US2721530A

US2721530A - Anchor

Info

Publication number: US2721530A
Application number: US354567A
Authority: US
Inventors: Vorenkamp Egbert Roelof
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1953-05-12
Filing date: 1953-05-12
Publication date: 1955-10-25
Anticipated expiration: 1972-10-25

Description

Oct. 25, 1955 E. R. voRENKAMP ANCHOR Filed May 12, 1955 F'lGUKE; 3

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E R VorenKar-n BL, l 1L# We \s Aojen United States Patent O ANCHOR Egbert Roelof Vorenkamp, New Orleans, La., assignor to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application May 12, 1953, Serial No. 354,567

4 Claims. (Cl. 114-206) This invention relates to anchors and pertains more particularly to ship or barge anchors adapted to be readily worked in mud to securely anchor a drilling rig barge or other type of vessel on mud flats such as those commonly encountered along the coast of Texas and Louisiana.

The present anchor is also applicable for use with any type of ship vessel or barge where an anchor with high holding power is desired for use in soft, unconsolidated soil conditions on the sea oor. Anchors of high holding power are required to insure immobility of drilling tenders while on or near drilling locations, to obtain controlled movement to or from these locations and to protect all types of vessels, ships, etc., during hurricanes, typhoons and/ or other adverse conditions in or near inland waters bordering the Gulf of Mexico. The principal disadvantage of the anchors now in use is that they depend partially on the weight to obtain high-holding power. Additionally, the ilukes of the anchors presently used are not designed or arranged so as to cause deep penetration in a soft, muddy sea bottom, and the area of bearing surface is insufficient to develop high-holding power in soft soil conditions. Furthermore, their design is such that they are not inherently stable during burial.

lt is, therefore, a primary object of the present invention to provide an anchor having high-holding power in very soft soil conditions.

A further object of this invention is to provide a lightweight anchor which is inherently stable during burial in soft, muddy sea bottoms.

Another object of this invention is to provide a light weight anchor which may be readily pulled into or from deep penetration depths in a soft, unconsolidated seat iloor.

Another object of this invention is to provide a lightweight anchor adapted to be sunk deep in the mud without the addition of excess weights during the sinking operation. f

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

Figure l is a plan view of the present anchor showing the chains or cables by which the present anchor may be connected to a vessel.

Figure 2 is a diagrammatic view in front elevation of the present anchor.

Figure 3 is a cross-sectional view taken along the line 3-3 of Figure 2.

Figures 4 and 5 are diagrams illustrating changes in position of the present anchor when a force is applied to the anchor cable.

Figure 6 is a diagrammatic view illustrating a barge towing the present anchor and embedding it in the thick layer of soft, unconsolidated soil under a body of water;

Figure 7 is a schematic diagram illustrating the forces applied to the present anchor when it is sunk into posi'- tion.

Referring to Figure l, 2 and 3 of the drawing, the pres' ent anchor comprises a triangular main plate 11 having ixedly secured thereto as by welding a normally vertical ice supporting guide plate 12, and, if desired, one or more reinforcing normally horizontal members 13. If a single horizontal support plate 13 is employed, it is preferably secured across the main plate 11 near the bottom thereof, or, in other words, parallel to the side of the triangular main plate which serves as the base of the anchor. While the horizontal support member 13 is shown as an angleiron, a at supporting member 13 may be employed instead in order to reduce the resistance of the anchor as it passes through mud and water.

The vertical supporting guide plate 12 is preferably triangular in shape and is xedly secured to the main plate 11 so that it extends outwardly therefrom with the heavier or larger portion of the guide plate 12 secured adjacent to the base of the triangular main plate 11 in order to concentrate the weight near the bottom or base of the anchor. The vertical guide plate 12 is preferably secured to the main plate 11 along a line extending from the apex or top 14 of the anchor to the mid-point in the base 15 of the anchor. The shape of the verticalL supporting plate 12 and its position on the main plate 11 is such that the main plate will stand at an angle of about 25 degrees (which is the desired angle for penetration) from the vertical when resting on the lower edges of the main and supporting

plates

11 and 12, respectively. If desired, a plurality of teeth 16 may be provided on the lower edge of the main plate 11 to insure initial penetration of the anchor.

