Patent Description:
This disclosure is directed to dynamically controllable foil systems, and to methods for controlling such systems. Applications include, but are not limited to, dynamically controlled foil and hydrofoil systems configured to position and maintain spacing between seismic sources and other elements of a marine seismic array.

Seismic arrays with sources and streamers are used to study rock strata and other structures below the surface, for example, as described in <CIT>.

One or more marine vessels are typically used to tow the source and/or receiver arrays, in order to obtain relevant geological data covering a desired surface area of the ocean floor. For example, a single surface vessel may simultaneously tow both a source array and an array of seismic streamers, or different vessels can be used to tow separate source and receiver arrays. Alternatively, a towed source array can be used in conjunction with stationary receivers, for example, an array of ocean-bottom nodes, or with ocean-bottom cables deployed on the seabed.

During operation, acoustic shock waves generated by the source array propagate through the water to penetrate the ocean floor and are reflected from subsurface structures. The reflected acoustic waves are recorded as signals or seismic responses by the receivers, e.g., hydrophones and/or geophones towed behind a vessel or deployed on the ocean floor.

Lateral forces are applied to maintain position and spacing of the seismic sources and other array elements as they are towed behind the vessel. The spacing depends on the number of sources and/or streamer cables that are deployed, and on the spacing between adjacent source and/or receiver components. Typically, a number of source sub-arrays or strings are deployed behind the vessel using a tow rope configuration to spread the sources over lateral distances of approximately ten to one hundred meters or more. Streamer cables are typically deployed over much larger lateral distances, for example, from one hundred meters to a kilometer or more, and may extend for several kilometers behind the tow vessel.

Lateral spacing can be achieved by deploying a paravane or diverter apparatus on a dedicated tow rope arrangement using a spreader or series of individual tether lines to provide the desired spacing between adjacent cables. Positioning devices can also be provided along each streamer cable, in order to maintain depth and/or lateral offset along the cable length.

Generally, paravanes, doors, diverters and similar steering solutions tend to increase drag forces, and require substantial deck area during storage, deployment, and retrieval. Steering response can also be limited, not only by the diverter operating system, but also due to the complex nature or the additional tow ropes, tag lines, and other required elements. As a result, there remains a need for position control systems to provide improved dynamic control with less drag without being subject to other limitations of the existing prior art.

The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention as defined in the claims is to be bound.

This application relates to seismic prospecting and to foil systems for source and receiver arrangements for gathering seismic data and methods for controlling the same. For example, the foil systems may be applied to an apparatus for positioning and maintaining spacing between seismic sources, sub-arrays, and/or streamer cables during a seismic survey, e.g., in a source array towed behind a vessel, or in a towed marine seismic array. The application also relates to foil systems for ocean bottom cable deployment, e.g., dual (or multiple) ocean bottom cable deployment utilizing a sub-sea sled or towed object with a dynamically control foil system to provide lateral displacement, up/down lift, or both.

According to a first aspect, there is provided an apparatus including a positive buoyancy device, a pair of control cables, a plurality of foil sections, an actuator, and a controller. The pair of control cables are attached to the buoyancy device and extend downward from the buoyancy device to a submerged end. The plurality of foil sections are disposed along the control cables between the buoyancy device and the submerged end. The actuator is disposed at least partially within the positive buoyancy device and is configured to adjust attack angles of the foil sections by changing a tension in one or both of the control cables. The controller is disposed at the positive buoyancy device and in data communication with the actuator. The controller is configured to direct the actuator to adjust the tension in one or both of the control cables and thereby regulate lift generated by the plurality of foil sections.

In an implementation of the present teachings, a system includes a surface or subsurface buoyancy device, a forward control cable, an aft control cable, an actuator, and a plurality of foil sections. The forward control cable may be coupled to and extend beneath the buoyancy device. The aft control cable may also be coupled to and extend beneath the buoyancy device. The actuator may be mounted to the buoyancy device. The actuator may be configured to adjust tension in the aft control cable with respect to the forward control cable. The plurality of foil sections may be disposed along the forward and aft control cables. The foil sections may be configured to generate lift based on attack angles thereof. The attack angles of the foil sections may vary as a function of the tension.

