You've probably already gone, but, while this is not about your camera, but look for the "green flash" underwater. That's how the white parts of the whale look, just before they come up. As far as the camera goes, shoot in sport mode, because you \may get lucky and get a good one

Was there in February with no problems except for being VERY sure to take a dry bag and being careful your jaw doesn't lock from the big smiles. Also, Drakes Passage is VERY rough so dramamine if you're susceptible and crystalized ginger makes it easier to endure.