timeline item
Results
Here is the information we have
on the item you selected
This entry was funded by
More like this
NEW SEARCH
| |
sign up for our newsletter
© 2017 Engineering Timelines
engineering-timelines@severalworld.co.uk
engineering timelines
explore ... how   explore ... why   explore ... where   explore ... who  
home  •  NEWS  •  search  •  FAQs  •  references  •  about  •  sponsors + links
Skerryvore Lighthouse
Skerryvore, Tiree, Inner Hebrides, Scotland, UK
associated engineer
Alan Stevenson
date  1837 - 1844
era  Victorian  |  category  Lighthouse  |  reference  NL839262
ICE reference number  HEW 2456
Skerryvore is the tallest lighthouse in Scotland. Its name, and the name of the exposed rock it sits upon, is derived from the Gaelic words for ‘great’ and ‘rock’. It was the crowning achievement of its designer Alan Stevenson and marked the first use of a Fresnel lens in Britain. Now automated, it was built for the Northern Lighthouse Board and remains a vital part of the national lighthouse network.
Skerryvore is the largest in a cluster of jagged rocks forming a gneiss reef some 20km west south west of the island of Tiree, Inner Hebrides. Many ships have been wrecked on this reef — at least 26 were lost between 1790 and 1844. It is wreathed in near-perpetual spray and is exposed to the full fetch (length of open sea over which waves can travel) of the Atlantic Ocean. Wave forces here can exert pressures of 291kN (almost 30 tonnes) per square metre.
The Northern Lighthouse Commissioners Act 1814 provided for construction of a lighthouse at Skerryvore, though the daunting nature of the task delayed a decision to implement the proposal until the 8th July 1834. Surveys of the reef began in autumn that year and were completed in summer 1835. The creation of the lighthouse was an extraordinary achievementbut it took its toll on the health of its engineer, Alan Stevenson (1807-65).
Stevenson also designed and directed the building of the Hynish shore station (NL986392) on south Tiree, on land purchased from the 6th Duke of Argyll, George Campbell (1768-1839). Hynish is the nearest land within sight of the lighthouse, and the purpose-built stone complex was equipped with a pier, a dry dock, stores, houses, a reservoir and a signal tower. The dock is about 12m wide by 4.9m deep, fitted originally with double entrance gates consisting of timber booms 6.4m long, lifted into position by a hand-operated crane as required.
The shore works began in 1837, with construction on the reef commencing in June 1838. The method used was similar to that used by Stevenson’s father Robert Stevenson (1772-1850) at Bell Rock Lighthouse, by first erecting a temporary barrack beacon on the reef from which to carry out the work. It was not completed by the end of the season in September, and was destroyed by the sea during November storms.
Unlike the works at Bell Rock, Skerryvore’s foundation is above high water level and its lower masonry courses are not dovetailed, resulting in a considerable cost saving. Stevenson chose a hyperbolic curved profile for the tower as this kept the centre of gravity as low as possible — in this case 12.566m above the base — for stability, and also producing an elegant structure.
The first three courses are of Hynish gneiss, which was convenient but proved difficult to work. The remainder of the lighthouse is built of pink granite quarried from the Ross of Mull 42km away, and brought to the shore station for dressing before shipment to the reef. Stevenson was concerned that each block should fit snugly with its neighbours, and specified a dimensional tolerance of just 3mm on the worked stone.
A fresh start at sea was made in May 1839 and the barrack was erected successfully by the close of work in September. Stevenson discovered that the column of water spouting regularly from the rocks originated in a submarine chamber and changed the position of the lighthouse to avoid it — he also had the chamber infilled.
Work resumed on the reef in April 1840 and the 7th Duke of Argyll, John Campbell (1777-1847), laid the foundation stone for the tower on 7th July. The exacting work of shaping the stone blocks ashore was repaid by swift progress and by the end of the season the tower was 2.5m high, with six courses completed.
The solid lower part of the tower, 7.9m in height, was completed between May and July 1841. When work halted in August, 37 of the 97 courses were finished. Stonework continued from May 1842 and the last stone in the tower was laid on 25th July. The lantern was built in August and September.
