The Art of Dredging

Dredging and shipping

Update on G.P.S. systems


The Global Positioning System (G.P.S.) was initiated by the US Department of Defense (DOD) as a position-finding system to be used for military purposes. 


Originally, it was envisaged for use by nuclear submarines so that they could better aim their ballistic missiles. The system was so good that it rapidly expanded to other military uses. When other federal agencies and foreign governments learned of the system and clamored for access, DOD made a somewhat degraded version (selective availability or S.A.) publicly available. After further pressure, the U.S. military made the high-precision signals available to all users. 


Russia has its own version of GPS called “GLONASS”, although its constellation of satellites is not as large as that of the United States (currently 24 US satellites, and 18 out of 24 planned Russian satellites)). 

The European Union and China are setting up their own navigation systems. 

The EU system is named “Galileo”, and will be operational in 2013, after many delays.

China is developing “Compass”, due 2015.


GPS receivers are now fairly inexpensive and have become inevitable. They are found on the bridge of every ocean-going ship or yacht in the world and are so relied upon that many mariners do not know no more about traditional methods of position-finding, such as use of the sextant, or even bearings by sight.


As a matter of fact; I got trainees –fresh from nautical college- who were unable to plot a radar-bearing and -distance on a paper chart. GPS has become an addiction.

When I as was a trainee, that old sea-dog captain switched of the position-display and challenged me to find my way around the river, simply by looking out of the bridge windows.  And he was so right…


While GPS is capable generally of identifying the position of the receiver within several meters, the accuracy may be degraded in a variety of manners. Because the radio signal transmitted by the satellite is weak, it is readily subject to interference. 


Since all GPS-systems, existing and under development are still liable to much the same errors, voices have been raised for an overhaul of the Loran-C system, which would be solely based on landstations. It is likely that the U.S. and parts of Europe will follow that philosophy to create an enhanced Loran (eLoran) as an alternative to GPS.

In the future, GPS receivers will be able to process “GLONASS”, “Galileo”, “Compas” and eLoran signals.


Space weather, such as solar flares, may disrupt the signal. 


Intentional jamming of GPS signals was utilized sporadically by the by Iraqi forces during the Iraq War. 

U.S. Navy vessels are reported to have that capability.

I have experienced such jamming in the Persian Gulf, in the immediate vicinity of an aircraft carrier.


There is now concern that terrorists might use GPS jamming to disrupt shipping and possibly induce collisions and groundings. In the United Kingdom tests are done to determine the susceptibility of ships to such GPS errors. Jamming of a GPS signal is particularly straightforward, using jammers that can be bought on internet.


With the compulsory use of ECDIS, it is only to be feared that navigation will depend more and more from GPS, including all of its errors, and faults, in many technological layers stacked one on top of each other.


And that ECDIS will be manned with a new generation of mariners, who are scantly trained in anything else than ECDIS, complacently happy with GPS as only source for navigation, erasing what little navigation knowhow may still be left.




Marc Van de Velde,

October 2009


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