Anchors for mooring of objects in a marine environment

An anchor for mooring of objects in a marine environment for floating vessels, floating, grounded structures etc, which is resistant to hooking or snagging on underwater objects, such as pipelines The anchor comprises a fluke and a shank, and embeds itself into the seafloor when tension is applied to a line connected to the anchor In either a side or top profile view, the shape of the anchor presents a profile which does not have a hook shape, and therefore tends to nde over and slide off of, rather than hook onto, underwater obstructions that the anchor may be dragged over Embodiments disclosed include an anchor having a shank rigidly fixed to the fluke, and one in which the shank is rotatably connected to the fluke An elastic member, which may be a coil spring, biases the shank toward a relatively closed position with respect to the fluke.

BACKGROUND

1. Field of Art

This invention relates to apparatus and methods for securing objects to the sea floor. With further particularity, this invention relates to apparatus and methods for embedment type anchors, which present a reduced chance of snagging or hooking upon underwater obstructions, such as pipelines and the like.

2. Description of the Preferred Embodiment

Disclosed are several embodiments of anchors (and improvements thereof), for use in mooring physical objects, including but not limited to floating vessels and structures, and/or grounded structures, typically (but not exclusively) in an marine environment. The anchors, in their various embodiments, have particular (but not exclusive) application in the anchoring of Mobile Offshore Drilling Units (“MODUs”) and related production facilities used in offshore oil and gas operations.

One type of anchor in common use, and well known in the art, is called a High Holding Capacity (“HHC”) anchor, which generally comprises a fluke and a shank. The fluke is generally substantially plate shaped, and in normal conditions, the fluke is substantially horizontal or aligned with the plane of the sea floor, while the shank extends generally upwardly therefrom in a plane generally at right angles to the plane of the fluke. A line, which may be the mooring line to the object being moored, is connected to the shank, and runs to the vessel or structure being moored. After lowering the HHC to the sea floor, tension applied to the line will pull the HHC anchor such that it digs into the sea floor, and eventually buries itself to some design depth. Once the anchor is set, the angle of the mooring line with respect to horizontal is generally relatively small.

Another type of anchor in common use is that known as a Vertically Loaded Anchor (“VLA”). Such anchor typically comprises a plate, the plate being connected to an installation and mooring line. The plate is pulled into the sea floor to a (typically) greater depth than an HHC anchor, and the angle of the mooring line with respect to horizontal is generally greater than the equivalent mooring line angle with an HHC anchor.

There are many pipelines and other obstructions on the sea floor. In the course of installing HHC and VLAs, it can be appreciated that if pulled over a pipeline or other obstruction, the anchor may hook onto or snag same, with potentially disastrous consequences (e.g. ruptured pipelines). Certain weather conditions, such as hurricanes, can impart sufficient forces on the moored vessel or structure so as to overcome the mooring or holding capacity of its anchors, and thereby drag anchors over long distances, again giving rise to the possibility of hooking onto a pipeline or other structure. Even if the anchor is improperly aligned, for example where an HHC anchor is positioned so that the fluke is substantially vertically (as opposed to horizontally) oriented, it is still possible for a fluke “wing” to hook a pipeline or other underwater object.

Another issue exists with conventional HHC anchors. The angle of the shank with respect to the fluke (for example, seeFIG. 3, where the referenced angle is annotated as “shank angle”) is fixed. This fixed angular relationship does not allow the anchor to be pulled at optimum angles for all conditions. Ideally, the angle between the shank and the fluke would increase as soil resistance and consequently mooring pull increase, and thereby permit the fluke to assume a steeper dive angle and allow greater resistance to vertical loading in the soil. Current, fixed angle HHC anchors do not permit such behavior.

Still another issue arises when anchors, namely HHC anchors, are retrieved to an MODU and vessels with outboard anchor racks. Conventional HHC anchors are stored by hooking the flukes on a rack; any anchor design which prevents such anchor mounting presents an issue with efficiently and safely carrying the anchors aboard the vessel.

