motivated by the traditional romance associated with the sea, it’s openness to possibility, the constant flux of the tides and the grandeur of it.

Metaphorically, this could be about life itself. Faced with the monotony of life, the speaker might be hoping for some adventure to come his way. He also may be trying to motivate himself to make a change in his life, to interrupt the monotony or to live more freely. He compares the trick (steering a ship) with the gull’s way, the whale’s way and the wind: completely free.

But he definitely indicates that there are downsides. The sea is lonely. The sky is grey. The wind is like a “whetted knife.” He wants a “a quiet sleep and a sweet dream when the long trick’s over.” He wants adventure but knows it will be difficult. He also eventually wants to come back to his current life.

One of the most memorable phrases for me from this excellent poem is when the speaker yearns in the final stanza to go back to "the vagrant gypsy life." He is a man that has obviously spent a long time on the sea as a sailor, and now that he is living on land, he finds himself caught up in a desperate desire to live on the sea again and experience the same itinerant, wild lifestyle that does not chain you to any specific location. He wants the same excitement and closeness to the sea and nature that such a lifestyle would give him. Note the first two lines of the last stanza:

I must go down to the seas again, to the vagrant gypsy life,

To the gull's way and the whale's way where the wind's like a whetted knife...

This then is the kind of life he wants: a life that is spent following the path of the gull, the whale and the wind, and a life that is "vagrant" and not stationary.

The speaker's deep desire, as the title of the poem suggests, is to go back to sailing the seas in a boat. The sea is in his blood: he has a fever for it.

The speaker says he wants a tall ship. Unlike others who might want a ship to kill a whale (like Captain Ahab), to find a treasure, to explore new places, to make a fortune, or to find a new home to settle in, the speaker simply wants to be on the sea for the sake of being there. He longs for the sea breezes, the gray mists, the wind, the white clouds, and the sound of the seagulls crying. He yearns for this freeing environment, where he can live the "vagrant gypsy life" untethered from the shore.

To the speaker, the seafaring life is a simple life where one can find happiness in the natural world, in telling stories with a friend (a "fellow rover"), or in sleeping and dreaming sweetly.

Literally speaking, the speaker asks for a number of things in this poem.  He asks for a tall ship and a star to steer by.  He asks for a merry yarn and a good sleep after his long trick.  He asks for many other things in between.  So the real issue is to think about what this means in a figurative sense.

Figuratively, I would argue that the speaker is asking for freedom and excitement.  Although he feels compelled to go to sea, his words about the sea are full of the language of freedom.  He wants to hear the sails cracking and the wind driving him along.  He wants to be like the gulls and the whales.  These requests convey to me an image of freedom and of doing things that are thrilling.  He is not chained to a desk in a closed room or to any other sort of mundane thing on the land.  Instead, he is out there on the ocean, pitting himself against the elements.

Figuratively, then, the speaker is asking for a fulfilling life.  One in which he is free to do what he wants and to challenge himself.  Afterwards, he wants a good rest, but while he is alive, he wants to live life to its fullest.

The speaker in "Sea Fever" longs to go to the sea again because it is the place that speaks to his soul. He longs to connect with the powers of the sea and doesn't need sophisticated boats to satisfy this calling: "all I ask is a tall ship and a star to steer her by."

The speaker reproduces the sound of the wind in the alliteration of the third line: "the wheel’s kick and the wind’s song and the white sail’s shaking." He needs to get back to the tide of the sea because it is wild and free. He loves the sounds of the sea: the cry of the gulls and the sound of the wind. He loves the sights of the sea, from the grey mists to the white clouds.

In short, the speaker has a sense of wanderlust that is fulfilled through a connection to the sea, a call to explore and to live adventurously. The nature that surrounds him at the sea is addictive, always calling him back for more.