GUERNSEY HISTORY 

30th October 1724
The first lighthouses were built on the Casquets

The Casquets, a series of large rocks due west of Alderney, have long been recognised as a threat to shipping. So it was that in 1724 the rocks’ owner, Thomas Le Cocq, built three lighthouses under license from the British lighthouse authority, Trinity House.

Why three rather than just one lighthouse? In order to help ships navigate, Trinity House wanted to make the lights on the Casquets distinctive so they wouldn’t be confused with those on mainland England or France. They were therefore arranged such that the lights themselves would form a horizontal triangle.

Le Cocq earned half a penny for every ton of shipping that passed by them safely. £50 of this would be sent to Trinity House in exchange for the license to operate the lights.

Called Donjon (some say Dungeon), St Thomas and St Peter, the fires on the top of each one were initially lit by coal. In 1790, five years after Trinity House had taken ownership, they were converted to oil.

Casquets lighthouses

Initially, they didn’t flash the way lighthouses appear to do now since there were no moving parts. However, clockwork rotating dishes were installed almost 30 years later to send out a beam across the sea. Managing these was labour-intensive as the mechanism would only run for 90 minutes before it needed to be wound up again.

Changing configuration

Today there is only one lighthouse on the Casquets, as has been the case since 1877. In that year, the westernmost tower was raised and the other two were switched off.

The remaining tower is 23m tall, putting the light 37m above mean high water when the height of the rocks is taken into account. It was electrified in 1952 and automated in 1990. Being so far off shore, it is powered by solar panels and wind turbines, which are sufficient to cast the beam of its LED lights 18 nautical miles.

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