John Harding remembers the construction of Kish Lighthouse, 30 years ago.

Kish Lighthouse being towed from Dun Laoghaire Harbour

Consider the pocket telescope. A series of concentric tubular sections designed to slide into one another, reducing the instrument to a nice, compact size. Nothing too difficult there.

But what about a 6,700-ton telescope made of steel and concrete, reaching over 150 feet at its full extent and designed to float upright on the Irish Sea? Now that requires a little more thought.

This was the unique feat of engineering that the citizens of Dun Laoghaire saw being realised in the town's Coal Harbour during the summer of 30 years ago.

A Danish firm, Christiani and Nielsen, and the Commissioners of Irish Lights were bringing the construction of the Kish Lighthouse tower to its final stages. By mid-July 1965 the structure had been towed six miles to its eventual resting place and sunk into a prepared seabed. On 27th July the tower was raised to its present height of over 100 feet above sea level.

The telescopic design had been used before by the Swedish Lighthouse Board, but these towers were smaller than the Kish and were located close in-shore. So, in terms of size and distance towed, the Lighthouse was a pharological first (I had to look it up too). Previously, the Kish Bank had been marked by a Lightship.

Weather was the main reason for building the new tower in the shelter of the Coal Harbour, and even then the structure wasn't completely safe from the force of winter storms.

In December 1963 the base of the tower was damaged in bad weather and thereafter was fit only for use as a platform on which a completely new structure was begun. The old base was eventually towed to Greystones, where it forms part of the harbour breakwater.

Even in summertime unpredictable conditions on the Irish Sea remained a hazard. No sooner had the structure been towed to the sandbank than a freshening wind caused its temporary moorings to break, forcing the engineers to sink it before it was correctly positioned.

Settling unevenly on the seabed, the Kish remained in an ungainly lopsided state for two weeks before being refloated and correctly positioned.

In spite of the scale of the structure, the basic principle of the telescopic tower was simplicity itself. It comprised two circular watertight chambers, or caissons, the inner one being the tower itself.

Part of the outer caisson was flooded to sink the structure on to the seabed. Its central chamber was flooded to float the tower through 50 feet to its full height, with final adjustments made by stressing cables and jacks. Gravel was then pumped into the water-filled chamber to give the tower a permanent base.

Christiani and Nielsen were known not only for innovative engineering, but for being a good firm to work for as well, according to Charlie O'Shea, now Office Attendant at the Lighthouse Depot, who worked on the tower.

A social fund to help celebrate the completion of each phase of the construction was set up and every pound the workers contributed was matched by the firm. The fund gave a great boost to the morale of the workforce, to say nothing of the extra business it gave to the town's pubs, where rounds of up to 70 drinks were called from time to time.

Perhaps some Irish workers weren't ready for such enlightened standards of management. Charlie tells of one worker who routinely 'fell' into the water whenever there was horse-racing on television, knowing that he would be given a few hours off to go home and get changed.

The completion of the tower and its journey to the Kish Bank attracted huge public interest. All along, in fact, crowds had been travelling to Dun Laoghaire to see the extraordinary project as it took shape and a special viewing platform had to be built to accommodate them.

Once finished, the Kish could confidently claim to be the last word in lighthouse sophistication. Some of the Keepers, however, had doubts about exchanging the eight-foot granite walls of traditional towers for 10 inches of reinforced concrete.

But the Kish tower has withstood the worst that 30 winters on the Irish Sea have to offer and looks set to withstand many more.

Reprinted from An Irishman's Diary by kind permission of The Irish Times