timeline item
Results
Here is the information we have
on the item you selected
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
Bishop Rock Lighthouse
Bishop Rock, 6km west of St Agnes, Isles of Scilly, UK
associated engineer
James Walker
Sir James Nicholas Douglass
date  1852 - 1st September 1858, 1881 - October 1887
era  Victorian  |  category  Lighthouse  |  reference  SV807064
ICE reference number  HEW 75
Bishop Rock is an island of hard pink granite that is visible at low tide, located near the Isles of Scilly. The impact of severe Atlantic storms on this isolated rock can be enormous, throwing spray and rock debris 30m into the air. Before Bishop Rock Lighthouse was built, many ships were wrecked around the Scilly Isles, as the lighthouse on St Agnes was difficult to see in poor weather.
James Walker, chief engineer to Trinity House (the lighthouse authority for England and Wales), began constructing the first lighthouse on the rock in 1847. Its lantern and accommodation were supported on an open structure with six cast iron screw pile legs, designed to minimise the effects of wave action. However, before the lamp could be installed, the lighthouse was swept away in a storm on 5th February 1850.
Undeterred, Walker began on a second lighthouse in 1852. This time he chose a circular granite tower, similar in design to John Smeaton’s Eddystone Lighthouse, with interlocking dovetailed blocks. A cofferdam was used so that the foundation blocks — some 300mm below low water — could be laid in dry conditions. The tower was 10.7m in diameter at the base and 21.3m high.
Granite was brought from quarries at Carnsew and Lamorna to St Mary’s for dressing before being shipped to Bishop Rock. In all 2,540 tonnes of dressed stone was used, and the lighthouse cost £34,560. The structure was completed in 1857, and the light was exhibited for the first time on 1st September 1858.
However, the lighthouse was still not strong enough to resist the sea, and some of the granite blocks split. In 1881, Walker’s successor, James Douglass began extensive strengthening works.
The foundations were enlarged into a cylindrical base, with the new granite blocks being secured by 38mm diameter metal bolts into the rock. The remainder of the tower was encased in a granite sleeve around one metre thick, and extended into a new top section that raised the light to 43.6m above mean high water.
The additional weight of granite was 3,270 tonnes, bringing the lighthouse’s weight to 5,810 tonnes. A new lantern, still used today, was added with two sets of lenses — only one set was used when the weather was clear. Douglass’s modifications cost £66,000 and were completed in October 1887.
In 1973, the oil lamp was changed to a hyper radial rotating 400W light, when electricity was brought to Bishop Rock. The lamp emits two white flashes every 15 seconds and has an intensity of 600,000 candela. It has a range of 45km.
In 1977, a steel helicopter deck was added at the top of the structure — now standard on all offshore lighthouses.
The lighthouse was automated in 1991, and the last keepers left on 21st December 1992. The fog signal was stopped on 13th June 2007.
Research: ECPK
bibliography
"Cornwall's Lighthouse Heritage" by Michael Tarrant
Twelveheads Press, Truro, 1993
www.trinityhouse.co.uk
reference sources   CEH South
Location

Bishop Rock Lighthouse