Monument MPM1099 - Tunnel Connecting Mast Pond to Harbour, Portsmouth Dockyard

Tunnel connecting the Mast Pond (now a boat pond) in Portsmouth Dockyard to the Harbour via the South Camber. A channel appears to have been located in much the same position since 1668. This was covered over and lined with stone during the 18th and 19th centuries. Additional gates were added to form a lock in the 19th century when the Mast Pond began to be used for repairing boats.

Tunnel connecting the Mast Pond (now a boat pond) to the Harbour via the South Camber. A channel appears to have been located in much the same position since 1668. This was covered over and lined with stone during the 18th and 19th centuries. Additional gates were added to form a lock in the 19th century when the Mast Pond began to be used for repairing boats. An approximate location for the tunnel has been added as a polygon to the HER record.

A short recording exercise was carried out on the channel during refurbishment works in 1999. This revealed that the channel appears to have originally been a simple cut, with a single gate controlling the water level and allowing easy passage for masts. It is likely the inner covered end was stone-lined by 1743, the style of stonework recorded being consistent with this date. The outer end of the tunnel appeared to have been lined with stone when Boathouse 4 was built in the 19th century, and a three gate system for controlling the water level almost certainly dates from this period. The Mast Pond's change in use to boat repair was reflected in two of the three gates forming a lock. The stonework in the gated section of the channel is different to that in the tunnel, and is of a later date.

The cartograhic evidence shows a channel in much the same position in 1668. At this date the channel appears to have had an open top with a gate near the inner end, the outer end being wider than the centre. The 1716 map shows a wider gate, which probably carried a walkway. By 1743 most of the Mast Pond end is covered, and there are faint lines, possibly representing a tunnel.

The floors of the tunnel and chambers are made of stone, with timber fixed by iron dog-spikes in some places within the lock chambers. The lock walls are made of large squared and dressed ashlar blocks, with two vertical channels cut on either side. These were possibly for the use of stop-boards for the emergency control of water levels. A slight difference in the angle of the line of the tunnel and lock chambers, the stone blocks in the tunnel being smaller than those in the locks, and the tool marks running diagonally rather than vertically, would suggest that the lock chambers were constructed much later than the tunnel. The cartographic and documentary evidence would appear to support this theory. It is unclear whether the tunnel structure itself was built in more than one phase.

The three gates were noted to appear to be too close together to allow access to the size of boats known to have been in use during the 19th and 20th centuries. It was suggested this feature would warrant further investigation.

[1]

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The tunnel entries are segmental-arched with giant voussoirs aligned to the stonework courses, and at west end are recesses for former lock gates (added 1797, Riley p7). The west entry ( off South Camber) appears to have the quay wall built up against it (indicating possibly earlier date of tunnel).

Source: RC Riley - Title: The Evolution of the Docks and Industrial Buildings in Portsmouth - Date: 1985 - Journal Title: The Portsmouth Papers - Page References: 3-12

[2]

<1> Higgins, P & Barnes, I, 1999, Summary Report on an Archaeological Watching Brief at Boathouse No. 6 and the Recording of Boathouse No. 4 Locks, Portsmouth Dockyard, Hampshire. 1999 (Unpublished document). SPM117.

<2> Historic England, The National Heritage List for England (Index). SPM35.