Navigation Rules reference
Boat sound signals
Every signal in Helm's catalog, 47 in all, with the rule it comes from and a clip you can play. The same short blast says different things under different rules, so each one is marked International, Inland or both.
The basics
Short and prolonged blasts. A short blast is about 1 second. A prolonged blast is 4 to 6 seconds. Clips use 1 and 5 seconds. Rule 32(b), (c); 33 CFR 83.32
Intervals. "Not more than 2 minutes" means the gap between signals can be shorter, never longer. Each clip plays one signal. In real fog you keep repeating it. Rule 35
When fog signals apply. In or near an area of restricted visibility, by day or by night. You don't have to be inside the fog. Rule 35; 33 CFR 83.35
Meeting and crossing
- Altering course to starboardInternationalone short blast
- Altering course to portInternationaltwo short blasts
- Operating astern propulsionInternational and Inlandthree short blasts
- Proposing a port-to-port passInlandone short blast
- Proposing a starboard-to-starboard passInlandtwo short blasts
- Agreeing to a port-to-port passInlandone short blast
- Agreeing to a starboard-to-starboard passInlandtwo short blasts
- Passing agreed by radioInlandNo set pattern
Overtaking
- Overtaking on the other vessel's starboard sideInternationaltwo prolonged blasts, then one short blast
- Overtaking on the other vessel's port sideInternationaltwo prolonged blasts, then two short blasts
- Agreeing to be overtakenInternationalone prolonged blast, then one short blast, then one prolonged blast, then one short blast
- Overtaking on the other vessel's starboard sideInlandone short blast
- Overtaking on the other vessel's port sideInlandtwo short blasts
- Agreeing to be overtaken on your starboard sideInlandone short blast
- Agreeing to be overtaken on your port sideInlandtwo short blasts
Warnings
- Danger or doubtInternational and Inlandat least five short, rapid blasts
- Nearing a bendInternational and Inlandone prolonged blast
- Answering a bend signalInternational and Inlandone prolonged blast
- Leaving a dock or berthInlandone prolonged blast
- Attracting attentionInternational and InlandNo set pattern
Light signals
Fog, underway
- Power vessel making wayInternational and Inlandone prolonged blast
- Power vessel stoppedInternational and Inlandtwo prolonged blasts
- Limited vessels, underwayInternationalone prolonged blast, then two short blasts
- Limited vessels, underwayInlandone prolonged blast, then two short blasts
- Fishing or restricted, at anchorInternationalone prolonged blast, then two short blasts
- Fishing or restricted, at anchorInlandone prolonged blast, then two short blasts
- Vessel being towedInternational and Inlandone prolonged blast, then three short blasts
- Composite unit making wayInternational and Inlandone prolonged blast
- Composite unit stoppedInternational and Inlandtwo prolonged blasts
- Pilot vessel identityInternational and Inlandfour short blasts
Fog, anchored or aground
- At anchor, under 100 metersInternational and Inlandrapid ringing of the bell
- At anchor, 100 meters or moreInternational and Inlandrapid ringing of the bell, then rapid ringing of the gong
- Anchored vessel's warningInternational and Inlandone short blast, then one prolonged blast, then one short blast
- Aground, under 100 metersInternational and Inlandthree bell strokes, then rapid ringing of the bell, then three bell strokes
- Aground, 100 meters or moreInternational and Inlandthree bell strokes, then rapid ringing of the bell, then three bell strokes, then rapid ringing of the gong
Small vessel rules
Distress
Drawbridges
Common questions
What does one short blast mean?
It depends on the rules you're under. International: I am altering my course to starboard (Rule 34(a)). Inland: I intend to leave you on my port side, and the other vessel answers if it agrees (Inland Rule 34(a)).
What does three short blasts mean?
I am operating astern propulsion. The signal is the same under both sets of rules (Rule 34(a)).
What does five short blasts mean?
The danger signal: at least five short and rapid blasts, sounded when you don't understand the other vessel's intentions or doubt it's doing enough to avoid collision (Rule 34(d)). At a drawbridge, five short blasts carry a different meaning under 33 CFR 117.15.
How long is a short blast and a prolonged blast?
A short blast is about 1 second. A prolonged blast is 4 to 6 seconds (Rule 32).
What is the fog signal for a power vessel?
One prolonged blast at intervals of not more than 2 minutes when making way, and two prolonged blasts when underway but stopped (Rule 35(a), (b)).
Test yourself
4 questions. Pick an answer to see its rule.
You are operating a vessel in a narrow channel. Your vessel must stay within the channel to be navigated safely. Another vessel is crossing your course from starboard to port, and you are in doubt as to his intentions. According to Rule 9, which statement is TRUE?
Show the answer
A. You may sound at least five short and rapid blasts on the whistle
When you can't tell what the other vessel intends, International Rule 9(d) lets you sound the danger signal of at least five short and rapid blasts. Inland Rule 9(d) says must.
Rule 9(d), Rule 34(d). Source: NMC sample exam.
Which statement is TRUE concerning the fog signal of a canal boat 25 meters in length, anchored in a "special anchorage area" approved by the Secretary?
Show the answer
D. The vessel is not required to sound a fog signal.
Vessels under 20 meters, and barges, canal boats, scows and other nondescript craft of any length, need no anchor signal in a special anchorage area under Inland rules.
Inland Rule 35(l), 33 CFR 83.35(l), 33 CFR 110.1(a). Source: NMC sample exam.
You are approaching a sharp bend in a river. You have sounded a prolonged blast and it has been answered by a vessel on the other side of the bend. Which statement is TRUE?
Show the answer
D. If power-driven, both vessels must exchange passing signals when in sight and passing within half mile of each other.
The prolonged bend signal doesn't replace passing signals. Power-driven vessels still exchange them once in sight within half a mile.
Inland Rule 34(a)(i), 34(e). Source: NMC sample exam.
Two power-driven vessels are meeting. What would a two blast whistle signal by either vessel mean?
Show the answer
A. "I am altering course to port"
International signals are signals of action: two short blasts means 'I am altering my course to port'. Inland signals state an intention to pass.
Rule 34(a). Source: NMC sample exam.
More in the free Rules of the Road practice test.
Hear them until they stick
Helm drills every signal with flashcards and spaced review, on the web and iPhone.
Start freeKeep studying
- Free OUPV practice testReal sample questions, each with its rule. No sign-up.
- Lights and shapesWhat each vessel shows at night and by day.
- What the exam coversThe modules, and what to confirm in your letter.
- Six-pack licenseWho needs one and what the regulations ask for.
- Rules of the roadWho gives way, and how Inland differs.
- BuoysRed right returning, and what each mark means.
Sources
- USCG NAVCEN, Amalgamated Navigation Rules
- 33 CFR Part 83, Inland Navigation Rules
- 33 CFR 117.15, drawbridge signals
Helm is an independent study aid, not affiliated with or endorsed by the U.S. Coast Guard or the National Maritime Center. This page is for study, not navigation guidance or legal advice. Check the current rules before you rely on anything here.
NAVCEN Amalgamated Navigation Rules and eCFR Title 33 current to 2026-10-29.