Patent Publication Number: US-2005118905-A1

Title: Maritime safety system

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
      This application claims priority to Australian Patent Application No. 20044900824, filed Feb. 19, 2004, and Australian Patent Application No. 2003905841, filed Oct. 24, 2003.  
     BACKGROUND OF THE INVENTION  
      When a member of the crew of a maritime vessel is lost overboard, the time elapsed before an alarm is raised is critical. This is particularly so in cold waters, where the chances of survival of the crew member diminish rapidly with time. However, even in warm waters, prompt recognition that the crew member is no longer on the vessel greatly enhances the chances of locating the crew member in a safe condition.  
      Existing systems for indicating that a crew member has fallen overboard require the overboard crew member to activate an alarm carried by the crew member, or another crew member on the vessel to activate an alarm disposed on the vessel.  
      However, both of these arrangements can result in appreciable delay, for example in a circumstance wherein the crew member lost overboard is unconscious and therefore incapable of activating the alarm, or in a circumstance wherein the absence of the overboard crew member is not immediately noted by another crew member.  
      The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the present application.  
      In the following description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.  
     FIELD OF THE INVENTION  
      The present invention relates to a maritime safety system and, in particular, to a maritime safety system of the type intended to provide a warning when a member of the crew of a vessel or an important article associated with the vessel is lost overboard. The present invention also relates to a base station for use with the maritime safety system.  
     BRIEF SUMMARY OF THE INVENTION  
      In accordance with a first aspect of the present invention, there is provided a maritime safety system comprising: 
          at least one transmitter unit, each transmitter unit being arranged to transmit successive signals by wireless communication at pseudo random intervals and each transmitter unit having an associated transmitter range;     a base station arranged to receive said transmitted signals; and     an alarm device;     said base station being arranged to cause the alarm device to generate an audible and/or visible alarm when a plurality of successive signals from a transmitter unit are not detected;     the arrangement being such that when a transmitter unit is disposed a distance from the base station which is greater than the transmission range associated with the transmitter unit and a plurality of successive signals are not detected from the transmitter unit, an audible and/or visible alarm is generated.        

      In this way, an indication is provided to crew members on the vessel that a crew member has potentially fallen overboard.  
      It will also be apparent that since an alarm is generated when signals from a transmitter unit are not detected, the alarm may indicate that the transmitter unit is damaged or that charging of a battery in the transmitter unit is necessary. In this sense, the system of the present invention is fail-safe in that an alarm is generated in the event of transmitter unit failure.  
      Preferably, the base station is arranged to cause the alarm to be generated when three successive signals are not detected.  
      In one arrangement, the transmitted signals are in the form of pulses periodically transmitted by the or each transmitter unit.  
      In order to distinguish signals transmitted from the or each transmitter unit from signals received from other sources, the base station may be arranged such that only signals of a predetermined frequency are detected.  
      In one embodiment, a plurality of transmitter units are provided and the system is arranged so as to distinguish the transmitter units from each other by allocating a unique code to each transmitter unit and incorporating a unique code into each transmitted signal.  
      In addition, or alternatively, the transmitter units may be arranged to transmit signals at different frequencies and the base station may be arranged to detect signals at the different frequencies and to distinguish detected signals on the basis of frequency.  
      In one embodiment, the base station further comprises a display for visibly displaying information associated with the safety system to a user. The information may be indicative of the status and/or operation of the transmitter units and may include information indicative of whether the or each transmitter unit is operating correctly, whether any of the transmitter units require charging, information indicative of the or each relevant identifier associated with the or each transmitter unit for which a signal has not been detected for a predetermined period of time, and so on. The display may be an LCD display.  
      The base station may also be arranged so as to interface with positioning means useable to determine the location of the base station. The positioning means may be a GPS-type positioning means arranged to generate GPS positioning data indicative of the location of the base station.  
      In one arrangement, the base station is arranged to interface with the positioning means so as to generate information indicative of the location of the base station when a plurality of successive signals from at least one of the transmitter units are not detected for a predetermined period of time.  
      The base station may also be arranged to interface with one or more external devices and to transfer an actuation signal to one or more of the external devices when a signal from at least one of the transmitter units is not detected for a predetermined period of time. The external devices may include a further alarm device, a dan buoy release, a self steering trip, an engine cut-out or a head-to-wind command to the autopilot. The external devices may also include an emergency position indicating radio beacon (EPIRB) assembly arranged to release an emergency position indicating radio beacon (EPIRB) when a signal from at least one of the transmitter units is not detected for a predetermined period of time.  
      In one arrangement, the system further includes a data storage device arranged to cooperate with the base station so as to store and selectively retrieve important system and transmitter unit information.  
      The or each transmitter unit may include a housing formed of at least partially transparent material so that any ingress of water into the housing is readily identifiable by a user, operative components of the transmitter unit being disposed in the housing.  
      The or each transmitter unit may include means for securing the transmitter unit to a person. The securing means may include a tab provided with an aperture for receiving a lanyard or a clip for attaching to an item of clothing.  
      The or each transmitter unit may include a status indicating device which may be in the form of an LED.  
      In one arrangement, the or each transmitter unit is arranged so that the LED is caused to indicate different status conditions depending on the current status and operation of the transmitter unit.  
      The or each transmitter unit may include a battery and a charging device which may be an inductive coupling type charging device for facilitating charging of the battery by interacting with an incident changing magnetic field so as to generate an induced voltage. The charging device may include a coil.  
      The or each transmitter unit may be arranged to transmit information indicative of the current status and/or operation of the transmitter unit.  
      In accordance with a second aspect of the present invention, there is provided a base station for a maritime safety system, the base station being arranged to receive signals transmitted from at least one transmitter unit by wireless communication, and the base station being arranged to generate an actuation signal when a plurality of successive signals from at least one of the transmitter units are not detected; 
          the arrangement being such that when a transmitter unit is disposed a distance from the base station which is greater than a transmission range associated with the transmitter unit, the actuation signal is generated.        

