The components of a typical wingboard are the Wings, a dark red/brown in the illustration, the Deck with its legs , shown in yellow and the Spyder which is dark grey/black in the illustration. The foot straps are attached to the Spyder and shown in bright yellow.
The role of the Spyder is to connect you, your weight and effort, via your two feet to the centres of lift of the two wings – that’s all – it’s virtually unconnected to the Deck, it is trapped inside the Deck moulding so they don’t fall apart but in use they act independently. You are directly supported by the centre of lift of the wings. The Spyder will have to be quite strong and rigid and will probably be made of carbon fibre and, unlike in the illustration, may be practically invisible, hidden inside the Deck.
The Decks job is to provide a depth reference for the leading edge of the wings by planing across the surface of the ocean while dragging the wings through the water beneath it by means of its Legs, (which also serve as fins for directional stability). The depth the Deck holds the Wing at is important, a wing needs about as much water covering it as its own chord, leading edge to trailing edge, to work properly. The planing of the Deck should be as efficient as possible but since it is not carrying any weight its drag will be minimal anyway.
The Wings are the stars of the show, providing the lift necessary to carry the rider with minimum drag. The high efficiency of the Wings, compared to planing surfaces, allow the use of much less steep regions of the water surface for playing in, along with much higher speed potential in the more active zones.