There are three major categories of information available about marine casualties: documents produced during the course of accident investigations (including the final reports of those investigations and the primary source documents they rely on), journalism about specific accidents, and scholarly or academic treatments of categories of accidents or factors that contribute to accidents.
The links to the left will allow you to explore these three categories. Once you have decided on a particular accident to research, the quickest way to find detailed information is usually through the NTSB and USCG investigation reports, which you can access below, as well as from the U.S. Government Resources page.