According to a second aspect, there is provided a seismic array including a plurality of towed seismic sources and a plurality of dynamically controlled steering systems attached to each of the seismic sources, respectively. Each steering system includes a positive buoyancy device, a pair of control cables, a plurality of foil sections, an actuator, and a controller. The pair of control cables are attached to the buoyancy device and extend downward from the buoyancy device to a submerged end. The plurality of foil sections are disposed along the control cables between the buoyancy device and the submerged end. The actuator is disposed at least partially within the positive buoyancy device and is configured to adjust attack angles of the foil sections by changing a tension in one or both of the control cables. The controller is disposed at the positive buoyancy device and in data communication with the actuator. The controller is configured to direct the actuator to adjust the tension of one or both of the control cables and thereby regulate lift generated by the plurality of foil sections.

According to a third aspect, there is provided a method of steering a seismic array. The seismic array includes a plurality of towed seismic devices and a plurality of dynamically controlled steering systems attached to each of the seismic sources, respectively. Each steering system includes a positive buoyancy device, a forward control cable, an aft control cable, a plurality of foil sections, an actuator, and a foil controller. The forward control cable is coupled to and extend beneath the buoyancy device. The aft control cable is coupled to and extend beneath the buoyancy device. The plurality of foil sections are disposed along the forward and aft control cables. The actuator is mounted to the buoyancy device and is disposed at least partially within the positive buoyancy device. The actuator is configured to adjust attack angles of the foil sections by changing a tension in one or both of the control cables. The foil controller is configured to direct the actuator to adjust the tension in either or both of the control cables and thereby regulate lift generated by the plurality of foil sections. The method includes: transmitting data from the foil controller to one or more of the steering systems in order to instantiate a mode in the corresponding actuator; and.

causing the actuator to adjust tension in the aft control cable with respect to the forward control cable to generate lift for steering the corresponding buoyancy device and attached seismic source.

A more extensive presentation of features, details, utilities, and advantages of the present invention as defined in the claims is provided in the following written description of various embodiments and illustrated in the accompanying drawings.

In the following disclosure, reference is made to a number of exemplary embodiments or specific implementations of the claimed invention. However, it should be understood that the claims are not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the claimed invention. Furthermore, the various embodiments may provide numerous advantages over the prior art. However, although such embodiments may achieve advantages over other possible solutions and over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the claims. Thus, the following aspects, features, embodiments, and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in the claims. Likewise, reference to "the invention" shall not be construed as a generalization of any inventive subject matter disclosed herein, and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in the claims.

<FIG> is a schematic illustration of a source array <NUM> towed by a seismic survey craft or other vessel <NUM>. As shown in <FIG>, tow lines or cables <NUM> are coupled to vessel <NUM> at one end and attached to a sub-array or string <NUM> of seismic sources at the other. For example, each tow cable <NUM> can be coupled to a series of air guns or other sources suspended from a head float, buoy, or other flotation apparatus <NUM>.

The source array <NUM> is directed along a navigational course or sail line by tow vessel <NUM>. Within the source array <NUM>, the relative positions of the individual sources (or sets of sources) can be controlled by providing a dynamically steerable foil system for each floatation apparatus <NUM>, or for groupings of floatation apparatus <NUM>, as described herein.

<FIG> is a side view of source array <NUM> illustrating representative configurations for dynamically controlled foil system <NUM>. In this particular example, a sub-array or string <NUM> of individual air guns or other seismic sources <NUM> is suspended from the floatation apparatus <NUM> via suspension ropes <NUM>, which determine the depth of sources <NUM> below surface S. Suspension ropes <NUM> are coupled to selected portions of float <NUM>, e.g., between head float section 18a and the trailing end of sausage float section 18b.

Float <NUM> is towed along surface S via a tow cable <NUM>, which is coupled to the head float section 18a via a tow leader <NUM>. The tow cable <NUM> typically comprises an umbilical <NUM> with data and power connections for seismic sources <NUM> and is connected to the foil system <NUM> at a cable connector <NUM>. In air gun applications, the umbilical <NUM> may include a pneumatic hose or conduit configured to provide pressurized air to the seismic sources <NUM> in order to generate acoustic shock waves when fired in response to direction by a control system. The shock waves (or other seismic signals) propagate from the seismic sources <NUM> through the water or other medium, penetrating the ocean floor and reflecting back from subsurface features. The reflected signals are recorded by seismic sensors (e.g., hydrophones or geophones in a streamer cable or ocean-bottom array) and processed to generate geophysical image data representing the subsurface structures.

