RTGs (radioisotope thermal electric generators) seem a bit exotic and government-ish. They use a very radioactive fuel source, e.g., Plutonium, which normal people can't obtain. If the presence of RTGs becomes known, the boat becomes a target for eco-activists and is probably banned from several countries, e.g., New Zealand. Terrorists who believe that "Plutonium is the most dangerous substance on Earth" might target the boat to obtain the fuel. Maybe this becomes a new plot complication!

And RTGs don't really produce much power. Current state of the art is 290 watts (about 1/3 horsepower). For less money, and a lot less hassle, go solar.

IIRC, the Soviet Union developed some small fission reactors for spacecraft. Now that would be exotic!

73, de N4PYB