Title text:
Turning in other directions can be accomplished by using a magnetized centerboard and ocean currents, since a current flowing through a magnetic field induces a Laplace force.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3090/
Well that doesn’t look right but I’m not a boat physicist so I’ll just accept it at face value.