Model of an Artificial Reef

Seen from above, they are octagons with sharp points in the corners. In side view, they look like inverted pyramids with anchor chains at the bottom point. The lower part of one is an inverted pyramid with a square base, closed with planks (C); in the second, the same part is a pyramid with an octagonal base, closed with planks, with an anchor on the chain and the radial beams are supported by knees (B); the third is left open and also has knees to support the radial beams. A central standard connects all construction elements (A). [combined description]