You should read Lynn Cox's book, Swimming to Antarctica. She did her early training in that area. It takes an intense and focused person with the physiology to handle the cold water
and big swells not to mention the boat
traffic. Lynn talks about getting separated from her chase boat
one time and having to deal with a large ship heading toward her. Not fun...
Having done some (day time) open water
swims near Half Moon Bay (south of San Francisco), I just can't imagine doing that swim, especially at night!