WHAT IS VESSEL DOCUMENTATION?
Vessel documentation is a national form of registration. Think of documentation as a Social Security number for your boat. Once your boat has a Documentation Number, that number will continue with the boat from owner to owner unless an owner decides at some point to not renew the Documentation and instead register the boat at the State level. Your documentation certificate is not valid for operation of the vessel until the vessel is marker with the name, official number and hailing port as shown on the certificate. Your original documentation certificate must be kept aboard at all times when operating the vessel.
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. You may find that some lenders require or at least prefer documentation to registration. Some states may actually require registration in addition to Documentation.
You can find further information on Boat Documentation at the US Coast Guard – National Vessel Documentation Center
WHAT ARE THE VESSEL MARKING REQUIREMENTS?
Documented vessels do not display their official numbers on the outside of the hull, but are identified by the name and hailing port. The application for documentation must include a name for the vessel composed of letters of the Latin alphabet or Arabic or Roman numerals and may not exceed 33 characters. The name may not be identical, actually or phonetically, to any word or words used to solicit assistance at sea; may not contain or be phonetically identical to obscene, indecent, or profane language, or to racial or ethnic epithets. Once established, a vessel's name may not be changed without application, fees, and the consent of the Director, National Vessel Documentation Center. There is no rule against duplication of names for documented vessels, so hailing ports are helpful in identifying vessels.
HOW DO I MARK MY VESSEL?
The official number assigned to documented vessels, preceded by the abbreviation "NO." must be marked in block-type Arabic numerals at least three inches high on some clearly visible interior structural part of the hull. The number must be permanently affixed so that alteration, removal, or replacement would be obvious and cause some scarring or damage to the surrounding hull area.
The name and hailing port of a recreational vessel must be marked together on some clearly visible exterior part of the hull. The vessel name of a commercial vessel must also be marked on the port and starboard bow and the vessel name and the hailing port must also be marked on the stern. All markings may be made by any means and materials that result in durable markings and must be at least four inches in height, made in clearly legible letters of the Latin alphabet or Arabic or Roman numerals. The "hailing port" must include both a place and a State, Territory, or possession of in the United States. The state may be abbreviated.