      In accordance with a third aspect of the present invention, there is provided a transmitter unit for a maritime system, the transmitter unit being arranged to transmit successive signals by wireless communication, each signal being transmitted at a pseudo random offset relative to a predetermined time interval so as to thereby reduce the likelihood during use of signal transmissions from two transmitter units occurring simultaneously.  
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
      The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
       FIG. 1  is a diagrammatic representation of a maritime security system in accordance with an embodiment of the present invention with the system shown in a non-activated state;  
       FIG. 2  is a block diagram of a base station of the maritime safety system shown in  FIG. 1 ;  
       FIG. 3  is a diagrammatic representation of a transmitter unit of the maritime safety system shown in  FIG. 1 ; and  
       FIG. 4  is a diagrammatic representation of the maritime safety system shown in  FIG. 1  with the system shown in an activated state. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to the drawings, in  FIG. 1  there is shown a maritime safety system in accordance with an embodiment of the invention during use. The system comprises a base station  10 , first, second, third and fourth transmitter units  12 , 14 ,  16  and  18  respectively, an alarm device  20  and a positioning means, in this example in the form of a vessel global positioning system (GPS)  22 . In the present example, the safety system also includes an emergency position indicating radio beacon (EPIRB) assembly  24  having an EPIRB  26  and an EPIRB releasing device  28 .  
      During use, the base station  10 , the alarm device  20 , the vessel positioning means  22  and the EPIRB assembly  24  are disposed on a maritime vessel  30  and each of the transmitter units  12 ,  14 ,  16 ,  18  is secured to or otherwise carried by a crew member  32  of the vessel  30 . Each of the transmitter units  12 , 14 , 16 ,  18  is of sufficient power that a signal transmitted by a transmitter unit  12 ,  14 ,  16 , 18  is capable of being received by the base station  10  provided that the transmitter unit  12 ,  14 ,  16 ,  18  is located within a range  35  of the base station  10 .  
      The base station  10  is arranged to receive signals from the transmitter units  12 ,  14 ,  16 ,  18  and is arranged to distinguish the transmitter signals from signals received from other sources, for example by arranging the base station  10  such that only signals of a predetermined frequency are detected and by arranging each transmitter unit to periodically transmit a signal at the predetermined frequency.  
      The nature of the signal transmitted by each transmitter unit is such that the base station  10  is able to identify the transmitter unit  12 ,  14 ,  16 ,  18  and distinguish the transmitter units from each other. In this example, this is achieved by allocating a unique identification code to each transmitter unit  12 ,  14 ,  16 ,  18  and incorporating the relevant unique identification code into the signal transmitted by the relevant transmitter unit.  
      However, it will be understood that other arrangements for ensuring that the base station  10  is able to receive and distinguish signals from the transmitter units are possible. For example, the transmitter units may be arranged to transmit signals at different frequencies.  
      In order to reduce the likelihood that one or more transmitters will transmit signals simultaneously, the interval between successive transmissions for each transmitter unit may be different.  
      In this example, the transmitter units are arranged such that each transmitter unit  12 ,  14 ,  16 ,  18  transmits a signal to the base station  10  at pseudo random intervals, for example once every second and at a random offset within each one second interval. Such an asynchronous transmission protocol serves to reduce the likelihood of two signal transmissions occurring simultaneously.  
      In order to further reduce the likelihood of simultaneous signal transmissions, the base station  10  is arranged so as to generate an audible alarm only when several expected transmissions are not received from a transmitter unit. For example, the base station  10  may be arranged so as to expect a signal from each transmitter unit every second and to generate an audible alarm when three successive signal transmissions are not received from a transmitter unit.  
      The base station  10  interfaces with the alarm device  20 , the vessel global positioning system  22  and the EPIRB assembly  24  such that when three successive signals are not detected by the base station  10  from at least one of the transmitter units  12 ,  14 ,  16 ,  18 , the base station  10  generates an actuation signal which causes the alarm device  20  to activate and generate an audible alarm. Non-detection of three successive signals also causes the vessel global positioning system  22  to log the location of the vessel  30  and the EPIRB releasing means  28  of the EPIRB assembly  24  to activate and release the EPIRB  26  into the surrounding water.  
      The base station  10  is shown in more detail in  FIG. 2 . The base station  10  includes a control unit  33  for controlling and coordinating operations in the base station  10 , one or more receivers  34  for receiving transmissions from the transmitter units  12 ,  14 ,  16 ,  18 , an LCD display  36  for visibly displaying information associated with the safety system, and a data storage device  38  for storing important system and operational information.  
      The control unit  33  in this example includes a  16 -bit microprocessor with 16 MHz clocking speed. The control unit  33  is arranged to interface with the alarm device  20  such that an audible alarm is generated in response to receipt of an actuation signal from the control unit  33  indicative that no signal has been detected from at least one of the transmitter units  12 ,  14 ,  16 ,  18  by the or at least one of the receivers  34  for three successive transmissions.  
      The control unit  33  may also be arranged to interface with positioning means other than the vessel global positioning means, such as an external active GPS antenna  40  arranged to supply GPS data in the absence of GPS data from the vessel global positioning means  22 .  
      The control unit  33  is also arranged to interface with the LCD display  36  so that information relevant to the status and/or operation of the security system may be visibly communicated to a user. For example, information indicative of the status and/or operation of the transmitter units may be displayed, such as whether the transmitter units are operating correctly, or whether any of the transmitter units require charging. The display may also show the or each relevant identifier indicative of the or each transmitter unit  12 ,  14 ,  16 ,  18  for which a signal has not been detected for a predetermined period of time. In the present embodiment, the LCD display  36  is caused by the control unit  33  to display the following conditions where appropriate: 
          “Logged on-battery good”       

