eh, there are lots of "green" sources of energy that would maintain jobs in the US maritime industry.
Offshore wind is one, ocean thermal energy conversion is another. An OTEC offshore plant would look very much like an offshore oil rig, requiring merchant mariners to supply it and people there to operate it. The difference is that instead of pumping up fossil fuel, it pumps up water. Surface water heats ammonia to the boiling point, and the steam turns a turbine.
These guys have an experimental onshore OTEC plant in Hawaii, and are planning an offshore one that will be far more powerful:
Makai OTEC plant
Lockheed is also interested:
Lockheed OTEC project
As far as offshore wind, that involves 200 foot tall slowly turning wind turbines that float on the surface of the water. They're connected to each other and to the shore. Of course it requires merchant mariners to go out on ships to maintain the wind turbines. Statoil just got a contract in Scotland to build a small pilot/experimental floating offshore wind plant:
Statoil offshore wind projects
There's a company that wants to build a floating wind power plant just south of the Bay Area, here in California. I hope they get to do it. It is a great idea. And it will employ people to build it and it will require merchant mariners to maintain it.
So yeah...I think you guys sound just like people complaining about how there wouldn't be jobs to take care of horses because the car was going to replace them. Well, lots of people make money taking care of cars, now, instead of horses. People used to say, oh these personal computers, they're so horrible, this paperless office will eliminate so many jobs, what will happen to the people who make money pushing paper? Well, businesses still deal with documents and files, but they're all on computers. And people make lots of money in Information Technology. Indeed, people even said that about engines replacing sails. Oh no! Where will all the jobs go now that a ship won't require all those people to operate the rigging??
Fossil fuel power will go away. It is rapidly becoming obsolete. The last new coal plant will probably be made in this decade. The people who currently operate fossil fuel power plants will get new jobs, working on Wind or Solar or Nuclear instead of Coal.
There will be offshore platforms in the future...but they will be OTEC or Floating Wind platforms. The ships that maintain them will run on hydrogen generated in port from seawater using green energy sources.
IEEE Spectrum article on floating offshore wind platforms.
Article about what kind of boats and ships are needed to work on offshore wind platforms.