The speaker begins with an admission: they could heal themselves if only they could face their "thorn," the private wound they keep avoiding. The poem never says what the thorn is. Instead it turns to a picture of a captain who has lost his ship and sits drunk in his cabin. It is a odd image, since the ship is gone and yet he is still hiding in a room built for sailing.
Then the captain is on shore, in the woods, and he "would not sing." The sea was where his voice and purpose lived, and on land he has gone quiet. The last lines ask what other night could come to "be broken open" now that he is "confined to land." The question feels both hopeful and bleak. Breaking open could mean release or ruin. The mood is brooding and wistful, and the speaker seems to see themselves in this man, stuck between wanting to heal and not knowing where the storm that might do it will come from.