Offshore drilling of large diameter holes in rock formations

Apparatus for drilling large diameter vertical holes in rock outcroppings on a sea bed, said apparatus comprising a drilling structure including legs extending up from the sea bed to a location above the surface of the sea, a platform supported by said legs above the sea surface, a drilling mechanism on the platform, said drilling mechanism including a rotary rock drill cutter assembly, a drill string extending up from the rock drill cutter assembly, a rotary driver on the platform to rotate the drill string and a lowering device on the platform to lower the drill string, and a drill guide secured at its upper end to said platform and having its lower end resting on the sea bed, said drill guide comprising a plurality of spaced apart vertical guide rails and a plurality of vertically spaced apart supporting sections, each supporting section interconnecting each of said guide rails and maintaining same in a rigid open framework configuration with minimal surface area to minimize stresses produced by waves and current and drill string centering elements arranged to move up and down along said guide rails to hold said drill string centered therebetween, whereby said drill string and cutter assembly are maintained in proper orientation for beginning a drilling operation and said frame assembly provides substantial rigidity with minimal resistance to waves and currents from the sea.