Island in the Sea of Time by S.M. Stirling
Mr. Stirling got a lot of mileage out of this book, at least eight other books have been written based on this one, with only two being direct sequels. The story starts off with the island of Nantucket, and a Coast Guard training sailing ship that was just offshore, being transported back to the Bronze Age. That is good for a trilogy right there. What happended to to rest of the planet with Nantucket disappeared is good for at least two more trilogies.