If you've never set foot on any kind of boat, you're a landlubber, someone who's either brand new to sailing or is totally unfamiliar with it.
The word landlubber comes from the obsolete lubber, which isn't a funny way to say "lover," but a term that evolved from meaning "clumsy oaf" to "inexperienced seaman." Back in the 15th century, lubber was also used as a verb, to mean "sail badly." These days, a new, inexperienced crew member on a schooner might be called a landlubber. If your brother gets queasy on a short ferry ride, feel free to call him a landlubber too.