Sevenstones Lightship

Sevenstones
History
United Kingdom
Operator: Trinity House
General characteristics
Type: Lightvessel
Sevenstones Light Vessel
Coordinates 50°03.616′N 006°04.337′W / 50.060267°N 6.072283°W / 50.060267; -6.072283Coordinates: 50°03.616′N 006°04.337′W / 50.060267°N 6.072283°W / 50.060267; -6.072283
Focal height 12 m (39 ft)
Range 25 nmi (46 km; 29 mi)
Characteristic Fl 3 / 30 Seconds
Racon O
Managing agent Trinity House

Sevenstones Lightship is a lightship (also known as a lightvessel) moored off the Seven Stones Reef which is nearly 15 miles (24 km) to the west-north-west (WNW) of Land's End, Cornwall, and 7 miles (11 km) east-north-east (ENE) of the Isles of Scilly. The reef has been a navigational hazard to shipping for centuries with seventy-one named wrecks and an estimated two hundred shipwrecks overall, the most infamous being the oil tanker the Torrey Canyon on 18 March 1967.[1][2] The rocks are only exposed at half tide and it was not feasible to build a lighthouse so a lightvessel was provided by Trinity House. The first was moored near the reef on 20 August 1841 and exhibited its first light on 1 September 1841. She is permanently anchored in 40 fathoms (73 m) and is 2.5 miles (4.0 km) north-east (NE) of the reef.[3][4] Since 1987, the Sevenstones Lightship has been automated and unmanned.[1]

The Seven Stones lightvessel also acts as an automatic weather station.[5] A series of Trinity House lightships stationed near the Sevenstones Reef have measured significant wave heights (Hs or SWH)—the periodic average of the highest one third of waves in a spectrum—since the early 1960s using Ship Borne Wave Recorders (SBWR).[6] The Sevenstones Lightship is in a very exposed location and is open to most North Atlantic storms.

First lightvessel

Sevenstones Lightship, showing moorings

As early as 1826 the government was petitioned to build a light on the reef and a second petition in 1839, supported by the Chamber of Commerce of Waterford, merchants from Liverpool and the Bristol Channel ports resulted in a meeting being held in Falmouth on 21 February 1840. It was declared that a light on or near the reef would shorten the passage around Scilly by up to thirty-six hours.[7] As a result, the first lightship was moored, in 40 fathoms (240 ft; 73 m) on a slate and sand bottom, near the reef on 20 August 1841 and shone its first light on 1 September 1841. Originally there was a crew of ten with five on station at a time.[1] A few months after being placed in position she drifted from her anchorage and was consequently provided with a new "mushroom" anchor which was better suited to lightships. The West Briton of 25 November 1842 reported that her cable parted and she almost became a wreck when she drove over the reef at high tide. The crew steered the ship to New Grimsby, Tresco, from where she was towed back, and on 6 January 1843 she broke adrift again. The following March, she was found drifting in a moderate southwest breeze, and was again towed to New Grimsby. She was towed back to her position on 10 April, and anchored in 42 fathoms (252 ft; 77 m).

Relief occurred monthly with the master or mate and twelve men always on board, with the other officer and three men on shore in rotation. Houses were provided on Tresco for the crew and provisions were procurred by crew members rowing and sailing to New Grimsby in the vessel's longboat.[3] Two of the crew drowned on 15 October 1851 when one of the lightship's longboats capsized in a squall, while on a journey from Scilly with stores.[7] Following a dispute with Augustus Smith, the governor of the Isles of Scilly, accommodation and provisions were provided from Penzance.[3] The crew would have had a fright when a meteor exploded over the lightvessel, at 2 am on 13 November 1872, showering the deck with cinders.[8] On 30 January 1873 the London barque Athole came too close and caught her rigging on the lightship's bumpkin carrying away her main and mizzen halyards, and the starboard light.

Design

Built by William Pitcher of Thames Ironworks and Shipbuilding Company, Blackwall, the cost of the hull came to £3,128 8s and the fully equipped vessel £4,416 8s 7d. Built of wood, with a tonnage of 162, her length was 80 ft (24 m), breadth 21 ft (6 m) and her two masts for the lights were 69 ft (21 m) and 60 ft (18 m) tall. She carried one lugsail, a staysail and a jib. Red balls were fixed on each mast to distinguish her from other lightvessels. The two lights were displayed at 38 ft (12 m) and 20 ft (6 m), were of the catoptric system and could be seen from 10 miles (16 km) away. She also carried a gong fog signal.

