This from the park's website shows details.

Chantey Sing Saturday, September 7, 8:00pm–12:00. No fee. Aboard an historic vessel at Hyde Street Pier. Reservations required: call 415–556–6435 or email peter_kasin@nps.gov Sing traditional working songs aboard a floating vessel. Bring a cushion, a mug for hot cider, and join the fun!

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