VHF radio and satellite phones didn’t always exist. Back in the day—way, way back, as long ago as ancient times—sailors would hoist flags to communicate with one another. You know, so they could send messages along the lines of, “My dear lord Perseus, that saber-toothed tiger is heading toward your cannons.” Seriously, though, it’s from those long-ago communications that today’s system of nautical flags, or boat flags, evolved. Today’s official name for boat flags is international maritime signal flags. There are 26 international maritime signal flags, each representing a different letter of the alphabet, and each having a second meaning that’s a message to other boaters.

Nautical flags can have many meanings:

  • Complex messages

  • Warnings

  • Secret coded messages

  • Military communication

  • Indications for speed and direction

  • Race start signals and shortened courses

nautical flags

As an experienced boater, it's important to be familiar with the common meanings for many popularly used nautical flags.

Because of their dual nature, nautical flags can be hung individually or strung together to send more complex messages. For instance, the delta or “d” flag means “I am maneuvering with difficulty, keep clear.” The victor or “v” flag means “I require assistance.” People who can spot the “d” and “v” flags on sight—a yellow-and-blue striped flag next to a white flag with a red X through it—know that the message being sent is, “I am maneuvering with difficulty, and I require assistance.”

That whole message comes through, about what could be, say, malfunctioning steering gear, all from two pieces of cloth hanging on a line.

The delta or “d” flag means “I am maneuvering with difficulty, keep clear" (see left). While the victor or “v” flag means “I require assistance.” When both are flown next to each other, it means “I am maneuvering with difficulty, and I require assistance.”

Nautical flags can serve as warnings for everything from divers in the water to dangerous leaking cargo. They can communicate something routine, such as a change in course. They also can be a plea for help at a time when a person can’t talk, say after a heart attack on board; the “w” or whiskey flag means “I require medical assistance.”

Of course, if two parties can agree on alternate meanings, then boat flags can be used to send secret coded messages, too. Militaries have used nautical flags for coded messages for centuries. There’s nothing stopping you on your express cruiser and your buddy on his sportfisherman from agreeing that “tango-yankee” hung side-by-side off the portside bow at 5 p.m. means “meet me at the bar on shore.”

Other boat flags can have all kinds of meanings. There are 10 numerical flags for the numerals 0 through 9 (the first numerical code system for the U.S. fleet was published way back in 1797). NATO, the North Atlantic Treaty Organization, has a series of flags that can be used to address everything from speed to direction, as well as certain groups of boats. Race committees have a bunch of nautical flags that alert sailors to postponed starts, shortened courses and the like. And, of course, yacht club commodores and other officers may fly boat flags identifying their presence aboard a certain yacht during a regatta.

With all of these nautical flags—and most other flags you’re likely to see out on the water—the most important thing to remember is that a message is being sent. Boat flags, outside of a parade or boat show, aren’t usually flown just to be pretty. Somebody is trying to communicate something. The good news is that, these days, it’s probably not an approaching saber-toothed tiger. Even still, it’s best to learn what boat flags mean, just in case of trouble.

To become familiar with more of the basics of boating and navigation, read...

Editor's Note: This article was last updated in March 2022. 

Written by: Kim Kavin
Kim Kavin is an award-winning writer, editor and photographer who specializes in marine travel. She is the author of 10 books including Dream Cruises: The Insider’s Guide to Private Yacht Vacations, and is editor of the online yacht vacation magazine www.CharterWave.com.