Thanks for the explanation of моряк and матрос. I suppose that моряк would best be translated as "sailor" (which is a more general term) while матрос is best translated as "seaman" -- which is sometimes synonymous with "sailor," but can also be a specific term of rank in the navies and civil fleets of the US, UK, and other English-speaking countries. (In the US Navy, for example, a "Seaman" is approximately equivalent to a "Private" in the Army or Marine Corps.)