SUMMARY OF THE INVENTION

Disclosed are several embodiments of the present invention, which may be used singly or in combination with one another. The present invention presents solutions to the problem of anchors hooking onto pipelines and other subsea obstructions, in the course of installation or under anchor dragging scenarios; presents a solution to the problem of controlling soil penetration behavior of HHC anchors under the influence of mooring line loads in excess of a specified design load; presents a solution to the problem of efficiently storing certain anchor designs on an AHV or MODU, and presents an anchor which may be selectively used in either fixed or rotatable shank mode.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring toFIGS. 1-4: the snag-resistant anchor, fundamentally, has a shape, particularly evident when viewed from the side as inFIG. 3, or the top as inFIG. 4, which minimizes (if not eliminates) any “hook” shape which can potentially snag a subsea obstruction.

The anchor10comprises a fluke20joined to shank30. Shank30further comprises a leading edge shank snag inhibiting member40, which yields a side-view profile (readily seen inFIG. 3) which has little or no hook shape, therefore which greatly minimizes, if not eliminates, the possibility of snagging an underwater obstruction when the anchor is being pulled, while in its usual “upright” orientation. It is to be understood that shank inhibiting member40and shank30may effectively be formed as a single structure; said another way, shank30may simply have a shape which, when viewed in side profile, presents little or no hook shaped component.

Anchor10further comprises lateral fluke snag inhibiting members50, extending generally from each wing of fluke20to a position on shank30. The lateral fluke snag inhibiting members50therefore create a top-view profile (readily seen inFIG. 4) which has little or no hook shape component, therefore which greatly minimizes, if not eliminates, the possibility of snagging an underwater obstruction when the anchor is being pulled, when the anchor is essentially on its side (that is, with fluke20oriented substantially vertically).

As is well known in the relevant art, anchor10is advantageously fabricated from plate steel, with the different components joined by welding, bolting, etc. It is understood that other component shapes could also be used, for example tubular pieces for the leading edge shank snag inhibiting member40and the lateral fluke snag inhibiting members50. A line, namely a mooring line, connects anchor10with the object being moored (typically, a vessel or other structure); typically, the mooring line is attached to anchor10by connection to shank30, for example by connection to a connection plate60of anchor10, typically by a padeye and shackle fixed to the mooring line. Dimensions and weight of the anchor can be varied to suit particular applications. The particular shape of the anchor components may also be varied, while retaining the attributes of minimizing, if not eliminating, any hook shaped profile, whether viewed from the top or a side.

WhileFIGS. 1-4show various snag-resistant attributes on an HHC anchor, it is to be understood that the same principles, and similar structures, may be used on a VLA.

Another embodiment of the present invention is shown inFIGS. 5,6and7. This embodiment comprises an anchor having a hinge or rotatable connection between the shank and the fluke, the hinge connection being elastically biased toward a first “closed” position (in which position the anchor is effectively an HHC anchor); but which permits the shank angle (as earlier described, and illustrated inFIG. 3, the angle between the fluke and shank, when viewed from the side) to increase with increasing mooring line load. The changed angle thereafter permits the anchor to behave (in terms of penetration into the soil) in a manner similar to a VLA (namely, a steeper dive angle into the soil).

Referring toFIGS. 5-7: similar to the anchor embodiment previously described, anchor100comprises a fluke110and a shank120. Fluke110and shank120are joined by welding or other means known in the art. Similar to the first embodiment, anchor100may comprise a leading edge shank snag inhibiting member130of shank120, which creates a side profile minimizing or eliminating any hook shape, therefore minimizes or eliminates snagging; and lateral fluke snag inhibiting members140, in combination yielding an anchor having both side and top profiles which minimize, if not eliminate, snagging on underwater obstructions. It is to be noted thatFIGS. 5-7illustrate an anchor in which the leading edge snag inhibiting member130and shank120are effectively a unitary piece, i.e. the anti-snag aspect is achieved by shape of shank120.

