Ships – Implements – Underwater cutting
Patent
1992-07-21
1994-06-28
Mitchell, David M.
Ships
Implements
Underwater cutting
114242, 102402, B63B 2100
Patent
active
053237269
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and a device for sweeping marine mines having a magnetic sensor using at least three electrodes which are spaced apart, and are tractored by a vessel and behind each other, said electrodes being provided with electric current from said vessel for generating a magnetic field in the water surrounding said electrodes, each of said electrodes separately being provided with electric current of an individually adjustable strength.
When sweeping marine mines having a magnetic sensor a magnetic field has to be generated, said magnetic field being sufficiently strong and sufficiently similar to a magnetic field generated by a vessel to be regarded by the mine as a vessel target, thereby detonating the mine. For the protection of the vessel carrying out the mine sweeping it is desirable to limit the magnetic field of such a strength to an area safely distanced from the mine sweeping vessel, so as to prevent a mine detonated by said magnetic field from damaging said mine sweeping vessel.
A sweeping operation must fulfil two primary demands. A first demand is to make mines having a low sensitivity detonating even if they are displaced a large distance in the transverse direction of the track of the vessel and thereby being actuated by a comparatively weak magnetic field from the sweep. A second demand is that mines having a high sensitivity shall not be triggered within a certain security zone surrounding the sweeping vessel. These claims are partially conflicting because a strong magnetic field required to achieve said first demand hampers the achievement of said second demand. Furthermore, the characteristics of the magnetic field generated by the sweep should be such that it is identified by the mine as a magnetic field generated by a target vessel, even if the mine is provided with means for analyzing surrounding magnetic fields.
The method of sweeping marine mines having a magnetic sensor by means of an electrode sweeping arrangement comprises the following steps. Two or more electrodes are placed in the water and tractored by one or several vessels. The electrodes are supplied with electric current from said tractoring vehicle, the current in the cables and through the water generating the desired magnetic field.
U.S. Pat. No. 2,937,611 discloses a system in sweeping marine mines by means of a plurality of vessels, each vessel being provided with a pair of electrodes. The system provides a pulsating magnetic field between the electrodes. U.S. Pat. No. 2,397,209 relates to a system in mine sweeping according to which a pulsating magnetic field is provided between two of the electrodes tractored by the vessel. A more complicated system in mine sweeping is disclosed in U.S. 3,946,696. The system comprises two electrodes, a controlled current generator, and a magnetic field sensor. There is also included a control system controlling the current through the electrodes dependant on the magnetic field in the vicinity of the mine sweeping vessel. By measuring the magnetic field adjacent to the mine sweeping vessel the desired safety of the mine sweeping vessel can be obtained. SE,A, 8704069-7 relates to a method and a device in sweeping marine mines having a magnetic sensor. At least three electrodes are tractored spaced apart behind a vessel and behind each other, and said electrodes separately are provided with electric current of individually adjustable strength from said vessel for generating a magnetic field in the water surrounding said electrodes.
Another simple constructive step to increase the protection of the mine sweeping vessel without any impairing of the desired mine sweeping capabilities is to extend the mine sweeping arrangement behind the vessel. However, practical problems in dealing with long cables limit the length of the mine sweeping arrangements.
The magnetic field from a vessel moving normally and passing a mine varies in each position by time and can be regarded as combined by components in three directions of the co-ordinates in space. In each directio
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Mine Countermeasures at Defendory '86.
Avila Stephen P.
Hansson Anders
Mason, Jr. Joseph C.
Mitchell David M.
SA Marine AB
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