Boy - things have changed. When I worked on ships we could just say "um, please make my air ticket out for a few days later, i want to stay in the port a couple of days.
That was WAY back when, though. I actually understand very little of what these people above are saying.
I know as a US citizen when I disembarked in Germany I was simply on my own - I had a passport and I spent 3 weeks touring Europe. When I was flown to a ship, I happened to be going to Hawaii, so I flew in a few days early and just laid on the beach.
There are a LOT of organizations that work specifcally with "seamen" worldwide, though, and if you work on ships it is worth getting to know them. You can find cheap rooms to sleep in and cheap places to eat in many port cities that way.