This embodiment further comprises an upper shank extension150, rotatably connected to shank120by hinge160. A mooring line can be attached to the anchor, typically by connecting the mooring line to upper shank extension150by a padeye and shackle or other similar means well known in the art. An elastic member170biases upper shank extension150toward a first position (as inFIG. 6), with a smaller shank angle. In the first position, anchor100can be drug into the soil (of a seafloor) at relatively low load, in the mode of an HHC. As the anchor sees increased soil resistance, the mooring load must be increased to generate further penetration. With increasing mooring load applied to the mooring line, elastic member170yields (or “stretches,” when in the configuration shown here), the shank angle increases (i.e., the shank “opens up”) and the fluke assumes a steeper dive angle into the soil, behaving in the manner of a VLA. This behavior creates an optimum embedment path for the anchor to achieve maximum holding capacity with the shortest span of drag resistance. Elastic member170may take various forms, within the purview of the invention; spring members, such as coil springs, or elastic media; it is further understood that elastic member170may be positioned so as to be placed in compression, rather than tension. It is sufficient for this invention that some means for biasing upper shank extension150in a direction toward fluke110be provided.

Shear plates180(for example only, shear plates180are shown only onFIGS. 6 and 7) can be interposed at either or both ends of the connection of elastic member170to the anchor. When a predetermined load is reached on the elastic member, the shear plate shears, thereby preventing structural damage to the elastic member or to the anchor, and upper shank extension150is free to rotate on hinge160.

Another attribute which may be incorporated into the embodiment ofFIGS. 5-7is means for releasably fixing upper shank extension150to shank120, wherein the means for releasably fixing yields under a pre-determined load, and thereafter elastic member170controls the shank angle. In the preferred embodiment, the means for releasably connecting may comprise alignable holes151in upper shank extension150and shank120, through which a shearable pin152may be placed. It can be readily appreciated that once sufficient force is applied to the mooring line to shear pin152, then upper shank extension tends to rotate toward a more open position, as permitted by elastic member170; this position is readily seen inFIG. 7. Other means for releasably connecting upper shank extension150and shank120, such as shear plates and the like, could be used.

It is to be further understood that this embodiment of the present invention (namely, the hinge connection between the shank and the fluke) may be used not only in combination with the snag-resistant anchor described above, but also in combination with other, prior art configurations of HHC anchors (that is, such prior art HHC anchors that do not comprise the snag-resistant attributes of the anchor disclosed above).

An anchor comprising another embodiment of the present invention is shown inFIG. 8. When retrieved onto MODUs or other vessels, prior art HHC and VLAs were often racked on the vessels by hooking the flukes over a pipe, said pipe constituting an anchor rack. As is apparent from the previous description, anchors having the disclosed snag-resistant features are not adapted to be so hooked on a pipe or similar structure (such mounting is indeed very similar in concept to snagging a pipeline, which the anchors of the present invention are not susceptible to doing).

Disclosed is an anchor shank feature which can be incorporated into any embodiment of the present invention, including the anchors previously described. Referring toFIG. 8, anchor200(which may comprise any of the embodiments already disclosed) comprises a shank210having a generally Z-shaped racking notch220therein. Racking notch220permits anchor200to be lifted onto the vessel, then set down on an anchor rack, allowing the rack to slide into the Z-shaped groove, then lifted again to secure it in the anchor rack by engaging the bottom V-shaped groove in the Z-shaped notch. The advantages of the snag-resistant geometry described above are maintained; the shape and orientation of racking notch220is such that forward movement of anchor200does not present a potential snagging profile to an obstruction. Therefore, the addition of racking notch220to either of the anchor embodiments disclosed above does not reduce or impair the anti-snagging nature thereof, however gives the advantage of enabling simple and secure racking.

