Built from concrete, glass and steel, two bows and shafts rise from ground level to merge and form a sail shaped structure which will be the tallest accessible tower outside of London.

Three elevated viewing platforms 100m to 110m above the harbour are suspended between the shafts and bows.

The tower required 11,000m 3ofconcrete, its steel bows are made from 1,100 tonnes of structural steel and there are some 200km of steel reinforcement in the deck and shafts.

The Spinnaker Tower's foundations involved 84 large diameter steel piles driven up to 50m into the seabed for a total piling length of 3.3 km.

Supervising engineers Mouchel Consulting Ltd, acting on behalf of Portsmouth City Council, commissioned FES to carry out the initial site investigation to determine ground and groundwater conditions. To conduct the drilling in tidal waters, FES mounted a multi-purpose drilling derrick for both cable and rotary operations on a floating spud-leg platform. The rotary-cored sections of the deeper boreholes were achieved using a Pilcon marine power swivel assembly and a Geobore 'S' wireline coring system with polymer as the flushing media.

Four cable percussion boreholes 200 mm in diameter were drilled to depths of 18.5m.

Three of these were extended by rotary coring to a depth of 50m.

Several Standard Penetration Tests using a split-spoon, field-vane tests, and nine Self Boring Pressuremeter tests were successfully completed at intervals specified by the Engineer.

MJ Information No: 18228