Trevose Head Lighthouse, on the north Cornish coast, also had two lights and the Sevenstones light was reduced to one, to stop confusion between the two.[9] The single light was originally intended to be installed in 1878 but was postponed to May 1879[10] By 1891 only one white light was displayed at 38 ft (12 m) with three quick flashes followed by thirty-six seconds of darkness.[3] In stormy weather or in fog it was difficult for mariners to tell where they were and similar lights added to the confusion.

Temporary lightvessel

On Saturday 3 May 1879 a temporary lightvessel was towed to the Sevenstones from Milford by the new Trinity House yacht Siren and the old vessel towed to London.[11]

Second lightvessel

Lighthouse vessel 80 took up her position during the Second World War and was replaced with a lighted buoy after being frequently bombed and machine-gunned by German pilots.[4] She broke adrift in March 1948 and her engine failed in November 1950. She was replaced in 1958 by lightvessel 19.[3] Lightvessel 80's last known sighting was in a Sotheby's catalogue for sale at £85,000.[12]

Design

Lightvessel 80 was built by H & C Grayson, of Liverpool in 1914. She was 116 ft (35 m) long, had a breadth of 26 ft (8 m) and was 318 tons. In 1954 she undertook a refit with the provision of hot water, electric lighting, refrigerator, one and two-berth cabins and a roomy mess deck. Daily work on the ship such as watch-keeping and maintenance of the 600,000 candle power lantern could be carried out without going outside. Before, the refit crew had to climb up the mast every morning to trim the lamps, hauling their supply of oil with them; a dangerous task in rough weather.[3]

Third lightvessel

Lightvessel 19 was in position in 1958 and was on station when Torrey Canyon became, at that time, the largest shipwreck in world history.[3] The lightship was towed to Penzance for a few days while the wreck was bombed by Fleet Air Arm aircraft; in an attempt to release the remaining oil on board and set fire to it.[3]

Design

Lightvessel 19 was built by Philip and Son of Dartmouth and launched on 30 May 1958 and the Sevenstones was her first station. She is 133 ft (41 m) long and 26 ft (8 m) wide, a gross tonnage of 390 and cost £118,854. She had the same 600,000 candle power as the previous ship and shone a group of three white flashes every thirty seconds, visible in good conditions to 11 miles (18 km).[13]

Fourth lightvessel

Lightvessel 22 was built by Richards Shipbuilders of Lowestoft in 1967 with a displacement of 390 tons. Her length is 114 ft (35 m) and breadth 26.5 ft (8 m) and she was on station from 1998–2001. She is currently the St Gowan lightvessel.[14]

Fifth lightvessel

Lightvessel 2 was in position in October 2004.[15]

Automated weather station

The lightship serves as an automated weather station for the UK Met Office and is owned and maintained by Trinity House. On board equipment measures air pressure, wind strength and direction, temperature and humidity. The lightship also carries a Ship Borne Wave Recorder and measures significant wave height(abbreviated Hs)on an hourly basis (which is the average of the highest third of all waves),[16][17] as well as recording average wave frequencies (abbreviated Ts) meaning wave period in seconds.

Wave energy recorded at the Sevenstones Lightship

The largest waves tend to occur when there is a large westerly or west north westerly Atlantic fetch.

The Sevenstones Lightvessel does not currently measure maximum individual wave heights, but measures the significant or more 'consistent' wave values and these are given on an hourly basis. This gives mariners a general indication of the sea conditions in this notoriously hazardous shipping area. However it is worth noting that maximum wave heights in any sea state frequently exceed the significant pattern.[17][18][19] Rayleigh distribution shows statistically that if significant waves are for example 33ft, then 1 in 100 will be larger then 50ft. This tendency is frequently reinforced by eyewitness accounts.

In 1989 the Institute of Oceanographic Sciences' Deacon Laboratory published a report on wave measurements at the station from 1962 to 1988.[20] It revealed a high energy wave climate at the Sevenstones with significant waves (Hs) of over 11.15 metres (36.6 ft) recorded on 17 October 1982, and 10.99 metres (36.1 ft) recorded on 16 January 1974.

