Patent Publication Number: US-9422034-B2

Title: Actively steerable gravity embedded anchor systems and methods for using the same

Description:
The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/971,462 filed Mar. 27, 2014 and entitled “ACTIVELY STEERABLE GRAVITY EMBEDDED ANCHOR SYSTEMS AND METHODS FOR USING THE SAME” by Bauer et al., the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to systems and methods for mooring drilling vessels and other types of vessels. 
     BACKGROUND 
     High performance anchors used to moor sea surface vessels and other structures need to be embedded into the seafloor a sufficient depth in order to develop the required holding capacity. Two general methods have been developed over time for this purpose, to wit, drag-embedment and direct-embedment techniques. The method of drag-embedment involves either hauling-in or horizontal movement of the top of the mooring line such that the anchor attached to the lower end of the mooring line is moved horizontally; the anchor is designed such that horizontal movement causes the anchor to dive below the seafloor. The anchor will cease diving below the seafloor when an equilibrium between its holding capacity and the mooring line tension is reached. Methods of direct-embedment of anchors to their final penetration depth include the use of gravity, ballistics, hammers (impact and vibratory) and suction. Gravity has been used to accelerate anchors in free-fall and to force them into the seafloor with gravity followers. Ballistic anchors use a propellant to penetrate the anchors into the seafloor while suction is used in conjunction with suction pile (or suction follower) outfitted with a plate anchor at its tip. The suction follower in the latter case is only an installation tool and is removed after embedding the anchor to final penetration depth. In a similar manner, anchors can be embedded using an impact or vibratory hammer in place of the suction force. There are also hybrid techniques that use combination of free-fall to an initial shallow direct-embedment depth followed by drag-embedment to the final design penetration depth. 
     Current gravity-embedment techniques deploy a free-fall anchor from a pre-determined height above the seafloor and use the momentum of the falling anchor to adequately embed the anchor into and below the seafloor. Often a deployment height above the seafloor is used that will allow the anchor to reach terminal velocity before penetrating the seafloor. In general, this height is 50 to 150 meters above the seafloor; in deep water it can take a significant period of time to rig the anchor and orient it above the target location. 
     Gravity-embedded anchors that have been employed in the past have included free fall anchors that glide down at an angle to the seafloor in lieu of dropping relatively straight down to the seafloor. In some current configurations, gravity-embedded anchors are used that look much like darts or torpedoes. An exception to the free-fall anchor type is an anchor that uses a so-called flexible gravity follower to slowly push the plate anchor mounted on the follower tip to final penetration depth by means of the follower&#39;s dead weight only. Conventional gravity-embedded free-fall anchors are passively-stabilized with fixed and non-movable stabilizing fins. 
     SUMMARY OF THE INVENTION 
     Disclosed herein are actively steerable gravity-embedded anchor systems and methods of using the same that may be employed to actively control or steer the descent path of a falling gravity-embedded anchor. The steerable gravity-embedded anchors of the disclosed systems and methods may be provided with an embeddable anchor body and one or more active and controllable steering system components in order to control or otherwise alter the orientation and/or angle of descent of a steerable gravity-embedded anchor in real time as it falls through the water toward the seafloor. Examples of such steering system components include, but are not limited to, movable control surfaces (e.g., such as rudders, elevators, ailerons, etc.) that may be manipulated in real time between different positions, thrusters (i.e., water jets) that may be selectably activated in different directions and/or manipulated to vector thrust in different directions, motors or actuators or other suitable component/s that are configured to induce gyroscopic forces to rotate the anchor body as it falls to the seafloor, etc. 
     In any case, the disclosed steerable gravity-embedded anchor systems may be operated to actively steer a falling anchor in contrast to conventional non-steerable gravity-embedded free-fall anchors that are provided with fixed and non-movable stabilizing fins that only act to passively stabilize the downward path of a free falling gravity-embedded anchor without actively controlling the anchor descent path or trajectory. Moreover, the disclosed steerable gravity-embedded anchor systems may be configured for direct deployment from the stern of an Anchor Handling Vessel (AHV) in a manner that substantially avoids the complicated and time consuming rigging required to install conventional gravity-embedded anchors, i.e., current conventional systems can be more complicated as they may require two vessels for installation, or another line in addition to the lowering line for release of the anchor above the seafloor; and can be more time consuming as the anchor must be lowered to a point 50 to 150 meters above the seafloor for release, and the lowering line recovered, all at the anchor winch deployment rate which is substantially slower than the free-fall rate of disclosed steerable gravity-embedded anchor systems. This in turn provides an economic advantage that may be particularly important when mooring in deep water. 
     In one exemplary embodiment, a steerable gravity-embedded anchor may be provided as a self-directed gliding anchor that is provided with an embeddable anchor body having an on-board and self-contained control system that is configured to steer the embeddable anchor body to a target on the seafloor during anchor free-fall. The on-board control system may include navigation equipment (e.g., such as one or more on-board GPS-based sensors configured to monitor and establish the location of an initial anchor release position on the surface, on-board inertial sensors that are configured to monitor the downward trajectory of the anchor toward the seafloor once it is released to fall through the water, and/or on-board electronic compass/es configured to monitor north-south orientation of the anchor) and steering system components (e.g., movable control surface/s and/or thruster/s) that may be controlled by one or more processing devices and drivers to alter the anchor&#39;s trajectory in response to the real time monitored downward trajectory of the anchor as it falls in order to self-direct or autonomously steer the anchor in an autonomous manner to a target location on the seafloor as the anchor falls through the water. In such an embodiment, autonomous steering of the anchor body may be employed during free-fall of the anchor body to improve anchor placement with respect to a design target location on the seabed, e.g., by altering the path of the anchor to the seafloor to account for sub-surface currents and other anomalies. In one exemplary embodiment, the on-board control system may be activated/initialized on the surface (e.g., aboard an anchor handing vessel “AHV” or other type release vessel) prior to releasing the anchor to free fall to the seafloor. 
