Info taken from www.BoatSafe.com
Did you ever wonder what that strange series of letters and numbers on the transom of your boat are? They are Hull Identification Numbers (HIN) and are required. But, what do they mean?
All boats manufactured or imported on or after November 1, 1972 must bear a HIN. The HIN is a 12 character serial number that uniquely identifies your boat. The HIN has an important safety purpose. It enables manufacturers to clearly identify for boat owners the boats that are involved in a defect notification and recall campaign. A HIN is not the same as a State registration number, which may be required to be displayed on the bow of your boat. The HIN is a Federal requirement; your boat’s registration number is a State requirement similar to the license plate on your car. The HIN, however, is required to be shown on the State certificate of registration.
*Key to Month of Model Year
Figure 1 - HIN Formats Before August 1, 1984
The boat manufacturer must display two identical hull identification numbers, no less than one-fourth of an inch high, on each boat hull. The primary HIN must be permanently affixed (so that it can be seen from outside the boat) to the starboard side of the transom within two inches of the top of the transom, gunwale, or hull/deck joint, whichever is lowest. On boats without transoms or on boats on which it would be impractical to the transom, the HIN must be affixed to the starboard outboard side of the hull, aft within one foot of the stern and within two inches of the top of hull side, gunwale, or hull/deck joint, whichever is lowest. The starboard outboard side of the hull aft is the preferred HIN location for many manufacturers. On catamarans and pontoon boats the HIN must be affixed on the aft crossbeam within one foot of the starboard hull attachment.
Figure 2 - HIN Format After August 1, 1984
Boats manufactured or imported on or after August 1, 1984, also have a duplicate secondary HIN affixed somewhere on an unexposed location inside the boat or beneath a fitting or item of hardware. The purpose is to help authorities identify your boat if a thief or vandals remove or damage the primary HIN on the transom. It is illegal for anyone (manufacturer, dealer, distributor, or owner) to alter or remove a HIN without the express written authorization of the Commandant, U.S. Coast Guard.
The regulations prescribe the format of the HIN. The first three characters are a MIC (Manufacturer Identification Code) assigned by the Coast Guard to the manufacturer or the person importing the boat; characters four through eight are a serial number assigned by the manufacturer; the last four characters indicate the month and year the boat was built, and the model year. Prior to August 1, 1984, the manufacturer had the option of expressing this in the form of a model year designation.
The Coast Guard maintains a searchable database of MICs if you want to check yours out - click here.
Individuals building boats for their own use and not for the purposes of sale are what are referred to as "backyard boat builders." They must obtain a 12 character HIN from their State boating agency. The Manufacturer Identification Code at the beginning of the HIN for a "home built" boat is an abbreviation for the State followed by a "Z" which indicates that it is a State identification.