Lightvessel

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Image:Lichtschip Breeveertien.jpg Image:Lightship nantucket.jpg A lightvessel, or lightship, is a conventional ship which acts as a lighthouse.

They are usually anchored permanently and have no means of propulsion. Exceptions include some relief lightvessels, which were used as temporary replacements whilst the normal ship was in port for maintenance, and others which operated in arctic waters during the ice-free summer months only, such as the Lightship Finngrundet [1].

Lightvessels are used in waters that are too deep for a lighthouse, and instead of marking coastlines, usually marks marine traffic routes. It is superior to a buoy for this purpose because its navigational aids are more visible. They also usually carry data recorders used in oceanography for research purposes, such as wave recorders, and may also function as weather stations.

The first lightvessel was located off the Nore sandbank at the mouth of the River Thames in England, placed there by its inventor Robert Hamblin in 1732.

1 Appearance
2 Mooring
3 British Lightvessels
4 American Lightvessels
5 See also
6 External links

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Appearance

Image:Lightship Finngrundet.jpg They normally have red hulls to be easily visible against blue seas and gray skies, usually with the name of the station that they are marking painted in white upper case letters on it, although relief light vessels had the word RELIEF instead. A few have different colour hulls; for example, the Huron was painted black since she was assigned the black buoy side of the entrance to the Lake Huron Cut. The lightvessel that operated at Minots Ledge, Cohasset, and Mass from 1854 until 1860 had a light yellow hull to make it visible against the blue-green seas and the green hills behind it.

As well as the light, which operates at night and in fog, lightvessels are also equipped with red (or very occasionally white) day markers at the tops of masts, which are the first thing seen from an approaching ship. The designs varied; filled circles or globes, and pairs of inverted cones being the most common.

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Mooring

Early lightships used the fluke anchors which are still used on many vessels. These were not very satisfactory, since a lightship has to remain stationary in very rough seas which other vessels can avoid, and these anchors are prone to dragging.

Since the early Nineteenth century, mushroom anchors (the name comes from their shape) have been used, typically weighing 3-4 tons. They were invented by Robert Stevenson (lighthouse engineer). The first lightvessel equipped with one was an 82 ton converted fishing boat, renamed Pharos, which entered service on 15 September 1807 near to Bell Rock and which had a 1.5 ton example. The effectiveness of these anchors improved dramatically in the 1820s, when cast iron anchor chains were introduced (the rule of thumb being 6 ft of chain for every foot depth of water).

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British Lightvessels

Image:050123 28 bristol lightship.jpgIn England and Wales, Trinity House is in charge of all lightvessels. All are now unmanned, but had nine crew in the past. There are 11 lightvessels and 2 smaller lightfloats. The first lightvessel was changed to solar power in 1995, and all except the '20 class' have been converted. The '20 class' represents a slightly larger type of vessel that derives its power from diesel electric generators and has not been convered to solar power due to navigational requirements. Where a main light with a visible range in excess of 20 nautical miles (37 km) is required, a '20 class' vessel is used, as the main light from a Trinity House solar lightvessel has a maximum range of 19 nautical miles (35 km). There are currently hull numbers: 19, 22, 23 and 25 (the 20 class); 2, 5, 6, 7, 9, 10, 17 (solar lightvessels); and LF2 and LF3 (solar lightfloats). Solar lightvessels 93 and 95 have recently been decommissioned and scrapped.

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American Lightvessels

Image:Lightship Columbia.JPG The first United States lightship was established at Chesapeake Bay in 1820, and the total number around the coast peaked in 1909 with 56 locations marked with these vessels. A total of 116 stations have been marked with lightships, including ones on the Great Lakes. Approximately 174 vessels were constructed to man these stations. Of those ships, 168 were constructed by the U.S. Lighthouse Service and six by the U.S. Coast Guard, which absorbed it in 1939.

The official use of lightships in the United States ended March 29, 1985, when the U.S. Coast Guard decomissioned its last such ship, the Nantucket I. Many lightships were replaced with offshore light platforms called "Texas Towers" (as they were modelled after the small offshore oil drilling platforms first used off the Texas coast[2]) or large navigational buoys - all of which are cheaper to build and operate than lightvessels.

It is estimated that there are 15 left today. Three lightships are in New York Harbor: the Ambrose (No. 87) at the South Street Seaport; the Nantucket (No. 112), moored in Staten Island; and the Frying Pan (No. 115), docked at Pier 63 in Chelsea.

A fourth Lightship, Lightship No. 84 (135 feet long, weighing 683 tons), lies sunk in a shallow section of New York Harbor and its two masts are still visible above the surface [3].

The first lightship on the Pacific Coast, the Lightship Columbia, marked the entrance to the Columbia River, near Astoria, Oregon.

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