     In those embodiments employing movable control surfaces, an anchor body of a steerable gravity-embedded anchor system may be provided with one or more on-board actuators (e.g., electro-mechanical, hydraulic, pneumatic, etc.) that are configured and coupled to control one or more movable control surfaces provided in or on the anchor body. In one such embodiment, the on-board control surfaces of the anchor system may be optionally coupled to one or more fixed non-movable stabilizing fins that are themselves mechanically coupled to the anchor body. In those embodiments employing thrusters (e.g., impellers, propellers, etc.), an anchor body of a steerable gravity-embedded anchor system may be provided with one or more on-board motors (e.g., electro-mechanical, hydraulic, pneumatic, etc.) that are configured and coupled to actuate the thrusters, e.g., by rotating impellers, propellers, etc. In other embodiments, fixed non-movable stabilizing fins may be provided on an anchor body that are separate from the steering system components, e.g., separate from the movable control surfaces, thrusters, etc. 
     In one exemplary embodiment, the initial surface release location of a steerable anchor system may be directly above the target location on the seafloor prior to release of the anchor. In such an embodiment, an on-board navigation system of the anchor system may be tasked with using the on-board steering system components to maintain a direct path for the anchor to the target location on the seafloor, and to counteract forces attempting to cause the anchor to deviate from the target location as it falls. In such an embodiment, the on-board navigation system does not need to be capable of determining its absolute location (e.g., longitude and latitude) and may be, for example, an inertial guidance system that does not know its absolute location. Rather, marine positioning equipment (e.g., such as differential global positioning system “DGPS” and/or long range navigation “LORAN”) may be optionally employed to ensure the release vessel is located over the target location prior to anchor deployment. However, in another exemplary embodiment, an on-board navigation system may be provided that is capable of sensing absolute location of the anchor (e.g., such as GPS) may be used to allow the initial surface release location of a steerable anchor system to be offset from the target location, as long as the positional offset between the anchor location and target location is within the controllable glide envelope of the on-board steering system components. 
     It will be understood that the disclosed steerable gravity-embedded anchor systems may be implemented with an embeddable anchor body of any configuration that is suitable for embedment within a seafloor. For example, in one exemplary embodiment, a steerable gravity-embedded anchor system may be configured with an embeddable anchor body that is physically dimensioned similar to a conventional plate anchor (i.e., flat). In such an embodiment, the embeddable anchor body may be provided with integral control surfaces, or stabilizing fins in combination with control surfaces. As an example, one possible steering system configuration for a plate anchor body may include movable control surfaces in the form of a pair of ailerons positioned on the trailing edge of the fluke of the anchor body. In such a configuration, pitch of the anchor may be controlled directly, and the yaw direction may be changed by first rolling the anchor. In an alternate configuration, a non-movable vertical stabilizer with a movable rudder surface may be provided, in which case both pitch and yaw can be controlled directly. 
     In another exemplary embodiment, a steerable gravity-embedded anchor system may be configured with an embeddable anchor body that is physically dimensioned similar to a conventional torpedo pile, i.e., an elongated cylinder with stabilizing fins near the leading and/or trailing ends of the main body or, potentially, both ends. In such a configuration, movable control surfaces may be coupled to the trailing edges of one or more of the stabilizing fins. 
     Using the disclosed systems and methods, the anchor body of a steerable gravity-embedded anchor system may be configured to reach its final design penetration depth/distance in the seafloor by gravity-embedment alone, by a combination of gravity-embedment and drag-embedment, or by any other suitable embedment technique or operation. In one exemplary embodiment, a drag-embedment phase for a steerable anchor body may be accomplished by attaching a mooring line to the anchor&#39;s mooring pendant line and tensioning the mooring line to cause the anchor to penetrate further into the seafloor. 
     In a further embodiment, the same navigational data processed from the on-board navigation system (e.g., on-board inertial and inclination sensors) to steer an anchor body in its flight from the anchor drop point to the seafloor may also be retrieved and used to provide an interim or final penetration depth and orientation for the anchor body below the seafloor. Such navigational data may be retrieved in real time or from memory from an on-board control system of a steerable anchor system in any suitable manner after the steerable anchor body has been at least partially embedded in to the seafloor. 
     In one exemplary embodiment, stored or real time post-embedment navigational data (e.g., including anchor position and orientation data) may be transmitted electrically through a data transmission path of a suitably-configured anchor recovery line or retrieval pendant (e.g., such as a so-called synthetic mud rope) from the steerable anchor control system to a floating recovery buoy configured with one or more processing device/s, memory, and other electronic components that are configured with circuitry to transmit or re-transmit the received navigational data (e.g., as optical or acoustic signals) to data retrieval circuitry provided within a remotely operated vehicle (ROV). In this regard, data retrieval circuitry of the ROV may include communication modem circuitry or other type of suitable acoustic or optical sensor/s coupled to a corresponding acoustic or optical receiver that is configured to receive, decode and/or demodulate, the navigation data signals transmitted to the ROV by the recovery buoy, as well as one or more processing devices and memory configured to process and/or store the received navigation data on-board the ROV. Circuitry on board the ROV may in turn be configured to communicate the navigation data or visual camera images in real time to a computer terminal (e.g., notebook computer, desktop computer, tablet computer, smart phone, or other suitable computer device) on an AHV or other attached surface vessel via available empty channels of the ROV umbilical. Alternatively, the ROV may be provided with data logger memory configured to store the received navigation, in which case the stored data may be directly retrieved from the ROV memory upon return to the surface. 
     A recovery buoy may be configured in one exemplary embodiment as a remote input/output device for the anchor control system, such that the ROV may query and receive real time or stored navigational data from the anchor control system through a visual or acoustic I/O interface (e.g., optical sensor and transmitter, acoustic modem, graphical display device, optical modem, acoustic modem etc.) provided on the recovery buoy. In yet another embodiment, a recovery buoy may be configured with its own data logger memory to store the navigational data received from the anchor control system, e.g., for later transmittal to a ROV. It is also possible that at least a portion of the recovery buoy may be physically detachable from the recovery line after it has stored the navigational data in on-board memory of the recovery buoy, in which case the ROV may physically detach and retrieve at least a portion of the recovery buoy containing the stored navigation data in memory and bring the stored navigational data to the surface where it may be downloaded from the buoy. 
