(I hope this isn't too late... :'))

17th century.
Many feared pirates, maybe Blackbeard the most, but there was this creature that even made the infamous, bearded man be more careful about sailing at night. If she saw your ship, you'd wish you had stayed at home. (No, it's not his girlfriend)
Pirates and sailors spoke about this Grimataur, the soul-devouring beast. Captain of her own ship, having a crew made of spared soulsa and keeping the others in a lantern.
But this story may be just a horror story made by a drunk retired sailor. Like, a female captain? Devouring souls? Please. But think about it, how about the ships that never came back and the wrecks found hundreds of years later, without any explanation why it sunk.