A Global Navigation Satellite System (GNSS) is a satellite-based system that provides a means of obtaining continuous worldwide position, time and speed information. There are two such system available to ships which provide near global coverage:

  • Global Positioning System (GPS) operated by United States;
  • Global Navigation Satellite System (GLONASS) operated by the Russian Federation.

Whether as stand-alone equipment or as part of an integrated system, GNSS receivers provide:

  • Position (including service quality information and geodetic datum corrections)
  • Ground referenced course and speed;
  • Route stage and cross track distance (XTD) monitoring. By entering the passage plan into the GNSS receiver, the OWW has an independent method of monitoring the passage.

In cases that a sudden loss of GPS signal reception is been occurred, some inevitable effects are following, as described below. Firstly, various alarms activate and GPS loses input to the ship’s surface search radar, gyro units and ECDIS. As a result is observed no GPS data in position fixing, radar over ground speed inputs, gyro speed input and a loss of collision avoidance capabilities on the radar display. These unfavorable situations highlight the impact to navigation caused by GPS interference and the importance of understanding the dangers that the vessel or equipment face from a loss of GPS signal.

Host of problems in positioning signals are caused by interference from both natural and human error.  The most common types of interference are reception issues, usually due to bad installations, poor antenna positioning, faulty equipment or proximity to other radiating devices. The common problems under these circumstances is intermittent signal, no signal, or an incorrect signal and relatively disruptions should be reported immediately.  However, it is important to remember to use all available means for navigation and maintain in order to still navigate when primary GPS fails.

As the positioning system is the base that each ECDIS system is structured the possible loss of position is critical. However ECDIS systems provide a list of actions and positioning solutions in order to keep the system running.

All ECDIS systems are equipped with the function of entering positions manually. The so called operational fix is the most common solution. Navigator should used the “old fashion” navigational positioning with radar lines, bearings , depth lines, estimated or dead reckoning position and enter same into ECDIs system. The Radar overlay function can provided additional assistance to this.Navigator should always keep in mind that the basic knowledge and ability to fix the ship using ALL available methods (satellite or not, automatic or not) is essential.

SQE Marine provides a checklist to be used by the crew, in cases of an emergency situation, like intermittent signal and GNSS failure while using the ECDIS. Make sure that the listed actions have been followed as required!