     To facilitate transmission of navigational data from the anchor control system to the floating recovery buoy, a recovery line or retrieval pendant may in one embodiment be configured as a mud rope may having a suitable data transmission media or data link (electrically-insulated conductor/s for electrical data path, fiber optic conductor/s for optical data path, etc.) that extends through the recovery line or retrieval pendant (e.g., that is woven or threaded through the mud rope) between the anchor system and the recovery buoy to couple the anchor control system in data communication with the recovery buoy circuitry. In such a case, the recovery line or retrieval pendant and floating recovery buoy may be attached to the anchor system at the surface and dropped with the steerable anchor to the seafloor with the recovery line and recovery buoy trailing behind the anchor system. The recovery line may be provided in one embodiment as a mudrope that is neutrally buoyant to allow a relatively small recovery buoy to be employed. The recovery line may also be of any suitable length, but in one embodiment may have a length that is selected such that the recovery buoy floats high above the mudline when the anchor system is partially embedded in the seafloor, and such that the recovery buoy floats relatively close above the mudline when the anchor system is fully embedded in the seafloor. In either case, the ROV may approach the recovery buoy to query the recovery buoy circuitry and/or to query the control system in the anchor body through the recovery buoy circuitry. During this process, the ROV may grab the buoy or just hover nearby. 
     In one exemplary embodiment, post-embedment navigational data may be visually retrieved from the recovery buoy after anchor embedment, e.g., by a ROV. In such an embodiment, a recovery line supporting a data transmission media may be provided with a floating recovery buoy having an integral and waterproof visual display device (e.g., LED display, LCD display, etc.) that is configured to receive and display information representative of the post-embedment navigation data from the steerable anchor system through the suspended data transmission media. After anchor embedment, the end of the recovery line and recovery buoy may extend from the anchor to float above the seafloor, such that the video display device is in a position to display anchor penetration (e.g., anchor depth, anchor orientation, etc.) where it may be read, e.g., by a ROV, by a diver, etc. In one exemplary embodiment, a ROV may approach the recovery buoy and flash its onboard ROV lights at the buoy. The recovery buoy may be provided with an optical sensor or photo sensor to allow circuitry within the recovery buoy (or the control system within the anchor system) to sense the flashed ROV lights. The recovery buoy and/or control system circuitry may be configured to respond to the ROV lights by activating the control system to display anchor installation/penetration information (e.g., depth and orientation information of the embedded anchor system) visually on the integral buoy display screen. The ROV may then read the displayed data with its standard onboard cameras, and transmit or otherwise retrieve these images to a surface vessel. This visual data retrieval technique may be implemented in one embodiment in a robust and relatively inexpensive manner. 
     In another exemplary embodiment, direct hardwire data connection may be made between a ROV and a recovery buoy, e.g., by using suitable mating subsea electrical or fiber optic data connectors/plugs. In such an embodiment, a ROV-side data connector may be retrieved from the recovery buoy by the ROV, and temporarily connected to a suitable mating data connector provided on the ROV for data retrieval. Alternatively, a ROV-side connector may be mounted in the recovery buoy itself for connection to the ROV circuitry. 
     In another exemplary embodiment, stored post-embedment navigational data may be physically retrieved together with the control system circuitry, e.g., by a ROV. In such an embodiment, collected navigational data may be stored in data logger memory of a retrievable control system capsule (e.g., that includes non-volatile memory such as Flash memory module/s) that may be mounted by detachable data interconnect inside the steerable anchor system. A lanyard or other suitable capsule retrieval line (e.g., optionally having a relatively small attached floating capsule recovery buoy) may be attached to the retrievable control system capsule that is contained within the steerable anchor system such that the end of the lanyard and its optional capsule recovery buoy extend from the anchor to float above the seafloor after anchor embedment. Such a capsule retrieval line may be a separate line from an anchor mooring pendant and recovery line, which may also be present. The control system capsule may be physically detached from the embedded anchor (e.g., at a detachable interconnection point) and recovered after anchor embedment, e.g., by using a ROV to pull on the lanyard that runs from the anchor to the capsule recovery buoy floating above the seafloor. The control system capsule with data logger module may then be brought to the surface by the ROV, where the navigational data may be read from memory of the data logger. 
     In one respect, disclosed herein is a method for installing one or more anchor systems in a seafloor underlying a body of water. The method may include first deploying at least one steerable anchor system into the water from an installation vessel on the water surface. The deployed steerable anchor system may include: an embeddable anchor body, one or more steering system components, and an on-board control system having at least one processing device coupled to control the steering system components. The method may further include releasing the steerable anchor system to free fall through the water toward the seafloor; and then using the on-board control system to control the steering system components to alter the descent path of the anchor system to steer the anchor system to a target location on the seafloor. 
     In another respect, disclosed herein is a steerable anchor system, including: an embeddable anchor body, one or more steering system components, and an on-board control system having at least one processing device coupled to control the steering system components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an overhead view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 1B  illustrates a side view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 1C  illustrates a rear end view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 1D  illustrates a front overhead perspective view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 1E  illustrates a rear underside perspective view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 1F  illustrates an overhead view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 1G  illustrates a side view of an autonomous steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 2  illustrates in a plan view a steerable anchor system rigged for deployment off the stern of an Anchor Handling Vessel (AHV) according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 3  illustrates in an elevation view a steerable anchor system rigged for deployment off the stern of an Anchor Handling Vessel (AHV) according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 4  illustrates a steerable anchor system partially deployed off the stern roller on the AHV according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 5  illustrates a steerable anchor system fully deployed off the stern roller and prepared for release. 
         FIG. 6  illustrates a steerable anchor system at the moment of release as it commences free-fall. 
         FIG. 7  illustrates descent of a steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 8  illustrates a mooring line outfitted with a subsea connector being lowered by an AHV (or other installation vessel) to connect to an anchor mooring pendant of an embedded steerable anchor system according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 9  illustrates the mooring line of  FIG. 8  being moved towards the center of a mooring pattern by an AHV (or other installation vessel) after connecting to the anchor mooring pendant to cause the steerable anchor system to dive into the seafloor to its final design penetration depth according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 10A  illustrates the AHV&#39;s ROV querying a control system of the steerable anchor system for depth and orientation information according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 10B  illustrates the AHV&#39;s ROV querying a control system of the steerable anchor system for depth and orientation information according to one exemplary embodiment of the disclosed systems and methods. 
