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South Stack Lighthouse
Holyhead, Isle of Anglesey, Wales, UK
associated engineer
Daniel Asher Alexander
date  August 1808 - 9th February 1809
era  Georgian  |  category  Lighthouse  |  reference  SH202823
ICE reference number  HEW 756
South Stack Lighthouse is situated on a tiny rock islet off the west coast of Anglesey, accessed by a steep path and narrow bridge. Its traditional, rendered white-painted masonry tower rises some 60m above mean high water. The gallery and lantern are about 28m above the rock. Once lit by oil lamps, the lantern is now automated, and the refurbished Grade II listed structure is open to visitors.
South Stack Rock lies west of Holyhead Island, separated from it by a 30m wide strait of turbulent sea. From the mid 17th century, there had been proposals for a lighthouse here to guide shipping. However, plans did not come to fruition until the 19th century.
Daniel Alexander (1768-1846), engineer to Trinity House (the body in charge of British lighthouses outside Scotland), designed the complex. It consists of the tapering light tower and surrounding single-storey buildings with slate roofs, which house the engine room and provided accommodation for lighthouse keepers. The contractor was Joseph Nelson (1777-1833), who used stone quarried locally and on site.
As part of the construction, a flight of 400 steps was cut into the rock, on the Holyhead (east) side of the approach to the site. The 70-strong workforce and the building materials made the hazardous crossing of the chasm using a breeches buoy — a basket that slides along a rope, in this case 21m above sea level. A rope bridge later replaced this arrangement. The lighthouse tower alone cost £11,828 to construct.
The interior of the tower features a helical limestone staircase with cast iron handrail, cantilevered from the exterior wall. In the stairwell, cast iron tubes housing the weights for the lantern's rotating mechanism, run the full height of the tower. The light is carried on a cast iron base supported by cylindrical columns with square capitals and moulded brackets.
The light first shone on 9th February 1809, and from at least 1818, it was illuminated using Argand oil lamps. Seven lamps, backed by 540mm diameter reflectors, were arranged on each face of a three-sided rotating base powered by clockwork (21 lamps in all). The lantern took six minutes to rotate completely, so light flashed from one of its three sides every two minutes.
The Argand oil lamp was patented in 1780 by Swiss physicist and chemist François Pierre Ami Argand (1750-1803). They usually burned whale or vegetable oil, and burnt their wicks more efficiently and produced a brighter light than earlier oil lamp options.
In 1828, an iron suspension bridge (SH204822) costing £1,046 was constructed to replace the rope version. It hung on iron chains from rectangular-plan masonry pylons, 35.1m apart. The bridge was 1.5m wide with a clear span of 32.9m. The original chains and anchorages are still in place.
In 1832-40, a railway incline was installed to enable a secondary light to be lowered down South Stack cliffs to about 12m above sea level, as fog frequently obscured the tower’s main light. This mobile light was carried inside a 3m square wheeled lantern designed by Captain Hugh Evans, the harbour master at Holyhead. The rail track bed survives on the north side of the rock.
In 1854, a fog signal was installed on the west of South Stack. Its 2.5 tonne fog bell was one of the largest in Britain, but it was not always reliable as the salty and windy conditions affected its clockwork operating machinery. From 1861, the sound was augmented by a fog canon at North Stack (SH215839).
In 1874, the lighthouse tower was raised to 27.7m in height and a new lantern installed, with a lattice of cast iron diagonal glazing bars to its windows and a domed roof. The cantilevered walkway around the lantern is carried on stone corbels and has a cast iron railing.
The updated lighting system had a stationary multi-wick paraffin lamp surrounded by a six-sided series of Fresnel lenses with prismatic reflectors, which rotated on roller bearings and flashed every minute. The Fresnel lens was invented in the 1820s by French physicist and engineer Augustin-Jean Fresnel (1788-1827), and provided further improvements in perceived brightness.
In 1880, the mobile light was replaced with a stationary low light at the western tip of the island. A fog horn siren driven by two oil-fired engines superseded the fog bell in 1895.
The low light was removed in 1905-9, when the main light was changed to an early form of incandescent mantle burner fuelled by paraffin vapour (updated model installed 1927). The roller bearings were also replaced, and the lighting apparatus was floated on a low-friction bath of mercury. This enabled the rotation to be speeded up so that the light flashed every 10 seconds.
Between 1909 and 1926, an electrically-operated underwater fog signal was trialled but eventually scrapped. In 1936-8, a separate fog signal station was built to house a new diaphone (two-tone) horn run on compressed air generated by a diesel engine.
In 1938, the incandescent main light was replaced with a 1,000W electric lamp, also powered by a diesel engine. Its 2,500,000 candela light emitted a white flash every 10 seconds, and had a range of 45km.
In the 1960s, when the electricity grid reached South Stack, the fog diaphone was replaced with the electric horn in use today — its triple frequency fog signal sounds every 30 seconds. At this time, the lighthouse was converted to use electric power.
In 1964, the iron suspension bridge was demolished. Its replacement was an aluminium alloy suspension bridge. Chains passing over the original masonry pylons supported its top chords.
South Stack Lighthouse was Grade II listed in May 1971. Nine years later, the Royal Society for the Protection of Birds acquired its 316 hectare site from the Isle of Anglesey County Council, and it is now a nature reserve.
On 12th September 1984, the lighthouse keepers left South Stack and the station was automated. Since then the light and fog signal have been managed and monitored remotely from the Trinity House Operational Control Centre in Harwich, Essex.
In 1997, the present access footbridge was installed. It was designed and built by Laing and Mott Macdonald with grant funding of £182,000 from the Welsh Development Agency. The bridge was completed and the site officially opened to visitors on 9th August that year. The former keepers’ quarters are used for the display lighthouse equipment and artefacts.
In 1999, the lighthouse was refurbished and its 1,000W lamp was changed to a long-life 150W metal halide bulb, reducing its visibility to 32km.
Contractor: Joseph Nelson
Light supply (1874): Chance Brothers & Co, Smethwick
Research: ECPK
reference sources   CEH Wales

South Stack Lighthouse