Abstract: A building being erected is aligned with the vertical by projecting a main laser beam horizontally and splitting it into a vertically reflected test beam that is received on the building and used to ascertain proper alignment thereof with the vertical and a horizontally reflected adjustment beam that is received at a detector having an array of receptors around a central receptor. So long as the adjustment beam is received at the central receptor, the proper vertical positioning of the test beam is insured. If the adjustment beam moves off the center receptor, however, a positioning motor connected to the projector is actuated to reposition the main beam and the splitter to as to realign the adjustment beam with the central receptor and simultaneously realign the test beam with the vertical.

Abstract: A system for anchoring drilling or production platforms upon a plurality of posts anchored in the sea bottom or on an artificial island comprises a cylinder structure formed at the top of each of the posts and a plunger depending from a semi-submersible platform adapted to be received with clearance within each of the cylinders. The platform is provided with sand bunkers adjacent the respective plungers and with releasable closures which open upon positioning of the platform above the posts to cause granular material to flow into the cylinder around the respective plungers, thereby cushioning the engagement of the platform by the posts.