Vessel Registration – why Vessel State abbreviations can be different from USPS State abbreviations

If you find yourself in Ocean Springs, Mississippi, looking across the harbor at a vessel with State Registration letters on the bow beginning MI (the USPS abbreviation for Michigan), you may be a bit confused. Why is Mississippi abbreviated as MS by the United States Postal Service and MI for purposes of vessel registration? All of the Mississippi vessels seemed to have migrated to Boston Harbor, where Massachusetts used MS, the USPS abbreviation for Mississippi, as the Vessel Registration abbreviation.

The state abbreviations for vessel registration are incompatible with USPS abbreviations because the vessel system was created first.

When the U.S. Coast Guard (USCG) and state agencies established boat registration prefixes, they created a system independently without coordinating with the postal system. By the time the Post Office standardized its own codes, the two systems had fundamentally drifted apart.

Timeline of the Disconnect

The incompatibility stems entirely from historical timing and bureaucratic separation:

• 1958 (Vessel Registrations): The Federal Boating Act of 1958 gave states the authority to register undocumented watercraft. The USCG established a standardized numbering system using two-letter state prefixes. At this point in history, the Post Office did not use standardized two-letter codes; people simply wrote out the full state name or used traditional multi-letter abbreviations (like “Mass.” or “Calif.”).
• 1963 (USPS Abbreviations): Five years later, the United States Postal Service introduced the modern ZIP code system. To free up space on envelope labels for the new five-digit codes, the USPS created its own uniform two-letter state abbreviations. They did not consult the maritime registry when doing so, resulting in overlapping and conflicting codes.

Common Abbreviation Clashes

Because the two agencies operated independently, 11 states have noticeably different prefixes depending on whether you are looking at a mailbox or the bow of a boat:

11 Mismatch States	Vessel Registration Prefix	USPS Postal Abbreviation
California	CF	CA
Colorado	CL	CO
Delaware	DL	DE
Hawaii	HA	HI
Kansas	KA	KS
Massachusetts	MS	MA
Michigan	MC	MI
Mississippi	MI	MS
Nebraska	NB	NE
Washington	WN	WA
Wisconsin	WS	WI

Gulf Coast States	Vessel Registration Prefix	USPS Postal Abbreviation
Alabama	AL	AL
Florida	FL	FL
Louisiana	LA	LA
Mississippi	MI	MS
Texas	TX	TX

Why Changing Them is Unlikely

The U.S. Coast Guard and state departments of motor vehicles have kept their original 1958 prefixes to maintain historic database consistency and continuity. Changing millions of physical boat hull displays and state maritime titles to match the post office would create massive administrative headaches and financial costs for boat owners.

All States	State Abbreviation	State Abbreviation
State	United States Postal Service	Vessel Registration
Alabama	AL	AL
Alaska	AK	AK
Arizona	AZ	AZ
Arkansas	AR	AR
California	CA	CF
Colorado	CO	CL
Connecticut	CT	CT
Delaware	DE	DL
Florida	FL	FL
Georgia	GA	GA
Hawaii	HI	HA
Idaho	ID	ID
Illinois	IL	IL
Indiana	IN	IN
Iowa	IA	IA
Kansas	KS	KA
Kentucky	KY	KY
Louisiana	LA	LA
Maine	ME	ME
Maryland	MD	MD
Massachusetts	MA	MS
Michigan	MI	MC
Minnesota	MN	MN
Mississippi	MS	MI
Missouri	MO	MO
Montana	MT	MT
Nebraska	NE	NB
Nevada	NV	NV
New Hampshire	NH	NH
New Jersey	NJ	NJ
New Mexico	NM	NM
New York	NY	NY
North Carolina	NC	NC
North Dakota	ND	ND
Ohio	OH	OH
Oklahoma	OK	OK
Oregon	OR	OR
Pennsylvania	PA	PA
Rhode Island	RI	RI
South Carolina	SC	SC
South Dakota	SD	SD
Tennessee	TN	TN
Texas	TX	TX
Utah	UT	UT
Vermont	VT	VT
Virginia	VA	VA
Washington	WA	WN
West Virginia	WV	WV
Wisconsin	WI	WS
Wyoming	WY	WY