The Cutty Sark has been decaying in a dry dock at Greenwich for 50 years. But now architect Grimshaw has designed a cocoon to protect the record-breaking clipper during restoration.

Its days voyaging the high seas may be long behind it, but the Cutty Sark is still in peril. Time, weather and an unevenly supported hull have all contributed to the decay of the iconic Victorian tea clipper. In a worst-case scenario, it could soon be too dangerous to board.

Yet help is at hand in the form of a radical plan to restore the ship and build an exhibition centre to give tourists a richer experience. Architect Grimshaw has been engaged by the Cutty Sark Trust to design a solution that glazes over the ship’s dry dock and uses the space underneath as an exhibition floor. But because the boat could first take up to five years to restore, Grimshaw has also developed an eye-catching transparent ETFE temporary structure that enables visitors to watch the progress of the restoration (opposite). Now it’s just a case of raising the small matter of £25m.

It’s a high price, but supporters say that the illustrious past of the Cutty Sark richly deserves it. It was built in 1869 to import the new season’s tea from China as quickly as possible. It was subsequently used for the wool trade and broke records for the fastest time between Australia and the UK. In 1954 the ship was placed in a specially constructed dry dock at Greenwich, south London, and opened to the public. Since then, it has sat on a concrete plinth and been kept upright by a series of angled steel spars.

Grimshaw’s solution intends to change this arrangement for the first time in 50 years. “Our proposal is to lift the ship within its berth by 2 m and use the dry berth as habitable space,” explains Simon Beames, Grimshaw’s project architect. “The dry berth has a floor area of 1000 m2. At the moment it is underused, undervalued and detrimental to the public realm.”

To evenly support the hull, the boat will be suspended in a giant basket made from Kevlar, a super-strong fabric used for making bulletproof vests. This will support the hull in the same way as the sea once did. While the boat’s timber and interior are being restored, the metal cladding on the hull will be removed and the basket fixed in place. The cladding will then be replaced so the basket is hidden.

Steel beams cantilevering from the side of the dry dock will support both the Kevlar basket and the roof of the visitor centre, which will be made from glass curved in two directions to look like waves. This is proving something of a challenge for both architect and structural engineer, Adams Kara Taylor, as glass curved in two planes has never been used in a construction project before. Beames has located an Italian glassmaker, Sunglas, which is prepared to take the risk of making the glass. Meanwhile AKT has to design the supporting structure and work out the best way of arranging the glass cover. “You are trying to put a boat shape into a rectangular box, which is not easy,” says Albert Taylor, partner at AKT. “We are exploring a number of options to find out the best way of arranging the glass. We are also putting a lot of work into minimising the supporting structure. We want it to disappear so you concentrate on the boat.”

When the centre is finished, visitors will enter from Cutty Sark Gardens via a ramp. Because the boat is raised by 2 m, visitors will be able to fully appreciate the elegant hull. “The form of the hull within the dry dock is quite extraordinary,” says Beames. “It has a dynamic form similar to that used by iconic buildings such as the Bilbao Guggenheim.”

Visitors will be able to appreciate the ship as it was in its heyday. The ‘tween, or middle deck, will be stripped of an exhibition and gift shop. Interventions such as stairs will be made to look obviously modern to distinguish them from the original ship.

However, before things get to this stage the boat has to E E be restored (see ‘Stop the rot’, right), a task that will cost £12m. A 50 m high ETFE capsule will protect the ship during restoration and allow visitors to watch progress. The capsule will be supported by special beams called Tensairity made by Airlight which, despite being 1.5 m in diameter, are also transparent. The beams consist of a pressurized ETFE tube and thin metal strips that carry compressive loads (see detail on previous page). Wire cables wrapped around the tube carry tensile loads, and the ETFE tube prevents the compression members from buckling. Assembling the beams is straightfroward: the main spine will be pressurised on the ground then lifted up and bent into position. Secondary beams can then be attached. To prevent the capsule from acting as a giant sail and blowing over, it is also perforated. Wind turbines within the perforations will generate the power needed to keep the ETFE inflated, neatly reflecting the ship’s original source of power.

The proposal has universal support from all consultees and amenity groups, an impressive achievement considering that the ship sits in the middle of a UNESCO World Heritage site. “It’s an iconic statement that is good for Greenwich,” says Beames. “We presented it to the planners and the World Heritage committee and they have been more than supportive of the proposal.” Local groups, such as the Greenwich Society, also supports it.

Everything now depends on the Heritage Lottery Fund, which is considering an application for a crucial £11.75m grant. By the end of the year, it must decide whether or not to answer the venerable Cutty Sark’s distress signal.