Once you exceed the USCG vessel limit of 6 passengers you will have to find an Inspected Vessel - perhaps a ferry from Red Hook or a connecting Charlotte Amalie/// Tortola ferry can be an option.

do 1 year olds count as passengers?

Yes - any breathing person 🙂

Pia

You might try New Horizons II or Limnos

We are going in September as well and are renting a boat for 8 hours from Waters Edge Power Boat Rentals. I cannot say enough good things about Mitch. He has been so helpful and patient as I asked him 100's of questions. Waters Edge Boat Rentals

A USCG Licensed Captain who operates an Un-inspected Vessel with more than 6 passengers on board while acting as Captain risks their license and livelihood - Rental Companies will skirt this law by calling them a 'Guide' who is not operating the vessel under their USCG License that day - the renting party must then assume all responsibility for the boat financially and designate a member from their party to appear as Master on Customs and Immigration forms if going International [ BVI] . If there are any accidents or injuries the 'guide' cannot be held responsible because they cannot admit to using their license to operate an Un-inspected vessel with more than six passengers aboard.
It is more prudent legally and financially for a charterer with a party larger than six people to rent a vessel with a valid COI - [ Certificate of Inspection] from the USCG and have a Licensed Captain operate the vessel. Otherwise they should ascertain the risks and ask the rental company to provide in the written contract the responsibility and liability assignments and include the actual definition of 'guide' or Licensed Captain.

Thanks to everyone for the info - very interesting, had no idea about these details.