Complex sentence: After three years he became an apprentice to Captain Lloyd on the clipper ship, "Snow Squall", that left Long Wharf in Boston in September 1858 headed for Shanghai, China.
Split into simpler sentences: After three years he became an apprentice to one Captain Lloyd on a merchant ship. The clipper ship, Snow Squall, left Long Wharf in Boston in September 1858 headed for Shanghai, China.