US3508513A - Method and apparatus for increasing the holding power of anchors - Google Patents

Description

A ril 28, 1970 w. T. ILFREY ET ,5

METHOD AND APPARATUS FOR INCREASING THE HOLDING POWER OF ANCHORS Filed May 21, 1968 2 Sheets-Sheet l W Y r M FIG. 2

' a WWII ROBERT W. BECK WILLIAM T. ILFREY INVENTORS A T TORNE Y April 28, 1970 w. T. ILFREY ET AL 3,508,513

METHOD AND APPARATUS FOR INCREASING THE HOLDING PQWER OF ANCHORS I3 Sheets-Sheet 2 Filed May 21, 1968 ROBERT W BECK WILLIAM T ILFREY INVENTORS ATTORNEY United States Patent 3,508,513 METHOD AND APPARATUS FOR INCREASING THE HOLDING POWER OF ANCHORS William T. llfrey and Robert W. Beck, Houston, Tex.,

assignors to Esso Production Research Company, a

corporation of Delaware Filed May 21, 1968, Ser. No. 730,698 Int. Cl. B63b 2/26 US. Cl. 114-206 6 Claims ABSTRACT OF THE DISCLOSURE An anchor assembly for engaging hard submerged bottoms includes an elongated shank, an anchor attached to one end of the shank, a substantially flat fluke connected to the opposite end of the shank, and forming an acute angle with the shank, and means connected to the shank on the shackle end for excavating a hole in a submerged bottom large enough to receive the fluke.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the mooring of floating vessels and is particularly concerned with an anchor assembly including means for excavating a hole in a hard submerged bottom to enable the anchor fluke to dig in and hold.

Description of the Prior Art The anchors used for mooring floating drilling ships or similar vessels generally include an elongated shank having a shackle at one end to which a mooring chain or cable can be attached, a rod-shaped stock extending at right angles to the shank on the end opposite the shackle, and one or more substantially fiat flukes attached to the shank for digging into the submerged bottom and developing holding power. The fluke, which normally points in the general direction of the anchor shackle, may have a fixed or variable angle with respect to the shank. During setting operations the anchor is positioned on the sea floor and oriented by means of a crown line so that the flukes tend to dig into the bottom when the anchor is dragged by the mooring line. In most cases this digging action tends to embed the fluke deeper in the sea floor until the full holding power of the anchor is developed after the anchor has been dragged a relatively short distance. In some areas, however, particularly where the bottom is hard or smooth and resistant to penetration, the flukes may either fail to penetrate the bottom or plow constant depth furrows in the bottom Without ever attaining complete burial. This often precludes the effective use of anchors for mooring purposes and, in olfshore drilling operations, may make drilling from floating vessels difficult or impossible.

SUMMARY OF THE INVENTION This invention provides an improved anchor that digs into and developes increased holding power where bottom conditions are hard or smooth and resistant to penetration. Broadly, the anchor of the invention includes a supporting member, at least one fluke attached to the supporting member, a shackle or other means for securing an anchor line mounted on the supporting member, and means mounted on the anchor assembly for excavating a hole in the submerged bottom large enough to receive the fluke. The excavating means is normally positioned on the anchor shank or fluke to excavate a hole in the bottom in the direction the anchor will be dragged so that the flukes will enter the hole and be guided by it until they build up sufficient resistance against 3,508,513 Patented Apr. 28, 1970 'ice the bottom material to continue the digging action inherent in their geometry. This excavating means may be hydraulic jets fastened to the fluke and aligned with the fluke. The jets can be supplied with hydraulic fluid through a hose or similar conduit from a high-pressure pump on an anchor handling vessel. Preferably, however, explosive energy is used to excavate the bottom in front of the fluke tips. This can readily be done by mounting shaped explosive charges on the shank or elsewhere on the anchor assembly. In either case, the invention facilitates the setting of anchors in difficult areas and has significant advantages over anchoring procedures employed heretofore.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation of an anchor equipped with shaped explosive charges for excavating a hole in a submerged bottom. FIG. 2 is a schematic plan view of the anchor depicted in FIG. 1. FIG. 3 is a schematic elevation of an anchor equipped with hydraulic jets for excavating a hole in a submerged bottom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus shown in FIGS. 1 and 2 includes an anchor having an elongated shank 11, a stock 13 attached to the shank near one end thereof, and a substantially flat fluke 15 fastened to the shank adjacent the stock. The stock normally extends parallel to the ocean floor above the fluke to insure that the fluke engages the bottom. A charge carrier 25 is attached to the shank on the end opposite the fluke by means of an anchor shackle 19. Crown shackle 17 is mounted on the opposite end of the shank above the fluke so that the fluke will extend downwardly when the anchor is suspended by means of the two shackles. The tension-bearing main anchor cable 29 is connected to the vessel or other structure to be moored on one end and to the anchor assembly on the other. The crown line 21 is attached to the crown shackle and extends to a vessel, not shown, used in setting the anchor. It may conveniently be used to support an electrical detonator cable or other detonating line connected to explosives on the charge carrier on one end and to an actuator on the work boat, not shown, on the other end. The preferred detonating apparatus is a line explosive that extends down the crown line. The line explosive is initiated at the vessel and the whole length explodes thereby detonating the explosive charges. As depicted, the main anchor cable is attached to shackle 27 on the front end of the charge carrier. It will be apparent, however, that it could also be connected to anchor shackle 19 if the explosive charges were mounted on the shank, on the flukes, or in some other location in lieu of using a charge carrier ahead of the anchor. Although two lines are illustrated for lowering the anchor, the invention is not limited to this configuration, Additional crown lines may be used. This has the advantage of distributing the anchor weight between two or more work boats and may also be beneficial in positioning the anchor at a particular location on the sea floor. Alternatively, the crown line and the crown shackle can be eliminated entirely and the anchor can be lowered by the main anchor cable. If this is done, the detonator cable can be attached to the anchor or detonation can be accomplished sonically, by a time delay device or by other remote control means.

