Hanois Lighthouse

Thankyou everyone for your kind comments on my 100th blip yesterday.

I left my blip until late tonight. After dropping my daughter off at Cobo to join her friends watching a film at an outdoor cinema, I carried on along the coast to Pleinmont. You have to walk the last half mile to reach the most South West corner of the island. From here I watched the sunset over the Hanois Lighthouse. Here are some (quite technical) notes about the lighthouse.

The Hanois Lighthouse rises from a reef on the south west side of the Island of Guernsey, and takes its name from the group of rocks - Les Hanois. It was built in 1862. The tower is made of Cornish granite and is 33 metres high. The interior comprises six circular rooms 13 feet in diameter and 9 feet high. The lighthouse marks the western end of the Channel Islands indicating the shoals and reefs to the west of Guernsey and providing a position fix for vessels entering the Channel Traffic Separation Scheme.

Hanois Lighthouse is important in the development of lighthouse engineering, because not only all the stones in each course but also all the courses were dovetailed together to form one solid mass. Various methods of jointing the stones in rock towers have been employed. Smeaton developed the use of granite blocks for rock towers, and he connected them together with metal pins and marble dowels. Alan Stevenson used a similar method in the construction of the Skerryvore Lighthouse, whilst his father, Robert Stevenson, arranged stones of each course in the Bell Rock, so that they formed a series of dovetails. In this manner each course locked together into a solid single unit, and the courses were then pinned together. It was James Douglass who suggested that the stones might be dovetailed together both laterally and vertically. The cement mortar in the joint formed between the faces so locked the dovetails that the stones cannot be separated without being broken. This method was first employed at the Hanois Lighthouse, and it became the pattern for all sea rock towers.

A helideck was constructed above the lantern in 1979. Automation work began at the Hanois Lighthouse in July 1995 and the station was demanned in January 1996. The station was converted to solar power with panels mounted around the lower part of the helideck support structure.

A new two position lampchanger with 35 watt metal arc lamps was installed within the existing optic, the rotation of which was slowed down changing the character of the light from 2 white flashes every 5 seconds to 2 every 13 seconds. This is to keep the power requirement low enough to allow solarisation and to increase the length of the flash to achieve the required 20 mile range.

The existing air fog signal was replaced by a single directional electric emitter stack installed in a west facing space left in the ring of solar panels around the helideck support structure. The fog signal is controlled by an automatic fog detector. Hanois Lighthouse is now monitored and controlled from the Trinity House Operations and Planning Centre at Harwich via a telemetry link through the cellular radio.