Complex sentence: The Crest of the Frigate Hydra is the same as that of her predecessor, a copy of one of the versions of the flag under which the ships of Hydra sailed during the 1821 revolution.
Split into simpler sentences: The Crest of the Frigate Hydra is the same as that of her predecessors. It is a copy of one of the versions of the flag under which the ships of Hydra sailed during the 1821 revolution.