"you guys keep trying to claim that New York so dominated shipping that the south just HAD to secede"
No one is saying that. What is being said is that the Northeast was so fearful of the power of the Mississippi that politicians and media were urging Lincoln on to blockade the ports.
"Pea said that the number included steam boats/river traffic, implying that ocean shipping out of N.O. was less"
I made no such connection.
"s. boats" column is something unknowable."
That is, unless, you have some other data.
That is, unless, you have some other data.
Well, I think that the very heading of the table including the word "steam boats" would point to the column labelled "s. boats" to be a more likely candidate for that data than the one marked "st. ships". Furthermore, if multiple sources mention 3000+ steamboat arrivals a year in that period, I would contend that the column headed "s. boats" and showing 3000+ arrivals indeed represents steam boats, if it's rival for that position shows only 300 arrivals.
Begging your pardon, but I think you're being willfully obtuse on this point.