The Hull Identification Number (HIN) is a 12- or 14-character serial number that uniquely identifies a boat. The HIN is analogous to a VIN on a car.

All boats manufactured or imported on or after November 1, 1972, must bear a HIN, and this HIN must be identified during boat registration. Vessels manufactured or imported before 1972 are EXEMPT because they often do not have a HIN.

The HIN is found on a metal or plastic plate, typically on the transom of the boat, usually on the right starboard (right) side of the transom within two inches of the top of transom, gunwale, or hull/deck joint, whichever is lowest.

On vessels without transoms, or impractical to use transoms, the HIN is usually affixed to the starboard (right) outboard side of hull, aft, within one foot of the stern and within two inches of the top of the hull side, gunwale or hull/deck joint, whichever is lowest.

On catamarans and pontoon boats with replaceable hulls, the HIN is usually affixed to the aft crossbeam, within one foot of the starboard (right) hull attachment.