US3111926A

US3111926A - Apparatus for anchoring underwater vessels

Info

Publication number: US3111926A
Application number: US157678A
Authority: US
Inventors: Jr Howard L Shatto
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1961-12-07
Filing date: 1961-12-07
Publication date: 1963-11-26
Anticipated expiration: 1980-11-26

Description

Nov. 26, 1963 H. L. SHATTO, JR 3,1 1,

APPARATUS FOR ANCHORING UNDERWATER VESSELS Filed Dec. 7, 1961 2 Sheets-Sheet 1 INVENTOR H. L. SHATTO,Jr.

HIS AGENT Nov. 26, 1963 H. 1.. SHATTO, JR 3,

APPARATUS FOR ANCHCRING UNDERWATER VESSELS Filed Dec. '7, 1961 2 Sheets-Shee t 2 FlG.2

INVENTOR H. L. SHATTO,Jr.

HIS AGENT United States Patent (3 Delaware Filed Dec. 7, 1961, Ser. No. 157,678 6 Claims. (Cl. 114-206) This invention relates to apparatus for anchoring underwater vessels and pertains more particularly to apparatus for anchoring vessels at a predetermined depth below the surface of a body of water, such for example as over an offshore oil field in which one or more underwater wells have been drilled.

For some years there has been considerable development of oil fields at offshore locations with wells being drilled 70 miles or more offshore and in depths of water of 100 feet or more. Recently, there has been considerable interest in drilling wells in much deeper water with the wellhead assemblies being positioned on the ocean floor. For producing wells in water depths up to 100 feet, the well flowlines generally run to a production platform containing various tanks, separators, pumps, manifolding equipment, etc., where the produced oil is gathered, separated and treated and then pumped to shore or to a barge. Since it is not feasible to build production platforms of the permanent fixed type in waters of 100 feet or more in depth, deep water or isolated wells are generally produced into a barge or boat positioned on the surface of the water in the vicinity of the well. The use of barges or boats for this purpose is both costly and troublesome in that personnel must remain on board in charge of the boat or barge which becomes a navigational hazard to ocean-going vessels. At the same time the boat or barge being employed for production purposes is exposed to the forces of wind and wave at the surface of the ocean and it must be normally disconnected from the well during severe storms. Thus, considerable production time may be lost when the barge or boat is oif location due to a storm.

It is therefore a primary object of the present invention to provide an underwater vessel positioned at a depth below the surface of the water and anchored at a suitable depth by the apparatus of the present invention so as to provide a large measure of insulation or cushioning from the violent action which often exists on the surface of the ocean. v A further object of the present invention is to provide apparatus which provides firm lateral and vertical control of a vessel in its submerged position while at the same time permitting an easy and well-guided ascent of the vessel to the surface.

Another object of the present invention is to provide an underwater vessel with anchoring apparatus which positions the vessel at a fixed location while leaving the vessel relatively free to move with the orbital motion of the waves so that the anchoring apparatus is required to resist only a relatively small percentage of the wave forces.

A still further object of the present invention is to pro vide an underwater vessel with an anchoring apparatus that may be readily repaired or replaced without the necessity of moving the vessel from its offshore position.

Still another object of the present invention is to provide an'anchoring apparatus for an underwater vessel which is secured to the vessel in a manner such that the vessel is not subjected to excessive tilt in the event that a portion of the anchoring system is broken.

These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

FIGURE 1 is a schematic longitudinal view illustrating a vessel anchored to the ocean floor;

FIGURE 2 is a diagrammatic view taken in longitudinal elevation illustrating one method of connecting anchor lines to a vessel;

FIGURE 3 is a plan View of the underwater vessel of FIGURE 2; and

FIGURES 4, 5, 6 and 7 are diagrammatic view showing various forms of auxiliary anchors or variable weight devices adapted to be installed in, or secured to, the anchor lines of an underwater vessel.

Referring to FIGURE 1 of the drawing, a vessel 11 is illustrated as being positioned at a predetermined depth, say from 50 to 200 feet below the surface 12 of a body of water 13. The vessel 11 is anchored in a more or less fixed position by means of three or

more anchor lines

14 and 15, only two of which are shown for ease of illustration. The anchor lines may be secured to any suit-able type of anchor. For example, anchor line 14 is shown as being secured to a short stub pile anchor 16 which has been fixedly secured to the ocean floor by cement 17. Anchor line 15, on the other hand, is attached to a kitetype anchor of the type described in US. Patent No. 2,73 8,750. A kite-type anchor 18 is especially effective in very soft bottom locations where the kite may be pulled deep into the mud.

