Navigation system to stop operating

April Fools' Day takes on a particular significance in mariners' diaries this year. The previous evening, March 31st, a trusted navigation system, the Decca terrestrial chain, will issue its last reliable waypoints for latitude and longitude.

In the Irish Sea, however the Decca terrestrial chain will continue to operate until May 19th, according to the Department of the Marine and Natural Resources.

For most skippers relying on the satellite Global Positioning System (GPS), this may come as no great shock.

However, the row over the erection of a mast in Co Clare for the Decca replacement, Loran-C, means there is no back-up for GPS if that system suffered any degradation.

The Commissioners of Irish Lights have warned repeatedly that these electronic systems are "aids" to navigation, and no single one should be relied on in isolation.

The commissioners have been providing a Differential Global Positioning System (DGPS) service on a trial basis, primarily to monitor the integrity of GPS. However, DGPS relies inherently on GPS, which is outside the control of the General Lighthouse Authorities of Britain and Ireland.

Also, all radio navigation systems are subject to interference which, as the commissioners state, can "adversely affect their reliability".

However, Decca's passing is no great loss, according to Mr Barry Sharkey of Barry Electronics in Killybegs, Co Donegal - a man who has fitted receivers in most Irish-registered wheelhouses.

"Like an old man, its time has come," he says.

"The company charged fishermen a very heavy rental, and GPS handheld receivers can now be purchased at a fraction of that."