Unless your ocean-colony is going to be setting up shop in the South China sea I wouldn’t worry too much about the pirates…
There’s no way you can maintain a viable culture on a ship indefinitely. You can’t maintain it, you can’t spare the manpower for things like research, teaching, child care, etc. A technological society needs millions of people working together.
So you have to have contact with the ‘outside world’. Why not make that part of the plot of your story? If a bunch of people decided to go off and live on a ship, they’d have to make strategic partnerships with various groups to provide them with hardware, fuel rods for the nuclear reactor, specialists to fix problems that people on board can’t do, etc.
So what happens if this society of maybe 50,000 people is living on a giant mother of a ship, and a critical partner on shore reneges on their agreement? The reactor has a year of operation left, and the country who was going to supply replacements has been overthrown and the new dictator refuses to honor the agreement. What now?
How do the people defend themselves? How about a plot where some government decides that the people on the ship should be taxed? Or an environmental group thinks they are a danger to the world because of their large nuclear reactor, and tries to stop them? Or a world government forms, and decides that the way the people on the ship live is not right, and decides to regulate them? Then the people on the ship have an ace or two up their sleeves, and intrigue ensues…
I would also suggest reading Damon Knight’s CV. Your idea sounds a little similar, but hopefully without the whole alien intelligence thing that makes the novel kind of weird.
Whew. I was on a one-week vacation which is why I haven’t responded to the excellent posts here. Thanks all (especially Sunspace and Tuckerfan), I’ll check out all the links and literary works.
I started out just trying to see if this could be reasonably done, as the ship civilization is not the main thrust of the story; it’s just there for background. Then I got fascinated by it as this discussion drove on, and now I’m starting to really wonder if this could be done… but I don’t think I can find a few thousand people to help me find out.