The volume of shipping navigating in the Shannon Estuary has increased dramatically in recent years, with Limerick Port alone handling 8,332 million tonnes of cargo in 1997. The size of ships entering the Shannon is also increasing, the largest to date being the 189,000 tonnes dwt Panamanian ship Buccleuch-bigger than the Titanic-which arrived in April 1998 at Moneypoint with 169,000 tonnes of coal from South Africa. This was the biggest dry bulk carrier ever to dock in Ireland. The Shannon Estuary is also the principal harbour of refuge on the exposed north-east coast of Europe and the only Irish port which can give refuge to deep draft vessels.
A major problem for these huge vessels is the narrow channel at the mouth of the Estuary, in places only 315 metres wide, through which these ships must pass. Concern for the safety of very large vessels navigating in this channel led to discussions between Irish Lights and Shannon Estuary Ports with a view to providing a new Aid to Navigation to guide ships through these narrows.
The initial proposal was for a daytime port entry light (PEL), a high intensity precision sector light. This option was eventually dismissed as the required daytime range of 7 nautical miles was found to be unachievable with a PEL. It was then decided that a conventional leading lights system was the best solution. The two lights, one behind the other, appear to line up when viewed from the centre of the channel.
Calculations using the International Association of Lighthouse Authorities' Recommendations for Leading Lights suggested three possible configurations which, theoretically, seemed to satisfy such critical factors as brightness, equality of illuminance, glare, separation, and sensitivity. To confirm that the designs would work in practice, these three configurations were tested in Dun Laoghaire in February 1996. Temporary lights of the same brightness, height above sea level, and separation as was proposed for the Shannon Estuary were set up on the West Pier, Dun Laoghaire, and viewed from the Irish Lights Tender Granuaile in Dublin Bay as it simulated the approach of a large ship into the Shannon. The trials in Dun Laoghaire confirmed the theory. When it had been established that all three possible solutions would work, the decision as to which one to use was based on site conditions at Corlis Point.
The next step was to purchase suitable sites for the front and rear lights at Corlis Point and Querrin Quay, approximately half way between Kilrush and Kilkee, Co Clare. Once the sites had been bought work got underway in earnest to design and build the two stations. The unusually wet winter of 1997-8 delayed the building work as the track to the front site, which two months previously had been completely dry, turned into a mud bath. The conditions were so bad that, in the end, building materials had to be flown onto the site by helicopter.
Eventually the buildings to house the equipment were constructed at both sites and a 24m high steel tower was erected at the rear site. An optic system was designed, comprising an array of high-power range lanterns at each site for daylight use, and a single smaller lantern at each site for night-time use, all controlled electronically. gps synchronisation units, which tune in to the time signal transmitted by orbiting satellites, ensure the simultaneous flashing of the front and rear lights, and control the switchover from the high intensity daytime light to the less intense night-time light.
After installation and commissioning the lights were verified by Granuaile and operated on a test basis from 1 August. A Notice to Mariners was issued and the lights became a fully operational Aid to Navigation on 20 September 1998.