Emirates Spinnaker Tower two large, white, sweeping metal arcs, which give the tower its spinnaker sail design. The steelwork was fabricated by Butterley Engineering. At the top is a triple observation deck, providing a 360° view of the city of Portsmouth, the Langstone and Portsmouth harbours, and a viewing distance of . The highest of the three observation platforms, the Sky Deck, has only a wire mesh roof, so visitors are open to the elements. The windows extend above head height, so it is not possible to get a view unobstructed by glass. A glass floor is located on the first viewing deck
Spinnaker the top of the packing. Asymmetrical spinnaker resembling large jibs and flown from spinnaker poles are not a new idea and date back to at least the 19th Century. However in the 1980s a new concept appeared, starting with the Sydney Harbour 18ft Skiff fleet. Since the 1960s many faster sailing craft, starting with catamaran classes, had discovered that it is faster to sail downwind on a series of broad reaches with efficient airflow across the sail rather than directly downwind with the sails stalled. This technique had developed to the extent that in bar conversation at the end of