You are starting to make arguments in what I consider to be a rational manner. You are looking for sources and evidence, which is exactly how people should argue.
But just off the top of my head, subsidizing Northern shipping for 10 years is a pretty good benefit to Northern shipping, is it not?
Also, Charleston did build deep water vessels. "The Horizon" was built there in the 1790s. I happen to know because I researched what could be learned of that vessel in regards to the topic of "natural born citizen".
They didn’t subsidize Northern shipping as you have been claiming. They subsidized 3 shipping companies who either carried mail or were considered to be important for national defense. And they didn’t create any monopolies as you claimed.