Extending downwardly from the vessel 11 are a plurality of flexible flow lines 20, 21, 22, 23 and 24 which run along the ocean floor 25 to a distant location. For example, at least one flow line 'would connect each underwater well (not shown) with the vessel 11. In the event that the underwater well was not a flowing well, it would be necessary to extend a second flow line between the vessel and the well by which gas under pressure could be transferred from the vessel 11 to the -well in order to produce the well by the gas lift method. Other flow lines may extend from the vessel 11 to shore, or to a production platform located at a remote location. Thus, some of the flexible flow lines would be used to transfer the production fluid from the vessel 11, or in the event that the vessel 11 was provided with an oil, gas and water separator, one or more of the flow lines would be utilized to transfer the separated phases of the production fluid to shore or to production facilities located at other remote places. Additionally, at least one of the flexible flow lines may extend from the vessel 11 to a remote production handling center so as to provide the vessel 11 with a suitable supply of gas under pressure from the center in order to operate the vessel and the equipment thereon. It is to be understood that the flow lines running along the ocean floor 25 to a position underneath the vessel may be either flexible or of rigid pipe but it is essential that at least a portion of the flow lines he flexible. The flexible portion of each flow line would be the portion connected to the vessel 11 and be of a length sufficient to extend from the vessel to the ocean floor when the vessel 11 was floating on the surface 12 of the body of water 13.

Mounted for sliding movement along the

anchor lines

14 and 15 are

slidable carriers

28 and 29 which may be tubular in form or of any other suitable design. Movement of the

slidable carriers

28 and 29 along the

anchor lines

14 and 15 is limited by a pair of stop means 30 and 31 which are fixedly secured to the

anchor lines

14 and 15. Depending from the

slidable Carriers

28 and 29 are flexible and automatically variable weight means 32 and 33. The combination of the position of the stop means 30 and 31 and the length of the weight means. 32 and 33 is such that when the vessel 11 is in its normal anchored position below the surface of the water 13, at least a portion of each weight means or auxiliary anchor means 32 and 33 is in contact with the ocean floor 25.

Secured to each

carrier

28 and 29 is a

retrieving line

34 and 35, respectively, which extends to the top of the vessel 11. The

retrieving lines

34 and 35 are employed any time that it is desirable to change the weight and configuration of the weight means 32 and 33. Additionally, the

retrieving lines

34 and 35 may be used to retrieve the weight means 32 and 33 when they are in need of repair. Although the

retrieving lines

34 and 35 facilitate repair and alteration of the weight means 32 and 33, they are not an essential part of the present anchoring system as each of the weight means 32 and 33 could be fixedly secured to the

anchor lines

14 and 15 at the stop elements and 31, or at any other desired point on the anchor lines. It is preferred, however, that the weight means 32 and 33 be readily removable by securing them to the

slidable carriers

23 and 29.

The upper ends of the

anchor lines

14 and 15 of the anchor system of the present invention may be secured to the vessel 11 in any suitable manner. It is preferred, however, that when a small number of anchor lines, say three, are being employed, that the upper ends of the anchor lines be secured relatively close together below the center line of the vessel, that is, the center of buoyancy so that in the event that one of the anchor cables brakes the vessel 11 will be subjected to less tilt. One arrangement of a central supporting device for anchor lines is shown in FIGURE 2 wherein an anchor post 4%) extends downwardly from the vessel 11 and has secured to the lower end thereof an anchor plate 41. Fixedly secured to the sides of the vessel 11, as by welding, and extending vertically down along the side of the vessel and bending into a position inboard of the periphery thereof where they may be secured to the anchor plate 41 are a pair of

anchor tubes

42 and 43. As shown in FIGURE 3, the

tubes

42 and 43 are provided with longitudinal slots 44 and 45 which are wider than the diameter of the

anchor lines

14 and 15.

