Deflector

Details Deflector Deflector

1999-05-28

2001-05-22

Morano, S. Joseph (Department: 3617)

Ships

Towing or pushing

Towing by means of cable

C367S015000

Reexamination Certificate

active

06234102

ABSTRACT:

This invention relates to a deflector for towing after a vessel, especially for use in seismic surveys at sea, being adapted to pull equipment to a transversal position in relation to the vessel's moving direction, comprising at least one connecting point for coupling, through wires or similar, to the vessel and the equipment to be towed, and two or more deflector wings adapted to provide a lifting force transversally in relation to the direction of the vessels movement.
In seismic studies at sea acoustic sources are used being mounted in or close to a vessel, and directing acoustic signals toward the sea floor. Reflections of these signals are received by a number of receivers being positioned in seismic cables being towed behind the vessel. These cables are spread out to a relative width to provide measurements of the geological conditions over an area with a certain width. As the use of the seismic vessel is expensive it is advantageous to make the width of the tow as large as possible, with a large number of seismic cables, so that one single pass over the area to be measured covers as large an area as possible. To spread the seismic cables transversally in relation to the seismic vessel deflectors are usually used.
Such deflectors are traditionally passive devices comprising one or more wings providing a lift in the required direction. Because of the towing resistance in the water, caused both by the deflector and the towed cables, there are, however, limits to the lift which may be obtained using passive deflectors, which in turn, together with a wish in seismic studies to keep the seismic cables as close to the vessel as possible, limits how far the deflectors may be pulled transversally. When the deflector is used in seismic surveys it will in addition be loaded with the seismic cable to be pulled sideways. Today there is a limit to the width of the cable tow with passive deflectors being approximately 800 meters, with approximately 10 seismic cables.
In relation to passive deflectors it is known that the largest effect is obtained using one single wing. This solution is, however, very unstable, which is a disadvantage in seismic surveys, where it is important to keep the seismic cables in the correct position and also to keep them separated to avoid damage on the equipment being mounted on the cables.
Many types of active systems have been suggested in different occasions to obtain a lift, e.g. using the so-called Magnus effect. This means that a rotating cylinder being moved in a medium with the axis of the cylinder moving perpendicular to the axis of the cylinder will experience a lift. The lift pulls in the direction of movement of the part of the cylinder facing the flow. This effect has been suggested in many applications, such as shown in U.S. Pat. No. Re 18.122 (Flettner). A disadvantage related to active deflectors is that they are dependent on power supplies. If the power supply fails the lift is lost, in seismic surveys making it impossible to keep the seismic cables separated, with resulting damages on equipment and cables.
It is an object of the present invention to provide a stable deflector with an increased lifting ability, and which does not loose its lift in case of failure in the power supply. This is obtained using a deflector as defined above and characterized as given in claim
1
.
The invention provides an active deflector which, depending on its dimensions, may double the width of the seismic survey, and thus halve the number of passes of the vessel over the area to be surveyed. Possibly the deflector according to the invention may be used in surveys with ordinary widths, where the dimensions are reduced, so that the towing resistance from the system is reduced. Because of the shape of the cylinder it will not affect the passive lifting capability of the deflector significantly, so that the seismic cables are kept at a certain distance from each other even if the power supply fails, and damages on the seismic cables are reduced.
The use of a number of wings in the deflector will also make the deflector more stable than previously known deflectors.


REFERENCES:
patent: Re. 18122 (1931-07-01), Fletther
patent: 4130078 (1978-12-01), Cholet
patent: 4323989 (1982-04-01), Huckabee et al.
patent: 4630997 (1986-12-01), Cousteau et al.
patent: 4729333 (1988-03-01), Kirby et al.
patent: 4890568 (1990-01-01), Dolengowski
patent: 5357892 (1994-10-01), Vatne et al.
patent: 5532975 (1996-07-01), Elholm
patent: 0562780 A1 (1993-09-01), None
patent: 2293806 (1996-10-01), None
patent: 177248 (1995-09-01), None

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