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 wind (reaching) develop most of their lift on the forward quarter, where the airflow remains attached. When correctly set for reaching, the leading edges of a symmetric spinnaker should be nearly parallel to the wind, so the flow of air over the leading edge remains attached. When reaching, the sail camber allows only some attached flow over the leeward side of the spinnaker. On running the spinnaker is angled for maximum drag, with the spinnaker pole at right angles to the apparent wind. The symmetric spinnaker also requires care when packing, since the three corners must be available on