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 performed while under sail. Due to the size of spinnakers (the spinnaker is often double or more the size of the mainsail) this can be a difficult operation, since the sail will immediately catch the wind. Typically the symmetric spinnaker is packed in its own bag, called a "turtle", with the three corners on top for ready access. The clews (lower corners) are controlled by lines called "sheets". The sheets are run in front (outside) of the forestay and lead to the back of the boat. The head (top corner) is attached to the spinnaker halyard, which is used to