I actually interpret Clarke's quote, which you're referencing, to mean that the Southern states wouldn't attempt to compete with the Northern states in the coasting and carrying trade and against all foreign tonnage. Could be wrong. Presentation of Clarke's diary is simply posting what I've found. I gave no indication of how I interpret any of it; that's something you've assigned. If you wish to verify your interpretation of Clarke's quote, I'd suggest starting with Elliot's Debates.
Already been there, and there's nothing that supports your interpretation. Maybe you can find it. Here's a link. But the page number indications in your sources don't match the edition, so you have to dig a little deeper. Go by the dates.