Years ago I went whale watching off the coast of Monterey. We left in the early morning, cruising out in the fog, sipping coffee to keep warm. I had never seen a whale before and was unprepared for how big they were. I remember several large shapes gliding by our vessel, causing waves that violently rocked us up and down. As the day warmed and the fog burned away, we were able to see more whales further from the boat. One of the highlights of the day was when a gray whale breached, leaping into the air and making a huge splash. Our experienced captain kept the boat a safe distance from the whales, telling us that not only were they big, they were unpredictable. An incident yesterday, where a breaching whale landed on a boat, killing one man, demonstrates that wisdom.
Another tip: Don't try to shoot with a telephoto lens while you are on a small boat in rough water. The "ocean motion" is magnified and seasickness is assured.