Here are some possible explanations:
* A mishearing: You might have heard "root nautical" instead of a similar sounding phrase like "route nautical," which could refer to a specific seafaring route.
* A metaphor: "Root" could be used metaphorically to represent something fundamental or originary, and "nautical" referring to the sea. For example, "The root of nautical navigation lies in the stars."
* A slang term: It's possible that "root nautical" is a slang term specific to a particular region or community, but it's not commonly known.
If you can provide more context about where you encountered this phrase, it might be easier to determine its meaning.