The poem uses an extended metaphor to compare the sea to a dog. In the first stanza, the choppy grey sea is depicted as a hungry dog with shaggy jaws, gnawing and churning on the stones like a restless animal. The second stanza describes the sea howling at the moon at night, beating its spray against the cliffs. The final stanza depicts a calm scene, where the once restless sea is now asleep like a sleeping dog on a warm quiet day. The poem shows the unpredictable and unrestrainable power of nature.