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.
It should not be confused with the vessel's weight, which may also be expressed in tons. Most vessels more than 25 feet in length will measure five net tons or more. For information about how tonnage is determined, including a web-based interactive form that calculates tonnages, visit the U.S. Coast Guard Marine Safety Center's web site at the Marine Safety Center's Tonnage Page . Vessels that do not operate on the navigable waters of the U.S. 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.