Steam launch Cygnet

Cygnet is owned by the The Tamesis Trust for public display

Cygnet seen in 1970 at a steam boat Rally near Eton



Open launch built 1870 by J.I. Thornycroft & Co. Ltd. at Chiswick, works number 9. LOA: 29' 10", LWL: 29', Beam: 5' 10", Draft: 1' 3". Riveted steel plate. Slightly raked stem, transom stern, front wheel steering with a chain/cable connection to the tiller.

Engine Single cylinder 3¾" × 5" working as non-condensing. Built in 1870 by J.I. Thornycroft & Co. at Chiswick.
The engine has a ‘D’ type slide valve fitted with Stephenson link reverse gear. The cylinder block is mounted on 4 turned columns, with a gunmetal main bearing base plate. The engine cylinder has bracing bars connected to the hull to stiffen up the engine, side to side, and fore and aft. This was a common feature on Thornycroft steam launches and allowed engines to be lightly built.

Locomotive type.  Side coal fired with a grate area 12" × 15½", the boiler barrel is 16" diameter and has 39 1¼" brass fire tubes in rows arranged as 7+8+7+8+7+2

The boiler is offset to allow side firing, 4' long fitted with twin Salter type safety valves. Auxiliaries are:- a ½ inch Gifford type steam injector, a hand feed pump, a bilge ejector, a blower, Bourdon pressure gauge, and a small bell whistle. 

Propeller Fitted aft of the rudder. A damaged propeller was removed and replace with a 2 bladed 20" diameter propeller in the 1960's.
History of Cygnet

Little is known of the early history. The Thornycroft construction ledger states No.9 was built in 1870. Cygnet has two builders plates, one is cast with the boat number but no date; this is thought to be the original. The second is engraved with No.9 and dated 1873; this is thought to have been added later.

Original steering is shown as only by tiller on a 1873 GA plan. There are other features which indicate that the front cockpit wheel steering was added at a later date.

Cygnet was stored in the roof of Thornycroft’s Boatyard shed at Hampton and virtually forgotten between 1920-1968. She was photographed by the SBA Historian in 1961, who noted that she had a Conservancy licence plate dated 1919. When the Hampton works closed mid 1960’s Cygnet was taken over by Michael Turk who replaced some hull plates under the boiler and then fibreglass sheathed the hull all round up to about 6 inches from the gunwale.  Following this repair Cygnet was steamed again on the Thames, taking part in a steamboat rally near Eton in 1970, and is reported to have been steamed for the last time as a film prop in 1983. Cygnet was then loaned to the National Motor Boat Museum, Watt Tyler Park, Basildon for static display from 1995 until closure in 2009. The Thames Boats Trust purchased Cygnet in April 2010 for public exhibition at Beale Park, near Pangbourne. Funds for the purchase were raised by private donations and a substantial  MLA PRISM grant. The ownership of Cygnet has now been taken over by the Tamesis Trust for future museum display.

The Thornycroft boat building ledger of boats built at Chiswick shows that there were five other launches of this length using the same size engine, built over a five year period.

The engine design was later developed for use as an auxiliary service engine in torpedo boats of the 1880/90’s, but without reverse gear and also using a modified design for the base plate in cast iron. An example of these later engines is fitted in the 1997 steam launch Arlette; this engine had been modified many years ago to include reverse gear.

Cygnet has had several minor alterations and repairs carried out but still remains very much as built, providing a unique example of an early Victorian steam launch built at a time when the Cutty Sark was making her maiden voyage.

About Thornycroft

John Isaac Thornycroft started building his first boat 'Nautilus' in 1859 when aged 16, he completed this steamboat  in 1862. His boat building work then moved to Church Wharf at Chiswick in 1866.

Steam launch Cygnet (works No.9) was built in 1870, followed by a 46ft launch Miranda (works No.10) built in 1871. Miranda caused astonishment among naval architect circles by running at a speed of 18 knots, something that was thought impossible for such a small boat. Extensive speed trials were conducted on the Thames by Professor Bramwell who presented a lecture paper to the Institute of Naval Architects in 1872.

By 1873 the Admiralty were looking at ways of firing the new self propelled Whitehead torpedoes from small fast steam launches.  Thornycroft produced the first of these new torpedo boats for the Norwegian Navy in 1874, this vessel, named RAP, was 60 ft long and is on display at the Norwegian Naval museum. In 1876 the 85ft long Lightning was the first torpedo boat supplied to the British Admiralty. These 80 footers were designated as 2nd class torpedo boats by the Admiralty. J.I. Thornycroft & Co. went on to build large numbers of  torpedo boats and torpedo boat destroyers for navies around the world; over 200 torpedo boats were built at Chiswick.

Thornycroft moved to Southampton in 1904 and also established works at Platts Eyot on the Thames in 1908.

Thornycoft was an important warship builder but also constructed many other types commercial vessels.

The company merged with Vospers of Portsmouth in 1964 to become Vosper Thornycroft, and is now the VT Group. The works on Platts Eyot closed shortly after this merger, Cygnet and Eva both owned by Thornycroft had been held in store here for many years. Eva was sold in 1975 and is now displayed at the Henley River & Rowing Museum.

For more information about the steam launch Cygnet, please contact The Tamesis Trust

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The Tamesis Trust - registered charity number 1159891.