         FIG. 11  illustrates a block diagram of an anchor system, ROV and topside operator terminal according to one exemplary embodiment of the disclosed systems and methods. 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIGS. 1A, 1B, 1C, 1D and 1E  illustrate multiple respective views of one exemplary embodiment of an autonomous steerable gravity embedded anchor system  100 . In this embodiment, anchor system  100  is illustrated as plate anchor having two active movable control surfaces  105 A and  105 B that are hingeably coupled to the trailing edge of flukes  104 A and  104 B of the anchor body of system  100 . However, it will be understood that other configurations are possible, including plate anchor configurations having more than two active movable control surfaces  105  coupled to the trailing edge of fluke/s  104  of a plate anchor body. In other embodiments, additional active movable control surfaces may be provided on a plate anchor body, for example a movable rudder hingeably coupled to the trailing edge of center plate  101  and/or small active movable fins for trim purposes placed on the extremities of the flukes  104 A and  104 B. In other alternate embodiments, different types of anchor bodies may be provided with one or more active movable control surfaces. For example, a steerable anchor system  100  may be provided with an anchor body that is configured similar to a torpedo pile, e.g., having an elongated cylindrical anchor body and fixed (i.e., non-movable) stabilizing fins coupled to the anchor body near the leading and/or trailing ends of the main anchor body, with active movable control surfaces hingeably coupled to the trailing edge/s of one or more of the non-movable stabilizing fins. 
     In the embodiment of  FIGS. 1A, 1B, 1C, 1D and 1E , outwardly-extending flukes  104 A and  104 B are coupled to also extend outwardly to form a downward anhedral angle of about 20 degrees relative to the horizontal plane normal to the orientation of center plate  101  (i.e., an angle α of about 70 degrees relative to the vertical plane of center plate  101  as shown in  FIG. 1C ), it being understood that outwardly-extending flukes  104 A and  104 B may be coupled to extend outwardly from center plate  101  to form any greater or lesser angle α suitable for a given application, for example, in one exemplary embodiment at any angle α from about 60 degrees to about 80 degrees relative to center plate  101  it being understood that angle α may alternatively be greater than 80 degrees or less than 60 degrees in other embodiments. As further shown, in this embodiment vertical center plate  101  extends upward from flukes  104 A and  104 B to form a vertical stabilizer portion above flukes  104 . It will be understood that in other embodiments a center plate  101  may not extend below flukes  104 A and  104 B, e.g., a center plate  101  may be coupled to extend upward from flukes  104 A and  104 B as shown, but with no portion of the center plate extending below flukes  104 A and  104 B. 
     Also shown in  FIG. 1C  are horizontal bottom plates  106 A and  106 B that are coupled between respective flukes  104 A and  104 B to create right and left anchor system internal cavities  193 A and  193 B between each respective fluke  104 A and  104 B and bottom plate  106  as shown in cut-away view in  FIG. 1C . End caps  115 A and  115 B may be further provided as shown in  FIG. 1C  to close off the rear side of internal cavities  193 A and  193 B as shown to provide sheltered location/s for electrical and mechanical components of the steerable anchor system  100  that protect the electrical and mechanical components of the steerable anchor system from subsea and subsurface environments, e.g., with any suitable or necessary openings defined through center plate  101  to provide for routing of electrical conductor and/or hydraulic or pneumatic conduits of system  100  between cavities  193 A and  193 B. In another embodiment where center plate  101  does not extend below flukes  104  (or extends only partially between flukes  104  and a bottom plate  106 ), then only a single continuous cavity  193  and single bottom plate  106  may be present. It will also be understood, however, that presence of one or more internal cavities  193  is optional, and that in other embodiments the underside of anchor system  100  may be open beneath flukes  104 A and  104 B, e.g., with no bottom plates  106  and/or end caps  115 A and  115 B provided. 
       FIG. 1D  illustrates a front overhead perspective view of the embodiment of  FIGS. 1A, 1B and 1C ; and  FIG. 1E  illustrates a rear underside perspective view of the embodiment of  FIGS. 1A, 1B and 1C . 
     Still referring to the exemplary embodiment of  FIGS. 1A-1E , anchor system  100  includes stored energy sources in the form of hydraulic and/or pneumatic accumulators  107 A and  107 B that are charged pressure vessels containing pressurized fluid/s (e.g., including high pressure gases) are configured to provide the necessary energy to move the control surfaces  105 A/ 105 B by actuating the hydraulic or pneumatic pistons and cylinders  108 A and  108 B that move the control surfaces  105 A/ 105 B at the command of internal navigation system component/s optionally contained in capsule  109  which may provide additional protection (e.g., such as waterproofing and/or protection from hydrostatic pressure) for electrical components. In this regard, control surfaces  105 A and  105 B may be independently actuated or actuated in tandem using custom and/or off-the-shelf electrical, hydraulic and/or pneumatic systems that are all controlled by the internal navigation system components of the control system (e.g., that may be present within capsule  109 ) via appropriate drivers, and/or or by other control system configuration. In the illustrated embodiment, accumulator  107 A and piston/cylinder  108 A may be contained within internal cavity  193 A, and accumulator  107 B and piston/cylinder  108 B may be contained within internal cavity  193 B. However, in other embodiments, accumulators  107  and piston/cylinders  108  may be mounted in any other suitable manner, e.g., hung from flukes  104  when no internal cavities  193  are provided. 
