The Coast Guard says it has no plans to investigate the cause of the major alert off the Wicklow coast on Sunday and Monday, due to lack of evidence.
It also says it does not intend to take any action over the discovery of a large area of debris at sea during the initial search, extending over a five-mile area. Lifeboat sources have suggested that the debris may have been dumped by a fishing vessel which had been working out of Howth, Co Dublin, but which was from a south-east port.
However, a spokesman for the Irish Coast Guard said it would be almost impossible to pinpoint the debris to one vessel. Strong tides in the particular area off the Codling Bank could also have caused a coincidental "confluence" of material from various sources.
Rescue personnel have said the quantity of material over one area was highly unusual. Samples were taken from an oil slick some nine miles off Greystones, Co Wicklow, by the Naval Service patrol ship, LE Róisín, on Sunday night.
The distress message issued on Sunday morning on a ship-to-ship frequency would not have been taped, unlike messages relayed to the Coast Guard on VHF channel 16. Taping of messages in the past has helped to eradicate hoax calls, which put considerable strain on rescue services.
No figure has been put on the cost of the search, which lasted from early Sunday until lunchtime on Monday. It involved three Naval Service patrol ships at various stages, an Air Corps Casa maritime patrol aircraft, two Irish Coast Guard Sikorsky helicopters from Dublin and Waterford, three RNLI lifeboats from Dún Laoghaire, Arklow and Wicklow, and the Greystones Coast Guard.
In a separate development, the British Maritime and Coastguard Agency said yesterday that its rescue capabilities would not be affected by a computer bug. The Internet "Sasser Worm" virus infiltrated its databases and other computer-held information, but a paper-based system was put into effect for a period, the agency said.