The stretch of water between the Marquesses and Dry Tortugas can be nasty, especially if you're thinking about cruising along the hump, which is the skinny water between the Marquesses and Rebeca Shoals. When the tide is running hard, and in opposition to the wind, the waves here can be nasty. However, when conditions are right, slight tidal change, moderate winds, you can make a wonderful passage to the Tortugas through some of the most beautiful water in the region. This one can be a crap-shoot, but if you're properly prepared, it's a wonderful trip. There is a catamaran that runs from Key West to the Dry Tortugas daily. I highly recommend taking the trip on the cat and observing the waters they traverse. It's well worth the expense.