Complex sentence: The Naval Act of 1794 had specified 36-gun frigates; however, "Constellation" and her sister-ship were re-rated to 38s because of their large dimensions, being in length and in width.
Split into simpler sentences: The Naval Act of 1794 had specified 36-gun frigates. However, "Constellation" and her sister-ship were re-rated to 38s because of their large dimensions, being in length and in width.