The poem's title points to the old idea of the seafarer, someone who sets out on a grand voyage. Its opening line seems to promise that, with "All things go to sea." Then the speaker undercuts it with a flat, funny turn: "I went to fat." Where everything else heads outward toward the ocean, he puts on weight instead, going nowhere.
The second pair of lines works the same way. "All things wash to bed" sounds gentle and natural, like waves reaching the shore. But the speaker is "cold and coughing," so rest looks less like peace and more like sickness. The mood is wry and self-mocking, with a thread of loneliness underneath.
The speaker seems to feel left behind by the great movement of things, and he admits it with a shrug rather than a complaint. The humor makes the sadness easier to bear, but it doesn't erase it. In just four short lines, the poem sets grand adventure against ordinary bodily decline and lets the small, awkward reality win.