Complex sentence: Both are four-year residency courses consisting of a three-years of academic studies (first, second, and fourth years) and one-year apprentice training (third year) aboard commercial vessels plying the international sea lanes as deck or engine cadets.
Split into simpler sentences: Both are four-year residency courses consisting of a three-years of academic studies (first, second, and fourth years). The one-year apprentice training (third year) is aboard commercial vessels plying the international sea lanes as deck or engine cadets.