TQ 76 NE CHATHAM MAIN ROAD (West side) Chatham Dockyard 762-1/8/78 No. 7 Slip Cover and Machine Shop No.3 GV I Dry dock cover. 1852-5, designed by Col. GT Greene and built by Grissell and Peto. Cast- and wrought-iron frame with corrugated-iron sides and roof. PLAN: rectangular aisled plan. EXTERIOR: single storey; 10-bay range. A wide gable with the frame exposed, the central bay open to a canted upper brace between the tops of the two columns with diagonal bracing above, the aisles sheeted in above the ground floor in 3 stages with horizontal ties to the corner posts. Roof has 2 tiers of continuous clerestory lights and a ridge lantern. INTERIOR: cast-iron H-section columns connected at lower level by cast-iron beam with parabolic bottom flanges, cast-in supports for gantry cranes to main roof and aisles, to wrought-iron roof trusses, and longitudinal lattice and trussed aisle beams, with diagonal bracing. Members carry the inscription H & MD GRISSELL/LONDON 1853. HISTORY: covers to ship-building dry docks were introduced to Navy yards from c1814, because of the rapid deterioration of wooden ships exposed during construction to the weather. However, by the 1860s and the move to metal ships, slip covers were largely obsolete, although No.7 was used for submarine building in this century. No.7 slip cover represents an important advance on the earlier slip covers toward the now-universal rigid portal-braced frame, fully developed by Greene at the Sheerness Boatstore (qv), and the technological peak of development of slip covers. This slip cover was not intended to simply provide protection from the weather (which was becoming largely irrelevant with the advent of iron and steel shipbuilding) but one which was built for and provided with travelling cranes over all three aisles. It represents a significant part of the remarkable progression in the development of engineering frames, with former slip cover from Woolwich dockyard, the Boilershop ( qv), in the N end of the Dockyard. Forms a fine group with the 1837 timber slip cover and the 1845-7 iron covers to the S, and the surviving iron sheds in the former Dockyard to the N. (Sources: Coad J: Historic Architecture of Chatham Dockyard 1700-1850: London: 1982: 182 ; Coad J: The Royal Dockyards 1690-1850: Aldershot: 1989: 115-117 ; The Buildings of England: Newman J: West Kent and the Weald: London: 1976: 206; Journal of the Newcomen Society: Sutherland RJM: Shipbuilding and the Long-Span Roof: London: 1989). Listing NGR: TQ7599469570