As shown in <FIG>, the dynamically controlled foil system <NUM> can be coupled between the floatation apparatus <NUM> and a submerged portion of the tow cable <NUM>, e.g., at the cable connector <NUM> between the head float 18a and the umbilical portion <NUM> of the tow cable <NUM>, aft of a tow leader <NUM> and forward of the seismic sources <NUM>. Alternatively, the submerged end of the foil system <NUM> can be coupled to one of the seismic sources <NUM> (e.g., to the first gun plate in the string).

In these configurations, the foil system <NUM> is configured to steer the head float 18a by generating hydrodynamic lift forces, which are controlled to achieve the desired lateral positioning of the seismic sources <NUM> within the source array <NUM> and with respect to the tow vessel <NUM>. Alternatively, one or more foil systems <NUM> can be coupled to the sausage float section 18b and positioned along (or in place of) any of a number of suspension ropes or cables <NUM>, for example, in a forward position at the lead seismic source <NUM>, in an intermediate position between individual seismic sources <NUM>, or in an aft position at (or trailing behind) the last seismic source <NUM>.

<FIG> is a cross-section view of a foil segment or foil section <NUM> for the dynamically controlled foil system <NUM>, e.g., as shown in <FIG>, above. As illustrated in <FIG>, the foil section <NUM> extends from a leading edge <NUM> to a trailing edge <NUM>, defining a chord or chord line (CL) between a first surface <NUM> (e.g., a pressure surface) and a second surface <NUM>(e.g., a suction surface).

A forward rope or control cable <NUM> extends through a front conduit <NUM> in the front portion of the each foil section <NUM> toward the leading edge <NUM>. An aft rope or control cable <NUM> extends through a rear conduit <NUM> in the back portion of the foil section <NUM> toward the trailing edge <NUM>. The front and rear conduits <NUM>, <NUM> may extend in parallel with each other and with the leading edge <NUM> of the foil sections <NUM> and reside in a common plane with each other, the leading edge <NUM>, and a longitudinal bisector of the trailing edge <NUM> of each of the foil sections <NUM> The control cables <NUM>, <NUM> are arranged generally in parallel as they extend through the front and rear conduits <NUM>, <NUM> in the foil sections <NUM>. In embodiments in which the widths of the plurality of foil sections <NUM> between the leading edge <NUM> and the trailing edge <NUM> are the same or substantially equivalent, the control cables <NUM>, <NUM> may be positioned equidistantly apart along their length.

As shown in <FIG>, the front and rear conduits <NUM>, <NUM> are generally centered along the chord line (CL), proximate to the leading edge <NUM> and the trailing edge <NUM>, respectively. This arrangement increases or substantially maximizes the longitudinal separation between the forward and aft cables <NUM>, <NUM>, but is merely representative. More generally, the longitudinal positions of the front and rear conduits <NUM>, <NUM> (and the forward and aft cables <NUM>, <NUM>) vary between the leading edge <NUM> and the trailing edge <NUM>, as do the corresponding lateral positions with respect to the chord line (CL) between the first and second opposing foil surfaces <NUM>, <NUM>.

The front and rear conduits <NUM>, <NUM> can thus be provided for stringing the forward and aft cables <NUM>, <NUM> in various positions between any floatation apparatus <NUM> and a submerged end, cable, or component, e.g., as shown above in <FIG>. Rotation of the foil section <NUM> about the forward cable <NUM> is controlled by adjusting the relative length or tension in the forward and aft cables <NUM><NUM> in order to steer foil section <NUM>.

The dynamically controlled foil system <NUM> can thus be provided as a steerable fairing, vane, or hydrofoil apparatus utilizing one or more foil sections <NUM>, which are controlled via the forward and aft cables <NUM>, <NUM> to generate desired hydrodynamic lift or steering forces. Alternatively, the foil system <NUM> can be described as a dynamically steerable fairing string, utilizing either a plurality of individual foil sections <NUM>, or a single continuous flexible foil <NUM>, with segments <NUM> defined along the spanwise length.