The anchor lines or

cables

14 and 15 are provided with

holding elements

46 and 47 or stop means at the top thereof which are of a size sufliciently small to pass down the

anchor tubes

42 and 43 while having

cable sockets

48 and 49 of a size to extend through the slots 44 and 45 in the

anchor tubes

42 and 43. A retrieving cable 51 is secured to the holding element 46 and extends up through the anchor tube 42 to the upper end thereof where it is secured to a ring 52 or other suitable stop element which is of a diameter greater than the anchor tube 42 so that it will not pass downwardly therethrough.

In the event that it was desired to replace one of the anchor lines 14, the vessel 11 would first be raised to the surface 12 of the body of water 13 (FIGURE 1) in any suitable manner well known to the art, such as by pumping air or gas into buoyancy tanks which would be contained within the vessel 11. With the vessel positioned at the surface of the ocean, a temporary anchor (not shown) would be set and the upper end of the temporary anchor line would be connected to an anchor ring 53 (FIGURE 2) fixedly secured to the top of the vessel 11 close to the anchor tube 42. A hook (not shown) could then be inserted in the ring 52 so as to pull the anchor line holding element or stop means 46 out of the anchor tube 42. The hook would be attached to a hoist or winch line provided by a service barge. After the old anchor line 14 was removed a new anchor line could be inserted.

The auxiliary anchoring device or weight means 32 may take several forms and be of any desired configmration depending upon the amount of weight that it is desired to add to the anchor lines for every foot that the anchor lines move upwardly from their normal position. Two forms of weights 32 are shown in FIGURES 6 and 7 as depending from slidable carriers 28 that are mounted on the anchor line 14. In FIGURE 6 the weight comprises two links of heavy anchor chain while in FIGURE 7 the weight 32 consists of five links of similar chain mounted in side-by-side relationship.

The simplest form of a flexible and automatically variable weight to be secured in an anchor chain is illustrated in FIGURE 4 with an anchor line 54-5461 having a section 5412 formed of a length of anchor chain having many times the weight per foot of length that the adjacent sections of anchor line 54 and 54a have. Normally, at least a portion of the chain section 54b of the anchor line would rest on the ocean floor 25. As the vessel started to move upwardly due to water movement, more weight would be added to the anchor line 54 by more of the links of the chain section 54b being picked up off the ocean floor 25. Conversely as the vessel is forced downward, the reduction of chain weight adds to the available buoyancy to resist the downward force. Since a chain of this type is subject to wear because it is being repeatedly picked up and set down on the sand of the ocean floor 25, there is greater possibility of the anchor line 54 breaking than with the form shown in FIGURES 6 and 7. In the event that it is desired to employ a single length of chain as shown at 5411 in FIGURE 4, it may be desirable to provide a length of anchor line 54b interconnecting the anchor lines sections 54 and 54a (FIGURE 5) as a guide against breaking the tie anchor line when the chain section 54b breaks.

The vessel 11 (FIGURE 1) would normally be provided with sufficient sealed buoyancy tanks so as to provide suflicient buoyancy to keep the vessel 11 within the range of the pendant chains even if the variable buoyancy tanks should become completely flooded. A vessel 11 equipped with the anchoring apparatus of the present invention possesses a vertical stabilizing characteristic which is pro vided by the

pendant weights

32 and 33 which are attached to the anchor lines 14 and 15 in such a manner as to offer rapidly increasing resistance to upward movement or downward movement of the vessel from its normal operating depth of, say, feet. The

pendant weights

32 and 33 are preferably multiple strands of anchor chain giving the desired weight per foot slope to a weight curve. The

pendant anchor chains

32 and 33 provide resilient compliance to orbital wave motion by means of their spring characteristic as they are alternately picked up and laid down on the sea floor. The chain weights are preferably used as they are less likely to crush a flow line than say large solid steel anchors. It is to be understood, however, that other forms of elongated flexible weights can be employed as Well as a large link anchor chain. Thus, a multiple number of small weights connected together by eye hooks could be substituted for the chain. Likewise, instead of using five links of chain as shown in FIGURE 7, five short cables could be employed with a weight hanging on each cable at a different distance from the anchor line 14 so that only one weight is picked up off the ocean floor at a time. The anchoring apparatus of the present invention holds a vessel firmly yet allows it to move with the wave orbit.

