Civil Engineering heritage: Highland and Islands
Date 2007
Event ID 610304
Category Descriptive Accounts
Type Publication Account
Permalink http://canmore.org.uk/event/610304
The creation of Skerryvore Lighthouse, on an occasionally 5-ton rock swept reef, exposed to the full fetch of the Atlantic 12 miles west-south-west of Tiree, was an extraordinary human achievement. Sadly, it took its toll on the health of its designer/resident engineer, Alan Stevenson, who also designed and directed the building of the Hynish shore station at Tiree with its pier, dock, stores, houses, reservoir and signal station.
The masonry tower supporting the lantern is 13812 ft high with a diameter of 42 ft at the base, tapering to 16 ft at the top. It houses a flashing white light 150 ft above high water with a nominal range of 26 miles. Unlike the Bell Rock Lighthouse (2-10) its base is above high water level and its lower masonry courses were not dovetailed, resulting in a considerable cost saving in stone working. Apart from the first three courses, which were of Hynish gneiss which proved difficult to work, the lighthouse is built of granite from the Ross of Mull brought to Hynish shore station for dressing before shipment to the rock.The Hynish facilities included a dry dock 20 ft wide by 16 ft deep, the double entrance gate of which consisted of timber booms about 21 ft long which were lifted into position by the crane when required (see Paxton and Shipway, 2007, Highlands and Islands, 6-7).
The method of conducting the work was basically similar to that used by his father at the Bell Rock Lighthouse, by first erecting a temporary barrack beacon on the reef from which to carry out the work. Construction of the beacon started in 1838, but it was destroyed by the sea before completion. A fresh start was made in 1839, the barrack was successfully erected, and the tower was built from 1840–43. The light was first exhibited on 1 February 1844. The cost was nearly £87 000. This structure represented a landmark in scientific lighthouse design for mass combined with elegance of outline. Stevenson calculated the centre of gravity for towers offive different curvatures, finding that of the rectangular hyperbola to be the best, resulting in a solid tower of 62 915 cu. ft with its centre of gravity 41.227 ft from the base. He took issue with Smeaton’s analogy of an oak tree in lighthouse design, considering the action of the materials and forces to be quite different. But he acknowledged that, in general terms, Smeaton had implemented the correct design concept, which was for a tower with sides curved as ‘a solid generated by the revolution’ of the form of curve ‘about its asymptote as a vertical axis’, which had the lowest centre of gravity. The lighthouse’s exemplary design was the model for Alguada Reef Lighthouse, Burma, erected from 1862–65.
The revolving dioptric light apparatus (operating by refraction through lenses instead of reflection from mirrors), was the most advanced in the world in 1844. Stevenson’s innovation of prismatic rings below the Fresnel central lens belt further extended the dioptric effect. The prisms were made by M. Soliel at Paris under the direction of M. Le´onor Fresnel. The light source was an intricate and finely executed oil lamp with four concentric wicks, now preserved at the Northern Lighthouse Board headquarters at 84 George St, in Edinburgh.
The lighthouse was severely damaged internally by fire in 1954 and refurbished in the following year.
Paxton and Shipway 2007.
Reproduced from 'Civil Engineering heritage: Scotland - Highlands and Islands' with kind permission from Thomas Telford Publishers.
