Les Hanois Lighthouse was constructed between 1860 and 1862 to a design by James Walker, and was first lit on 8 December 1862. It is sited on the rock known as Le Biseau, or Le Bisé, part of the reef Les Hanois one mile north west of Pleinmont where the Trinity House cottages were built. It was erected in response to an increasing number of shipwrecks on the treacherous rocks off the western coast of Guernsey.
Planning
Shipwrecks shortly before the construction included the wreck of () in 1807 A further wreck in 1816 of the Marie Elizabeth, a merchant ship from Copenhagen, at Rocquaine triggered letters and discussions about undertaking a nobel project, Trinity House was contacted and in January 1817 about a possible lighthouse on the Pleinmont cliff top, they wrote back saying a lighthouse was not necessary as the lights on Les Casquets and at Portland were sufficient and a new lighthouse would be confusing and do more harm than good. The Trinity House Brethren appear to have misunderstood the request as these locations are 45 km and 125 km away and neither can be seen from south of Guernsey.
Additional ships were wrecked in 1820, 1834 and 1835, with pressure being exerted on Trinity House, who in 1847 reconsidered the proposal and sent a representative to visit the island. Local shipowners were against a tax to pay for a lighthouse as they knew of the dangers and did not need it. A further wreck in 1848 of the Emmanuel carrying timber from Canada to Hull had mistaken the Casquets light for the Portland light and erroneously sailed further south to disaster.
The Rector of Torteval proposed putting a light on the top of the 105m(above sea level) church steeple which was considered by Trinity House in 1849 as a possible cheap alternative, but after an inspection, the steeple was found to be unsuitable. Arguments for and against abounded, the Guernsey Chamber of Commerce were against, the Jersey Chamber was for, Trinity House was informed that they did not have jurisdiction to build a lighthouse in Guernsey and that Guernsey had no funds to pay for it. An article appeared in The Times on 15 July 1850 asking about the necessity of a Lighthouse at Pleinmont Point
Trinity House agreed that a lighthouse was necessary and the Bailiff of Guernsey now stepped forward, confirming that the island was not opposed and the precedent of the Casquets lighthouse gave Trinity House the necessary authority but would not consent to a levy or taxation by an English Board. In 1851 the British government agreed to pay for the lighthouse provided Guernsey and Jersey would defray the maintenance costs, subject to a maximum of £900 per annum. Guernsey objected to the cost, proposing to pay just £75p.a.. The House of Commons got involved, reviewing the costs in 1852 and proposed to add a clause to the 1854 Merchant Shipping Bill. Guernsey objected to the proposed removal of their 1204 rights of self taxation and the Privy Council relented and asked what the Channel Islands would contribute, £100 p.a. total was the answer. The impasse was resolved by England stating that they would levy dues on Channel Island ships docking in England, so collecting over £900 per annum. This forced the issue but the cost was reduced when it was decided that Channel Island shipping would in future be treated as coastal shipping, rather than pay the dues at the overseas rate.
Construction
In July 1858 Trinity House inspected the rocks to determine which was practical. A local pilot advised using Le Bisseau rocks as it could be landed on in most sea conditions whereas La Mauve rocks were in a better location. The cost of construction, measured by the number of days it was possible to access the rocks, decided the issue with Le Bisseau chosen.
The design required the light to be above high water. A width of at the base, at the waist and at the light. This dictated 24,542 cu ft of masonry would be needed, weighing 2,500 tonnes. A circular staircase would serve six rooms, one on each level.
The tapered granite tower, painted white, is notable in terms of lighthouse engineering because it was the first to be built with all the stones dovetailed together both laterally and vertically, thereby making the construction a single solid mass. The cement mortar in the joints formed between stone faces locks the dovetails so that the stones cannot be separated without being broken. This method, used for the first time at the Hanois Lighthouse, became the pattern adopted for subsequent lighthouses built on sea rocks.
The cement was a quick drying type invented by John Smeaton.