Complex sentence: On 11 June, the ship ran aground on Frederick Reefs, her masts were cut away to steady her while the crew and soldiers moved to shore with water and provisions before she sank.
Split into simpler sentences: On 11 June, the ship ran aground on Frederick Reefs. Her masts were cut away to steady her, while the other crew members and the soldiers moved to shore with water and provisions before she sank.