Hi Taras,
Well, not quite so "..simple to just stick to 6 PAX." I believe that, unless the boat is under 40' LOA, it must be not only US built (or with a Jones Act exemption), but documented and endorsed for commercial trade. BUT, unless the vessel is >100 gross tons, not necessarily inspected. This applies, irregardless of number of passengers. And no, not an "act of Congress" to achieve an exemption. USCG issues those, but only after soliciting comment from the various states impacted by the requested exemption. Yeah, you might need an "act of Congress" to overturn an adverse USCG determination, so you're correct as far as that unicorn goes.
Obviously, this is (as most bureaucratic issues go), a complicated subject, involving crew and master credentialing, vessel requirements, insurance, out-of-CONUS (i.e. foreign) operations, ownership liability, etc. etc.
To the original poster-this is a tough row to hoe. While some boat owners may well have accomplished moving a foreign-built boat into successful crewed charter service, I personally was not successful. And I tried hard to do so, as it was going to be my retirement "job". After LOTS of letters, phone calls, lawyer visits, USCG applications, vessel improvements to conform to uninspected commercial eligibility (life jackets, flares, numbers, documents, proper color of heaving line on throwable device, lights, nav rules, ship radio telephone license, yada yada yada) I retreated into simply enjoying my boat with non-paying friends aboard, and spent the next 20 years in peace.
A maritime lawyer is your friend here. Find a good one, pay them well, and listen to their advice. What you're getting on this forum is shotgun patterning of miscellaneous misinformation. Some hits the mark, most misses the boat. And sorry for the pun!
Regards,
Pete