Suitable materials for the foil section <NUM> include composites or polyurethane and other plastics or durable polymers. In one embodiment, for example, a continuous, flexible-span polymer or composite foil <NUM> can be threaded between forward and aft cables <NUM>, <NUM> to form a substantially unitary fairing or fairing string. Alternatively, a plurality of discrete rigid or flexible foil sections or vanes <NUM> can be threaded onto the forward and aft cables <NUM>, <NUM>, in either a spaced or abutting configuration and with or without interconnecting linkages.

In these embodiments, the foil sections <NUM> may be formed of either flexible or rigid materials, and each foil section <NUM> may have substantially the same span, or the spans can be individually selected. Similarly, each foil section <NUM> may have substantially the same foil geometry, or the foil geometries may vary as a function of depth or position (e.g., between the surface float and submerged cable attachments). The foil sections <NUM> can also be provided in either symmetric or asymmetric form, for example, using one or more NACA series, Gottingen, or Eppler designated foil geometries.

<FIG> is an alternate view of foil section or segment <NUM>, illustrating an angle of attack θ as defined with respect to the flow direction (F). The lift or steering forces generated by the foil section <NUM> are designated by arrow (L).

In general, the lift (L) depends both upon foil geometry and the angle of attack θ. Adjustments in the relative length of or tension in the forward and aft cables <NUM>, <NUM> can thus be used to control the steering forces on each foil section <NUM> by changing the angle of attack. Note, however, that for asymmetric foil sections <NUM>, the lift (L) is typically generated in a positive sense (e.g., in the direction from the pressure foil surface <NUM> toward the suction foil surface <NUM>), even for zero or somewhat negative attack angles θ. For symmetric foil sections <NUM>, on the other hand, the lift (L) can change sign with the angle of attack θ.

Asymmetric foil geometries thus provide a more stable configuration, in which the direction of the lift (L) is substantially determined by the orientation of the pressure and suction foil surfaces <NUM>, <NUM>, and steering is accomplished by changing the angle of attack to increase or decrease the magnitude of the corresponding steering forces on the foil sections <NUM>. One such asymmetrical foil cross section is defined by the NACA <NUM> foil, but other suitable geometries may be utilized, including, but not limited to, other NACA, Gottingen, and Eppler foil geometries. Alternatively, the forward and aft cables <NUM>, <NUM> may be offset by providing off-chord conduits <NUM> and <NUM>, laterally displaced from chord line (CL) as described above.

<FIG> is a schematic illustration of the dynamically controlled foil system <NUM>, illustrating lift effects. Each foil system <NUM> may be composed of a plurality of foil sections <NUM> aligned with and stacked on top of each other as shown in <FIG> such that the leading edges <NUM> and trailing edges <NUM> are all aligned in substantially the same direction, respectively. The foil sections <NUM> are held in alignment with each other by the forward and aft cables <NUM>, <NUM> passing through the front and rear conduits <NUM>, <NUM> in each foil section <NUM>. As lift (L) is generated, individual foil sections <NUM> will typically take on a curved or sinusoidal profile along the span of the foil system <NUM>, between the floatation apparatus <NUM> on the surface (S) and the submerged end or at the connection between the cable connector <NUM> and a tow cable <NUM>, a seismic source <NUM>, or other submerged cable <NUM>. Even when the foil system <NUM> curves under tension, the leading and trailing edges <NUM>, <NUM> of the foil sections <NUM> maintain a common directional orientation, respectively.

Note that the amplitude of the effect is not to scale, and is exaggerated in <FIG> to illustrate the relative displacement of the foil sections <NUM> with respect to vertical (V), as defined generally perpendicular to the surface (S). Generally, a twist will also develop along the span, so that the angle of attack may be relatively smaller for the top and bottom foil sections <NUM> near the floatation apparatus <NUM> and the cable connector <NUM> to the submerged cable <NUM>, respectively, and relatively larger for the foil sections <NUM> in the mid-span region. Thus, the foil sections <NUM> in the mid-span region may tend to generate more lift than the top and bottom sections, resulting in the "billowing" or sinusoidal effect of <FIG>.

