It's time to set sail and pick some movies!
Let Them All Talk by Steven Soderbergh
The Hunt for Red October
As a german I have to second Das Boot as well, even though I haven't watched it meself yet either.
The Caine Mutiny (1954)
I’m so excited for Master and Commander! Das Boot would be a great foray into a foreign language film. If we pick that one, though, please pronounce the word “Boot” as “Boat”, since that’s how it would be in German ;)
I’d also second The Life Aquatic. Pirates of the Caribbean would be a good one I think to compare-contrast with Master and Commander.
The Big Blue, there will be be a lot to talk about.
The Incredible Story of the Giant Pear - 'Cause y'all need some Danish culture.
Any of these would be pretty interesting:
20,000 Leagues Under the Sea
The Life Aquatic
A Night to Remember
Das Boot and Waterworld!
I would suggest "Das Boot", one of the best german films. However, there are three different versions: the original 150 minutes theatrical cut from 1981, the 290 minutes tv cut from 1984 and a 208 minutes director's cut from 1997. I haven't seen the director's cut yet, but both other cuts are definetly worth watching -- https://en.wikipedia.org/wiki/Das_Boot
Not a movie, my suggestion is useless, but worth a mention: The Rime of the Ancient Mariner by Iron Maiden, and Obra Dinn
Again, useless, but these two came to mind.