But they took Vingilot, and hallowed it, and bore it away through Valinor to the uttermost rim of the world; and there it passed through the Door of Night and was lifted up even into the oceans of heaven.
The Silmarillion | OF THE VOYAGE OF EÄRENDIL AND THE WAR OF WRATH
This passage explained it. The Valar hallowed the boat, which means to make it holy. They obviously imbued it with the power to sail the skies.