Alternatively, the foil geometry of individual foil sections <NUM> may be selected to reduce lift in the mid-span region between the floatation apparatus <NUM> and the submerged cable <NUM>, as compared to the top and bottom foil sections <NUM>. For example, the foil sections <NUM> may have different foil geometries selected to generate more uniform lift across the span or to increase or reduce span-wise lift effects.

<FIG> is a schematic illustration of a representative the adjustment mechanism <NUM> for the dynamic foil system <NUM>. As shown in <FIG>, a turnbuckle <NUM> and a pulley <NUM>, ratchet, winch, or similar cable guide and feed mechanism may be mounted to the floatation apparatus <NUM>, e.g., between the top end of the aft control cable <NUM> and an aft anchor point <NUM> on the back or rear section of the floatation apparatus <NUM> (in the trailing edge direction of the foil sections <NUM>). The forward cable <NUM> is mounted to a forward anchor <NUM> attached to the front section of the floatation apparatus <NUM> (in the leading edge direction of the foil sections <NUM>).

The adjustment mechanism <NUM> can be configured for adjusting either the forward cable <NUM> or the aft cable <NUM>; both embodiments are encompassed. Another option is to use an adjustment mechanism <NUM> that provides differential adjustments to both forward and aft cabled <NUM>, <NUM>; e.g., by shortening one cable while lengthening the other at the same time. In some designs a single control cable may be used, extending from the forward cable anchor <NUM> down along a forward cable section <NUM>, then passing through a cable return or wrapping or inflecting around a cable connector <NUM> attached to a submerged cable <NUM>, and back up along an aft cable section <NUM> to the aft anchor <NUM> through the pulley <NUM>. Alternatively, separate forward and aft control cables <NUM>, <NUM> may be provided, e.g., individually attached at the submerged cable connector <NUM>. The submerged cable <NUM> can be provided either as a tow line for a streamer cable <NUM> or as an umbilical for a source gun array.

A control device <NUM> for the adjustment mechanism <NUM> may be located at either the top or bottom end of the foil system <NUM>, for example, inside the floatation apparatus <NUM>, as shown in <FIG>. Suitable control devices <NUM> include processor, memory, and software components configured to direct the adjustment mechanism <NUM> to selectively vary the length and/or tension in the forward and aft cables <NUM>, <NUM>, in order to regulate the lift and steering forces generated by the foil system <NUM> by changing the angle of attack along individual foil sections <NUM>. For example, the control device <NUM> may be configured to control an electric motor or similar drive in order to actuate the adjustment mechanism <NUM>, providing for automated steering by adjustment of the relative length and tension in the forward and aft control cables <NUM>, <NUM>. Other control options include, but are not limited to, hydraulic and pneumatically controlled ram or piston mechanisms, electric winch drives, and motor-driven rack and pinion arrangements.

<FIG> is an isometric view of the adjustment mechanism <NUM> in an external, horizontal mount configuration on a head float 18a. In this example, the adjustment mechanism <NUM> includes a linear actuator <NUM> and the pulley <NUM> mounted horizontally in a concave recess <NUM>, which is defined on the exterior surface of the head float 18a.

The recess <NUM> extends longitudinally along the bottom (or ventral) portion of the head float 18a, from just aft of the forward end, opposite the sausage section 18b, through to the aft end of the head float 18a, proximate to the sausage section 18b. A number of structural bands <NUM> can be provided to encircle the head float 18a with a number of brackets <NUM> for handling during deployment and retrieval.

<FIG> is a cutaway, isometric view of the head float 18a, showing the adjustment mechanism <NUM> in an internal, vertical mount configuration. In this example, the linear actuator <NUM> is mounted inside the aft end of the head float 18a and operates to drive a ram <NUM> vertically up and down. The ram <NUM> is coupled to the aft control cable <NUM>, which extends down through a funnel-shaped coupling <NUM>. The coupling <NUM> provides a bend radius for the aft control cable <NUM>.

Generally, the tension in the aft control cable <NUM> can be increased to "power up" the foil system, increasing the angle of attack and increasing the corresponding lift. Conversely, the tension in the aft cable <NUM> can be decreased to "depower" the system, decreasing the angle of attack and reducing the lift. In alternate embodiments the rigging can be reversed, for example by providing aft cable <NUM> with a fixed tension and increasing or decreasing the tension in the forward cable <NUM> or by implementing differential rope length adjustments.

