The Aker H-3 is a series of self-propelled semisubmerisble 3rd-generation rigs, popular in the 1980's. In the early 1990's, most if not all of these rigs underwent upgrade programs. 37 were built in all (out of a total of 44 3rd-generation semisubmersibles), making them uniquely prolific.
Design work commenced in 1968. The rig was designed for the harsh weather conditions and depths of the North Sea's continental shelves, particularly pertinent to the Norwegian oil & gas industry, considerably more strenuous than the dominant Gulf of Mexico environment. Sales consultation began in 1971, with the first rig entering production in 1974.
The Aker H3 original design consisted of an 8-column, dual pontoon unit with columns squared off top & bottom. The columns additionally have lateral pipe supports across the bottom, and individual diagonal bracing to the rigs deck (truss-bracing).
Despite the upgrades, the H3 rigs as a whole are somewhat aged and starting to show the limitations of their size. With offshore oil moving into deeper, harsher environments, H3 modernization solutions have been developed (see Fred Olsen), but cannot match the flexibility & range of capabilities of the newer, larger semisubmersibles now available.
Aker has continued evolutionary development of the H-3 design; see