shipping: seagoing vessels named together as one body rather than one at a time
Hebrew has a separate word for ships taken as a group. Where אֳנִיָּה names one vessel, the ship a traveler boards or a merchant loads, this word names the ships together, close to how English uses "shipping" or "a fleet." That grouping is why a king stands behind almost every use of it: ships in numbers meant money, organization, and a crown able to pay for both.
Four of its five verses sit inside one story, the sea trade King Solomon ran out of Ezion-geber on the Red Sea. He builds the ships, Hiram of Tyre supplies sailors who actually know the water, and the vessels come back from Ophir carrying gold, silver, ivory, rare wood, apes, and peacocks. What the writer describes is commerce on a royal scale, a voyage that came home once every three years, and not a war fleet.
The fifth verse turns the picture inside out. Isaiah imagines Zion as a place of broad rivers and wide streams where no rowed ship can travel and no proud vessel (צִי) can pass. The very thing that carried wealth into Solomon's kingdom becomes, in the prophet's vision, the thing that cannot reach God's city at all. Ships are power and reach, and the point of the promise is that none of that power gets in.