Ah, the mysterious Black Pearl. Oops. We mean unnamed black ship.
She's old—very old, conjuring in our narrator "an unaccountable memory of old foreign chronicles and ages long ago" (16). It may be a ghost ship, since its crew hardly seems alive (and indeed hardly seems to care about the prospect of dying). It's also crazy powerful, as it's able to sail in a hurricane, rather than, say, capsize like a normal ship. Sheesh.
So what are we to make of all this? In the end, not much—and that's precisely the point. The ship, like the sea, is enshrouded in dark mystery. Since we're only reading the narrator's message in a bottle, and we only get things from his perspective, we'll never learn what these zombie sailors were up to. And we're not meant to. Poe's the master of mystery, and he wouldn't have had it any other way. By leaving us in the dark about the nature of this ship, he's reminding us that sometimes, the unknown is a-okay.