Ribbon foil depressor
A ribbon-foil depressor is incorporated into a towed seismic array to provide downward lift to array sections or components. The ribbon-foil depressors may be deployed on the port and starboard spur lines or on the outboard separation ropes. The ribbon-foil depressors may be used to submerge and operate seismic equipment at depths as low as 60 m or more and are capable of maintaining towed seismic streamer cables at these depths and still remain stable through various speed changes and turns.
1. A depressor foil for submerging a towed cable comprising
a body with a foil shape having a leading edge, a trailing edge, which define a chord length therebetween and further defining
a cambered first surface extending between the leading edge and the trailing edge configured to provide negative lift;
a relatively flat second surface with respect to the first surface extending between the leading edge and the trailing edge;
a first lateral side that extends between a first lateral edge of the first surface, a first lateral edge of the second surface, the leading edge, and the trailing edge; and
a second lateral side that extends between a second lateral edge of the first surface, a second lateral edge of the second surface, the leading edge, and the trailing edge;
a first tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein adjacent to the leading edge, and opening to each of the first and second lateral sides;
a second tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein aft of, adjacent to, and parallel to the first tubular conduit, and opening to each of the first and second lateral sides, wherein the first and second tubular conduits are positioned within a forward half of the chord length; and
a third tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein adjacent to the trailing edge within an aft half of the chord length, parallel to the second tubular conduit, and opening to each of the first and second lateral sides.
2. The depressor foil of claim 1 , wherein a form of the body is solid with the exception of the first and second tubular conduits.
3. The depressor foil of claim 1 further comprising a fourth tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein adjacent to, aft of, parallel to the second tubular conduit within a forward half of the chord length, and opening to each of the first and second lateral sides.
4. The depressor foil of claim 1 further comprising a tail flap section forming a portion of the trailing edge, extending above and aft of the first surface, and forming an angle with respect to the chord length.
5. The depressor foil of claim 4 , wherein the tail flap section comprises between 5% and 25% of the chord length.
6. The depressor foil of claim 4 , wherein a measure of the angle with respect to the chord length is between 5 degrees and 30 degrees.
7. A seismic array comprising
a plurality of lead-in cables;
a plurality of streamer cables;
a plurality of seismic sensors attached to respective streamer cables;
one or more separation cables attached to aft ends of one or more groups of lead-in cables, wherein the separation cables provide for a maximum separation distance between the aft ends of adjacent lead-in cables and forward ends of adjacent streamer cables;
a pair of paravanes each attached at an opposing lateral end of the seismic array;
a pair of spur lines each connected between a paravane and an aft end of an adjacent one of the lead-in cables; and
a pair of ribbon-foil depressors pivotably attached to at least a portion of the spur lines, the separation cables, or both, each ribbon-foil depressor further comprising a plurality of depressor foils arranged adjacent to each other in a series;
each depressor foil further comprising
a body with a foil shape having a leading edge and a trailing edge and further defining
a cambered first surface extending between the leading edge and the trailing edge configured to provide negative lift;
a relatively flat second surface with respect to the first surface extending between the leading edge and the trailing edge;
a first lateral side that extends between a first lateral edge of the first surface, a first lateral edge of the second surface, the leading edge, and the trailing edge; and
a second lateral side that extends between a second lateral edge of the first surface, a second lateral edge of the second surface, the leading edge, and the trailing edge;
a first tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein adjacent to the leading edge, and opening to each of the first and second lateral sides;
a second tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein aft of and parallel to the first tubular conduit, and opening to each of the first and second lateral sides, where in the first and second tubular conduits are positioned within a forward half of the chord; and
a third tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein adjacent to the trailing edge within an aft half of the chord, parallel to the second tubular conduit, and opening to each of the first and second lateral sides.
8. The seismic array of claim 7 , wherein a form of the depressor foil body is solid with the exception of the first, second, and third tubular conduits.
9. The seismic array of claim 7 , wherein each depressor foil further comprises a fourth tubular conduit configured to receive a cable therethrough, defined within the body and extending laterally therein adjacent to, aft of, and parallel to the second tubular conduit within a forward half of the chord, and opening to each of the first and second lateral sides.
10. The seismic array of claim 7 , wherein the depressor foil further comprises a tail flap section forming a portion of the trailing edge, extending above and aft of the first surface, and forming an angle with respect to the chord.
11. The seismic array of claim 10 , wherein the tail flap section comprises between 5% and 25% of the chord.
12. The seismic array of claim 10 , wherein a measure of the angle with respect to the chord is between 5 degrees and 30 degrees.
13. A method of providing downward lift to a portion of a seismic array comprising
providing a ribbon-foil depressor for attachment to a laterally-oriented cable within the seismic array, wherein the ribbon-foil depressor comprises a plurality of depressor foils arranged adjacent to each other in a series; each depressor foil further comprising
a body with a foil shape having a leading edge and a trailing edge and further defining
a cambered first surface extending between the leading edge and the trailing edge configured to provide negative lift;
a relatively flat second surface with respect to the first surface extending between the leading edge and the trailing edge;
a tail flap section forming a portion of the trailing edge, extending above and aft of the first surface, and forming an angle with respect to a chord of the foil shape; and
a plurality of conduits formed within the body at a plurality of pivot points located in a forward half of a chord of the foil shape; wherein each of the conduits is configured to receive the cable therethrough;
selecting a pivot point from the plurality of pivot points;
pivotably affixing the ribbon-foil depressor to the cable by threading the cable through one of the plurality of conduits located at the selected pivot point in each of the depressor foils; and
towing the seismic array through a body of water.
14. The method of claim 13 , wherein
each depressor foil further comprises an aft conduit formed within the body in an aft half of the chord of the foil shape and configured to receive a cable therethrough; and
the method further comprises
threading a control cable through the aft conduit; and
adjusting a length of the control cable to modify a catenary of the ribbon foil depressor along the laterally-oriented cable.
15. A device for providing downward lift to a cable in a towed marine seismic array comprising
a cable connector configured to attach to the cable;
a rigid rod configured to be oriented in parallel with a surface of a body of water through which the array is towed;
two or more depressor foils pivotably mounted on the rigid rod, wherein each depressor foil further comprises
a body with a foil shape having a leading edge and a trailing edge and further defining
a cambered first surface extending between the leading edge and the trailing edge configured to provide negative lift;
a relatively flat second surface with respect to the first surface extending between the leading edge and the trailing edge;
a tail flap section forming a portion of the trailing edge, extending above and aft of the first surface, and forming an angle with respect to a chord of the foil shape;
a first lateral side that extends between a first lateral edge of the first surface, a first lateral edge of the second surface, the leading edge, and the trailing edge; and
a second lateral side that extends between a second lateral edge of the first surface, a second lateral edge of the second surface, the leading edge, and the trailing edge;
a first tubular conduit defined within the body and extending laterally therein adjacent to the leading edge and opening to each of the first and second lateral sides; and
a second tubular conduit defined within the body and extending laterally therein aft of and parallel to the first tubular conduit and opening to each of the first and second lateral sides; and
a bridle connected at a first end to opposing ends of the rigid rod and connected at a second end to the cable connector.
16. The device of claim 15 , wherein the cable connector comprises a clamp configured to fixedly connect with the cable.
17. The device of claim 15 , wherein
the cable connector is configured to slide along or comprises a sliding mechanism that slides along the cable; and
the device further comprises a tagline connected to the cable connector and configured to adjust a position of the cable connector with respect to the cable and to limit sliding of the cable connector in an aft direction.