GB2108666A

GB2108666A - Personnel or object detection at sea

Info

Publication number: GB2108666A
Application number: GB08223345A
Authority: GB
Inventors: James Butts Barnes
Original assignee: BARNES MANAGEMENT AND DEV SERV
Current assignee: BARNES MANAGEMENT AND DEV SERV
Priority date: 1981-08-27
Filing date: 1982-08-13
Publication date: 1983-05-18
Also published as: GB2108666B

Abstract

A detection system comprises a transmitter 2 suspended from a person 6 in the water 7 by a line 8, and a receiver 14 suspended from a search vessel 16 by a line 18. In operation when the person 6 is in the water, the transmitter 2 is released and descends to a desired depth of from 2 to 6 metres and emits an ultrasonic signal. The receiver 14 is suspended at a similar depth to the transmitter 2, and the receiver 14 is rotated by turning the search vessel 16. When the search vessel 16 is within range of the transmitter 2 and pointing towards the transmitter 2, the receiver 14 picks up the ultrasonic signal. The receiver 14 includes a transducer and indicating means to give an indication of the strength and direction of the received signal. <IMAGE>

Description

SPECIFICATION A detection system for personnel or objects at sea Technical field The present invention relates to a system of detecting people or objects at sea and is particularly, but not only, concerned with tracing a man overboard", with following the course of a diver, or with such a system which facilitates navigation at sea.

Background art The tracing of individuals in the sea has always presented difficulties, whether because of the area to be searched or because of weather conditions and it has long been an aim of seagoing people to alleviate these difficulties. Some of the proposals made have involved reflecting signals off the personnel in the water and thereby identifying their position, and other proposals have involved giving the Individual in the sea, or in a liferaft, some means of sending a signal to searchers. Among examples of these proposals are a smoke- or light-emitting flare for visual contact, a whistle for aural contact, a device for firing radar-reflecting material into the air for radar contact or a radio transmitter for radio contact.All of these proposals require that some device is made available to the individual to transmit or reflect a signal, for example by attachment of the device to the liferaft or to a life jacket worn by the "man overboard", but many of the proposals have the disadvantage that they are short term, i.e. the flare will extinguish after a short period, or that they rely on good weather conditions for detection. In the case of the radio transmitter attached to a lifejacket or Ilferaft, the signal strength may vary strongly according to the height of the device and in the trough of a wave may be blanketed almost completely. One method of overcoming the difficulty posed by waves, at least in the case of a light signal, is proposed in U.K. Patent Specification No.

1,505,842 which describes a balloon device which is inflated on contact with the water and rises on the end of a tether. However, experiments have shown that such balloons are very severely affected by winds and air currents and may cause a great deal of drag on the article to which It is attached.

Similarly, in the case of navigational aids such as buoys and lighthouses weather conditions are known to severely affect the signal given out by them. Thus, fog will effect the light signal of a lighthouse, as well as diffusing sound, making it very difficult to pinpoint the direction of a foghorn.

It is also known for buoys to give off a radio signal, but radio signals are also affected by weather conditions and by interference on the crowded radio waveband.

Accordingly it would be highly advantageous to have a system which could be used for both a navigational aid and for tracing personnel at sea and which would alleviate all the aforementioned problems associated with the prior proposals.

Statement of invention and advantages According to the present invention there is provided a detection system for personnel or objects at sea comprising a transmitter adapted to emit an ultrasonic signal underwater from adjacent the personnel or object and a receiver carried by a water craft and comprising transducer means located below the waterline on the craft to receive the ultrasonic signal and means connected to the transducer to give an indication of the signal received.

We have surprisingly found that while an ultrasonic signal emitted below, the surface of the water, preferably at a depth of 2 to 6 metres, is affected to some degree by interference from, for example, reflectance off waves and other objects in the water, the signal is nevertheless indicative of direction to the source of the signal since peaking occurs in that direction with a drop off in the strength of the signal through up to 900 clockwise and anti-clockwise from that direction.

