As long as it takes to pass A ship keeps raising its hull;
By the second stanza, we've really got our eyes fixed on the sea. So it's not just the folks "along the sand" that are checking out the water. The speaker is directing our attention to the sea as well.
Line 5 gives us a sense of time—"as long as it takes"—but the speaker is also giving the impression that there's no clear beginning or end to this particular length of time.
Line 6 gets a bit more specific about what we're looking at: "a ship raising its hull." A hull, for us non-nautically savvy folks, is the very bottom of a ship. It's the part you see dipping in and out of the water when a ship hits some waves.
So as long as it takes for that ship to pass, the ship itself will consistently "raise its hull," over and over again, because it's always dipping in and out of the waves.
How would you describe this imagery, Shmoopers? We think there's something repetitive and monotonous about it.
How? Well, check out the speaker's diction. He says "keeps" when he refers to the ship, which suggests that this sort of thing happens all the time. There's nothing particularly exciting or shocking about it. And yet the people keep looking at the sea all day as if it's the most amazing thing they've ever seen. What gives?
The wetter ground like glass Reflects a standing gull
Finally, the land gets its chance to be in the spotlight.
In these lines, we readers see a seabird standing on the sand right where the waves meet the shore. How can we tell? Since the land is "wetter […] like glass."
But check it out—we don't technically see this gull. What we see is the gull's reflection. See, the ground is so wet, that it's actually acting like a mirror here. That means we're one step removed from actually seeing the gull ourselves.
We'd be remiss if we didn't point out an interesting contrast here: remember all those people from stanza one? They were in one big group, all lumped together like an indistinguishable mass of humanity. But this gull? He stands alone.