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Sea drilling tower (Fife), site of
St David's Harbour, Fife, Scotland, UK
associated engineer
Guy Anson Maunsell
Maunsell, Posford & Pavry
date  1954 - 1955
UK era  Modern  |  category  Mining/Quarrying  |  reference  NT285884
In the early 1950s, engineer Guy Maunsell designed two sea drilling towers for the National Coal Board, which were used to assess the extent of undersea coal reserves through analysis of borehole cores. The first was successfully deployed in the Firth of Firth near Seafield Colliery (closed 1988) in Fife. The second was in Northumberland, and both are now demolished.
The design of the towers was reminiscent of the army sea forts that Maunsell designed for sea defences in the Thames Estuary (1942-3), in that they consisted of large steel pods mounted on slender tubular legs. However, the drilling towers were intended to be moved around to different locations. As with the forts, Maunsell's colleague John Posford had the task of overseeing the structures' deployment.
The bases of the towers, which rested on the sea bed, were X-shaped in plan. Each leg of the ‘X’ was a steel box girder 49.7m long, 900mm wide and 2.1m deep. The chambers inside the girders could be filled with either air for transportation or water for ballast.
Inclined tubular steel legs 610mm in diameter were connected to the ends of the box girders, cross-braced diagonally with 460mm and 380mm diameter tubes. At some 20m above the base of the girders, the legs were 13.7m apart and continued vertically upwards to the underside of each tower's pod, 18.3m above. These vertical sections were also cross-braced diagonally and had raking support tubes from the legs to the edges of the pods below the decks. All 90 tubular steel members on each tower, and their joints, were prefabricated and sealed to prevent corrosion.
The octagonal steel pods were 25.9m wide and each had two timber decks, one for the crew accommodation and power supply, and one for the drilling rig, the workshop and a 2 tonne mobile crane. Power came from three 50kW diesel generators and fresh water was obtained by distilling sea water. The towers were floodlit to allow 24 hour drilling.
Each complete tower weighed some 500 tonnes and was 56.4m tall from base girders to the top of the drilling rig. They were designed to resist winds of up to 129km/hour and waves 9m deep (crest to trough). A motorboat was provided to move crew members, supplies and drill cores between tower and shore.
The structures were not self-propelling and for towing into position, the cruciform box girder base of each was shackled to a pair of pontoons and cross-braced by 460mm diameter steel tubes 28.8m long. Each pontoon had two electric winches and a 6kW auxiliary generator.
The drilling equipment used on the towers was the same as comparable land drilling rigs of the time, except that the drill rods were protected by a 610mm diameter steel tube 44.2m long driven into the sea bed to prevent sea water entering the borehole.
The first of the towers was constructed in the Fife shipyard of James A. White & Co Ltd, at St David’s Harbour near Inverkeithing, north-east of the Forth Road Bridge. It was towed into its first position 1.6km offshore of what was Seafield Colliery (see map) on 22nd May 1955 by three Admiralty tugs, aided by a mooring vessel.
The first borehole drilled was some 550m deep and took nine months to complete. The tower was moved later to a second position 4.4km offshore. It was used at a further six locations before being scrapped.
A second tower was constructed at Blyth in Northumberland in 1955 and was deployed 6.4km offshore of Blackhall Colliery (NZ461397) near Peterlee in County Durham. It was operational from August 1958, working in 30m of water and drilling into the sea bed at an average rate of 8.8m per day. In January 1959 it was moved 3.2km further north.
National Coal Board chairman Lord Robens (1910-99) visited the second tower in October 1961. Between 1958 and 1966, it drilled 18 boreholes 600m deep in the North Sea and proved that there were 560 million tonnes of workable coal offshore of County Durham.
Contractor (Fife): Cleveland Bridge & Engineering Co Ltd
Tubular steelwork (Fife): Tubewrights Ltd
Tubular steelwork fabrication (Fife): Stewarts & Lloyds Ltd, Clyde
Drilling (Fife): Foraky Boring & Shaft Sinking Co Ltd
Generators (Fife): Crompton Parkinson Ltd
Research: ECPK
"Positioning the sea drilling tower", in Colliery Engineering, Tothill Press, London, July 1955
"Sea Boring”, in Colliery Engineering, Tothill Press, London, January 1959
"Maunsell: The Firm and its Founder" by Nigel Watson and Frank Turner, AECOM Technology Corporation, 2005

Sea drilling tower (Fife), site of