Somewhere in the middle of the Atlantic, we were in about 10 foot seas maybe after a big storm. Relaxing a bit, enjoying the much drier conditions, when I see a Giant Sea Serpent off to port. Convinced I'd had too much of the canned hamburger the night before, I closed my eyes, tried to adjust to reality, and looked again. Sure enough there were four dolphins jumping out of the top of the waves in perfect formation. When you viewed their four arched backs from just the right angle, they looked like the sea serpents that you see drawn on ancient charts.
I didn't even see my best whale-sighting. That same trip, I was on the midnight watch by myself on a fairly calm night, counting in prime numbers to keep myself awake (it works) when I heard "whoooossshhffffkkk" off to starboard. What the heck was that? Then I smelled it, musty nasty dank whale breath, about ten seconds later. If it hadn't been pitch-black and moonless I would have been truly freaked out; thankfully, by the time I figured out how how close that monster must have been, he was far gone.