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 US or the EEZ or between the EEZ and points in the US and dredges operating in the US or the EEZ must be documented.
Tonnage is determined by volume.
Most vessels more than 25 feet in length will measure five net tons or more. Vessels that do not operate on the navigable waters of the US Or in the fisheries in the EEZ, are exempt from the requirement to be documented. A Certificate of Documentation may be endorsed for fishery, coastwise, registry, or recreation. Any documented vessel may be used for recreational purposes, regardless of its endorsement, but a vessel documented with a recreational endorsement only may not be used for any other purpose. Registry endorsements are generally used for foreign trade.