The anchor can have a variable angle fluke instead of the fixed angle fluke shown in FIGS. 1 and 2. If variable angle flukes are used, they normally are pivotally attached to the shank. During setting operations, the flukes are extended past their pivot point when the anchor is The explosive'charge or charges can be"mounted in positions on the anchor assembly other than the one shown in FIG. 1. It is not essential that a charge carrier be used. The charges may instead be mounted on the anchor flukes or on the shank. If a charge carrier is employed, it may be positioned farther away than that shown in the drawing. The principal limitation with respect to the mounting of the charges is that they must be close enough to the anchor assembly that when the anchor is dragged by the anchor line 29, the flukes will enter the hole 39 created by detonation of the explosives. I

It is preferred that the longitudinal axis of the hole created by the explosive charges form substantially the same angle with the ocean bottom as the angle that the fluke forms with the shank. The walls of such a hole will guide the anchor flukes downwardly until the flukes build up sufficient resistance against the bottom material to continue the digging action inherent in their geometry or until they can penetrate no further into the earth material. In eitherevent, the holding power of the flukes will be substantially increased. This is not essential, however, since any hole in the ocean bottom that is large enough to admit the anchor fluke will generally be of substantial benefit. Directional explosive charges can be used to control the angle of the hole. The charge carrier depicted in FIG. 1 contains four shaped charges 31 mounted on frame 33. Such a carrier may be provided with ballast material having a density greater than that of sea water to insure that the carrier and charges will sink to the bottom and remain in the position depicted in FIGS. 1 and 2.

Shown in FIG. 3 is an anchor equipped with hydraulic jets for excavating a hole suitable to receive the fluke. The anchor assembly shown again includes an elongated shank 51, a rod-shaped stock 53 extending perpendicular to the shank, and an anchor shackle 61 mounted on the leading end of the shank. The anchor shown has a substantially flat fluke 55 attached to the shank and traversed by a fluid channel 57.

Two lines are used for lowering the anchor shown in FIGURE 3. Mooring cable 65 attached to the anchor shackle is the main anchor cable. This cable connects the anchor with the ship or other structure to be moored and is in tension during normal operation of the anchor system. The second line is crown line 63. This is connected at the surface to a Winch on a work boat, not shown. The other end of the crown line is attached to the anchor assembly by crown shackle 59.

A high-pressure hose 67 or similar conduit is connected to fluid channel 57. This conduit is generally flexible and fastened to the pendant line for support. It extends upwardly along the pendant line to the work boat at the surface where it is connected to a pump discharge or other means for forcing fluid through the conduit and nozzle. A rigid conduit completely independent of the pendant line can also be used. At the opposite end of the fluid channel, at or near the tip of the fluke, is a jet nozzle 69 through which the pressurized fluid passes at a high velocity before striking the submerged bottom 71.

Although it is preferred that the high pressure conduit be connected to the jet nozzle by means of a fluid channel in the anchor fluke, it will be apparent that other configurations are possible. For example, the jet nozzle can be mounted on the fluke or on the shank or frame adjacent thereto and may be directly connected to the conduit. A plurality of jet nozzles may also be used.