      This indicates normal operation of a transmitter unit  12 ,  14 ,  16 ,  18 . 
          “Logged on-battery low”       

      This indicates that the transmitter unit is operating but the battery in the transmitter unit is low and needs recharging. 
          “Not logged on”       

      This indicates that a transmitter unit is switched off. 
          “Charging”       

      This indicates that a transmitter unit is being recharged. 
          “MOB”       

      This indicates that a signal has ceased being received from a transmitter unit and the transmitter unit appears to be lost. This condition causes an emergency response screen to be displayed. An MOB condition also causes the control unit  33  to display an identifier unique to the lost transmitter unit, the time that the transmitter unit was lost and the GPS location of the vessel on the LCD display  36 . This information is also stored in the data storage device  38 .  
      Although the display used in the present embodiment is an LCD display  36 , it will be understood that other display devices are envisaged, such as an LED display device.  
      The control unit  33  is also arranged to interface with the data storage device  38  so as to save and selectively retrieve all important system and transmitter unit information, for example in the event that power to the base station  10  is lost. The data storage device  38  may be in the form of a non-voltile memory.  
      Optionally, the control unit  33  may also be arranged so as to interface with an external device  42  such that an appropriate actuation signal is forwarded to the external device  42  when a signal is not detected from one or more of the transmitter units for a predetermined period of time. For example, the external device  42  may be an additional alarm unit, a dan buoy release, a self steering trip, an engine cut-out, a head-to-wind command to the autopilot, and so on.  
      A transmitter unit  12  is shown in more detail in  FIG. 3 .  
      The transmitter unit  12 ,  14 , 16 ,  18  includes a housing  44 , in this example formed of lightweight impact resistant polycarbonate material, the housing  44  being ultrasonically sealed so as to be waterproof to a rating of IP68. The housing  44  is also at least partially transparent so that any ingress of water into the housing  44  is readily identifiable by a user. Integral with the housing  44  is a tab  46  provided with an aperture  48  for receiving a lanyard.  
      However, although each transmitter unit  12 ,  14 ,  16 ,  18  of the present embodiment includes a tab  46  and an aperture  48  for receiving a lanyard, it will be understood that other arrangements for securing the transmitter unit to a person are envisaged. For example, the housing may include a clip for attaching to an item of clothing, a belt, and so on.  
      Inside the housing  44  is disposed a control unit  50  for controlling and coordinating operations of the transmitter unit, a transmitter  52  for periodically transmitting a signal under control of the control unit  50 , an indicating device in this example in the form of an LED  54  for indicating transmitter unit status to a user, a battery  56  for supplying electrical power to components of the transmitter unit  12 ,  14 ,  16 ,  18 , and a charging device  58  for facilitating charging of the battery  56 .  
      In the present example, the LED  54  is caused by the control unit  50  to indicate different status conditions depending on the current status and operation of the transmitter unit. For example, the LED  54  may be caused to emit a short pulse of green light once every two seconds so as to indicate that the battery  56  is sufficiently charged and the transmitter unit is transmitting a signal, to emit a short pulse of red light once every two seconds so as to indicate that the battery charge is low and the transmitter unit is transmitting a signal, to emit a relatively long pulse of green light once every five seconds so as to indicate that the transmitter unit is disposed in a charger and the battery  56  is fully charged, to continuously emit red light so as to indicate that the transmitter unit is disposed in a charger and charging is in process but is not yet complete, and to emit no light so as to indicate that the transmitter unit is switched off.  
      However, it will be understood that other arrangements may be used so as to indicate transmitter unit status and/or operation.  
      The transmitter unit  12 ,  14 ,  16 ,  18  is also arranged to transmit a signal in the form of a data packet containing the unique identification code associated with the transmitter unit once per second.  
