Experimental Boat Testing Tank Facility, Steyne Wood Battery


Heritage Category:
Listed Building
List Entry Number:
Date first listed:
Statutory Address:
Steyne Wood Battery, Hillway Road, Bembridge, Isle of Wight, PO35 5PG


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Statutory Address:
Steyne Wood Battery, Hillway Road, Bembridge, Isle of Wight, PO35 5PG

The building or site itself may lie within the boundary of more than one authority.

Isle of Wight (Unitary Authority)
National Grid Reference:


An experimental tank for testing model boats located in a purpose-built structure. Designed in 1910 by the engineering firm L G Mouchel for Sir John I Thornycroft.

Reasons for Designation

The experimental boat testing tank facility at Steyne Wood Battery, designed in 1910 by the engineering firm L G Mouchel for Sir John I Thornycroft, naval engineer and inventor, is listed at Grade II for the following principal reasons:

* Historic interest: a building commissioned by and for the important naval architect, engineer and inventor Sir John I Thornycroft whose designs were of national significance. In particular, he here perfected his surface-skimming hulls which led directly to the construction of his firm's Coastal Motor Boats which were important to the Admiralty during the First World War and influenced the design of numerous later naval and civilian vessels;

* Technological interest: a ferro-concrete tank built to designs by the celebrated engineering firm L G Mouchel using the innovative Mouchel-Hennebique system of concrete reinforcement;

* Rarity: this is likely to be the earliest surviving private experimental tank facility for testing boat/ship models nationally, and the second such to be commissioned, and is one of very few experimental tanks of this kind known and surviving in England;

* Architectural interest and intactness: the tank facility is as built with its function dictating its form, allowing an understanding of how the building worked under test conditions.


In May 1909 Steyne Wood Battery (built 1889-94 and operational to 1898) was sold at auction along with 12 acres of adjoining land. The purchaser was Sir John Isaac Thornycroft (1843-1928) a prominent naval engineer and resident of nearby Steyne Wood House; his country home. At the battery site in circa 1910 he had built an experimental tank facility (hereafter ‘the boat testing tank’) to designs by the engineering firm L G Mouchel. The design drawings, dated October and November 1910, are held by the Institute of Civil Engineers (reference Shel C 666A). Mouchel was an obvious choice of engineering firm to design a concrete tank in the early C20. It was a leading engineering practice set up by Louis Gustave Mouchel (1852-1908) who, in 1897, took out a patent in Britain for the innovative ‘Hennebique’ system of concrete reinforcement, or ‘ferro-concrete’. This system of ‘béton armé’ or ‘armoured concrete’ involved strengthening slabs with steel rods. The system was used in buildings, such as the Grade II* listed King Edwards Buildings Post Office, Newgate Street, London (NHLE 1194097), also for bridges, reservoirs, sewage tanks and other related structures.

Thornycroft was a naval architect, engineer, prolific inventor and founder of the company John I Thornycroft & Co. After working as a draughtsman with Palmer’s Shipbuilding Company at Jarrow (Tyne & Wear), Thornycroft studied natural philosophy and engineering at Glasgow University. In 1866 he established a shipyard at Chiswick with the financial help of his father. Thornycroft’s obituary in The Engineer notes that this shipyard was “the foundation of what was destined to become one of the most famous shipbuilding businesses in the country”. Between 1866 and 1870, Thornycroft continued his studies in naval engineering at the Royal School of Naval Architecture and Marine Engineering in South Kensington. One of Thornycroft’s early designs was for the steam launch ‘Miranda’, which achieved a record speed of over eighteen miles-per-hour. In 1873, Thornycroft built the ‘Gitana’, the first torpedo boat. This lead to ‘HMS Lightening’ in 1877, the first torpedo boat used by the British Navy. Thornycroft transferred the Chiswick yard to a site acquired in 1904 at Woolston in Southampton, which could accommodate larger vessels such as destroyers. Thornycroft was an Honorary Vice-President of the Institution of Naval Architects, an Honorary Life Member of the Institution of Mechanical Engineers and elected a Fellow of the Royal Society in 1893. In popular culture, Thornycroft was the subject of a comical verse published in ‘Mr. Punch’ (entitled ‘No Rose Without a Thorn (-ycroft)’) and a cartoon by Sir Leslie War that was published in Vanity Fair on 19 January 1905. Thornycroft accepted a knighthood in 1902. He died at Steyne House on 28 June 1928. His eldest son, Sir John Edward Thornycroft, succeeded as head of the company.

It is possible that Thornycroft purchased the battery with the intention of using it as a site on which to build a boat testing tank, as he had been conducting research into machinery designed for experimental tanks for some time. In November 1908, he had applied to register a patent for ‘Improvements in or relating to Driving Means for use in Experimental Tanks and for other analogous purposes’. Thornycroft submitted a complete specification in June 1909 and the application was accepted on 30 September 1909. Thornycroft’s invention represented an improvement in the technique for testing the resistance of models in experimental tanks. This was delivered by means of a weighted pulley system that allowed the potential energy to be varied at the start of an experiment, so as to ensure that the energy value was accurate.

An obituary published by the Institute for Civil Engineers notes that during the First World War “Sir John, assisted by his daughter Blanche, an Associate of the Institution of Naval Architects, did a considerable amount of work with his experimental tank”. As a result of the tests conducted at the facility, Thornycroft established “the resistance of the mooring-ropes of mines when inclined at different angles to the current”. Thornycroft also completed many experiments focussed on developing improvements in hull forms: his obituary in The Engineer notes that “the experience gained with this tank was of the utmost service in the design of the coastal motor boats (CMBs also known as ‘scooters’), which were built by his firm during the war and which performed signal service in combating the submarine menace”.

