No. 2 Cavitation Tunnel (Buildings 46 and 47), Haslar Road, Gosport

No. 2 Cavitation Tunnel (Buildings 46 and 47), Haslar Road, Gosport

The site comprises two adjoining rectangular buildings, both oriented north-west to south-east. Building 46, the smaller structure located to the south-west, houses water tanks for the tunnel. Building 47 contains the No. 2 Cavitation Tunnel itself and ancillary accommodation.

Both buildings are of steel-frame construction encased in English bond red brick with flat roofs hidden behind parapets. Window and door surrounds are of concrete.

Building 46 has a pedestrian access door and single first-floor window in its north-west elevation. The north-east elevation is blind and features an enclosed angled bridge joining Buildings 46 and 47 at first and second floors respectively, with a pipe run beneath the bridge. The south-east elevation contains one blocked opening and a pair of part-glazed double-doors elevated above ground level without access steps. The south-west elevation has six elongated windows arranged 1:1: 2: 1: 1 across both floors, retaining original nine-over-nine steel-framed casement windows. Building 46 retains its original steel-framed windows throughout.

Building 47's principal elevation faces north-east with seven bays, the end bays elevated in a turret-like manner above the roof line. Windows are elongated across all floors except the southernmost bay, which stops at first-floor level. The central bay has triple lights above a large wooden folding machine-bay door with glazed upper lights. A pedestrian door (modern unit in original opening) is surmounted by a large projecting concrete rain hood. Above this is a decorative date-stone bearing an anchor, rope, and the date 1955. The north-west elevation has a replacement modern roller shutter door in an original opening, above which is a beam for lifting machinery. A triple arrangement of elongated windows lights the interior stair. The south-west elevation has seven bays with elongated windows; grilles and a fire-escape are later additions. The south-east elevation is in two parts: to the west are three elongated windows, the middle wider than the outer examples. At first-floor level the middle window is interrupted by brickwork indicating a former connecting doorway to the No. 1 Cavitation Tunnel Building which previously stood to the south. To the east are a pair of elongated windows to first and second floors and a folding part-glazed door. Modern replacement windows (circa 1990s) are fitted within original openings. Mobile phone masts are fixed to the roof. Rainwater goods have been replaced in plastic.

Interior

Building 47 has a wooden-handrailed staircase wrapping around a lift shaft in its north corner, the handrail being original. The south-west side houses the Cavitation Tunnel across two floors. The north-east side contains ancillary accommodation over three floors: a large maintenance room at ground floor; offices, WCs, a kitchenette and possible drawing office on upper floors. Office spaces are simply arranged with visible structural piers and roof girders; simple wooden doors with glazed lights (rectangular or diamond-shaped) survive, some retaining original Bakelite fittings.

The ground-floor cavitation tunnel room has a series of grilles in the floor along the north-east side providing access to services. A large full-height pair of timber double doors connects the maintenance room and tunnel room. A large trap door in the ceiling at the north-west end allows equipment to be lifted through the external doors and up to the upper floor. The upper floor accommodates a gantry crane running the length of the cavitation room, understood to be a replacement of 1970s or 1980s date, along with switch cabinets and an illuminated control panel along the north-east wall.

The Cavitation Tunnel itself consists of a vertically mounted asymmetrical but broadly ovular tube mounted on two large pedestals. The tunnel is made up of eleven welded mild steel plate sections with heavy steel joint flanges; two of the bends are of cast iron. The interior is zinc-sprayed and painted. Motors with drive shafts are located to the north-west: one at ground-floor level (the impeller motor circulating water through the tunnel) and one at second-floor level (the model drive or propeller motor to drive the propeller under test). The overall dimensions are approximately 63 feet (19.2 metres) in length and 40 feet (12.19 metres) in height. The sectional dimensions at the test section within the uppermost horizontal tube are 7.8 feet wide (2.38 metres) by 3.9 feet tall (1.19 metres), which in 1962 was the largest in the world. At ground-floor level is a pit underneath the tunnel allowing access to services, with rollers for expansion and flex at the south-east end. Upper level observation windows are made of toughened glass, located both in the sides and top of the tunnel, with a spare solid top panel for use when top observation was not required. The comprehensive control panel and experimenter's console are located on the upper floor adjacent to the model drive motor.

Building 46 is accessed at ground-floor level and via a narrow pedestrian staircase encased in a brick bridge from the upper floor of Building 47. The building is almost entirely filled with three large water tanks. Inlet and outlet pipes are colour-coded red for water and yellow for pressurised air (to force water between the tanks and the Cavitation Tunnel). The concrete beam roof is exposed with two metal grill floors creating a mezzanine at "first-floor" level and a part-raised plant floor at ground level. A ladder in the west enables access between levels. The mezzanine's south-east section contains racks for storing propeller shafts for testing.