Fixedly secured as by welding to the triangular main plate 11 near the apexes thereof are three shackles or

ring connectors

17, 18 and 19 of suitable design. Flexible cables or

chains

21, 22 and 23 which may be of a xed or adjustable length extendv from each of the

shackles

17, 18 and 19 and are secured to a common shackle or connecting ring 24 in a manner to form a bridle on the sideA of the main plate 11 opposite from the side to which the

support members

12 and 13 are attached.

Cables

21, 22 and 23 are adjusted so that the two lower bridle links 21l and 22 are equal in length while the length of the upper bridle link 23 is of a length such that a horizontal plane passing through the common shackle perpendicular to the main plate 11 and parallel to the lower edge thereof intersects the main plate 11 below its center of gravity as shown in` Figure 4. Thus, with a towing or anchor cable 25 attached to the common shackle 24, the main plate of the anchor 11 is tilted at an angle such as shown in Figure 5 when a force is applied to the cable 2S. A retrieving or handling shackle 26 is attached near the upper apex of the main plate 11 as shown in Figures 2 and 3 to facilitate removal of the anchor from the muddy sea bottom and for ease in handling the anchor when itis desired to lower the anchor to an upright position on the' sea floor.

The principle of operation of the present' anchor may be readily understood by reference to Figures 4, 5 and 7 of the drawing. When a force is exerted on a plate 11 through its bridle 22 and 23' (Figure 4) the plate rotates, due to the resisting forces of the surrounding rnediurn, to a position such as shown in Figure 7 where the acting force F passes through the center of gravity of plate 11. Since the major resisting force R acts perpendicular to the plane of the plate, a component of this force, Ry, is exerted on the plate. If the plate 11'is in a medium of substantially uniform fluid, the plate will move through an angle 0 from a position X to a position Y as shown in Figure 6.

Considering position Y of Figure 6 as the general case for angles of Q. between 0 and 90 and analyzing the forces', it' can be seen that the component Ry is always greater than Fy. Consequently, the plate moves in the direction of Ry until Ry is balanced against the sum of Fy and Ny, the component of the resisting force N acting on the lower edge 27 of the plate. Applying these forces to the main plate 11 of the present anchor, it can be seen that the anchor will penetrate into very soft soil conditions (comparable to a fluid medium) on the sea bottom. The actual depth of penetration is a function of the magnitudc of force on the anchor line, the length ofthe anchor line, and the resistance of soil in the sea bottom. In operation, as illustrated in Figure 6, the anchor 11 is immersed in a body of water at any desired distance from a barge 27, the anchor line 25 being secured to the barge in any suitable manner, for example, by means of a winch (not shown). The kite-shaped anchor 11, which is preferably made of plate steel, together with its wire bridle offers only a minimum of resistance as it sinks and buries itself deep into the soft, unconsolidated soil on the sea floor. Any force applied to the anchor line 25 pulls the anchor 11 more deeply into the soft soil. Because of the large bearing arca of the main plate 11, high-holding power is obtained even in very soft, soupy soil since the anchor penetrates down through the very soft soil to firmer soil. As the anchor line pull increases, the developed holding power also increases. It is to be noted that the supporting Vertical guide plate 12 provides a stabilizing action and guides the anchor 1l during burial in the direction of the pull in addition to reinforcing the main plate.

In off-shore drilling operations the present anchor may be used to secure a portable drilling rig barge on its location and thereafter may be employed to supply the required pull in moving the barge to another drilling location. One of the problems commonly encountered in off-shore drilling operations in the Gulf of Mexico is that of moving a barge-mounted drilling rig a distance of several miles over a bottom consisting of mud when the draft of the rig barge is one foot greater than the apparent depth of the water which is usually effected by dropping the anchor at some distance ahead of the barge, pulling up the barge to the anchor, raising the anchor and dropping it further ahead of the barge, and repeating the operation. the anchor on the ground, which conventional anchors often fail to give. For example, during offshore operations in the Gulf of Mexico, a 2850 lb. Danforth anchor offered no resistance at all in the soft mud encountered, at one particular location. Another anchor Weighing 5 tons was readily moved through the soft clay with a pull of only 20 tous which was by no means suflicient to budge a drilling barge. However, the barge could be easily moved by employing an anchor according to the present design as described above, which only weighed 650 lbs. and withstood a pull of 70 tons because it had dug itself to a depth of 46 feet into the soft mud.