The (CMBs), vessels with an innovative single-step hull design that allowed for surface-skimming, were used successfully during the First World War and are the subject of a pamphlet published by John I. Thornycroft & Co. According to the pamphlet, the 55-foot CMBs based at Portland, Portsmouth and Dover served in anti-submarine work and were used to launch torpedoes at enemy vessels and bases. The vessels were also used to great effect in the Zeebrugge Raid in April 1918 to create a smoke screen and release flares to assist in coordinating the attack with accuracy. In 1919, the CMBs “scored notable successes” in attacks against the Bolshevik fleet in the Gulf of Finland. An example of this craft is in the collection of the Imperial War Museum, Duxford (Cambridgeshire).


An experimental tank for testing model boats located in a purpose-built structure. Designed in 1910 by the engineering firm L G Mouchel for Sir John I Thornycroft.

MATERIALS Design drawings of the building indicate that the tank is of ferro-concrete construction, built using the Mouchel-Hennebique system. The experimental tank building is also of ferro-concrete construction and its walls made of shuttered concrete. The flat roofs above the subsidiary areas on the north and south ends of the building are constructed of breeze blocks covered with asphalt. The pitched roof above the experimental tank is supported by steel trusses and is part-glazed, part tile-clad.

PLAN The experimental tank is housed within a rectangular, two-storey, purpose-built building oriented roughly north-south. The tank is central to the building under a pitched roof. At either end of the building are two storey, flat-roofed sections. The upper floors are accessed by external concrete stairs against the north elevation which return onto an elevated walkway along the eastern side of the building, which enters the building through a first floor doorway at the south-east corner. Internally the central tank is flanked, to the south and north by first floor rooms. Above the south end of the tank is a cantilevered gallery and extending along the western side of the building a cantilevered walkway, both accessed by steps to the south-west.

EXTERIOR The exterior of the tank facility expresses the location of the tank in its form: a pitched top-lit roof in the central part of the building identifies the area containing the tank internally. This central section is delineated by flues projecting above the eaves line and is also flanked by two-storey flat-roofed sections. Bay divisions are marked by projecting concrete piers, and to the west elevation are concrete buttresses to support the weight of the tank internally. The central tank area is blind on the west elevation, but the upper floor to the east elevation has ten multi-paned, timber-framed cross-casements with both side and top hung lights. A concrete walkway with metal railings runs along the length of the building here, between the floors. Below the walkway and between the projecting concrete piers are six angled glazed panels (giving the appearance of a set of cold-frames) which are understood to have been installed by Blanche Thornycroft as part of her interest in hydroponics (the boiler to the east of the building within the battery warming the water for this). The flat-roofed end sections are lit by the same form of window as described above. The south elevation, which is of three bays, has a central four-panelled door providing access to the ground floor, this is flanked by two three light windows and there is a single central window above. The north elevation is largely blind except for a six-panelled door to the north-west (its position is off-centre because of the external stairs which rise to the north-east) and a matching first floor central window.

INTERIOR The tank, built along the north-south axis, is 67 feet 6 inches long, 30 feet wide and 13 feet 9 inches deep. This was filled with fresh water pumped from a nearby well. The internal walls of the tank are gently curved towards its base. Shallow extensions of the tank project to the south and north for the insertion and removal of the models under test. This central zone is well-lit and features a roof supported on steel trusses. The aforementioned walkway along the western side of the tank, and overlooking it, also the cantilevered gallery above the south end of the tank have steel safety railings. Pipes are also exposed along the west wall. The subsidiary, compact spaces at the north and south ends of the tank are separated from the tank by concrete columns and have lower ceiling heights due to their flat roofs. In the floor of each is a rectangular opening leading to the room beneath. On the ground floor the room to the south was not inspected but that to the north contains a circular well (marked as ‘pit’ on the design drawings). This is 20 feet deep and 3 feet wide, with a wall-mounted ladder down and steel safety railings; similar is marked on the original plans for the south end of the building. There is also exposed pipework and a ceiling mounted winch.


Books and journals
Barnaby, K C, 100 years of specialised shipbuilding and engineering: John I. Thonycroft Centenary 1964, (1964)
Thornycroft & Co, J I, A short history of the revival of the small torpedo boat (C.M.Bs.) during the Great War and subsequently in the Baltic, Caspian & Archangel expeditions of 1919, (1932)
Mouchel and ferro-concrete, accessed 13 November 2014 from http:://www.engineering-timelines.com/who/Mouchel_LG/mouchelLousieGustave4.asp
Ship Tanks, accessed 13 November 2014 from www.npl.co.uk/about/history/research/ship-tanks/
Thornycroft, Sir John Isaac (1843-1928), Oxford Dictionary of National Biography, accessed 13 November 2014 from www.oxforddnb.com/view/article/36512
Boat Testing Tank housed within purpose built concrete building, Steyne Wood Battery, Bembridge. Isle of Wight County Archaeology and Historic Environment Service, Historic Environment Record reference 8129 – MIW13491
Sir John I. Thornycroft in The Engineer, 6 July 1928, 6
Sir John Isaac Thornycroft Obituary, Institute for Mechanical Engineers, December 1928, 1053


This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.

End of official listing

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