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Eddystone Lighthouse

CIVIL ENGINEERING

Construction of the first Eddystone Lighthouse presented a major new challenge to civil engineers at the end of the 17th century.

Until then, most lighthouses had been built on the mainland, but shipwrecks around the treacherous Eddystone Rocks 23km south west of Plymouth led to calls for one of the first off-shore lighthouses.

The challenge was to build a lighthouse robust enough to withstand the force of waves more than 30m high. A small rocky reef, surrounded by treacherous currents and only accessible in calm weather, was the location.

The first attempt by Winstanley was a disaster. It was built between 1696 and 1698 and then strengthened in 1699. But the 36m high structure, fastened to the rock by iron pegs, was obliterated in a storm in 1703.

A shorter replacement was then built between 1706 and 1709. This was sturdier but still only lasted 14 years. The timber structure was destroyed by fire after a spark from the candle-powered light set fire to dry timbers in the lantern house roof.

John Smeaton started his stone replacement in 1756. This lasted much longer, largely because the base was made from seven layers of stone blocks shaped to interlock like dovetail joints and held together with mortar.

The blocks at the bottom of the structure were also fitted into specially carved recesses in the rock to prevent the structure sliding off. Marble blocks set into matching recesses in the upper and lower faces of each base level provided an extra key and helped to withstand lateral movement.

Work was hampered by poor weather, which prevented access to the rocks. Stone blocks had to be ferried to site on small sailing boats from a large storage ship anchored about 800m away.

The structure was finally completed in 1759 and stayed in service until 1882. Smeaton's lighthouse remained structurally sound until the end and helped win him a reputation as one of the most accomplished engineers of the 19th century.

His structure had to be replaced when a taller, further reaching light was needed. Also, the rock on which it stood had started showing signs of weakening. Part of the structure now stands on Plymouth Hoe as a monument to Smeaton's achievement.

The robust design influenced those of other lighthouses in similarly difficult locations, notably Bell Rock and Fastnet. But it also influenced Sir James Douglass's design for the 40m tall Eddystone replacement which still stands today.

Douglass developed Smeaton's design further by using interlocking bed joints and vertical joints throughout to give it extra rigidity.

The relatively recent invention of steam power helped Douglass's efforts. He used a steamboat to ship rock to site, plus a steam powered crane to lift blocks from the ship and into position. Lifting operations are believed to have taken just three minutes - considerably quicker than Smeaton's efforts using block and tackle.

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