warning. One reason for having to remove some of the anchor lines quickly is to permit the ship to be headed into the direction of the storm. After the storm has subsided, it is necessary to re-attach the anchor line to the ship with a minimum loss of time. In the past in the face of a sudden storm, the anchor lines have been merely severed and dropped to the bottom of the ocean floor. When this occurs the common way to recover them is with grappling hooks, which is a time consuming operation. I have provided an improvement so that the anchor chain can be more quickly recovered.

SUMMARY OF THE INVENTION

This invention relates to the recovery of an anchor chain which has been severed from a floating vessel. A buoy of sufficient buoyancy to lift one end of the chain from the bottom to the surface is incorporated into or attached to the anchor chain. During normal operations this buoy is filled with water. Attached to the buoy is a container holding a propulsion charge which, when actuated, expels the water from the buoy through a check valve, thus deflooding the buoy so that it can rise to the surface, bringing the chain with it.

In another embodiment of this invention the water-filled buoy is placed on the bottom of the body of water and connected to the anchor chain by a small line with sufficient strength to lift the end of the anchor line. Then when it is desired to retrieve the anchor line, the buoy is deflooded and rises to the surface, taking with it the small line. Then the small line is used to retrieve the anchor line.

DESCRIPTION OF THE DRAWINGS

Various objects and a better understanding of the invention can be had when taken in conjunction with the following description and the drawings.

FIG. 1 illustrates a ship floating on a body of water and having a water-filled buoy attached to the anchor line near the ship;

FIG. 2 is similar to FIG. 1 and shows a different embodiment wherein the water-filled buoy is resting on the ocean floor and is connected to one end of the anchor chain by a small line.

FIG. 3 illustrates the structure of the buoy in greater detail.

Attention is directed to FIG. 1 which shows a vessel 10 floating on a body of water 12 having a bottom 14. An anchor 16 is placed in the bottom 14. An anchor line 18 extends from anchor 16 through hawse pipe 20 to an anchor windlass 22 to storage compartment or chain locker 24.

A buoy 26 is attached to link 28 of chain 18 near the vessel 10. Buoy 26 has been made non-buoyant by filling it with water. When buoy 26 is empty of water, it has sufficient lifting capacity to lift the end of anchor chain 18 to the surface so that it may be readily retrieved.

Attention is directed momentarily to FIG. 3 for details of buoy 26. Buoy 26 contains a valve 31 so that water may be injected thereto. It also contains an outlet conduit 29 having check valve 30 which permits fluid to flow only outwardly. The interior of buoy 26 contains a first compartment 40 and a second compartment 41. These two compartments are separated by a partition such as piston 42. Compartment 40 contains water and compartment 41 contains a propellant which when actuated generates gas under high pressure. The gas forces the piston to the left which drives the water out of compartment 40. The propellant is actuated by an igniter 43 which has a sonar receiving head 44 which can be actuated by operating a sonar transmitter carried by a vessel at the surface of the body of water. A suitable propellant is identified as Amoco Chemical AGF, which is an ammonium nitrate base with an asphaltic filler and commercially available from Amoco Chemical Corporation, Seymour, Ind. This particular propellant gas generates 16 cu. ft. of gas at 14.7 p.s.i. pressure and 32.degree. F. from one pound of propellant. Most anchoring is in water less than about 400 feet, where pressure is 177.7 p.s.i. and water temperature is 57.degree. F. Volume of gas generated by one pound of AGF propellant under these conditions is 1.5 cu. ft. Suitable means for detonating a propellant in a container underwater from the surface is commercially available as sonic initiating devices from various sources such as Raytheon Company, General Electric Company, Westinghouse Electric Corp. and others.

In normal operations the buoy 26 is connected to the anchor chain 18 and filled with water through valve 31. After it has been filled with water, the valve is closed. Compartment 41 is also provided with the proper propellant charge and means for actuating the charge as described above. Care must be exercised so that the connecting link connecting the buoy 26 to link 28 of anchor chain 18 is sufficiently short so that under normal operation, movement of the chain 18 does not permit buoy 26 to touch bottom 14. If the buoy does touch bottom, there is a danger that the dynamic tension in anchor line 18 can be increased over what it would otherwise be. In the event of a sudden storm the anchor chain 18 is severed at the ship such as by a cutting torch. The anchor line 18 and the buoy 26 both quickly drop to the bottom of the body of water. After the storm has subsided, it is desired to raise the anchor chain. At this time the propellant in compartment 41 is actuated from the vessel and the generated gases drive the water out through check valve 30. The buoy has been sized so that it will have sufficient lifting capacity to raise the end of the anchor chain to the surface. At this time the anchor chain is then readily recovered and reattached to drilling vessel 10. The size of the propellant charge in compartment 41 is capable of generating sufficient gas to expel the water from buoy 26 and at pressure sufficient to overcome the backpressure embodied on the water in the buoy due to the depth of the water.

Attention is now directed to FIG. 2 which shows the more preferred system for raising the end of the anchor line. In this embodiment, buoy 26 in normal operations rests on the bottom 14. A small line 34 connects this sunken buoy to link 28 of chain 18. In normal drilling operations anchor line 18 does not stay in a fixed position. Wind and wave action on the ship 10 causes the anchor chain 18 to more or less oscillate. This anchor chain thus moves up and down. When a ship is moored in heavy seas, sharp periodical variations of chain tensions have been observed. These sharp variations are called dynamic tension. Line 34 is of sufficient length so that during normal drilling operations the movement of anchor chain 18 will not lift buoy 26 off the bottom. Thus, line 34 always remains slack during normal operations. This is important because if line 34 becomes taut, it may, in fact, increase the dynamic tension on chain 18 over that which it would be without the connection. Therefore, care should be taken that line 34 is of sufficient length to prevent this.

In operation, then, the embodiment of FIG. 2 is similar to that of FIG. 1. Buoy 26 if filled with water and connected through line 34 to link 28 in chain 18. I emphasize that care is taken that line 34 is of sufficient length, as discussed above, so it does not become taut during normal anchoring. When it suddenly becomes necessary to move the ship, the anchor line 18 is severed at the ship. The ship is free to ride out the storm or seek shelter. When the storm has subsided, vessel 10 returns. The ship operator then actuates the propellant in buoy 26. This forces the water out through the check valve and the buoy rises to the surface, bringing with it small chain 34. Chain 34 is used to retrieve large anchor chain 18. Chain 34 is of sufficient strength to lift one end of chain 18. However, as chain 34 can be much smaller than chain 18, the buoy in the embodiment of FIG. 2 only needs to be large enough to lift line 34. Thus, in the embodiment of FIG. 2, the buoy 26 can be much smaller than the buoy required in the embodiment shown in FIG. 1.

While the above embodiments have been described with a great deal of detail, it is possible to produce modifications thereof without departing from the spirit or scope of the invention.

Claims

I claim:

1. An anchoring system for connecting a vessel floating on a body of water to an anchor in the bottom thereof which comprises:

an anchor line connecting said vessel to said anchor;

a non-buoyant container;

connecting means connecting the container to said anchor line near said vessel, said connecting means is a line small in comparison to said anchor line, said connecting line being of sufficient length so that said container while non-buoyant always remains on the bottom of said body of water during normal anchoring operations;

means attached to said container and operable from the surface to make said container buoyant.

2. A system as defined in claim 1 in which said non-buoyant container includes:

water within said container

a check valve in the wall of said container permitting the water to move only in the direction from the inside of said container;

means to drive said water out said check valve.

3. A system as defined in claim 2 in which said water expulsion means includes a propellant for generating gas under sufficient pressure and volume to expel the water from said container.