Two of my favorite books on the subject:
The Handbook of Ocean and Underwater Engineering, edited by Meyers, et al. There's a second edition that's expensive; you may be able to find an inexpensive copy of the 1969 edition on EBay or some other auction website.
Introduction to Offshore Structures by W.J. Graff, published in 1981 by Gulf Publishing.
The handbook is one of the best all-around refererences for work in the ocean and possibly the only one that doesn't require post-doctoral work in mathematics to use in a practical matter!
The latter is a great explanation of the history of offshore structures, steel jacket design and concrete gravity platform design.