In February 2014, peak significant wave heights of 10.6 metres (35 ft) were recorded on 1 February at 15.00 GMT and 10.4 metres (34 ft) on 8 February at 10.00 GMT [21][22]

More recently, on February 8, 2016 at 10.00 GMT significant waves of 11.73 metres (38.5 ft) were recorded at the station resulting from the Atlantic storm Imogen.[23] BBC News, citing the UK Met Office reported that maximum wave heights off the Cornish Coast on this day were recorded at 63 ft (19.1m) at the nearby Wave Hub Buoy stationed at 50° 20.833'N 005° 36.853'W.[24][25] Based on the swell direction, its close proximity and similarly comparative Hs values, the Sevenstones Lightship would most likely have encountered similar scale maximum wave height values.

Generally wave patterns in this area are believed to correlate with the North Atlantic Oscillation Index.[17]

Temporary lightvessels

See also

References

  1. 1 2 3 Jones, R. (2011). Lighthouses of the Southwest. Wellington: Halsgrove. ISBN 978 0 85704 107 4.
  2. ↑ Gill, C; Booker, F; Soper, T (1967). The Wreck of the Torrey Canyon. Newton Abbot: David and Charles Limited.
  3. 1 2 3 4 5 6 7 8 Noall, Cyril (1968). Cornish Lights and Shipwrecks. Truro: D Bradford Barton.
  4. 1 2 Petrow, Richard (1968). The Black Tide. In the Wake of Torrey Canyon. London: Hodder and Stroughton.
  5. ↑ Liddiard, John. "Seven Stones". Retrieved 19 February 2012.
  6. ↑ "Charting Progress: The State of UK Seas" (pdf). DEFRA.
  7. 1 2 Larn, Richard (1992). The Shipwrecks of the Isles of Scilly. Nairn: Thomas & Lochar. ISBN 0 946537 84 4.
  8. ↑ "Seven Stones Lightvessel". Engineering Timelines. Retrieved 7 December 2013.
  9. ↑ "Lighthouse News". The Cornishman (42). 1 May 1879. p. 4.
  10. ↑ "The Seven Stones Lightship". The Cornishman (11). 26 September 1878. p. 5.
  11. ↑ "Local News". The Cornishman (43). 8 May 1879. p. 6.
  12. ↑ Klempau, Iris. "Trinity House Lightvessel No. 80". Lightships from all over the world. Retrieved 20 January 2014.
  13. ↑ Klempau, Iris. "Trinity House Lightvessel No. 19". Lightships from all over the world. Retrieved 20 January 2014.
  14. ↑ Klempau, Iris. "Trinity House Lightvessel No. 22". Lightships from all over the world. Retrieved 20 January 2014.
  15. ↑ Klempau, Iris. "Trinity House Lightvessel No. 2". Lightships from all over the world. Retrieved 20 January 2014.
  16. ↑ Butt, T.; Russell, P. (2002). Surf Science. Alison Hodge. ISBN 9780906720363.
  17. 1 2 3 Butt, T. (2009). Waves, Coasts and Climates. Alison Hodge. ISBN 9780906720585.
  18. ↑ Kampion, D. (1989). The Book of Waves; Form and Beauty on the Ocean. ISBN 0-916567-14-1.
  19. ↑ http://www.channelcoast.org/
  20. ↑ Bacon, S.; Carter, D.J.T (1989). Waves Recorded at Seven Stones Light Vessel 1962–86 (PDF) (Technical report). Institute of Oceanographic Studies Deacon Laboratory. Report 268. Archived from the original (pdf) on 2005-05-20.
  21. ↑ "Sevenstones Lightship". UK Met Office.
  22. ↑ "National Data Buoy Center". National Oceanic and Atmospheric Administration.
  23. ↑ http://magicseaweed.com/Sevenstones-Lightship-Wave-Buoy/61774/?start_format=07+Feb+2016&end_format=08+Feb+2016&spot_id=
  24. ↑ http://www.bbc.co.uk/news/uk-35516741
  25. ↑ http://coastalmonitoring.org/data_management/real_time_data/charts/?chart=116&tab=waves&disp_option=
  26. ↑ "Trinity House Lightvessel no. 1 MARY MOUSE 2". Lightships from all over the world. Retrieved 20 January 2014.
  27. ↑ "Trinity House Lightvessel No. 21". Lightships from all over the world. Retrieved 20 January 2014.

External links

This article is issued from Wikipedia - version of the Thursday, February 11, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.