It's not wrong to assume that the whole poem is a metaphor in a way. It talks about Abraham Lincoln's (the captain) death, the mourning, and the the good destiny to where the ship is going. The Voyage was the Civil War, and the ship, we can conclude that it was the United States of America.
The correct answer is D. An enjoyment of solitude. Both loved living in the outdoors and being alone with their thoughts in the woods. This can be seen in the work "Walden" by Thoreau.
