The bow and stern GPS/SLONASS sensors produce highly accurate positional information and integrate it with the Course Over Ground (COG) and Speed Over Ground (SOG). Other proprietary NMEA data signal sentences are also used. Generic data is produced and transmitted from the sensors at a high update rate. The sensors initialise messages, which automatically select the baud (data speed) rate, the number and type of fixes, and specify output data. This procedure is accomplished using the GPS Regulator And Control Interface Equipment (GRACIE). This device receives and re-transmits propriety data sentences.
The NMEA protocol is used in all the stages of the SMIDS operation, therefore the system is not restricted on cable length for data acquisition and retransmission. Long structured cable runs are therefore not a problem when replacing doppler systems. Bow and stern data is recognised by GRACIE. It is then organised to appear on the pre-programmed SMIDS displays.
Most modern gyroscopes have an NMEA output or generic propriety ships heading sentence. The relatively new data signal standard is not prevalent in the older gyro specification. This factor could give interface problems for vessels operating with ageing equipment. The system can recognise traditional gyro signal outputs and convert then into a standard data format without additional conversion units.
The main electronics unit (MEU) comprised three independent processors, which are pre-programmed to meet individual needs.
This unit can output to and interface navigation equipment modules. Dedicated data ports provide signal paths to personal computer equipment used for survey or dredging operations. Other built-in redundancies include additional NMEA ports, speed log channels and an output to facilitate blue booth signals transmitted to hand-held monitors, providing the ship’s master with selective navigational data. This facility also provides a wireless data transmission network, eliminating the need for structured cabling. A back-up DC power supply sustains the system due to the low power consumption.