The story of the "Windline Marcher" is an old one. The earliest versions of the tale appear in the Exalted Age. Said to be a two-mast brig that set sail from Antiva City carrying cargo bound for the Free Marches, the "Marcher" was lost in a storm, and never made port.
Weeks later, she is seen on the Waking Sea, miles out from Kirkwall. A sentry from Hightown spots her floating in the mists, her sails full though there is no wind. Boats are launched, but no matter how far out to sea they go, they are unable to reach the "Marcher." Finally, the ship recedes into the mists and is gone. From that day on, she is spotted by sailors on the Waking Sea, always though mists and always before a storm, and is said to herald a violent death for all who see her.
Of course, the legend of the "Windline Marcher" is often dismissed as superstition, and in recent years the sighting of phantasmal vessels was proven to be nothing more than a trick of light upon the water. Still, the story continues to be told, its intent to chill, amuse, or even titillate. As a consequence, the tale has grown more colorful over time. In many later versions, the "Marcher" is manned by a crew of stunningly beautiful spirits, who can fulfill one's deepest (carnal) desires, should one succeed in boarding the ship. In one particularly outlandish retelling in these versions, the "Marcher" is sent on a disastrous journey to pilfer the secret recipe for Qunari ale and is lost to their cannons. She later reappears at important moments in Thedosian history and abducts legendary figures (Andraste included) who then band together aboard the phantom ship to attack Par Vollen.
——From Thedas: Myths and Legends, by Brother Ferdinand Genitivi