I've done some digging around on Wikipedia. Here's some thoughts.
Setting: 1715. Treaty of Utrecht ends Queen Anne's War (War of the Spanish Succession). Thousands of sailors, privateers, and paramilitary are out of a job. Cross-Atlantic colonial shipping trade is on the rise. Many normal, well-adjusted, but poor people are turning to piracy to pay the bills, while true-blue, crazy-eyed pirates are happily accepting all the fresh recruits. Even the normally law-abiding merchants of colonies and countries alike are overlooking - even funding - pirate voyages in the interest of profit.
Hook: The captain (or sponsor) of [your ship here] comes across a book describing the Lost City of R'lyeh, a city where an "ancient god and all His treasures" waits to be discovered. The book doesn't show the way to the lost city, but does hint that the book's author still lives in Ponape, one of many seemingly innocent islands in the Pacific region. It's a long way from your normal stomping grounds of the Indian Ocean, but the captain is eager to begin the search. Perhaps too eager.
Quest Line
- Sail the old Pirate Rounds to Ponape. Speak with [local mystic] and get directions.
- Learn from [local mystic] that R'lyeh is not just lost, but deep underwater.
- Steal the experimental Diving Engine from the English inventor, John Lethbridge.
- Sail to Point Nemo, a.k.a the Pole of Inaccessibility.
- Descend to R'lyeh using the Diving Engine.
- Find R'lyeh's treasure. (re: roll SAN loss)
I was thinking that a maritime "professor of occult" would fit well with this setup. The captain/sponsor has probably been looking for R'lyeh for a while now and has called on the services of educated men to help with the search. A character with an emphasis on knowledge skills could still be involved with the game even if they aren't an actual seaman.