46 USC 12102 - Vessels requiring documentation

(a) In General.— 
Except as otherwise provided, a vessel may engage in a trade only if the vessel has been issued a certificate of documentation with an endorsement for that trade under this chapter.
(b) Vessels Less Than 5 Net Tons.— 
A vessel of less than 5 net tons may engage in a trade without being documented if the vessel otherwise satisfies the requirements to engage in the particular trade.
(c) Barges.— 
A barge qualified to engage in the coastwise trade may engage in the coastwise trade, without being documented, on rivers, harbors, lakes (except the Great Lakes), canals, and inland waters.