Complex sentence: Irby sent Pascoe back in a small schooner to reconnoitre and saw that the two frigates were unloading a Portuguese prize before preparing to sail to intercept British home-bound trade.
Split into simpler sentences: Irby sent Pascoe back in a small schooner to reconnoitre. Pascoe reported back that the two frigates were unloading a Portuguese prize before preparing to sail to intercept British home-bound trade.