Accordingly, many of the disadvantages of radio frequency detection systems are overcome. The strength of the ultrasonic signal. picked up by the receiver is believed to be directly proportional to the distance from the transmitter and in the case of a personnel detection system for use in "man overboard" conditions, it is probable that a range of 1 or 2 miles (1600--3200 metres) is satisfactory. When the transmitter is carried by a liferaft, a diver, or a navigational aid such as a buoy, the. range may require to be greater. The range of the transmitter will be at least partly dependent on the power avallable thereto which itself may relate to such factors as the size of device which can be attached to for example a personnel buoyancy aid.The frequency band of the ultrasonic signal may be between 100 KHz and 160 KHz and generally the power output will be in the region of 1.8 to 5.0 Watts.

Where the detection system is for use In tracing personnel in the sea or in a liferaft, the transmitter is preferably retained in a pocket or by other suitable means on a personnel buoyancy aid or on the lifefraft to be released to its operating depth on a tether automatically or manually.

Automatic release may be by triggering means which is actuated automatically on contact with water, and on such release the ultrasonic signal may be initiated automatically. Alternatively, the signal may be initiated manually or, for example, by a signal emitted from the receiver such that, when the receiver is within range and pointing in the general direction of the transmitter, the transmitter is only then actuated thereby saving power. The transmitter may be provided in a small sealed container and be powered by self contained batteries which are replaceable or rechargeable. Preferably all lifejackets and liferafts would include a transmitter of a device in accordance with the invention which would all be adapted to emit a signal on the same frequency.

The transmitter will conveniently emit an omnidirectional signal or if it is a unidirectional emitter the transmitter may be caused to spin in the water, for example with its movement in the water by means of suitable vaning.

Where the detection system is for use as a navigational aid, the transmitter, which may be similar to that aforedescribed, should be permanently suspended in the water and preferably should give off an ultrasonic signal of different frequency to that of the personnel detection system. The frequency of the signal may also differ between that given off by a transmitter for a navigation buoy and by a transmitter, for example, for a lighthouse or other means marking a hazard to watercraft. In either case the transmitter may give off a coded signal to identify the particular buoy or hazard. The signal emitted may also be directional in order to give further information, and a suitable power supply would be required to give the requisite range.

The preferred depth for the transmitter of 2 to 6 metres is believed to be optimum to alleviate interference from wave patterns on the surface while not being so deep that the signal is otherwise interfered with. Further, in the case of a personnel detection system where the transmitter is fitted to a lifejacket, the transmitter, tether and power supply means must be provided in a compact package which is unobtrusive to the wearer during normal use on board, so a shorter tether is preferred. Naturally where the transmitter is attached to a free diver a depth of 6 metres will invariably be exceeded and this may require the transducer means of the receiver to be angled downwardly suitably.

The transducer means carried by the watercraft adapted to receive the ultrasonic signal is preferably mounted on the hull below the waterline although it may be carried on a suitable support put out over the side of the vessel when required. The transducer means may comprise a single transducer, which tends to be only capable of picking up signals in a 900 sector, which is aimed forwardly so that as the watercraft is turned towards the transmitter, the signal received peaks. Alternatively, the transducer means may be omnidirectional; for example, four of the aforementioned single transducers may be provided to each cover independent 900 sectors, whereby whichever direction the watercraft is facing within range of the transmitter a signal will be received.

The indicating means may comprise a moving coil meter, a series of light-emitting diodes or other means of displaying signal received by the transducer means. Where the transducer means is omnidirectional the indicating means should give information, for example on a compass-type dial, as to which direction the signal is from as well as its strength.

The receiver may, as aforementioned. emit a signal which actuates the transmitter and is conveniently operable on the one or more frequencies of the signals given off by the different transmitters as aforedescribed. Thus, the receiver may be crystal controlled and switchable from one frequency to another whereby when navigational aid is required the receiver may be switched to one of the appropriate frequencies and when the watercraft is being used in searching for a person at sea a further appropriate frequency may be selected to cut out navigational signals. The receiver may comprise a generally conventional ultrasonic detecting device which would preferably include suitable electrical circuitry to reduce such spurious noise and interference that may be produced by, for example, the watercraft itself.

Figure in the drawings An embodiment of the invention will now be described by way of example with reference to the accompanying illustrative drawing which is a block schematic diagram of one detection system of the invention.