In January 1843 Stevenson was appointed Engineer to the Northern Lighthouse Board. The work that year consisted mainly of fitting out the interior of the lighthouse and pointing the stonework. This was done with mortar made from equal parts of Aberdda lime and Pozzolano earth — identical with that used by John Smeaton (1724-92) at Eddystone Lighthouse.
A light was first exhibited from Skerryvore Lighthouse on 1st February 1844. The project had cost £90,268 and for the workforce of up to 150 men it was hard labour — 17 hours a day on the reef, and not much less in the quarries and the shore station. The barrack was not dismantled until 1846.
The masonry tower supporting the lantern is 42.2m high with a diameter of 12.8m at the base, tapering to 4.9m at the top. The walls are a maximum of 2.9m thick. Inside the tower there are 11 rooms, one per storey. The tower has a volume of1,780 cubic metres, of which 1,660 cubic metres is solid rock weighing some 4,380 tonnes. A balcony encircles the lantern and its light is 45.7m above high water.
The revolving dioptric light apparatus, which operates by refraction through eight lenses instead of reflection from mirrors, was the most advanced in the world in 1844. Stevenson had met the brothers Augustin (1788-1827) and Léonor Fresnel (1790-1869) in 1824, and visited France in summer 1834 to see Léonor Fresnel again, to study their work on dioptrics. His subsequent paper On Illumination of Lighthouses by Means of Lenses influenced future practice in British lighthouses.
Stevenson’s innovation of prismatic rings below the Fresnel central lens belt further extended the dioptric effect and increased the light’s intensity — it could be seen up to 34km away. The prisms were made by Jean Jacques François (1798-1878) at the Soleil factory in Paris under the direction of Léonor Fresnel. The light source was an oil lamp with four concentric wicks, now preserved at the Northern Lighthouse Board’s headquarters at 84 George Street in Edinburgh.
The Institution of Civil Engineers described Skerryvore Lighthouse as "the finest combination of mass with elegance to be met within architectural or engineering structures". Stevenson’s nephew, Robert Louis Stevenson (1850-94), declared it to be "the noblest of all extant deep-sea lights”.
Its iconic design was the model used for the design of the Alguada Reef Lighthouse, offshore of Burma (now Myanmar) in the Indian Ocean, built 1862-65.
The lighthouse was severely damaged internally by fire on 16th March 1954. A temporary light vessel was brought into operation 6km away on 24th March that year and remained lit until July 1955, to be replaced by a series of lights on the reef while the lighthouse was being repaired. This work was completed in 1959, when the light was converted to electric power provided by three diesel generators. The new light has a nominal range of 42.6km.
Both lighthouse and shore station have been Category A listed buildings since July 1971. In 1972 a concrete helipad, with additional fuel storage tanks, was constructed on the rocks adjacent to the base of the tower. Skerryvore Lighthouse was automated in 1994.
In 1984, the Hebridean Trust restored the Hynish signal tower (NL985391) and converted it into the Skerryvore Lighthouse Museum, which opened in 1987.
Resident engineers: Alan Stevenson, Thomas Stevenson
Lamp machinery: John Milne, Edinburgh
Lenses: Jean Jacques François, Paris
Research: ECPK
bibliography
“Account of the Skerryvore Lighthouse, with Notes on the Illumination of Lighthouses” by Alan Stevenson, Adam and Charles Black, Edinburgh, 1848
“Lighthouses: their architecture, history and archaeology” by Douglas B. Hague and Rosemary Christie, Gomer Press, Llandysul, 1975
“Bright Lights: The Stevenson Engineers 1752-1971” by Jean Leslie and Roland Paxton, published by the authors, Edinburgh, 1999
“The Early Development of the Fresnel Lens” by Thomas Tag, in The Keeper's Log, U.S. Lighthouse Society, Washington, spring 2005
“Dynasty of Engineers: The Stevensons and the Bell Rock” by Roland Paxton, The Northern Lighthouse Heritage Trust, Edinburgh, 2011
www.hebrideantrust.org
www.nlb.org.uk
www.scottish-places.info
reference sources   CEH SHILightStev
Location

Skerryvore Lighthouse