TB23 - Electronic nav aids


Electronic navigational aids are not foolproof and traditional navigational techniques should, whenever possible, be practiced

Are you putting too much reliance on electronic navigational aids?

The Club is aware of an incident where a ship was using a Japanese datum in the Mediterranean (WGS 84), seven years after build. As a result, the GPS was providing navigational information with a near 5 cable inaccuracy, resulting in a half mile error on all the vessel’s waypoints transposed from GPS onto the ships ARPA radar.

Had the ship been relying on GPS to navigate (rather than visual fixing) or had been using electronic charts, the inaccuracy of the positions shown on the screen would have been highly dangerous.


The global positioning system has been an important and usually reliable addition to ships’ navigational equipment, however a passenger vessel ran aground in US waters because of a faulty GPS.

The shield wire of the antenna had separated from its connection causing the unit to send inaccurate position data to the integrated bridge system resulting in the ship being 17 miles off course, eventually running aground 10 miles east of Nantucket Island, Massachusetts.

The vessel had been navigated solely by GPS for more than 30 hours prior to the stranding and although only 10 miles from shore when she stranded the officers had not attempted to fix the ship’s position.


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