     It will be understood that the particular types of actuators, energy source/s (e.g., accumulator, battery, etc.) may be chosen and configured to fit a given application based on such factors as control time duration, maximum control surface stroke and safety of personnel working near or servicing the anchor&#39;s control system, etc. For example, other examples of suitable energy sources include, but are not limited to, combustion reaction chambers charged with components that react to provide pressurized fluid energy, electrically actuated and powered hydraulic pumps or gas compressors, etc. In this exemplary embodiment, a data logger, system drivers and batteries may also be contained within capsule  109  as further illustrated in  FIG. 11 . Other features shown in  FIGS. 1A-1E  is an attachment opening in the form of an integral mooring pendant line pad-eye  102  defined through center plate  101 , and deck winch attachment loops  110 A and  110 B. As shown in  FIG. 1B , a forward area of center plate  101  may in one embodiment be provided with an upwardly extending portion to raise the position of the mooring pendant line attachment point provided by opening  102  above the remaining aft portion of center plate  101  so as to allow for a greater degree of rotation of a mooring pendant line shackle connected to opening  102  when anchor system  100  is descending through the water as shown in  FIG. 7 . An optional cheek plate may be provided in one embodiment around opening  102  to provide strength for resisting mooring line tension. It is alternatively possible that more than one opening  102  may be defined in more than one locations of center plate  101  as may be desired or needed for attachment to a mooring pendant line according to a given application. 
     With regard to the exemplary embodiment of  FIGS. 1A-1E , the anchor body of anchor system  100  includes plate anchor elements  101 ,  104 ,  106  and  110  to which other components of steerable anchor system  100  have been assembled to form the steerable anchor system  100 . Such other components may include, but are not limited to, control surfaces  105 , energy sources  107  and actuators  108 , together with various control system components as further described herein. With regard to the anchor body of system  100  of  FIGS. 1A-1E , it will also be understood that the geometry of the anchor&#39;s attachment point (e.g., via mooring pendant line attachment to pad-eye opening  102 ) with respect to the anchor fluke&#39;s center of pressure may be selected to provide the proper angle of attack for the drag-embedment phase to be successful. Alternatively, the angle of the attachment point could be controlled by the ailerons or other control surfaces used to direct the anchor system  100  in the correct dive path beneath the seafloor  300 . 
     It will be understood that the illustrated exemplary plate anchor embodiment of  FIGS. 1A, 1B, 1C, 1D and 1E  is exemplary only, and that different configurations are possible in other embodiments, including plate anchor configurations having different number, geometry and/or types of attachment features (e.g., attachment opening/s such as pad-eye/s  102  or other types of attachment features such as threaded openings, mechanical connectors, etc.), having different fluke and/or center plate dimensions/geometry, etc. For example,  FIGS. 1F and 1G  illustrate respective overhead and side views of another exemplary embodiment of an autonomous steerable gravity embedded anchor system  100 . In this exemplary embodiment, attachment openings in the form of mooring pendant bridle attachment pad-eyes  102 A and  102 B are provided as shown for attachment to respective parts of a mooring bridle and triplate assembly as further illustrated in  FIG. 10B . It will be understood that with regard to the embodiment of  FIGS. 1F and 1G , the geometry of the anchor&#39;s attachment point (e.g., via bridle attachment to pad-eye openings  102 A and  102 B) with respect to the anchor fluke&#39;s center of pressure may be selected to fit the characteristics or needs of a given application, and/or the angle of the attachment point may be set to 90° and ailerons or other control surfaces used to direct the anchor system  100  in the correct dive path beneath the seafloor  300 . 
       FIG. 2  shows the anchor system  100  of  FIG. 1  rigged for deployment off the stern of an installation vessel  200 ; in this embodiment, an anchor handling vessel (AHV). As shown, winch lines  111 A and  111 B run from deck winches  114 A and  114 B, around tow pins  113 A and  113 B and attach to the fluke attachment loops  110 A and  110 B via hooks  112 A and  112 B. In this embodiment, hauling in on the deck winches  114 A/ 114 B will move the anchor  100  aft onto the stern roller  123 . Also shown is mooring pendant line  117  connected to mooring pendant attachment pad-eye  102 . In this exemplary embodiment, the upper end of the mooring pendant line  117  is outfitted with a submersible buoy with an integral subsea connector receptacle  118 . It will be understood that other subsea connection methods and/or apparatus would be suitable; for example, the use of a subsea ROV hook available from Irizar Forge Lifting &amp; Mooring of Lazkao, Spain; a HK12 “KS Hook” available from GN Rope Fittings B.V. of Nieuwkoop, The Netherlands, etc. Attached to the retrieval line attachment point opening  103  on the trailing edge of the center plate  101 , is the recovery pendant line  116 . In this illustrated embodiment, pendant line  116  is a synthetic mud rope although other any other suitable line type may be employed. At the upper end of the recovery pendant  116 , a small submersible recovery buoy  119  may be attached as shown; this recovery buoy&#39;s purpose is to keep the recovery pendant suspended above the seafloor  300  for later recovery of the anchor  100  by means of hauling in of the recovery pendant  116  by the AHV  200 . The top end of the buoy  119  may be outfitted with a master link that is part of the anchor  100  pelican hook release device  120 . Anchor hold-back during the anchor  100  deployment may be accomplished using the AHV  200 &#39;s workwire  121  which may be attached as shown to the top of the pelican hook  120 . As the deck winches  114 A/ 114 B move the anchor  100  towards the stern of the AHV  200 , the vessel&#39;s main winch  122  deploys the workwire  121 , maintaining equilibrium. In the alternative anchor system configuration embodiment shown in  FIG. 10B , assembled triplate  126  and mooring bridle parts  127 A and  127 B may be alternatively connected to the mooring pendant line  117  for deployment of the anchor system  100  off the stern of an installation vessel  200  in a manner similar to that described above. 
     In  FIG. 3 , the rigging for deployment of anchor system  100  of  FIG. 2  is shown in an elevation view. At the point illustrated in  FIG. 3 , the AHV&#39;s stern is located over the target location  301  and the internal control system for the anchor system  100  may be initialized, e.g., by wirelessly docking a laptop computer configured with suitable software to the anchor&#39;s internal control system components (e.g., within capsule  109 ) via radio and initializing the inertial navigation system and/or GPS system. At this point the accumulators  107 A/ 107 B are fully charged as are the batteries of the internal control system, e.g., within capsule  109 . 
     In  FIG. 4 , the anchor system  100  is shown partially deployed off the stern roller  123 . This has been accomplished by hauling in on the deck winches  114 A and  114 B and paying out the workwire  121  on the main winch drum  122 . At the point illustrated, the center of gravity of the anchor  100  is outboard of the stern roller  123 ; from this point onward, the deck winch lines  111 A and  111 B will no longer be needed for deployment and can be removed from the anchor system  100 . 
