Bishop Rock Lighthouse Isles of Scilly http://www.wildlifeincornwall.com/ History Bishop Rock Lighthouse stands on a rock ledge 46m long by 16m wide, 4 miles west of the Scilly Isles. The rocks rise sheer from a depth of 45m and are exposed to the full force of the Atlantic Ocean making this one of the most hazardous and difficult sites for the building of a lighthouse. The rocks around the Scilly Isles caused the wreck of many ships over the years including the loss of Sir Cloudesley Shovel's squadron of the British Fleet in 1707 in which 2,000 men died. The Elder Brethren of Trinity House decided that the lighting of the Scilly Isles, which at that time consisted of only the old lighthouse at St. Agnes, was inadequate, and resolved to build a lighthouse on the most westerly danger, the Bishop Rock. James Walker, Engineer in Chief to Trinity House, was against building a solid granite tower arguing that the rock ledge was too small and the elements too powerful, being exposed as it was to the full force of the Atlantic ocean. Walker demonstrated that the wind pressures at times exceeded 7,000 lb per sq.ft, and as many as 30 gales a year were not unusual in the area. Thus in 1847, it was decided to erect a screw-pile lighthouse at a cost of £12,000. The first task was to sink cast iron legs into the solid granite, braced and stayed with wrought iron rods. The designer maintained that the waves would be able to roll freely among the piles instead of being obstructed by the solid mass of masonry tower. When work was suspended at the end of 1849 the building was complete all but the installation of the lighting apparatus. Before it could be completed the following season, a heavy gale swept away the whole structure on the evening of 5th February 1850. Undismayed by the failure of the first lighthouse, James Walker once again turned to the idea of a granite tower based upon Smeaton's Eddystone. After surveying the site, he finally chose a small but solid mass giving room for a base 10m in diameter. The surface waves constantly swept over the site, and indeed the lowest blocks had to be laid a third of a metre beneath low water mark. A heavy coffer dam was erected around the site and the water within pumped out, so that the masons might be able to work on a dry rock face. Each granite block, weighing from one to two tons, was set into its preselected position, and each course dovetailed and keyed into position at the sides, top and the bottom thus forming an immovable mass. The workmen were housed on a small nearby uninhabited islet, where living quarters and workshops were erected. The men were carried to and from the site as the weather permitted. Working spells were brief, as well as being few and far between, and after seven years labour the tower was finally completed. All the granite was despatched from the mainland to the island depot where it was shaped and numbered before being sent to the rock. In all the 35 m tower contained 2,500 tons of dressed granite and cost £34,560. The light was first exhibited on 1st September 1858. During one particularly powerful storm, waves rolled up on the side of the lighthouse and tore away the 550lb fog bell from its fastenings on the gallery. In 1881 Sir James Douglass made a detailed inspection of the tower and reported extensive damage and weakness in the structure. It was decided to strengthen the tower and at the same time to increase the elevation of the light by 12m. The plans, though quite complex in nature essentially entailed the building of a new lighthouse around the old one, completely encasing it. The real weakness was the foundation and this Douglass proposed to strengthen and enlarge with massive blocks of granite sunk into the rock and held there by heavy bolts. It was an enormous cylindrical base, providing the lighthouse with an excellent buffer onto which the force of the waves could be spent before hitting the tower itself. The masonry casing, averaging a metre in thickness, was carried up as far as the new masonry required for the increased height of the light. The weight of the additional granite was 3,200 tons, making a total weight of 5,700 tons. Work was completed in October 1887 at a cost of £66,000. Bishop Rock was converted to automatic operation during 1991 with the last keepers leaving the lighthouse on 21 December 1992. The fog signal was discontinued on 13 June 2007. Filmed September 2013 Video Produced by Paul Dinning - Wildlife in Cornwall

• published: 08 Sep 2013
• views: 132