<FIG> is a schematic view of a representative towed seismic array <NUM> utilizing one or more dynamically controlled foil systems <NUM> for steering source and/or streamer components. As shown in <FIG>, the seismic array <NUM> includes a source array <NUM> and a streamer array <NUM>. Source array <NUM> includes a number of head/sausage type floats <NUM> from which individual seismic sources <NUM> are suspended with umbilical cables <NUM> for power, data, and pneumatic connections to the survey vessel <NUM>. The streamer array <NUM> includes a plurality of individual streamer cables <NUM> with seismic receivers distributed along each cable length to observe the reflected signals from the seismic sources <NUM>.

The streamers <NUM> are coupled to tow lines or other submerged cables <NUM> along a spreader or separation rope <NUM>, which is suspended at streamer depth below corresponding head buoys <NUM> using tag lines or depth ropes <NUM>. The streamers <NUM> may extend many kilometers from the head buoys <NUM> toward a corresponding number of tail buoys <NUM> at the aft end (not to scale).

As shown in <FIG>, the separation rope <NUM> is laterally extended by attachment to spur lines <NUM>, which are coupled to paravanes or diverters <NUM> via deflector straps <NUM>. Wide tow ropes <NUM> run between paravanes or diverters <NUM> and the tow vessel <NUM>. The dynamically controllable foil system <NUM> may be provided on or in place of one or more streamer tag lines or depth ropes <NUM>, extending from the head buoys <NUM> down to the forward end of the streamer cables <NUM>. The steerable foil systems <NUM> may also be provided between the tail buoys <NUM> and the aft ends of the streamer cables <NUM> and in intermediate streamer locations.

Seismic survey vessel <NUM> is provided with a navigational system <NUM> including one or more foil steering modules configured to communicate with the dynamically steerable foil systems <NUM> deployed variously in the source array <NUM> and the streamer array <NUM>, and/or among the other components of the towed seismic array <NUM>. The foil systems <NUM> can also be utilized, in addition to source steering, to independently steer and laterally position streamers <NUM> with or without a discrete spreader or separation rope <NUM>.

The steerable foil systems <NUM> can also be provided in lieu of diverters or paravanes <NUM>, for example in the end streamer positions as shown in <FIG>, without the need for a separate spur line <NUM> and wide tow rope <NUM>. Alternatively, the foil systems <NUM> can be used within or provided in place of one or more diverters or paravanes <NUM> using a similar spur cable configuration.

More generally, the foil system <NUM> can be utilized for steering a wide range of submerged cable and float arrangements, suitable not only to seismic source and streamer steering but also for ocean-bottom cable and node deployment, side scan surveys, and sonar applications. The dynamically steerable foil system <NUM> may also be adapted to more generalized (non-seismic) uses including generic paravane, diverter and hydrofoil systems. Use with paravane/diverter cable or P-cable and ocean bottom cables are additional options.

<FIG> is a cross-section view of a representative float or buoyancy device <NUM> with an internal, vertically-oriented cable adjustment mechanism <NUM>. <FIG> are side and top views of float or buoyancy device <NUM>, respectively.

The buoyancy device <NUM> can take the form of a surface or subsurface float, positive buoyancy device, or other arrangement that provides some form of upper and/or lower attachment point to which the stacked foil system <NUM> can be coupled and pull against. Suitable examples include, but are not limited to, a head float, a sausage buoy, a head buoy, a tail float, a tail buoy, or similar surface or subsurface flotation apparatus, configured either for seismic source or streamer steering, or for a generic dynamically steerable hydrofoil or vane application, as described above. In additional embodiments, the actuator system may be utilized with a horizontal foil string, e.g., to provide upward or downward lift. Similarly, dynamically controlled foils can be provided in a neutrally buoyant paravane system configured to tow a three-dimensional streamer spread under ice. The concept can also be used for a neutrally buoyant (e.g., under ice) source float device, e.g., for use in the Arctic or other cold water environment.