     In  FIG. 5 , the anchor system  100  has cleared the stern roller  123  and is hanging free below the stern of the AHV  200 . The AHV&#39;s navigation system may be checked at this point to ensure that the anchor system  100  is located directly above the selected target location  301  on the seafloor  300 . In those embodiments where anchor system  100  includes an internal control system configured to determine absolute location of anchor system  100  (e.g., such as an internal control system having global positioning system GPS capabilities), the anchor system  100  may not have to be released precisely from the AHV  200  over the target location  301 , but may be capable of adjusting for some horizontal offset as it falls toward the seafloor  300 , depending on water depth. 
     In  FIG. 6 , the pelican hook  120  has been released by the deck crew and the anchor  100  has started downward free-fall toward the target location  301  on seafloor  300 . 
       FIG. 7  illustrates descent of the steerable anchor system  100  through the water column showing how the active control system may use the control surfaces  105 A and  105 B to correct the downward path  301  of the anchor system  100  for varying currents and other anomalies. In particular, the free-fall of the anchor system  100  is depicted with potential deviations from the direct path to the target location  301  and resulting course corrections made by the internal control system (e.g., within capsule  109 ) operating the control surfaces  105 A and  105 B. Such deviations from a straight path may result from sea currents or anomalies (e.g., hydrodynamic imbalances) in the construction of the anchor body of system  100 . As shown, at the end of the free-fall period (i.e., at the terminal end of a downward path depicted by line  302 ), the anchor  100  must penetrate the seafloor  300  sufficiently to embed the complete length of the anchor body in the seafloor  300  to allow subsequent successful drag embedment operations, otherwise the anchor system  100  will need to be retrieved and re-set. In one exemplary embodiment, at the end of its decent the steerable anchor system  100  at a minimum penetrates the seafloor  300  such that the whole length of the steerable anchor system  100  is below the level of seafloor  300 . This ensures that later tensioning of the mooring line will cause the steerable anchor system  100  to dive to deeper equilibrium depth. Further shown in an inset box of  FIG. 7  is a vessel to be moored in the form of a MODU  400  that is optionally floating nearby on the same sea surface as AHV  200 , with a mooring line  128  attached to MODU  400  for mooring in a manner as described further herein. MODU  400  is shown in inset box of  FIG. 7  for purposes of scale. Alternatively, it will be understood that a vessel to be moored may be moved in later, and does not have to be present in the area during the placement of anchor system  100  into the sea floor. 
     The initial penetration depth of an anchor system  100  into seafloor  300  is a function of the anchor&#39;s kinetic energy just prior to impact with the seafloor  300 . A higher impact velocity gives a higher kinetic energy and, therefore, a deeper penetration depth. Reducing the anchor&#39;s drag coefficient is one means of increasing the impact velocity. Careful attention to the anchor&#39;s shape and geometry may be used to reduce the anchor&#39;s drag coefficient but alternative means originally developed for boat and ship hulls, such as the use of bubble curtains, may also be adapted for use with the disclosed steerable anchor systems. Bubble curtains are a mixture of micro air (or other gas) bubbles and water injected adjacent to the hull surface in order to reduce friction between the hull and the water. 
     As further shown in  FIG. 7 , ROV  124  may first visually check for penetration depth of anchor system  100 , once steerable anchor system  100  has penetrated the seafloor  300 . Distance marks optionally provided on the recovery pendant  116  may also be used to estimate anchor penetration. If a navigational data link is provided, the ROV  124  may approach the submersible recovery buoy  119  and download or otherwise recover the initial anchor installation (penetration and/or orientation) data as previously described herein, e.g., via electrical or optical signals transmitted through a suitable data transmission media or data link that extends through the recovery pendant line  116  to an optical or acoustic I/O interface (e.g., modem) provided on the recovery buoy  119  for communicating with I/O signal circuitry of the ROV; by physical retrieval of a control system capsule from the embedded anchor system  100 ; by visually reading the anchor installation/penetration information from a display device of the submersible recovery buoy  119 ; by receiving navigational data across a direct physical data path connection from a control system of the anchor system  100  via subsea data connectors that couple the ROV circuitry to an electrical or optical signal data transmission line that extends from a control system in the anchor system; etc. If based on the retrieved navigational data the anchor penetration depth is determined to be inadequate at this time, the AHV  200  may recover the anchor system  100  and re-deploy it. 
     In  FIG. 8 , the AHV  200  is shown lowering a subsea connector  125  on mooring line  128 . With the assistance of ROV  124 , the subsea connector  125  on mooring line  128  may be docked into the subsea connector receptacle  118 . 
     In  FIG. 9  the AHV  200  has moved together with the mooring line  128  towards the center of the mooring pattern, cutting the mooring pendant  117  into the seafloor  300  and causing the anchor  100  to dive and penetrate towards its final penetration depth as shown in  FIG. 10A  (and in the alternate embodiment of  FIG. 10B ). In  FIGS. 10A and 10B , the top or upper end of mooring line  128  has been handed over at the surface to MODU  400  floating on the sea surface that is to be moored with the anchor  100  that was pulled to depth by AHV  200  in  FIG. 9 . For purposes of scale, MODU  400  is shown floating on the sea surface in an inset box of each of  FIGS. 10A and 10B , with the top or upper end of mooring line  128  coupled to MODU  400  to secure it to anchor system  100 . The bottom or lower end of mooring line  128  is in turn coupled to mooring pendant  117  by subsea connector receptacle  118  as shown in each of  FIGS. 10A and 10B . 
     In the embodiment of  FIGS. 9 and 10A , the anchor  100  dives when the mooring line  128  is tensioned due to the geometry of the mooring pendant line attachment pad-eye  102  relative to the anchor&#39;s center of soil pressure for the embodiment of  FIG. 10A , or dives due to the geometry of the assembled triplate  126  and anchor bridle  127 A and  127 B for the embodiment of  FIG. 10B . In the embodiment of  FIG. 10B , a mooring bridle and triplate assembly is connected between anchor  100  and the mooring pendant line  117 , i.e., mooring pendant line  117  is connected via triplate  126  by attachment of anchor bridle  127 A and  127 B to multiple mooring pendant bridle attachment pad-eyes  102 A and  102 B, which are defined in center plate  101  that is configured for operable attachment to mooring pendant anchor bridle parts  127 A and  127 B as shown. Also shown is the mooring bridle and triplate assembly  115  which is connected to the mooring pendant line  117 . 
