Complex sentence: From September 1796 Broughton charted the east coast of Honshu and Hokkaidō before wintering at Macau where he purchased a small schooner to assist the Providence.
Split into simpler sentences: From September 1796 he charted the east coast of Honshu and Hokkaidō before wintering at Macau. There Broughton purchased a small schooner to assist the Providence.