Vessel documentation is a national form of registration.
It is one of the oldest functions of Government, dating back to the 11th Act of the First Congress. Documentation provides conclusive evidence of nationality for international purposes, provides for unhindered commerce between the states, and admits vessels to certain restricted trades, such as coastwise trade and the fisheries. Since 1920, vessel financing has been enhanced through the availability of preferred mortgages on documented vessels. In addition, towboats operating between points in the U.S. or the EEZ or between the EEZ and points in the U.S. and dredges operating in the U.S. or the EEZ must be documented. Net tonnage is a measure of a vessel's volume.