how does Delano interprets his own visual perception of ship in distress?

Delano is not a very perceptive man...... things have to be staring him in the face to be noticed. He is unable to interpret symbols and spends most of his time in the dark. Even the mutiny itself sneaks up on him. He's there; he hears the Ashanti wizards "clash[ing] their hatchets together, like symbols" and merely reaffirms his prejudice that blacks like to mix play in with their work; never for a moment does he understand the true portent of the "cymbals": that the Ashanti are issuing a threat to Cereno. (Melville plays with Delano's inability to read; "cymbals" sounds like "symbols," after all.)