History and construction

A proposal for a ‘Millennium Tower’ was approved by the Millennium Commission. The Tower’s structural engineering is extremely complex, its complicated shape and design required many mind bending geometric calculations. Not least, before the Tower was built, the space it occupies now was simply sea!

The Spinnaker Tower was conceived to mark the new Millennium and Portsmouth’s proud maritime heritage. Its sail shape symbolises the city’s seafaring spirit, reflecting Portsmouth’s unique maritime history and the harbour’s place as an international location for yachting. The Tower represents a sail billowing in the wind, a design accomplished by using two large, white, sweeping metal arcs, creating a spinnaker sail design but it wasn’t the only option – residents could choose between a “Globe,” a “Triple Tower,” and the “Spinnaker.” Over 60% (30,000) voted for the sail design in 1998. The tower was designed by HGP Architects with engineering by Scott Wilson. Originally called the “Millennium Tower,” delays meant it opened in 2005 under its now famous name

The tower stands on land that once formed part of HMS Vernon, Portsmouth’s torpedo training school and a vital Royal Navy base. Before that, the area was a tidal mudflat, reclaimed over the centuries for naval and dockyard use. To secure the tower on this soft, reclaimed land, engineers sank 84 reinforced concrete piles, each up to 50 metres deep into the seabed. These foundations anchor the 170-metre tower against storms, tides, and shifting ground. The Tower’s base was constructed first by driving 84 reinforced concrete piles into the sea bed, then building what was described by engineers as a concrete ‘cake tin’ on top. More concrete was pumped into this to form its solid base above the water level. These foundations support the weight of the Tower and provide a buffer against any accidental impact from a ship.

The Tower’s ‘legs’ were constructed from concrete by using a unique process called ‘slip forming’. This involved pouring 11,000 cubic metres of concrete into two shafts, one for each leg. Every 12 – 14 hours, as the concrete dried, the shaft was moved upwards. 75 metres were completed in just four weeks with the entire height of the legs taking three months.

The design of the bows was inspired by the shape of a Spinnaker sail, hence the Tower’s name. The steel structure of the bows was fabricated in Derbyshire, England and was transported in sections by road. This process used approximately 1,200 tonnes of structural steel.

The tower’s elegant curves are the result of 1,200 tonnes of steel, fabricated by Butterley Engineering. The sail’s “ribs” were built in prefabricated sections and craned into place high above the waterfront. At its tallest point, the tower is engineered to flex by up to 150 millimetres in strong winds, a movement undetectable to visitors but vital for safety. The steel, if laid end to end, would circle the Isle of Wight twice.

The bottom sections of the bows were lifted into place first. The bows are hollow, like a submarine and contain the lights and part of the fire detection system. There are 50 external lights that can illuminate the Tower as well as 7 aircraft warning lights.  Once the bottom sections of the bows were in place, a crane was used to lift the last 8 metre sections into place, slowly building the bows and ribs upwards over a period of months. There are 570 steps from the base up to View Deck 3, the Sky Garden.

The final dramatic construction phase was the installation of the ‘spire’. Measuring 27 metres, weighing 14 tonnes and partly made of fibreglass, this section was hoisted by one of the tallest tower cranes in the world, with a clearance of less than half a metre! After being lowered into place, it was then bolted to the main structure – the whole process was completed in less than a day! The tower features three viewing decks at 100m, 105m, and 110m, offering sweeping views across 23 miles of coastline. Its most daring feature is the glass Sky Walk, a panel strong enough to hold 2 black rhinos, allowing visitors to look directly down to the harbour 100m below. Today, a high-speed internal lift carry visitors to the top in 28 seconds.

The final stage was to install the 27-metre spire, weighing around 14 tonnes. One of the world’s tallest cranes lifted it into position with just half a metre of clearance – a remarkable feat of precision. The tower’s finishing touches included a specialist white paint, floodlighting systems,  and safety fittings. In total, the project cost around £35.6 millionThe Tower opened to the public in 2005. The concrete used to create the Tower would fill five and a half Olympic sized swimming pools and the steel used would stretch twice around the Isle of Wight. The structural steel used for the Tower’s bows weighed 1,200 tonnes, the equivalent of 12 blue whales!

When the tower opened on 18 October 2005, more than 1,000 visitors came through the doors in just three hours double what was expected. It quickly became the symbol of Gunwharf Quays, a major redevelopment of the former naval base into a waterfront destination with shops, restaurants, and leisure spaces. Today, the Spinnaker Tower is not only Portsmouth’s most recognisable landmark but also a focal point for the city’s regeneration story, attracting tens of thousands of visitors every year.