Building MPM792 - NUMBER 6 BOATHOUSE (BUILDING NUMBER 1/23) AND SLIPWAY TO FRONT

Boathouse designed by Captain RS Beatson RE in 1845. A watching brief carried out during refurbishment work in and around the building in 1999, revealed construction trenches for the boathouse, and a line of wooden stakes thought to relate to an 18th century system to control water flow. Evidence of boat-building was suggested by a number of wood shavings.

Boathouse designed by Captain RS Beatson RE in 1845.

Listed Building Entry:

Includes: No.6 Boathouse (Building No. 1/23) and slipway to front, MAIN ROAD HM NAVAL BASE Mast house, then boathouse with slipway at front. 1845; bomb-damaged 1941. Designed by Captain RS Beatson RE, contractor Mr Rigby. Yellow brick in ashlar bond with ashlar dressings, with internal cast-iron frame. Replacement mid-late C20 corrugated iron roof with roof lights. EXTERIOR: 3 storeys, on west side the ground level being lower to give access to adjacent mast pond. 5-sided, the rectangular plan having diagonal wall built across south-east corner. The bomb damage was to the east end, where the building remains a shell with first-floor windows blocked and 2nd floor missing. Ashlar plinth, to west elevation; band over ground floor; eaves band and cornice. Windows have flat brick arches, projecting ashlar sills, and CZO replacement metal windows; they are shorter on ground and 2nd floors. Loading doors have eared ashlar architraves with tripartite keystones. West elevation: 9 bays, 3 central bays breaking forward. At centre of each 3-bay section a large round- arched entrance with imposts, keystones, studded double board doors, fanlights, and lamp on left of central door. Iron mooring rings at low level. A brick chimney rises behind parapet at right-hand corner, tapering and corniced. Slipway along front, sloping down to Mast Pond (qv), is of stone setts with iron mooring rings and a track of granite slabs with iron rollers leading up to each entrance of the boathouse (that leading to the right-hand entrance now built over). North elevation: 15 bays, with 2-bay end breaks and 3-bay central break which has a central loading door on each floor, now blocked. East elevation: 6 bays, with loading doors on each floor of bays Z and 5. South-east elevation: 5 bays with central loading doors. South-west elevation: 11 bays with central3-bay break which has central loading doors, that on 1st floor with crane. Double board door to ground floor of bay 3. INTERIOR: cast-iron columns; cast-iron segmental-arched beams across shorter spans, and cast-iron trussed beams across wider spans. On 3rd floor, braced rivet ted steel roof trusses. Wooden floors. On ground floor, 3 slipways with a double row of columns between (14 columns to a row); above the central slipway the ceiling is open, to allow mast- fitting. At west end is a trap door, strengthened by Z extra columns. HISTORY: designed by Beatson to take an exceptionally heavy load, and of interest with his other work at Portsmouth, the Fire Station and Chain Testing Shop (qqv). This must have been one of the last uses of trussed beams before the 1847 Dee Bridge disaster enquiry discredited their use. A contrasting design to the traditional timber 1844 Lower Boat House at Chatham, and the innovative 1859 Boat store at Sheerness designed by GT Greene. Boats could be lifted internally through to the upper floors. Lloyd (1974) observes that "This is one of the earliest buildings where load-bearing iron-framed construction is used on such a massive scale, and with such sophistication". (Sources: The Buildings of England: Lloyd D: Hampshire and the Isle of Wight: Harmondsworth: 1985: 410 ; Portsmouth Naval Base Property Trust: Naval Heritage at Portsmouth, Visitor's Guide: Portsmouth: 1988; Lloyd DW: Buildings of Portsmouth and its Environs: Portsmouth: 1974: 72).

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A massive stone structure built in 1843 to take heavy loads on the first and second floors. The girders used in its construction are at least 1ft thick and have been strengthened by underslung trusses and are supported by iron columns. It is thought to be the earliest example of the use of stressed cast iron. The following has been inscribed on each girder 'The load on this girder should not exceed 40ft equally distributed over its length.' Vessels could be hoisted from the slipway for repair via openings in the floor. In 1984 the boathouse was still used to repair wooden whalers and small craft and housed Brunel's scoring machine and a spile machine for the mass production of wooden pegs. Both of the machines were still in use in 1984.

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A watching brief carried out during refurbishment work in and around Boathouse No. 6 in 1999, revealed construction trenches for the boathouse, and a line of wooden stakes thought to relate to an 18th century system to control water flow.

Inside the building, a contruction trench filled with concrete was revealed below a line of cast iron pillars. This trench and its fill appeared to be part of the original construction method used for the boathouse.

In area of level reduction for a new staircase outside the boathouse, a series of modern deposits overlay a cobbled road or path surface. This cobbled surface sealed a levelling layer, which had been cut by a foundation trench for the boathouse. The foundation trench was filled by the wall of the boathouse and loose shingle. A trench excavated to a depth of 2.2m where the base of the staircase was to be constructed, contained several layers, including a brick rubble levelling layer and a partly cobbled surface. The cobbled surface post-dated the construction of the boathouse, and was possibly part of a road, path or hardway. Modern artefacts were recovered from the fill of a large cut observed in the east facing section of the trench. This feature was interpreted as a recent disturbance, due to levelling and ditch-cutting.

A line of wooden stakes across a pit were revealed at the piling level in the same trench. The pit (211) had two fills, and cut an earlier channel which sloped down from east to west. A later cut (214), appeared to be a re-cut of at least part of the pit. The stakes appeared to have been rammed through the bottom of the pit into the natural deposits. The northernmost stake had been inserted at an angle, and there were indications the southernmost stake was inserted at an angle to correspond. A decayed wooden spread observed over the bottom of the pit and the higher side of the line of stakes, suggests that boards may have run along the line of the stake alignment. These features were dated to the early 18th century, and may relate to a system to control water flow, although its purpose is unknown. A large number of clay pipes dating to the early 18th century and post-1850 were recovered from the pit features.

Twenty-four small wood shavings were recovered from the fills of the pit (211) and later cut (214). Most of these shavings appeared to be short and relatively thick, which suggests they may have resulted from the use of a plane, spoke shave or similar tool. This would be consistent with the process of masting vessels, which is known to have taken place either at, or near, the Mast Pond.

The ramp leading from the Mast Pond to the Boathouse was also examined during the watching brief, although this was not affected by the refurbishment work. The rails had been replaced by a set of rollers to enable craft to move in and out of the work area. Both the rails and the rollers were of a later date than the cobbled surface of the ramp.


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A watching brief in 2025 recorded layers of made ground in geotechnical pits excavated beneath the existing concrete floor which may have related to the construction of the boathouse.

Borehole test pits excavated outside the building to the east and south contained rubble layers which may have related to dismantling and rebuilding following Second World War bomb damage.

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<1> Historic England, The National Heritage List for England (Index). SPM35.

<2> Moore, Pamela (ed), 1984, A Guide to the Industrial Archaeology of Hampshire and the Isle of Wight (Bibliographic reference). SPM470.

<3> 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.

<4> Hughes, V, Trim, P, 2025, National Museum of the Royal Navy, No. 6 Boathouse, Portsmouth Historic Dockyard: Archaeological Watching Brief (Unpublished document). SPM678.