New Englanders might have had to turn to the sea for a living in some cases .... not that their crops were dying in the fields as it was. New Englanders grew up on home-grown lentils (a better diet, btw, it's been pointed out in an American history course, than that of Southerners who lived on cornbread, ham, and bacon -- and soft water, which denied them an important source of minerals -- leading to shorter life expectancies).
But the South didn't lack for world-class estuarine anchorages (Norfolk, Charleston, Savannah, Jacksonville -- not during the colonial period, of course -- and the Carolina sounds), and timber interests logged enormous trees out of the areas around Great Smoky for over a century -- I'm talking about hickory logs eight and nine feet in diameter. (There's a house at Great Smoky National Park built of logs that big. Some "log cabin"!)
Rhett specifically charges undercutting, but he doesn't give details. I've seen another early-20th-century source that accused New England of capturing the cotton trade after the Civil War. I have a copy of it "somewhere" on media. If both charges are true, that would be enough to establish a "pattern and practice" of commercial predation by Northern mercantile interests. By what mechanisms, I'd like to know, if it's true at all and not just a bunch of crying by runners-up.
In the South, capital was drawn to agriculture, specifically the large plantation which consisted of thousands of acres. These were really industrial scale operations and the lion's share of that capital went to purchase slaves to work those plantations. Like shipping, the return on investment could be very good. Yes, it had it's risks -- a bad harvest could cause a loss. But unlike shipping, where you could lose your entire capital investment to Davy Jones locker, one bad harvest still left you with your land and slaves to try again the next season.
In the South, the smart money went into plantations, not into a more risky venture like shipping. It was a geographic thing. Money went to where it could best return a profit.
Rhett specifically charges undercutting, but he doesn't give details. I've seen another early-20th-century source that accused New England of capturing the cotton trade after the Civil War.
Well before the war, the cotton trade primarily passed through New York. The cotton was sold to "Factors" who were financed primarily by New York or British banks. The cotton mostly went by coastal trade ships to New York where buyers would purchase it. Before the war, more than 80% of the buyers represented English French and other European mills. New England mills used less than 20% of the cotton grown in the South. There was a world price for cotton -- they all paid the same at the New York warehouses.
After the war the South began building cotton mills itself -- something some southerners argued they should have done years before. Within 20 or 30 years, North and South Carolina were the center of the textile industry in the US, and remained so for nearly 100 years until 'cheep" Asia and Central American labor killed them.
I really don't know what Rhett meant by New England monopolizing the cotton trade. After the Civil War, textiles were a much smaller component of New England's economy which had moved on to higher value added products such as tools and machinery ... including the looms and sewing machines used in those Southern cotton mills.