Before heading out on a recent passage, my significant other teased me about having "a girl in every port." I retorted that the only thing I wanted to get in every port was a nap. The truth is, the days of a ship pulling into port for days or weeks at a time are over: it is the rare crewmember with time to hook up in every port.
Turnaround times vary with the type of vessel. The ships of the Alaska Marine Highway System only spend a couple of hours or so in port on a scheduled run. Cruise ships will usually spend a little bit longer, from a few hours to day. A ship carrying “break-bulk” cargo -- cargo that is carried in the ship’s holds or on deck in small, various-sized containers or crates – may spend one to three days in port. A container ship, one of the giants carrying hundreds of forty-foot standardized containers, will spend less than a day in port, the average being around sixteen hours.
These huge container ships are expensive to run: $30,000 to $40,000 a day. Shipping companies are always looking for ways to trim the time spent in port, using complex computer models to determine the best container arrangements, loading and unloading strategies, and other ways of trimming hours off a port call. The mariners on board have little, if any, time to get off the vessel and look around. A quip common among modern mariners is “join the merchant marine and glimpse the world.” And even if they had time, there is little to see: modern container terminals all look much alike, owing to the standardization of equipment and vessels. Container ports also tend to be far from urban centers and tourist areas and require huge areas to service not only the vessels, but the rail cars and trucks that take the containers to their final destinations. The nearest “waterfront” bar can be miles away.
Crew on US Navy ships may be spending more time in port due to recent budget changes. A navy crewmember can expect only about a week out of every twelve or so underway for “routine operations.” This can vary a lot, of course, depending on a ship’s particular mission. Smaller ships tend to spend more time in port than larger ones, like aircraft carriers. Port calls during a deployment for any vessel rarely last longer than a few days, but time between ports is usually less than a month.
US Coast Guard cutter deployment times are similarly variable, going out on various missions for a few weeks to a couple of months, then returning to their home port for a few weeks.
Even if a vessel is in port, that doesn't mean the crew has time to go ashore and mess around. Port calls, especially for vessels that only make short ones, can be the busiest times for a ship's crew. A port call is a time to unload passengers, cargo, and garbage and a time to take on new passengers, cargo, stores (groceries and other supplies), fuel, and fresh water. "There's always something to do on a ship," the saying goes, and a lot of work gets done in port (painting, etc.) that can't be done as easily underway. But, if you're lucky, you'll get a few minutes off to call home and tell them about all the interesting things you've glimpsed.
To see just how closely the whole issue of containerization is studied, see Intelligent Freight Transportation by Petros A Ioannou. Google Books has good excerpts (amazon.com has the full book for $140, if you're really that interested) at http://books.google.com/books?id=-HI1YZarRAkC&pg=PA13&lpg=PA13&dq=container+ship+turnaround+times&source=bl&ots=SfAmO56v-M&sig=NGwVHVqVlBaumarLHv9Rf8JCz8c&hl=en&ei=795OSuvNOpHasgPAv-yqDQ&sa=X&oi=book_result&ct=result&resnum=1.
For a less technical discussion on how it all got started, see Marc Levinson's book The Box: How the Shipping Container Made the World Smaller and the World Economy Bigger.