As shown in <FIG>, the adjustment mechanism <NUM> includes the linear actuator <NUM> with the vertically-actuated ram <NUM> coupled to the aft control cable <NUM>. The forward control cable <NUM> is attached to the floatation apparatus <NUM> via the forward mount <NUM>, for example, using a load cell or strain gauge <NUM> configured to determine the tension in the forward control cable <NUM>. An additional sensor system <NUM> can be configured to determine the vertical position of the ram <NUM> and the corresponding length and tension in the aft control cable <NUM>. Suitable components for the sensor system <NUM> include, but are not limited to, strain gauges, load cells, reed switches, and linear and optical encoder components. Rotary sensors or encoders can also be utilized, for example, to determine the position of the ram <NUM> by counting the number of revolutions of a screw shaft or other rotary drive component of the linear actuator <NUM>.

A foil control system <NUM> can be mounted within the buoyancy device <NUM> and is provided with suitable processor and memory components in data communication with the linear actuator <NUM> and the foil steering module (or modules) in the navigational system <NUM>. The foil control system <NUM> coordinates with the controller device <NUM> and the navigational system <NUM> to provide steering capability in a range of different operating modes as described below.

<FIG> are front, side, isometric and bottom views of the linear actuator <NUM> for a cable adjustment mechanism, e.g., the adjustment mechanism <NUM> as shown in <FIG> and <FIG> above. As shown in <FIG>, the linear actuator <NUM> may be mounted between a top bracket <NUM> and a bottom bracket <NUM>, which are adapted for mounting the linear actuator <NUM> inside a head float, buoy, or other positive buoyancy device <NUM> as described herein for use in adjusting control cable length and tension for a dynamically steerable foil or vane apparatus.

The actuator system <NUM> may include one or more of an actuator control <NUM>, actuator electronics (or motor controller) <NUM>, and an accumulator <NUM>. Alternatively, one or more of these components can be integrated into the foil control system <NUM> as described above. In additional embodiments, functions of the actuator and motor control can be incorporated into a foil steering module or into the more generalized navigational and control system.

Various operational modes can be programmed into the control software to provide for active navigation of source sub-arrays and streamers using dynamically controlled foil systems, as described herein. The software components can be included in both the local foil control systems, which are provided in the float device or with the actuator system, and in the corresponding foil steering modules, which are utilized with the navigational system on board the towing vessel. Alternatively, one or more of the software components can be configured for operation over a network, e.g., with an electrical, radio, or acoustic communication and command structure.

More specifically, the software is configured to control a linear actuator mounted on each source sub-array head float (or other float device). In order to change the lift of a steerable foil stack attached between the head float and the first gun plate or other submerged cable position. The linear actuator changes the relative length or tension in the aft control cable, as compared to the forward control cable, changing the angle of attack in order to provide a desired lift or steering force, as described above.

<FIG> illustrate representative source configurations for the various operational modes of the dynamically steerable foil system. These four configurations can be towed behind a source vessel, with <FIG> representing single source configurations, and <FIG> representing multi-source configurations.

<FIG> can be referred to for defining source and sub-array string numbers. Sub-array string numbers increment sequentially from starboard to port as well as all source numbers (combinations of sub-array strings that are fired coincidentally). Alternatively, the sub-arrays numbers can refer to streamer cable positions, rather than source positions, or to paravane or diverter indexes.

In operation, a navigation data feed will be supplied by the foil steering modules of the navigational system to the local foil control system, so that actuator commands can be determined based on the sub-array positions. The control software may include proportional-integral-derivative (PID) logic in order to maintain proper separations. In alternative designs for the control software, the foil control system and/or foil steering modules may replace one or more of the actuator control systems, and the actuator control software may be integrated into the foil control system, the foil steering modules, or the navigational system itself. For example, the respective control code may be included within either a source or streamer steering module. Both "future track" and 4D steering capabilities are contemplated, but neither may necessarily be required in any particular design.

The vessel navigation software can also provide positions of each sub-array or string in real time. Each sub-array can be configured with at least one global positioning system pod (e.g., dGPS or rGPS) and, in some cases, two. It is understood that at least one gun or source pod should be functional for communication of positional information with the control software. Acoustic, radar, or laser positioning systems could be used as well.

Two data messages are defined, one from the navigation system (or foil steering modules) to the foil controller with positional information, and one from the foil controller to the navigation system (or foil steering modules) containing foil system status and alarms. These navigation data messages can utilize an existing protocol to pass the navigation data, for example, in cooperation with a client-provided or dedicated steering control system. The message formats described here can be designed to be similar in content to existing navigational messages, but provide for dynamical steering of the foil systems, as described herein.

