Power
Are you on a boat? If the answer is yes, and you're a captain, then you might have all of the power—depending on the particular boat in question, of course. That's kind of the whole point of being the captain—you're entrusted with command of the entire vessel and everyone on it. Technically that means everyone has to listen to you. If they don't, the term for that is mutiny and you can totally punish them for it.
We don't really make anyone walk the plank anymore (sorry), so you'll just have to deal with the situation by firing them or docking their pay. Or, if they're a passenger, you can always try the parent move: "Young man, if you don't clasp close that life preserver this instant, I will turn this boat around. You have to the count of three—one...two..." You'll never get to three. That's the captain's power.
This is especially true on a ship that heads out into deep ocean territory. Think about it: not only are you in international waters, but you may in fact be literally thousands of miles from any sovereign country.
Ocean-going ships aren't democracies—they're small totalitarian regimes ruled by a dictatorial potentate, the captain. Basically when you're the captain you're Caesar at Sea—let's just hope no one tries to kill you for being too powerful.