In the past, it has been possible to move a drilling rig barge through a long and narrow ditch by securing a line to a stump or tree or any other solid object along the sides of the ditch, and subsequently, to move the drilling rig barge from one bank to another. This method of moving a barge is both time-consuming and undesirable in that the barge crew has to wade through the swamps to secure and later to untie the pulling line. By employing the present anchor the same drilling barge has been readily moved through a similar long and narrow ditch by lowering the anchor from the barge into the ground in the middle of the entrance of this ditch. By taking up the anchor line on a winch or hoist mounted on the barge, the barge was readily pulled through the ditch in one straight haul. The use of a cable or chain bridle allowed the anchor to penetrate deep into the soft sea bottom as the line pull on the anchor line is increased while the barge bearing surface of the anchor gives it high-holding power in very soft soil conditions. The holding power referred to herein is the ratio of the developed holding power to the weight of the anchor.

When it is desired to move the anchor to a new position, the anchor may be vertically withdrawn from the This requires, however, a firm grip of e mud by a cable (not shown) which is attached to the retrieving shackle 26 of the anchor 11 shown in Figures 2 and 3.

I claim as my invention:

l. An anchor possessing high holding power in soft muddy seat bottoms, said anchor comprising a flat triangular main plate of substantial weight so that the anchor readily sinks to the bottom, stabilizing plate means xedly secured to said main plate on one side thereof and normal thereto, the heavier portion of said stabilizing plate means having the greater area and weight thereof secured adjacent the base of the main plate to concentrate the weight near the downwardly directed base of the anchor, bridle means secured to said main plate near the corners of the other side thereof, and shackle means engaging said bridle means for securing an anchor cable thereto, said shackle means being positioned in said bridle means at a point below the center of lateral resistance of said main plate as the anchor is pulled through the water.

2. An anchor possessing high holding power in soft muddy sea bottoms, said anchor comprising a flat triangular main plate of substantial weight so that the anchor sinks readily to the bottom, stabilizing plate means fixedly secured to said main plate on one side thereof and normal thereto, support means affixed to said main plate adjacent said stabilizing plate means and normal thereto, the heavier portion of said stabilizing plate means having the greater area and weight thereof secured adjacent the base of the main plate to concentrate the weight near the downwardly directed base of the anchor, flexible bridle means secured to said main plate near the corners of the other side thereof, and shackle means engaging said bridle means for securing an anchor cable thereto, said shackle means being positioned in said bridle means at a point below the center of the lateral resistance of said main plate as the anchor is pulled through the water.

3. An anchor possessing high holding power in soft muddy sea bottoms, said anchor comprising a flat triangular main plate of substantial weight so that' the anchor readily sinks to the bottom, stabilizing plate means Xedly secured to the main plate on one side thereof and normal thereto and generally along an axial line bisecting one of the angles of said plate, the heavier portion of said stabilizing plate means having the greater area and weight thereof secured adjacent the base of the main plate to concentrate the weight near the downwardly directed base of the anchor, support means atlixed to said main plate adjacent said stabilizing plate means and normal thereto, teeth means secured to one'edge of said plate, llexible bridle means secured to said main plate near the corners on the other side thereof, and shackle means engaging said bridle means for securing an anchor cable thereto, said shackle means being positioned in said bridle means at a point below the center of the lateral resistance of said main plate as the anchor is pulled through the water.

4. An anchor possessing high holding power in soft muddy sea bottoms, said anchor comprising a fiat triangular main plate of substantial weight .so that the anchor readily sinks to the bottom, stabilizing plate means iixedly secured to said main plate on one side thereof and normal thereto and generally along an axial line bisecting one of the angles of said plate, the heavier portion of said stabilizing plate means having the greater area and weight thereof secured adjacent the base of the main plate to concentrate the weight near the downwardly directed base of the anchor, flexible bridle means secured to said main plate near the corners on the other side thereof, shackle means engaging said bridle means for securing an anchor cable thereto, said shackle means being positioned in said bridle means at a point below the center of the lateral resistance of the main plate as the anchor is pulled through the water, and a hoisting shackle aixed to one corner of said main plate for hoisting the anchor out of a muddy sea bottom.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Hamilton Oct. 27, 1908 Croney Dec. 29, 1931 Wilcoxen et al. July 2, 1946 FOREIGN PATENTS Great Britain Nov. 1, 1890 Sweden Aug. 2, 1908 Great Britain July 9, 1937 Great Britain Apr. 25, 1951