Complex sentence: Seymour's most immediate problem was to secure his prize: many of the unwounded prisoners were transferred to "Amethyst" under guard and at 01:05, the frigates were cut apart by severing the tangled rigging.
Split into simpler sentences: Seymour's most immediate problem was to secure his prize. Many of the unwounded prisoners were transferred to "Amethyst" under guard and at 01:05, the frigates were cut apart by severing the tangled rigging.