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Eddystone Lighthouse, Smeaton Tower substructure
Eddystone Rocks, 22.5km southwest of Plymouth, Devon, UK
Eddystone Lighthouse, Smeaton Tower substructure
associated engineer
John Smeaton
date  12th June 1757 - 16th October 1759
era  Georgian  |  category  Lighthouse  |  reference  SX383336
ICE reference number  HEW 72
photo  courtesy Cornwall Centre
John Smeaton's famous stone lighthouse was built on the Eddystone Rocks, 22.5km south of Plymouth. The substructure remains there to this day, although the tower was dismantled in 1882 and re-erected on Plymouth Hoe in 1884.
One of the highest points on the reef is House Rock, a sloping slab of gneiss less than 300 sq m in area. This rock was the site for Smeaton's lighthouse, and for its two timber predecessors. The first was built in 1696-98 by Henry Winstanley but destroyed by a storm in November 1703. The second was a smooth tapering cylinder built by John Rudyerd in 1708-09. It burnt down in December 1755.
Smeaton's replacement was built in stone, with a smooth outer surface to deflect the waves. Its design was inspired by the shape of an oak tree: a large heavy base rooted in the ground, with a curved tapering pillar above, keeping the centre of gravity low.
Smeaton mapped the surface of the rock in April 1756 using an early theodolite. Instead of blasting a level surface, he used the existing contours, trimming the rock into steps with dovetail recesses that connected with the tower's foundation courses in a jigsaw of blocks, until a full-circle level course of masonry was achieved. A solid stone core then rose from the foundations, above which was the tower. Each course was formed from interlocking blocks, weighing up to 2.5 tonnes, and was secured to courses above and below by oak trenails and marble joggles.
All the stone exposed to the sea was Cornish granite, with interior masonry of Portland stone. The blocks were bedded and jointed with a lime/pozzolana mortar that set in wet conditions, invented by Smeaton himself. The tower was almost 22m tall and some 7.6m in diameter at the base.
Each stone was cut to a template and courses were trial fitted at a yard at Millbay, Plymouth, before being shipped to the reef. Work began on site in 1756 and the first course of four stones was laid on 12-13 June 1757 at 2.7m below high water of spring tides.
The first 24 courses were solid masonry. Above that, the tower contained a series of rooms. The solid portion was completed in August 1758, and remains in place on the Eddystone rocks.
Smeaton's lighthouse first exhibited a light on 16th October 1759. In 1818, Robert Stephenson, the Scottish lighthouse engineer, became concerned that the cave beneath the building and the strength of the rock posed safety hazards to the structure. Further worries over the integrity of the bedrock in 1877 led to a decision to build a fourth lighthouse, which began the following year under Sir James Douglass. The top part of Smeaton's tower was removed in 1882 and re-erected on Plymouth Hoe.
Resident engineer: Josias Jessop (1756-59)
Research: ECPK
bibliography
"A narrative of the building and a description of the construction of the Edystone lighthouse with stone: to which is subjoined, an appendix, giving some account of the lighthouse on the Spurn Point, built upon a sand"
by John Smeaton, G. Nicol, London, 1793
"Smeaton's Tower" by Christopher Severn
Seafarer Books, Woodbridge, 2005
www.trinityhouse.co.uk
reference sources   CEH SouthJS
Location

Eddystone Lighthouse, Smeaton Tower substructure