      In order to minimise the likelihood of simultaneous signal transmissions by two or more transmitter units  12 , 14 ,  16 ,  18 , each transmitter is provided with a pseudo random number generator  57  which is used to determine the offset time within each one second interval at which the transmitter unit transmits the signal. In the present example, the pseudo random number generator  57  is in the form of a linear feedback shift register (LFSR). The output of an N bit LFSR ensures that 2N unit outputs will be generated before the LFSR repeats its sequence. For example, if a 20 bit LFSR is shifted every second, 220=1048576 different outputs will be generated every twelve days before the LFSR repeats.  
      In order to further reduce the likelihood of multiple successive simultaneous transmissions of two transmitter units, each LFSR is seeded with the respective unique identification code.  
      The data packet consists of word aligned data which is organised in such a way as to allow a simple UART to be used to transmit data.  
      Prior to transmission of a data packet, the transmitter  52  must be enabled for a minimum period, in this example 2 ms. During this time, alternating 1s and 0s are transmitted at 20 Kbit/s. This pattern allows the receiver  34  of the base station  10  to distinguish a binary 1 from a binary 0. A preamble precedes the remainder of the packet, the preamble containing a unique pattern that can not occur within the data, flags or error check portion of the data packet. The base station  10  uses the preamble to indicate the start of a new data packet.  
      The remainder of each data packet comprises the unique identification code, status flags, and an error check sequence, with each byte of data being scrambled using an exclusive OR process. The identification code and error check portions of the data packet make use of a data scrambling technique to ensure that a significant number of edge transitions occur on the transmitted data.  
      Each transmitter  52  is arranged so as to transfer data at a rate of 20 Kbit/s. With this transfer rate, in the present example, the length of a data packet is of the order of 4.4 ms. Accordingly, the total transmit time for each signal including 2 ms transmitter enable time is of the order of 6.4 ms.  
      The control unit  50  in this example includes a microprocessor which may be a 16-bit microprocessor with 16 MHz clocking speed.  
      The control unit  50  may also be arranged to cause the transmitter  52  to transmit information indicative of the current status and/or operation of the transmitter unit  12 ,  14 ,  16 ,  18 . For example, the transmitter  52  may be caused to transmit information indicative of whether the respective transmitter unit is operating correctly, whether the respective transmitter unit requires charging, and so on.  
      The transmitter  52  in this example is arranged to transmit signals in the 433 MHz ISM band with FSK modulation to reduce interference.  
      The charging device  58  in this example is an inductive coupling type charging device and for this purpose may include a coil and associated circuitry, the coil interacting with an incident changing magnetic field so as to generate an induced voltage across the coil useable to charge the battery  56 .  
      During use, in the event that a crew member  32  falls overboard as shown in  FIG. 4 , the distance between the transmitter unit  14  associated with the overboard crew member  32  and the base station  10  will exceed the range  35 . Accordingly, since the transmitter unit  14  is located outside of the range  35 , even though a signal is transmitted by the transmitter unit  14 , the base station  10  is incapable of detecting the signal. If three successive expected signals are not detected from the transmitter unit  14 , the base station  10  sends an actuation signal to the alarm device  20  which causes the alarm device  20  to generate an audible alarm. The base station also causes the vessel positioning means  22  to log the position of the vessel  30  and the time that the crew member  32  was lost overboard. In the present example, the base station  10  also causes the EPIRB assembly  24  to release the EPIRB  26  into the surrounding water.  
      It will be appreciated that since immersion of a transmitter unit in water has the effect of reducing the intensity of the signal transmitted by the transmitter unit, during use, if the transmitter unit is immersed in water, the signal will not be detected by the base station and an alarm will be generated.  
      Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.