It doesn't take us long to realize that we're dealing with a bunch of sailors in this poem, as the opening line begins with "And then went down to the ship" (1). Beginning with the word "And" gives this whole poem the sense of never really being in one place. Instead, Odysseus and his shipmates are always moving around, never settling in one spot. On top of that, the idea that these men are going "down" to the ships suggests a descent, which in a lot of ways predicts the descent that Odysseus will make into the underworld to look for the dead prophet Tiresias. The fact that the crew members' bodies are all "Heavy with weeping" (5) at the beginning of the poem also suggests that these men all feel some sense of sadness as they board their ship and get ready to sail. This sadness could come from the fact that they're scared of what they'll face on the high seas. But it could also mean that they feel sadness over the friends they've lost (they are, after all, fresh from fighting a super-long war).
In any case, the imagery of sailing generally creates the tone of homelessness in this poem that Pound wants us to connect to the spiritual environment of the early twentieth century. Popular religion was in decline, the world was in the middle of a brutal world war that seemed like it would never end, and people didn't really know where to turn. You could say that the world was "at sea" in a general sense. So the whole sailing thing seems like a good motif when you think about the world Pound was writing in.
Lines 1-7: The poem begins in medias res, which is just a fancy way of saying "right smack dab in the middle of something." No "Once upon a time" for Pound—instead we are set adrift in the middle of a story, and appropriately that story involves sailors getting on a boat and taking a sea voyage. Sounds like fun, right? Wrong. The sailors are distraught, "Heavy with weeping," (6) and so we get our first clue that being adrift at sea may not be all that much fun.
Line 17: "Ocean flowing backward"? Sounds like one of those crazy log flume rides at Six Flags. Here, though, it's a reminder that these sailors are adrift in a world that is dangerous and deranged.
Line 57: Sailing can also be a powerful source of identity, too, though. Elpenor asks Odysseus to bury him and mark his grave with the oar he rowed as a sailor, to remind the world of who Elpenor was in life.