     As shown in the embodiments of  FIGS. 10A and 10B , the ROV  124  deployed from AHV  200  may re-query the control system within the capsule  109  at the recovery buoy  119  to confirm that the final penetration depth and anchor orientation is acceptable. If the final penetration depth is not acceptable, the AHV  200  recovers the anchor and re-deploys it. At this point, the AHV  200  has connected the mooring line to the vessel to be moored as shown in inset of each of  FIGS. 10A and 10B . In this case, a mobile offshore drilling unit (MODU)  400  is the vessel to be moored, although the disclosed systems and methods may be employed for anchoring and mooring a wide variety of other types of vessels, e.g., drilling and other types of ships, naval vessels, oil tankers, etc. 
       FIG. 11  illustrates a simplified block diagram showing one exemplary embodiment of active components of a steerable anchor system  100  coupled via a data transmission path through recovery line  116  to a recovery buoy  119  that is configured with an acoustic modem  1116  and acoustic transducer  1114 . In this regard, recovery buoy  119  and its data transmission line/recovery line  116  may be provided as optional components of the steerable anchor system  100 . Also shown in  FIG. 11  is an acoustic modem  1110  and acoustic transducer  1112  that are provided on board ROV  124 . In  FIG. 11 , ROV  124  is illustrated in proximity to recovery buoy  119  such that acoustic signals representative of navigational data may be transmitted from acoustic modem  1116  via transducer  1114  of buoy  119  to acoustic modem  1110  via transducer  1112  of ROV  124  in a manner as described above. It will be understood that  FIG. 11  is exemplary only, and that recovery buoy  119  and ROV  124  may be alternatively configured with suitable optical and/or visual communication components (e.g., such as a display device replacing modem  1116  on buoy  119  and a video camera replacing modem  1112  on ROV  124 ) for communicating navigational data from buoy  119  to ROV  124  using other types of signals, such as optical signals or displayed and captured visual images in those manners described elsewhere herein. It will also be understood that other possible components of ROV  124  and buoy  119  are not shown that may be present to implement operations of ROV  124  and buoy  119  described elsewhere herein. Examples of such other components include, but are not limited to, battery or batteries, memory device/s, processing device/s, ROV propulsion and communication lines via ROV umbilical cord to surface, etc. 
     Also shown in  FIG. 11  is topside operator terminal  1102 , which in this case is provided in the form of a laptop computer  1104 , e.g., such as Windows, Linux or Apple OS-based computer having internal host processing device (e.g., Intel or AMD CPU), video display, storage, random access memory (RAM), keyboard, touchpad or mouse, etc. However, any other suitable operator terminal system may be employed, e.g., such as desktop computer, tablet computer, smart phone, etc. As shown topside operator terminal  1102  may also include a radio frequency (RF) radio system (e.g., Bluetooth or 802.11-based radio system) that includes a RF transceiver coupled to an RF antenna  1108 . Topside terminal  1102  may be utilized by a human operator on deck of a surface installation vessel  200  such as illustrated and described elsewhere herein, e.g., to communicate with anchor system  100  via radio  1106  and antenna  1108  to activate and/or initialize components of system  100  as described in relation to  FIG. 3 , and/or to wirelessly retrieve data or otherwise configure or run tests/diagnostics on one or more components of anchor system  100 . It will be understood that communication between a topside operator terminal and an anchor system  100  may alternatively be accomplished in any other suitable manner while anchor system  100  is on deck of surface vessel  200 , e.g., such as wired data communications through Ethernet cable, etc. 
     Still referring to  FIG. 11 , steerable anchor system  100  may be configured as shown with an optional waterproof control system capsule  109  (e.g., an environmentally sealed waterproof enclosure) that may be, for example, detachable and retrievable from anchor system  100  as previously described herein. Alternatively, a non-capsulated control system having similar components may be provided integral to an anchor system  100 . As shown in  FIG. 11 , control system components (e.g., within capsule  109 ) may include a RF radio system  1124  including a RF transceiver, and a coupled RF antenna  1122  that may be configured to provide communication between an anchor system processing device  1120  (e.g., CPU, microcontroller, controller, etc.) and external equipment such as topside operator terminal  1102  while anchor system  100  is on deck of installation vessel  200 . 
     As shown in  FIG. 11 , other components (e.g., within control system capsule  109 ) that may be operatively coupled to anchor system processing device  1120  include GPS module  1126  that may be employed to determine absolute location of anchor system  100  prior to release as described in relation to  FIG. 5 . Also shown coupled to anchor system processing device  1120  are components of inertial navigation system  1128 , which in this exemplary embodiment include 3-axis gyroscopes  1127  and 3-axis accelerometers  1129 . Components of inertial navigation system  1128  may be employed in a manner described elsewhere herein to control descent path of anchor system  100  via anchor system processing device  1120  and motivator systems  1150  as described further below. An optional electronic compass  1132  may also be provided as shown to monitor directional orientation of anchor system  100 . A data logger  1130  (e.g., including one or more of non-volatile memory, Flash or EEPROM memory, volatile memory, etc.) may be coupled to receive and store navigation data for transmittal and/or retrieval by ROV  124  in a manner as previously described.  FIG. 11  also illustrates control system power source  1140 , e.g., one or more batteries  1140  provided to power anchor system processing device  1120  and its coupled electronic components, as well as to provide power to servo driver  1142  that is coupled as shown to provide power signals  1144  to selectably actuate individual server actuators  1152 A,  1152 B and  1152 N of motivators  1150  under the control of anchor system processing device  1120  in a manner described further below. 
