Did you ever wonder what that strange series of letters and numbers on the transom of your boat are. Well, if you have taken the Nautical Know How course you know they are Hull Identification Numbers (HIN) and that they are required. But, what does a Hull Identification Number mean?

What Is A HIN?

All boats manufactured or imported on or after November 1, 1972 must bear a HIN boat hull number. The HIN is a 12 character serial number that uniquely identifies your boat. Think of these boat identification numbers like your car’s VIN.

History of the HIN

The United States Coast Guard was tasked with creating a system that would allow for easier tracking the history of boats and accidents back in 1972. They did not become a fully required feature until 1984, which we’ll touch on below. 

Prior to 1972 manufacturers used their own serial numbers but there was no universal format. As you can imagine, this made it more difficult to keep things organized and to cross reference any issues that may have related to recalls or manufacturing defects.

The new system, just as the VIN system in cars, allowed authorities to more easily track boats for safety purposes, to help reduce or track thefts, and to allow all vessels to be more user friendly for everyone involved by eliminating a potential wide range of formats or even number duplication that may have existed between manufacturers.

What Are Hull Identification Numbers Useful For?

The HIN has several important uses for boat owners. 

  • It enables manufacturers to clearly identify for boat owners the boats that are involved in a defect notification and recall campaign. 
  • The HIN number can allow authorities to track your boat in the event of theft or vandalism.
  • When buying a boat, the HIN allows you to learn more about the boat history including its age and where it came from.
  • The HIN is necessary to ensure your boat can be properly registered and insured. You will likely be required to provide this number if you’re looking for boat financing as well.

A HIN hull number 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.

Where to Find the HIN on a Boat

A HIN number should be clearly visible on a boat while it’s in the water. The ideal position is the upper starboard quarter on the outside of the transom within two inches of the top of the transom, gunwale, or hull/deck joint, whichever is lowest. However, if there is no transom on the vessel then it can be on the uppermost starboard side of the hull near the aft of the vessel. This will be the most easily visible location for your HIN but it’s not the only place it needs to be.

If you have a pontoon or catamaran which have replaceable parts, then the HIN needs to be to the aft crossbeam within one foot of the starboard hull attachment.

If the HIN will not be visible because the boat has railings, fittings or any attachments then it needs to be placed as close to the upper right of the aft hull/transom as possible while allowing it to be visible. 

The HIN needs to be permanently a part of the hull in this position in such a way that it would be obvious if it was removed. The digits of the HIN should be at least ¼ inch tall. 

A secondary HIN should be located on the interior of the boat. This one is more subtle. It can be under a piece of hardware or a fitting, or some other unexposed spot on the interior. This allows for a cross reference/match between the hull HIN and the interior if it’s ever required by the Coast Guard or even by you as a buyer of a new vessel to make sure everything is on the up and up.  The purpose is to help authorities identify your boat with a HIN decoder if a thief or vandals remove or damage the primary HIN boat serial number 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.

Beyond the physical numbers on a boat, the HIN should also be recorded in insurance documents, the title and the boat registration.

Understanding A Boat Serial Number:


*Key to Month of Model Year

Figure 1 – HIN Formats Before August 1, 1984


Figure 2 – HIN Format After August 1, 1984

Boats manufactured or imported on or after August 1, 1984, have that duplicate secondary HIN affixed somewhere on an unexposed location inside the boat or beneath a fitting or item of hardware.

What Do the Numbers Mean in a HIN?

The regulations prescribe the format of the HIN. 

  • The first three characters are an 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 perform a boat hull ID lookup. 

Do Boats From Outside the US Require a HIN?

For boats manufactured outside of the US, a U.S. importer must obtain a manufacturer identification code. The request must indicate the importer’s name and U.S. address along with a list of the manufacturers, their addresses and the general types and sizes of boats that will be imported. If a nation has a hull identification number system which has been accepted by the Coast Guard for the purpose of importing boats, it may be used by the importer instead of producing a new one.

Do Homemade Boats Need a HIN?

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 Hull ID Number 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.

The method of registering a boat, either homemade or others, can be found in our guide to registration numbers

The Bottom Line

Every vessel manufactured since 1984 has been required by the US Coast Guard to have a unique 12-digit HIN which works much the same as your car’s VIN. This number is an easy way for the Coast Guard, manufacturers and boat owners to identify a vessel. The number indicates who manufactured the boat with the first three numbers, the hull serial number with the next five, and finally the date of certification and model year for the vessel.

A HIN must be displayed on the starboard, aft section of the boat on the transom or in a clearly visible area within two inches of the top of the transom, gunwale, or hull/deck joint, whichever is lowest. The numbers must be at least ¼ inch tall and it must be permanently affixed to the hull. A duplicate number is required on the interior for all boats manufactured since 1984 as well.