Concave 'spoon' decks in surfboards

There's a lot of talk lately about surfboards with 'S' decks, step decks, concave decks and other deck shapes.Concave decks come in two varieties: Fore and aft concave and athwartships concave. Some surfboards are concave in both axes, for example the late model Greenough spoons.The main advantage of a concave deck is that for a given surfboard volume, it makes the board thinner in the riding area, this lowers the centre of gravity and the centre of effort of the surfboard and rider, and keeps the surfer's feet closer to the bottom area, which improves handling and control.Decks which are concaved in the fore and aft direction make the board tend towards a parallel profile, this also increases the flexibility of the board:By using a parallel profile we get the maximum possible fore and aft concave:Here the plank lines reveal the concave:.