Monument MPM1779 - Sluice gate structure, north-west of Dry Dock No. 3

A large sluice gate structure (penstock) observed to the north-west of Dry Dock No.3 in Portsmouth Historic Dockyard during an archaeological watching brief in 2010. The structure comprised a large stone foundation, stone culvert system and brick drain gully.

A large stone-built dockside feature/structure observed to the north-west of Dry Dock No.3 in Portsmouth Historic Dockyard during an archaeological watching brief in 2010. The structure consisted of a series of associated features comprising a large stone-built foundation (which included the opening of an inspection chamber) surrounded by a stone culvert system and brick drain gully. The structure was only partially exposed and it was thought to be more extensive. It was backfilled and preserved in situ. [1]

The structures exact function was unclear and it was originally suggested that it may have been part of the dry dock's gate opening assembly or that it might have formed part of a hydraulic power system which served the cranes and capstans operating on the dockside during the 19th century. However, the structure was reinterpreted as a sluice gate structure (Penstock valve) following the discovery of two identical structures on the north side of Dry Dock No.3 during a subsequent watching brief (EPM272). [2]

A large foundation, 4.50m2, had been constructed at a c60 degree angle relative to the dock. This had been built using irregularly laid Portland limestone blocks, although a small number of granite blocks had also been used. At the centre of the foundation was a rectangular recess, into which had been inserted a single 'staple' type iron ladder run on the inner side and a pair of iron ring fittings on the north and south sides. This appeared to be the opening of an inspection chamber which had been part backfilled with modern hardcore. The foundation was excavated to a depth of 0.77m but continued beyond this.

A stone culvert system flanked the above foundation on its north and west sides. The culvert ran north-west to south-east parallel with the foundation before turning west, heading towards a large capstan at the seaward end of the dock. It had been constructed using large flat limestone slabs laid on walls built of limestone blocks. The culvert measured 6.40m east-west x 2.00m north-south, and 4.00m north-south x 1.40m along the western edge.

The remains of a brick built drain gully surviving to a height of 0.40m were observed built into the north-east corner of the culvert. This would have originally enclosed a large ceramic waste water pipe. The bricks and mortar were dated to 1750-1850. The gully turned east at the corner of the culvert and continued beyond the area of excavation. [1]

<1> Watson, Stuart, 2011, Mary Rose New Museum Portsmouth Historic Dockyard Portsmouth Hampshire: Assessment of an Archaeological Watching Brief (Unpublished document). SPM397.

<2> Watson, Stuart, 2012, Mary Rose New Museum Portsmouth Historic Dockyard Portsmouth Hampshire: Assessment of Construction Phase Archaeological Watching Brief (Unpublished document). SPM618.