The numbers on the side of a boat are its state registration number, and federal rules require them on both sides of the forward half of the hull in plain vertical block characters at least three inches tall, in a color that contrasts sharply with the hull background, reading left to right.1eCFR. 33 CFR 173.27 – Numbers: Display; Size; Color Get the placement, size, font, or spacing wrong and you can draw a citation during a routine stop.
What the Number Looks Like
Every state uses the same format. The number starts with a two-letter state abbreviation, followed by a sequence of digits, and ends with a two-letter suffix. The three groupings are separated by spaces or hyphens, so a valid number reads something like “DC 5678 EF” or “DC-5678-EF.”1eCFR. 33 CFR 173.27 – Numbers: Display; Size; Color The specific digits and letters come from the issuing agency in the state where the boat is principally operated.2eCFR. 33 CFR 173.15 – Vessel Number Required
Where the Number Goes
The number must be painted on or permanently attached to each side of the forward half of the vessel, and it must read from left to right.1eCFR. 33 CFR 173.27 – Numbers: Display; Size; Color “Forward half” means ahead of the midpoint of the hull, where someone looking at the boat from the side would expect to see it. Both sides. Not just the port side, not just the starboard side.
Size, Font, and Color
Characters must be plain vertical block letters and numbers, at least three inches tall.1eCFR. 33 CFR 173.27 – Numbers: Display; Size; Color No script, no italics, no stylized fonts. The color has to contrast sharply with the hull so the number is distinctly visible and legible. Dark characters on a light hull work; light characters on a dark hull work. Blue on navy, or white on cream, does not.
Spacing Between the Groups
The space or hyphen between the state abbreviation, the number sequence, and the letter suffix has to be as wide as one regular character. The regulation says the gap should match the width of a letter other than “I” or a number other than “1,” since those two characters are unusually narrow.1eCFR. 33 CFR 173.27 – Numbers: Display; Size; Color This is the detail people miss most often with peel-and-stick lettering kits, where it’s easy to crowd the groupings together.
Validation Decal Next to the Number
Most states issue a validation decal (a sticker) when you register or renew the boat, and the decal goes near the registration number to show the registration is current. Federal rules on displaying the number don’t address decal placement, so the exact position is set by your state’s boating agency.1eCFR. 33 CFR 173.27 – Numbers: Display; Size; Color A common state requirement is within six inches of the registration number.
When You Display a Name Instead
Not every boat carries a state registration number on the hull. Vessels of at least five net tons owned by U.S. citizens or qualifying entities can be documented through the Coast Guard’s National Vessel Documentation Center instead of registering with a state.3Office of the Law Revision Counsel. 46 USC 12103 – General Eligibility Requirements A documented vessel displays its official name and hailing port rather than a state number. For a recreational documented vessel, the name and hailing port appear together on some clearly visible exterior part of the hull, in characters at least four inches tall made with durable materials.4eCFR. 46 CFR 67.123 – Name and Hailing Port Marking Requirements
Penalties for Missing or Wrong Numbers
The Coast Guard and state marine patrols check numbering during routine stops. A willful violation of recreational vessel safety regulations can bring a criminal fine of up to $5,000, up to one year in jail, or both, and in civil enforcement the vessel itself can be held liable, meaning authorities can seize the boat to satisfy the penalty.5Office of the Law Revision Counsel. 46 USC 4311 – Penalties and Liability Beyond the citation risk, faded or illegible numbers make a boat harder for search and rescue teams to identify in an emergency.