Additionally, the pendant anchor weights tend to restrain a vessel from moving any great distance horizontally. As the vessel moves horizontally in a direction away from an anchor line, some of the slack in the anchor line would be taken up causing the anchor line to lift at least a portion of the anchor weights or

chains

32 and 33 off the ocean floor, thus increasing the force exerted by that particular anchor line in restoring the vessel to its original position.

I claim as my invention:

1. Apparatus for anchoring a buoyant vessel below the surface of a body of water while permitting limited movement of said object therein, said apparatus comprising anchor means adapted to be fixedly positioned to the ground underlying said body of water and outboard of said object, anchor line means securing said anchor means to a submerged buoyant vessel, said anchor line means being of a length sufiicient to permit said vessel to be movably positioned below the surface of said body of water when extended to said anchor means positioned outboard of said object, flexible and automatically variable weight means secured to and depending from said anchor line means intermediate the ends thereof at a point where at least a portion of said weight means is in contact with the ground beneath said body of water, each of said Weight means comprising a plurality of weight elements connected together in flexible relationship one to another in at least one line, and carrier means slidably mounted on each of said anchor line means, one end of each weight means being secured to one of said carrier means.

2. The apparatus of claim 1 including cable means being connected between said carrier means and said vessel for retrieving said carrier means and said weight means.

3. The apparatus of claim 1 Wherein said anchor line means are secured to said buoyant object inboard of the periphery thereof, the secured ends of each of said anchor line mean-s being substantially equidistant from a vertical line through the center of buoyancy of said object.

4. The apparatus of claim 1 including anchor line support means depending centrally from said object and having said anchor line means secured thereto.

5. The apparatus of claim 4 including vertical anchor tubes secured to the outside of said buoyant object and substantially equi-spaced therearound, said anchor tubes being secured at the lower ends thereof to said anchor line support means, each of said anchor tubes having a longitudinal slot through the wall and extending the length thereof, an anchor line holding element receivable in and slidable within each of said tubes, a portion of each anchor line holding element adapted to extend through said slot in said tube and being secured to an anchor line means, and retrieving cable means attached to each holding element and extending to the top of said tube.

6. The apparatus of claim 1 including stop means affixed to said anchor line means for limiting the move ment of carrier means thereon.

References Cited in the file of this patent UNITED STATES PATENTS 832,420 Rinaldy Oct. 2, 1906 2,100,231 Armstrong Nov. 23, 1937 2,894,268 Grie'be July 14, 1959 3,082,608 Daniell Mar. 26, 1963 FOREIGN PATENTS 464,463 Italy July 4, 1951 598,037 Great Britain Feb. 9, 1948

Claims

1. APPARATUS FOR ANCHORING A BUOYANT VESSEL BELOW THE SURFACE OF A BODY OF WATER WHILE PERMITTING LIMITED MOVEMENT OF SAID OBJECT THEREIN, SAID APPARATUS COMPRISING ANCHOR MEANS ADAPTED TO BE FIXEDLY POSITIONED TO THE GROUND UNDERLYING SAID BODY OF WATER AND OUTBOARD OF SAID OBJECT, ANCHOR LINE MEANS SECURING SAID ANCHOR MEANS TO A SUBMERGED BUOYANT VESSEL, SAID ANCHOR LINE MEANS BEING OF A LENGTH SUFFICIENT TO PERMIT SAID VESSEL TO BE MOVABLY POSITIONED BELOW THE SURFACE OF SAID BODY OF WATER WHEN EXTENDED TO SAID ANCHOR MEANS POSITIONED OUTBOARD OF SAID OBJECT, FLEXIBLE AND AUTOMATICALLY VARIABLE WEIGHT MEANS SECURED TO AND DEPENDING FROM SAID ANCHOR LINE MEANS INTERMEDIATE THE ENDS THEREOF AT A POINT WHERE AT LEAST A PORTION OF SAID WEIGHT MEANS IS IN CONTACT WITH THE GROUND BENEATH SAID BODY OF WATER, EACH OF SAID WEIGHT MEANS COMPRISING A PLURALITY OF WEIGHT ELEMENTS CONNECTED TOGETHER IN FLEXIBLE RELATIONSHIP ONE TO ANOTHER IN AT LEAST ONE LINE, AND CARRIER MEANS SLIDABLY MOUNTED ON EACH OF SAID ANCHOR LINE MEANS, ONE END OF EACH WEIGHT MEANS BEING SECURED TO ONE OF SAID CARRIER MEANS.