In operation, the anchor depicted in FIGS. 1 and 2 is normally carried aboard a work boat to the surface position above the point at which the anchor is to be placed. The main anchor cable 29 is connected by anchor shackle 27 to the anchor assembly on one end and is attached to the vessel or other structure to be moored at the other end. The anchor is then slowly lowered by means of crown line 21 and anchor line 29 until it assumes a position as shown in FIG. 1 with the fluke pointed downwardly toward the submerged bottom and with the charge carrier 25 oriented so that the shaped charges are directed toward the submerged bottom. The charges 31 can be detonated by means of a line explosive 37 which detonates in response to an electrical signal that is directed down an electric detonator cable. As discussed above, the line explosive preferably is extended up the pendantline to the surface in lieu of an electric detonator cable. Detonation of the shaped charges contained within the charge housing results in a large hole being excavated in the submerged bottom, as depicted by reference numeral 39 in FIGS. 1 and 2. Once the hole has been excavated, the anchor assembly is advanced by means of the main anchor cable until the fluke digs into the hole, causing the anchor assembly to grip the submerged bottom. Tension within the main anchor line can then be increased sufliciently to moor the vessel or other structure at its other end.

Operation of the anchor assembly depictedin FIG. 3 is very similar to that of the assembly shown in FIGS. 1 and 2.. The primary distinction in operation is that, after the anchor assembly of FIG. 3 has been lowered to the bottom by means of crown line 63 and main anchor line 65, pressurized fluid is directed down high-pressure hose 67 through fluid channel 57 and out jet nozzle 69 at a high velocity so as to begin eroding a hole in submerged bottom 71. Fluid is forced through the highpressure hole for a period sufiicient to erode a hole in the ocean bottom large enough to accommodate the fluke 55. The period required, will vary with the competency of the ocean bottom, the properties of the fluid used, the pump pressure, and the nozzle velocity. In most areas where it is desired to set the anchor assembly, the bottom conditions are either known or can be evaluated from samp es and thus the time period can be readily determined. After the hole has been created, the anchor assembly is advanced by means of cable 65 so that the flukes will dig into the hole created by the nozzle in the submerged bottom 71 and thereby cause the anchor assembly to grip the submerged bottom.

It will be apparent that the method and apparatus of the invention are applicable to anchors other than the particular type shown in the drawing. Similarly, means for excavating a hole in the submerged bottom other than the shaped explosive charges or hydraulic jet nozzles referred to above may be used.

What is claimed is:

1. A method of setting an anchor comprising positioning an anchor assembly adjacent to the surface of a hard submerged bottom, said anchor assembly including an anchor having at least one fluke and including means for excavating a hole in the hard submerged bottom; actuating said excavating means to form a hole in the hard submerged bottom large enough to receive the said fluke; and moving the anchor assembly along the surface of the bottom towards the hole so that the fluke enters the hole and digs into the earth.

2. A method of setting an anchor comprising positioning an anchor assembly adjacent to the surface of a hard submerged bottom, said anchor assembly including an anchor having at least one fluke and including at least one explosive charge; detonating an explosive charge attached to said anchor assembly to create a hole in said hard submerged bottom that is laterally displaced from the fluke and is large enough to receive the fluke; and dragging the anchor along the surface of the bottom so that the fluke enters the hole and digs into the earth.

3. A method of setting an anchor having at least one fluke comprising positioning the anchor adjacent to a hard submerged bottom, eroding a hole in the hardsiibmerged bottom by means of apparatus attached to said anchor assembly, said hole being near the anchor located in a direction that the anchor will be dragged and large enough to receive the anchor fluke, and dragging the anchor until the fluke enters the hole and digs into the earth.

4. An anchor assembly comprising a supporting member, means for securing an anchor line to said supporting member, a fluke connected to said supporting member, and means including at least one explosive charge mounted on said anchor assembly for excavating a hole in a submerged bottom without requiring any movement of said anchor fluke, said hole being large enough to receive said fluke.

5. An anchor assembly comprising an elongated shank, a fluke fixed -to the shank and forming an acuate angle therewith, an anchor shackle connected to the shank, and means including at least one explosive charge mounted on said anchor assembly for excavating a hole in a submerged bottom without requiring any movement of said anchor fluke, said hole being large enough to receive said fluke.

6. An anchor assembly comprising:

(a) an elongated shank;

(b) a fluke fixed to the shank and forming an acute angle therewith;

(c) an anchor shackle connected to the shank;

(d) a charge carrier connected to said shank positioned forward of the flu-ke in a direct direction that the anchor will be dragged;

(e) at least one explosive charge mounted on said carrier; and

(f) means for detonating said charge.

References Cited UNITED STATES PATENTS 2,674,968 4/ 1954 Danforth 114-207 3,154,042 10/1964 Thomason et a1. 114206 3,280,782 10/1966 Holm 114-206 FOREIGN PATENTS 21,439 1893 Great Britain.

TRYGVE M. BLIX, Primary Examiner

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