[Heyworth]

Post 803 New York shipping interests, using the Navigation Laws and in collaboration with the US Congress, effectively closed the market off from competitive shipping, and in spite of the inefficiencies, was able to control the movement of Southern goods.

And yet according to the Statistical Abstract, a full one-third of all shipping tonnage entering US ports from foreign ports was foreign-flagged. That doesn't sound like a closed-off market.

[PeaRidge]

You misrepresent the quote. It is from "Charleston's Maritime Heritage. It was referring to the Eastern trade routes, not the Gulf.