Detailed description of the drawing Referring to the drawing, one detection system of the invention includes a transmitter 2 in the form of a pulse generator for emitting an omnidirectional ultrasonic signal in the frequency range of 100 KiloHertz (KHz) to 160 KiloHertz (KHz). The transmitter 2 is energised by batteries 4, and the repetition frequency of the transmitted pulses is determined by the life and size requirements of the batteries 4. The transmitter 2 is suspended from a person 6 in the water 7 by a line 8, and the transmitter 2 is maintained at the desired depth of from 2 to 6 metres by a weight 10 suspended from the transmitter 2 by a line 12.

In this specific embodiment the transmitter 2 has - a maximum range of one nauticai mile.

A receiver 14 is suspended at a similar depth in the range of from 2 to 6 metres from a search vessel 16 by a line 18. The receiver 14 comprises a transducer to receive the ultrasonic signal from the transmitter 2, and an indicator to provide on the vessel 16 an indication of the strength and direction of the received signal. The transducer may either be fixed to turn with the vessel 16, or it may be arranged to turn independently of the vessel 16.

This illustrated embodiment operates in the manner previously described in this Specification. If desired, the transmitter 2 may be activated by a pressure switch when it has descended to the desired depth in the range of from 2 to 6 metres. It will be appreciated that in this described embodiment the transmitter 2 and the receiver 14 are suspended at substantially the same depth as each other so that the receiver 14 receives signals which are transmitted in a substantially horizontal direction.

Claims

1. A detection system for personnel or objects at sea comprising a transmitter adapted to emit an ultrasonic signal underwater from adjacent the personnel or object and receiver carried by a water craft and comprising transducer means located below the water line on the craft to receive the ultrasonic signal, and means connected to the transducer to give an indication of the signal received.

2. A system as claimed in Claim 1 in which the ultrasonic signal is in the frequency range of from 100 KHz to 160KHz.

3. A system as claimed in Claim 1 or Claim 2 in which the transmitter power output is in the range of from 1.8 to 5.0 Watts.

4. A system as claimed in any preceding Claim in which the transmitter is adapted for automatic release to take up its submerged operational position.

5. A system as claimed in Claim 4 including triggering means actuated by contact with the water to effect said automatic release.

6. A system as claimed in any one of Claims 1 to 3 in which the transmitter is adapted for manual release to take up its submerged operational position.

7. A system as claimed in any preceding Claim in which the ultrasonic signal is initiated automatically on contact of the transmitter with the water.

8. A system as claimed in any one of Claims 1 to 6 in which the ultrasonic signal is initiated manually.

9. A system as claimed in any one of Claims 1 to 6 including an emitter operable to emit an actuating signal from the receiver to actuate the transmitter only when the receiver is in range and pointing in the general direction of the transmitter.

10. A system as claimed in any preceding Claim, in which the transmitter is energised by self-contained batteries.

11. A system as claimed in Claim 10 in which the batteries are rechargeable.

12. A system as claimed in any preceding Claim in which the ultrasonic signal is omnidirectional.

13. A system as claimed in any one of Claims 1 to 11 including means to rotate the transmitter in the water, in which the ultrasonic signal is unidirectional.

14. A system as claimed in Claim 13, in which the rotating means comprises vanes.

15. A system as claimed in any preceding Claim including means for coding the ultrasonic signal.

16. A system as claimed in any preceding Claim in which the receiver is adapted for mounting on the hull of the water craft.

1 7. A system as claimed in any preceding Claim in which the transducer means comprises a single transducer adapted for receiving signals in a 900 sector.

18. A system as claimed in any one of Claims 1 to 1 6 in which the transducer is omnidirectional.

1 9. A system as claimed in Claim 18 in which the transducer means comprises four transducers each covering independent 900 sectors.

20. A system as claimed in any preceding Claim including means adapted to display the signal received by the transducer means.

21. A system as claimed in Claim 20 in which the display means comprises a moving coil meter.

22. A system as claimed in Claim 20 in which the display means comprises a series of light emitting diodes.

23. A system as claimed in Claim 18 in which the indicating means is operable to indicate both the direction and strength of the received signal.

24. A system as claimed in Claim 23, in which the indicating means provides said directional information on a compass-type dial.

25. A system as claimed in any preceding Claim, in which the receiver is operable on a plurality of frequencies.

26. A system as claimed in any preceding Claim in which the receiver is crystal controlled.

27. A system as claimed in any preceding Claim in which the receiver includes noise and interference producing circuitry.

28. A detection system substantially as herein described and shown in the accompanying drawing.