A T-Boat is an inspected vessel under 100 gross tons that carries between 6 and 150 passengers for hire or has overnight accommodations for up to 49 passengers.
A vessel only intended to carry 6 passengers or less for hire would not need to be inspected by the Coast Guard and could be classified as a 6-Pack vessel.
The master of the T-Boat must be credentialed to sail on a vessel of that tonnage. The deckhands of a T-boat are not required to hold a TWIC card.
Other T-boats include:
A semi-submersible vessel carrying one passenger for hire.
What is a K-Boat?