Complex sentence: Captain Cheap was promoted to the distinguished rank of Post Captain and appointed to command the forty-gun ship HMS "Lark Sauchie", demonstrating that the Admiralty considered Cheap's many faults insignificant compared to his steadfast loyalty and sense of purpose.
Split into simpler sentences: Captain Cheap was made a post captain and appointed to command a forty-gun ship HMS "Lark Sauchie". This was a significant promotion which shows the Admiralty considered the many faults Cheap had were insignificant compared to his steadfast loyalty and sense of purpose.