The term “epic” has been usefully defined as follows:
It is a poem that is (a) a long narrative about a serious subject, (b) told in an elevated style of language, (c) focused on the exploits of a hero or demi-god who represents the cultural values of a race, nation, or religious group (d) in which the hero's success or failure will determine the fate of that people or nation. Usually, the epic has (e) a vast setting, and covers a wide geographic area, (f) it contains superhuman feats of strength or military prowess, and gods or supernatural beings frequently take part in the action. The poem begins with (g) the invocation of a muse to inspire the poet and, (h) the narrative starts in medias res [into the middle of things]. (i) The epic contains long catalogs of heroes or important characters, focusing on highborn kings and great warriors rather than peasants and commoners. [see link below]
The Old English poem Beowulf is an epic in practically all of these senses, with the possible exception of “e” and the definite exception of “g.” Beowulf definitely represents the ideal values of his nation (the Geats) and religious group (early Christians. His battles with the first two monsters help determine the fate of the Danish people, while his battle with the dragon helps determine the fate of his own people, the Geats. The poem opens with a long catalogue of previous Danish kings, and Beowulf’s enormous strength, his lofty values, and the fact that he fights on behalf of clear and lofty ideals all help make him an epic hero.
In contrast, the Old English lyric poem “The Seafarer” lacks almost all of the characteristics cited above. The speaker of this poem is certainly heroic in the sense that he has survived much physical and emotional pain and also in the sense that he actually seeks out challenging situations. However, “The Seafarer” is mainly a poem about a representative human being whose problems are mainly personal. He fights with no obvious monsters but instead seeks and displays spiritual strength. He is certainly more "heroic" than complacent people who live comfortably in cities, but he fights no battles on behalf of others. He spends much of his poem lamenting (understandably!) the sorrows he has endured – behavior not typical of the kind of epic hero epitomized by Beowulf.
"The Seafarer" is a much shorter poem than Beowulf and thus lacks the wide temporal scope we often associate with epics. Homer's Iliad describes events that take ten years to complete. His Odyssey describes events that take place over another ten years. The time scheme of Beowulf is, if anything, even broader, since the poem begins with Beowulf as a young man in the prime of life and ends by focusing on his old age, fifty years later. One senses that "The Seafarer" also covers more than a few years, but it does not seem to cover anything like the extended time period mentioned in Beowulf.