The final embodiment of the present invention is shown inFIGS. 9-11. Anchor300, as in the earlier described embodiments, comprises a fluke320and a shank330. Shank330is rotatably fixed to fluke320, for example by the pinned connection325. Lateral fluke snag inhibiting members321extend from fluke320to shank330. As can be seen inFIG. 11, this embodiment (as with the previously described embodiments) has a profile, when viewed from the side, which presents no hook-shaped aspect, therefore minimizes or eliminates any tendency for the anchor to snag any obstruction. An elastic member, in the figures shown as a coil spring340, best seen inFIG. 10, biases shank330toward a first position in which shank330is in a relatively “closed” position (i.e. a small shank angle—shank angle being depicted in a preceding figure) with respect to fluke320, as seen inFIGS. 9 and 10, and in the solid lines ofFIG. 11. By way of further explanation, with reference toFIG. 11, spring340biases shank330toward a first position in which the angle of shank330with respect to fluke320is relatively small (reference is made to the preceding discussion with respect toFIGS. 3,5,6and7, further explaining the angular relationship between the shank and the fluke). Preferably, shank330comprises an arcuate slot335(preferably two such slots, as shown), into which a projecting member on fluke320, such as a pin or through-bolt326, projects. The projecting member, by its placement in the slot, serves to stabilize the rotation of the shank on the fluke. It is understood that in this embodiment, two projecting members are provided, riding in each of the slots.

This embodiment permits use of the anchor as a Vertically Loaded Anchor (“VLA”), in which a typical sequence of deployment is as follows: initially, shank330is held at a relatively small angle with respect to fluke320, due to the biasing force from the elastic member. When tension is applied to a line attached to shank330of the anchor, flukes320start to embed into the sea floor and bury the anchor. With increased load, the angle between shank330and fluke320overcomes the force exerted by elastic member (as depicted, coil spring340), and the shank starts to “open up” with respect to the fluke. Depending upon the amount and duration of the embedment force, the anchor behaves as a VLA.

The embodiment ofFIGS. 9-11comprises another attribute which will now be described. If desired, coil spring340can be removed or disconnected, and shank330can be rotated to a more upward, “open” position relative to fluke320, as depicted by the phantom lines inFIG. 11. When rotated to a sufficient degree, holes400and410in shank330and fluke320are aligned, and a pin or similar means can be inserted through the holes, thereby holding shank330and fluke320in a desired, fixed angular position. Multiple sets of holes400can be provided in shank330, as can be seen in the drawings, so that different angles between shank330and fluke320can be fixed, as desired. It is to be understood that two sets of holes400in shank400are shown for illustrative purposes only; any number can be provided. With the shank now fixed in angular relation to the fluke, the anchor acts as a conventional, drag type or embedment-type anchor.

If desired, a means for releasably connecting the elastic member to shank330may be employed. By way of example, said means for releasably connecting the elastic member may comprise a shearable pin331connecting coil spring340to shank330. It is understood that shearable pin331could be at either or both ends of coil spring340, or some other releasable means could be used. When the force exerted by coil spring340on shearable pin331exceeds the design shear load, pin331shears, and shank330is then free to rotate to its most open position (i.e. the position with the maximum shank angle), as represented by the phantom lines inFIG. 11. In that position, the uppermost end of slot335bears against through-bolt326.

It is to be understood that the pinned-together connection between shank330and fluke320renders them releasably connected, one to the other, and permits easy interchangeability of different shanks with fluke320. For example, shanks330having different shapes and dimensions of may be mated to fluke330, to achieve a desired behavior (frequently referred to as “trajectory”) of the anchor as it buries itself in the seafloor under load. By way of example, changing the length of shank330changes the length of the moment arm, and consequently the magnitude of the rotational force imparted on the anchor.

While the preceding description sets out specifics regarding certain embodiments of anchors embodying the concepts of the disclosed inventions, it is understood that other embodiments are possible without departing from the scope of the invention. For example, the particular shapes of the shank and fluke can be modified as desired; dimensions and weights can be changed to accommodate particular load requirements; materials can be altered; the anchor can be used to fix any desired object to a seafloor, whether a floating vessel, MODU, or a structure fixed to the seafloor, but necessitating anchors for additional fixing in place and stabilization.

Therefore, the scope of the inventions is not limited to the specific embodiment(s) set out herein, but only by the scope of the appended claims and their legal equivalents.