“US law (among others, the Navigation act of 1817) caused “those imports to arrive in New York instead of the areas in the South where the trade goods were produced to pay for them.”
the Navigation act of 1817 requires cargos shipped between American ports be carried on American flagged ships. If a cargo was to be shipped from Boston to New Orleans, it had to be carried by an American flagged ship. That was what the 1817 Navigation act required. A British flagged ship carrying cargo from Birmingham England to the U.S. was free to go to any port in the United States that the ship’s captain chose.
The reason why New York, Boston, or Philadelphia handled more ships is because they had the capacity of handle large numbers of ships. New York’s capacity equaled the combined capacities of Norfolk, Charleston, Mobile and New Orleans.
Boston’s capacity was not to far behind New York, and was greater than any of the Southern ports. Philadelphia could also berth more ships than any of the Southern ports.
Each day at anchor, waiting for a berth to off load costs the ships owner money.
Giving virtually monopoly powers to the subsidized shipping industries of New York. Virtually all the packet shipping lines of the US operated from New York.
If a cargo was to be shipped from Boston to New Orleans, it had to be carried by an American flagged ship.
Making it utterly pointless for European ships to sail anywhere but New York or Boston or Philadelphia. It cost the same to do business in South Carolina as New York, but New York was 800 miles closer. That dynamic changes dramatically when taxes get reduced from 40-50% down to 13%. Suddenly there is a clear profit motive to sail to Norfolk or Charleston.
The reason why New York, Boston, or Philadelphia handled more ships is because they had the capacity of handle large numbers of ships.
Capitalization of the Southern ports would have remedied that, and with additional profits to be made by sailing to Southern ports instead of Northeastern ones, they would have done so, thereby depriving New York of most of it's traffic.