     In one exemplary embodiment, control system components (e.g., within capsule  109 ) may be provided with memory (e.g., non-volatile memory, Flash memory, etc.) that includes navigational reference data that may be provided in the form of a grid of location coordinates (e.g., longitude and latitude or other suitable geographic positioning coordinates), as well as a stored target location on the seafloor  300  and/or a pre-defined anchor path from the surface location to the seafloor. When optional GPS module  1126  is present, processing device  1120  of the control system (e.g., within capsule  109 ) may be configured to determine initial GPS-based location coordinates of anchor system  100  on the stored location grid prior to anchor system release based on location data provided above the surface of the water by GPS module  1126 , and to optionally calculate a pre-determined anchor path from the initial anchor location to the target seafloor location. After release of anchor system  100 , processing device  1120  may then be configured to use inertial-based navigation data from inertial navigation system  1128  to track and update the real time location of anchor system  100  on the stored location grid as the anchor system descends through the water to the seafloor  300 . Processing device  1120  of a control system may also be configured in one exemplary embodiment to compare the real time actual path of anchor system toward the seafloor  300  against a stored pre-defined path or a pre-determined anchor path to determine the desired real time output position of each of the control surfaces  105  to guide the anchor to a target location in the seafloor along the pre-defined or pre-determined anchor path. 
     In another exemplary embodiment, a control system (e.g., within capsule  109 ) may be programmed with initial offset or error information that represents the distance and heading that anchor system  100  needs to traverse (or minimize) to reach a given target location on seafloor  300  (e.g., without anchor system  100  being required to know its absolute geographic starting position from GPS data). For example, “50 feet North” may be programmed to indicate heading and distance that anchor system  100  needs to traverse from its starting point to the seafloor, or “0 feet” (dead center) to indicate that the starting point is directly over the target seafloor location and that anchor system  100  needs to dive straight down from its starting point to the seafloor  300 . This programmed error information may be provided to processing device  1120  of the control system (e.g., within capsule  109 ), for example, as data entered by an operator from topside operator terminal  1120  during system initialization on the deck of an installation vessel  200 . During anchor system descent, processing device  1120  may then utilize real time navigational data sensed by gyroscopes  1127  and accelerometers  1129  of inertial navigation system  1128  to control movement of control surfaces  105  in real time as necessary to minimize the error offset so that anchor system  100  penetrates the seafloor  300  as close as possible to the target seafloor location. It will be understood that any other suitable control technique may be implemented by on-board control system components (e.g., within capsule  109 ) to self-direct anchor system  100  to a target location. 
     In the illustrated embodiment of  FIG. 11 , two motivator systems  1150 A and  1150 B are shown provided that are mechanically coupled to controllably move respective control surfaces  105 A and  105 B during free fall descent of anchor system  100  to control (steer) the anchor system descent trajectory and/or path. One or more additional (spare) motivator systems  1150 N may be provided to controllably operate and move additional optional control surfaces, such as a movable rudder (not shown). In the illustrated embodiment, each of motivator systems includes an energy source in the form of a respective accumulator  107  that may contain pressurized fluid for selectably actuating a respective control mechanism  108  (e.g., such as pneumatic or hydraulic piston and cylinder) coupled to each control surface  105  under the control of a respective servo actuator  1152  (e.g., pneumatic or hydraulic electro-mechanical valve) that is actuated in a single step between on and off (or alternatively adjusted in continuous manner or in small steps between on and off positions) to selectably provide and withhold pressurized fluid to each control mechanism  108  to move a respective control surface  105  in response to individual power signals  1144  provided by servo driver  1142  under the direction of anchor system processing device  100  based on navigational and positional input received from inertial navigation system  1128 , GPS  1126 , and/or electronic compass  1132 . In this regard, anchor system processing device  100  may be programmed to execute navigational algorithm/s that are stored and loaded from on-board non-volatile memory, to determine how to move each of control systems  105  based on real time navigational data from inertial navigation system  1128 , GPS  1126 , and/or electronic compass  1132 . Also shown in  FIG. 11  are optional respective control system feedback paths  1160  that may be provided to communicate real time sensed position of each control mechanism  108  (and therefore real time position of each respective control surface  105 ) from suitable sensors (e.g., position sensors, proximity sensors, etc.) to anchor system processing device  1120 , which may use this sensed feedback position to correct and/or fine tune control movement of each control surface  105  to achieve the desired anchor system descent path. 
     It will be understood that the illustrated embodiment of  FIG. 11  is exemplary only, and that any other configuration and/or type of actuation components may be employed to move control surfaces  105  under the direction of an anchor system processing device, e.g., such as electro-mechanical actuators (i.e., rather than pneumatic or hydraulic actuation components) that are coupled to selectably move each of control surfaces  105  to control the descent path of a free-falling anchor system. Moreover, the particular arrangement and/or identity of components within a control system or control system capsule  109  may vary as desired or needed to fit the needs of a given application, e.g., additional or alternative components may be present, and/or radio  1124 , antenna  1122 , compass  1132 , etc. may be absent or replaced by different components. 
     It will also be understood that one or more of the tasks, functions, or methodologies described herein (e.g., including those performed by control system components (e.g. within capsule  109 ), ROV  124 , topside terminal system  1102 , etc.) may be implemented by circuitry and/or by a computer program of instructions (e.g., computer readable code such as firmware code or software code) embodied in a non-transitory tangible computer readable medium (e.g., optical disk, magnetic disk, non-volatile memory device, etc.), in which the computer program comprising instructions are configured when executed (e.g., executed on a processing device of an information handling system such as CPU, controller, microcontroller, processor, microprocessor, FPGA, ASIC, or other suitable processing device) to perform one or more steps of the methodologies disclosed herein. A computer program of instructions may be stored in or on the non-transitory computer-readable medium accessible by an information handling system for instructing the information handling system to execute the computer program of instructions. The computer program of instructions may include an ordered listing of executable instructions for implementing logical functions in the information handling system. The executable instructions may comprise a plurality of code segments operable to instruct the information handling system to perform the methodology disclosed herein. It will also be understood that one or more steps of the present methodologies may be employed in one or more code segments of the computer program. For example, a code segment executed by the information handling system may include one or more steps of the disclosed methodologies. 
     While the invention may be adaptable to various modifications and alternative forms, specific examples and exemplary embodiments have been shown by way of example and described herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the systems and methods described herein. Moreover, the different aspects of the disclosed systems and methods may be utilized in various combinations and/or independently. Thus the invention is not limited to only those combinations shown herein, but rather may include other combinations.