Steerable fairing string

1. A marine seismic array having a head float, the marine seismic array comprising:

a foil having a leading edge, trailing edge, chord and span for attachment between a first head float position and bottom submerged position below the head float on the array,

said foil being flexible along its span,

said foil having a first interior conduit rearward of the leading edge and a second interior conduit forward of the trailing edge, said first and second conduits being centered on or offset to either side of the chord and separated by a distance;

a first cable having a first length strung inside the first conduit and a second cable having a second length strung inside the second conduit; and

an adjustment mechanism to vary the length of the first cable relative to the length of the second cable or vice versa.

2. The marine seismic array as claimed in claim 1 wherein said first and second cables are suspension ropes for a seismic source array.

3. The marine seismic array as claimed in claim 1 wherein said first and second cables are float tag lines for a seismic receiver array.

4. The marine seismic array as claimed in claim 2 or 3 wherein said foil is asymmetrical.

5. The marine seismic array as claimed in claim 4 wherein said foil has a NACA Gottingen or Eppler designated air foil shape.

6. The marine seismic array as claimed in claim 5 wherein said foil is designated NACA 2318.

7. The marine seismic array as claimed in claim 4 wherein said second conduit is laterally offset to either side of the chord.

8. The marine seismic array as claimed in claim 4 wherein said first conduit is laterally offset to one side of the chord and said second conduit is laterally offset to an opposite side of the chord.

9. The marine seismic array as claimed in claim 4 wherein depressors are attached at top and bottom ends of the foil.

10. The marine seismic array as claimed in claim 4 wherein the span of said foil is divided into a plurality of discreet segments.

11. The marine seismic array as claimed in claim 4 wherein said span of said foil is divided into a plurality of discreet segments which are attached to each other.

12. A system comprising a marine vessel, one or more cables towed by the marine vessel, a surface reference head float, and a fairing string, wherein one or more of said cables is connected at one or more locations along its length to the surface reference head float, and wherein the fairing string comprises:

a foil having a leading edge, trailing edge, chord and span for attachment between a first head float position and bottom submerged position below the head float on the array,

said foil being flexible along its span,

said foil having a first interior conduit rearward of the leading edge and a second interior conduit forward of the trailing edge said first and second conduits being centered on or offset to either side of the chord and separated by a distance;

a first cable having a first length strung inside the first conduit and a second cable having a second length strung inside the second conduit; and

an adjustment mechanism to vary the length of the first cable relative to the length of the second cable or vice versa.

13. The system as claimed in claim 12 wherein said first and second cables are suspension ropes for a seismic source array.

14. The system as claimed in claim 12 wherein said first and second cables are float tag lines for a seismic receiver array.

15. The system as claimed in claim 13 or 14 wherein the adjustment mechanism is remotely controlled from said marine vessel.

16. The system as claimed in claim 15 wherein said remote control is wireless.

17. The system as claimed in claim 15 wherein said remote control is by an electrical connection between said marine vessel and said adjustment mechanism.