FROM the NAVIGATION SYSTEM to the FOIL CONTROLLER: Data can be provided from the navigational system to the foil control computer at regular intervals, e.g., once a second. The data output can be available at all times, independent of the vessel's operating mode (e.g., online, offline, etc.). The navigational system makes inwater positioning information available to the foil control computer in real time, e.g., information that is no more than <NUM> seconds old, or within another time window. A command message can be transferred, and each message can be time tagged with UTC time.

MESSAGE from NAVIGATION SYSTEM to FOIL CONTROL: These messages can be split into three sections: <NUM>) Main Body; <NUM>) Vessel Data; and <NUM>) Source Data. Consistent source numbering can be used for different source and streamer array components (e.g., <NUM> to N, Starboard to Port). Consistent sub-array string numbering can also be used (<NUM> to N, Starboard to Port). The SMA's are provided to alert the controller to any problems in positioning.

STATUS and ALARMS from FOIL CONTROLLER to NAV SYSTEM: Suitable Main Message fields related to status and alarms sent from the foil controller to the navigational system (or foil steering modules) include, but are not limited to: Header, Message Time (Time of Message; UTC), Source String ID (<NUM>. N; <NUM> = Starboard; N = Port), Actuator ID (Actuator S/N), Controller Status (Standby, Active, Fault), Rope Tension (e.g., <NUM>-<NUM>), Error message (If fault, fault code; otherwise zero), and EOM (End of Message; e.g. <CR><LF>). These fields can be repeated based on the number of source strings; e.g., once per source string.

The actuator software functions in one or more operational modes including, but not limited to, any of operational modes <NUM>-<NUM>, as enumerated below.

The actuator software also functions in either of two failsafe modes, as enumerated below.

<FIG> is a schematic illustration of dynamically controlled foil system <NUM> in a subsurface cable deployment application or apparatus <NUM>, for example, utilizing dynamically controlled foil system <NUM> as described above. As shown in <FIG>, a subsea apparatus <NUM> includes node connecting ropes or cables <NUM> for connecting nodes <NUM>. The cables <NUM> can be towed behind or deployed from vessel <NUM>.

One or more dynamically controlled foil systems <NUM> may be utilized in various locations within apparatus <NUM>, for example in a steering guide frame <NUM> or similar steering device configured to provide lateral force. Alternatively, one or more dynamically controlled foil systems <NUM> can be utilized in a depressor system <NUM>, e.g., in a horizontal configuration configured to provide a downward force or up/down lift. In some embodiments, foil systems <NUM> are utilized in both steering device(s) <NUM> and depressor system(s) <NUM>.

<FIG> is a schematic illustration of a subsea guide frame <NUM> or similar steering device for a subsea cable apparatus <NUM>. As shown in <FIG>, the guide frame <NUM> is coupled to the node connecting cable <NUM>. The guide frame <NUM> includes a dynamically controllable foil system <NUM>, instrumentation <NUM>, and an actuator <NUM> (e.g., the same as or similar to the actuator mechanism <NUM>, as described above). The instrumentation <NUM> may include additional components including, but not limited to, USBL (ultra-short baseline) or other acoustics systems, one or more motion sensors, a fathometer, acoustic Doppler current profiler (ADCP) systems, forward looking sonar, and power and communications equipment configured for communication with a foil control module or surface navigational system, e.g., on the tow vessel.

Claim 1:
An apparatus comprising:
a positive buoyancy device (<NUM>,<NUM>);
a pair of control cables (<NUM>,<NUM>) attached to the buoyancy device and extending downward from the buoyancy device to a submerged end;
a plurality of foil sections (<NUM>) disposed along the control cables between the buoyancy device and the submerged end; and
an actuator (<NUM>)
configured to adjust attack angles of the foil sections by changing a tension in one or both of the control cables; and
a controller (<NUM>) disposed at the positive buoyancy device (<NUM>, <NUM>) and in data communication with the actuator, wherein the controller is configured to direct the actuator to adjust the tension in one or both of the control cables and thereby regulate lift generated by the plurality of foil sections, characterised in that the actuator (<NUM>) is disposed at least partially within the positive buoyancy device (<NUM>, <NUM>).