How is that SFist has not heard of this event until now? The National Maritime Museum, at the Hyde Street Pier at the very end of Fishermans Wharf, hosts a chantey sing on the first Saturday of every month! All are welcome, but you have to reserve in advance (call 415-556-6435) and bring your own mug for cider. No word on whether the mug may be used for more potent potables as well.
In case you were wondering, a chantey is a work song sung by sailors to keep everyone moving together (for onerous tasks like hoisting the sail, clearing the bilge, or lifting the anchor), in contrast with a forbitter, which is a song a sailor sings just because hes happy. And drinking songs well, you can probably figure out when a sailor sings a drinking song now, can't you?
The Maritime Museum is also having a festival of sea songs in October! Accordians look to be prominently featured! This is awesome!