I think that we're getting bogged down in a discusson of the harbor characteristcs of Charleston, as if that's the only southern port worth mentioning. Clearly, from the figures presented in the document you linked to a while back, New Orleans was by far the more important southern port. Therefore, I think that when you present numbers for New York vs. Charleston, it's not as illuminating a comparison as New York vs. New Orleans would be.
Actually Charleston is the point. Mac truck has just admitted for your side that the harbor at Charleston completed a major dredging project in 1860 which would now allow direct transoceanic trade to both the East Coast and the Mississippi.
For what it's worth, the City of Charleston is one of the oldest seaports in the United States dating back to 1670. At the time of the American Revolution it was the fourth largest city in the Colonies, and several of the wealthiest Americans lived in Charleston at that time. The only impediment to Charleston's establishment of a shipbuilding industry prior to enactment by Congress of the Navigation laws [imo] was the predominantly foppish nature of it's inhabitants.