Manoeuvring Tank (now known as Ocean Basin), Haslar Marine Technology Park (Former Admiralty Experiment Works)

A large covered model ship manoeuvring tank, now known as Ocean Basin, constructed by Messrs Trollope and Colls between 1955 and 1959.

Materials

The building comprises a reinforced concrete tank housed within a two-storey structure. The walls are formed of ribbed aluminium 'Q' deck panelling backed by light steel sheeting, creating a cavity filled with wool insulation. The pitched roof consists of corrugated steel sheets carried on tubular steel trusses. Ancillary buildings surrounding the main structure are constructed of local red brick laid in stretcher bond.

Plan

The building is rectangular on plan, oriented on a south-west to north-east axis. One and two-storey ancillary buildings of brick wrap around the main building on all four sides.

Exterior

The principal two-storey building has a pitched roof covered with corrugated steel sheets, which was repaired in the early 21st century. Two rows of rectangular skylights to each roof slope permit light into the tank below. The two gable ends of the building and upper parts of the side walls are constructed from ribbed aluminium panelling.

Peripheral ancillary buildings of one and two storeys with flat roofs and cavity brick construction wrap around the principal building on all four sides, containing offices and storerooms. At the north-eastern half of the building these ancillary buildings are two storeys high, rising to near the roofline.

Fenestration to the south-east and north-west elevations of the principal building and all four elevations of the peripheral buildings mainly consists of five-pane uPVC casement windows, each with a tall pane in the centre and two smaller panes to each side, though other uPVC window arrangements and original metal-framed windows feature in places. The windows to the brick buildings have sills and lintels of concrete. On the upper level these project out from the brickwork and connect with vertical members to create a continuous concrete frame around pairs of windows. Vertical shutters to the north-east and north-west elevations provide access to ground-floor workshops and storage spaces. Some ground-floor windows and shutters to the south-east and north-east elevations have been bricked up.

The principal south-west elevation has the peripheral brick buildings to the ground floor with the blind gable end of the principal metal building rising up behind. The flat roof of the ancillary range is punctuated with eight skylights which light the model preparation rooms below. This range is fenestrated with groups of five-pane windows to the ground floor with corresponding rows of smaller three-pane windows above to light the mezzanine level. The wide central bay of this elevation is pushed forward slightly and has red brick laid in Flemish bond. A projecting canopy of concrete surrounds the shuttered entrance to the test tank. Above the canopy there is a plaque with an anchor carved in relief and the date 1958. Above this, the brickwork rises in a series of steps supporting an aluminium panelled clerestory with a glazed front and a shallow-pitched roof. This replaced the original flat-roofed clerestory, which was constructed from brick and was lit from each side by three groups of three-pane windows.

Interior

The interior space is dominated by a rectangular test tank of sectional reinforced concrete, which measures 122 metres by 61 metres. The tank is surrounded by walkways with metal railings that make up the first floor of the building. Around 1.5 metres of the tank's 5.5 metre depth is sunk below ground level. When full the tank holds 40,000 tonnes of water, making it one of the largest hydrodynamic testing facilities in the world.

The tank was constructed with expansion joints to address issues of settling and movement caused by the tank's proximity to the high water line. The tank floor was also designed to allow for settling and movement, consisting of two layers of reinforced concrete laid in a large grid pattern and separated by a layer of bituminous felt, abutting the heels of the walls. The walls of the tank have various bay lengths and different buttress designs with expansion joints between them. Twelve pairs of opposed buttresses along the two long walls of the tank support the 6 metre high walls as well as carrying the walkways around the perimeter of the tank. The eight buttresses in the south-western wall have recesses for the double slatted wooden beaches to minimise the reflection of waves generated during experiments.

Towards the south-west end of the tank there is a rotating arm 29 metres in length, supported by a central post which descends below the water and stands on a concrete base 6 metres in diameter constructed on 15 metre reinforced concrete piles. The arm itself is constructed from tubular steel. It is driven by an electric motor and can rotate through 360 degrees. It supports a model-testing carriage which can move along the length of the arm to vary the radius of manoeuvring experiments between 7.5 metres and 27.5 metres.

Two banks of five plunger-type wave generators, colloquially known as 'nodding donkeys', were originally positioned along the north-east end of the tank and along the eastern half of the north-west side. During upgrades in 2014 the redundant wave generators were all removed, but the supporting concrete pillars with cantilevers have been retained in situ across the north-east end and eastern half of the north-west side of the tank. The entire wave generating plant now operates from the north-east end of the tank, comprising a single bank of 122 electrically actuated flap-type wavemakers.

A dock area used for rigging model ships adjoins the south-western wall of the tank and is separated from the main body of water by a dock gate. Above the dock, raised on a steel frame, is a glass-fronted control room used for operating the rotating arm. A similar control room used for operating the wave generators stands at the opposite end of the tank. A further control room stands at floor level in the south corner of the space, and along part of the north-west side there are partitioned storerooms.

Above the tank the pitched roof is carried on exposed trusses of tubular steel that span the entire width of the building. Nine main trusses are carried on the buttresses that extend from the long walls of the tank, crossed above by tertiary Howe trusses parallel to the roof ridge. Suspended beneath the main trusses are four rows of corrugated aluminium sheets supported by steel frames that run the length of the tank and correspond with the four rows of skylights above to break the light entering from the roof.

The lower sections of the tank building walls beneath the aluminium panelling are of red brick cavity wall construction and form both the lower sections of the tank building and adjoining wall of the ancillary buildings which wrap around the tank on all four sides. These ancillary buildings contain offices, workshops and plant rooms, accessed by a corridor that runs around the outer wall of the tank. This corridor has doorways through hexagonal bulkheads at irregular intervals. The bulkheads correspond with the buttresses supporting the concrete tank.

A large room at the south-west end of the building, accessed via the principal entrance to the south-west elevation, originally housed the preparation rooms for wax, thermoplastic and wood models. Some partitions have since been added to the south corner of this space to subdivide it. Staircases leading up to the tank walkways are located at either end of this area. During the 2014 renovations additional partitions were added to the south-east corridor to create enclosed offices where some of the rooms were originally open to the corridor. The corridor and adjoining rooms have suspended ceilings and simple doorframes and doors of timber. There is an incomplete set of hydrometers attached to pillars around the ground floor of the tank, which were used to measure the extent to which the building settled and tilted when the tank was first filled with water.