Identifying Metaphor in Literature

Read the following excerpt and answer the question below:

In her latest novel, the author compares the protagonist's feelings of isolation to being 'adrift in a vast ocean, where waves of despair crash against the hull of her heart.' This vivid imagery illustrates not only the emotional turmoil experienced by the character but also highlights her struggle against seemingly insurmountable challenges.

Which of the following best identifies the figure of speech used in this excerpt?