Skull and Shackles
Characters unaccustomed to life on board ships run the risk of getting seasick. Such characters must succeed at a DC 5 Fortitude save or become nauseated for the rest of the day. On the following day, the character is entitled to a new save. On a success, the character is sickened instead of nauseated. On a failure, the nauseated condition persists for another day. Each day thereafter, a character is entitled to another Fortitude save. Making two successful saves in a row allows the character to recover from seasickness for the duration of the voyage. The DC of seasickness increases to 15 in rough weather, and those who succeed at a check to stave off seasickness for a day must make an additional save if conditions change for the worse.
Characters with 1 or more ranks in Profession (sailor) are never subject to seasickness.