Some of it is inherent in the laws requiring the usage of Northern ships. The Northern shipping industries could set whatever rules they wanted, because you were forced to use their services. If they said you must insure the cargo through their insurance agents, you had to do it. If they said you must use warehouses in New York, you had to do it. If they said you must take out a loan from a bank in New York, you either did it, or you didn't get your product transported. Look up "Company Town" to get an idea how this system works in practice.
This is why doing away with the Navigation Act of 1817 was such a financial boon for the South. It took away the power to coerce them to use services at excessively high rates, and allowed them to not only use cheaper European services, but they could avoid the gouging to their bottom line that New York and Washington DC's cut represented.
It cut New York and Washington DC out of their trade deals and their profits.
Remember, 73% of all US Trade was from the South.
“Some of it is inherent in the laws requiring the usage of Northern ships. “
What law said you had to use NORTHERN ships?
“Remember, 73% of all US Trade was from the South.”
You keep throwing that number around, without any documentation. And no, another poster’s comments do not constitute a legitimate source.