Not a state boating agency — not a government website
Keentune is a private study app, not affiliated with, endorsed by, or acting for the U.S. Coast Guard, NASBLA, any state boating agency, or any government agency. It is not an approved boater education course and cannot issue a boater education card; for those, use your state boating agency’s website.
10 chapters
·
about 17 min read
·
free
Most people meet the Navigation Rules as a list of who has right of way, and that framing causes the accidents. The Rules never grant a right of way. They assign two roles — one vessel keeps out of the way, the other holds its course so the first can predict it — and both roles come with duties, including the duty to break the pattern when the plan is failing. Everything else is machinery for making those roles visible: lights say what a vessel is and what it is doing, sound signals say what it intends, and buoys say where the water is. Read this in that order — roles first, then the signaling that supports them — and the individual rules stop needing memorization.
Each chapter opens with the short version. Tap one to read the detail.
What the Rules are, who they bind, and the rule that overrides the rest
~2 min
The Rules apply to every vessel, from a kayak to a container ship, and two sets exist — International offshore and Inland inside the demarcation lines. Rule 2 sits above all of it: no rule excuses you from the ordinary precautions a seaman would take.
There are two rule sets. International rules apply at sea; Inland rules apply landward of the demarcation lines drawn along the coast. They agree on most things and differ in specific, memorable places — which is why "the rules" is always a question of which set.
"Vessel" is defined broadly enough to include a paddleboard. There is no size threshold and no exemption for recreational craft; a kayak in a shipping channel is a vessel with duties.
Rule 2 is the one to internalize, and it cuts twice. It says nothing in the Rules exonerates anyone from the consequences of neglecting ordinary precautions — so complying with a rule is not a defense if you were careless in some other respect. And it says a departure from the Rules is required when necessary to avoid immediate danger. The Rules are not a script that absolves you when following it leads to a collision.
That double edge explains why experienced mariners talk about the "General Prudential Rule". Most disputes are not about which vessel had the technical obligation; they are about whether both did what a careful operator would have done.
Rule: if following a rule is visibly leading toward collision, Rule 2 requires you to depart from it — not to comply and be right.
Lookout, safe speed, and how risk of collision is actually judged
~2 min
Four duties apply at all times and in every condition: keep a proper lookout, proceed at a safe speed, determine whether risk of collision exists, and take action that is early, substantial and obvious. Most collisions fail at the first two.
A proper lookout means sight and hearing and every available means — which today includes radar and the automatic identification system if fitted. It is a continuous duty, not something you do before departure.
Safe speed is not a number. It is the speed at which you can stop or turn within the distance you can actually assess, given visibility, traffic density, your own stopping characteristics, sea state, background lights and radar limitations. A speed that is safe in open water at noon is not safe in a crowded anchorage at dusk.
The test for risk of collision is the compass bearing. If the bearing to an approaching vessel does not appreciably change, risk exists — even if the range is still large, and even if the vessel appears to be passing "well clear". A steady bearing with decreasing range is a collision course by definition. When in doubt, the Rules say to assume risk exists.
Action must be positive, made in ample time, and large enough to be obvious to the other vessel, visually or by radar. A series of small course changes is specifically discouraged: it reads as indecision and gives the other operator nothing to predict.
Concretely: a vessel sits broad on your starboard bow at three miles, bearing 040 by compass. Ten minutes later she is at a mile and a half and still bears 040. Rule 7 says that steady bearing is risk of collision, however wide the water still looks; Rule 8 says the answer is one alteration large enough to be readily apparent to her, made now — a succession of small alterations is the thing it tells you to avoid.
Rule: watch the bearing, not the distance — a constant bearing is the warning, and it arrives long before the range looks alarming.
The three geometries, and why "give-way" is a job description
~2 min
Every power-driven encounter reduces to head-on, crossing, or overtaking. Each assigns one vessel to keep out of the way and the other to hold course and speed — and the stand-on vessel's duty is an obligation to be predictable, not a privilege.
Head-on: two power-driven vessels approaching reciprocally. Both alter to starboard and pass port-to-port. Neither is give-way; the duty is symmetric. If you are unsure whether a situation is head-on, the Rules say to assume it is and act accordingly.
Crossing: the vessel that has the other on its starboard side keeps out of the way, and should avoid crossing ahead of it. The other holds course and speed.
Overtaking: any vessel coming up from more than 22.5 degrees abaft the beam is overtaking, and must keep clear until finally past and clear. This one overrides the others — an overtaking vessel does not acquire crossing rights by changing its angle, and a subsequent change of bearing does not make it a crossing vessel.
The stand-on vessel's duty is the part people misread. Holding course and speed exists so the give-way vessel can predict you. But as the stand-on vessel you may act when it becomes apparent the other is not taking sufficient action, and you must act when collision cannot be avoided by the give-way vessel's action alone.
Concretely: at night a vessel shows you a red sidelight and a masthead light about 40 degrees on your starboard bow, bearing steady. You have her on your starboard side, so Rule 15 makes you give-way — early and substantial action, and pass astern, since crossing ahead is what the rule says to avoid; she keeps her course and speed. Had she shown only a white sternlight you would be overtaking under Rule 13, and no later change of bearing turns that into a crossing.
Rule: name the geometry first, then the roles — and remember that "stand-on" is a duty to stay predictable, with a duty to act when predictability stops working.
Rule 18's pecking order, and its two big qualifications
~2 min
When vessels of different types meet, a ranking decides who keeps clear: not under command, restricted in ability to maneuver, constrained by draft, fishing, sailing, then power-driven. The ranking is real, but it does not survive a narrow channel or an overtaking situation.
The order runs from least able to maneuver to most. A vessel not under command (unable to maneuver through some exceptional circumstance) and one restricted in its ability to maneuver (by the nature of its work — dredging, cable-laying, servicing a navigation mark) sit at the top. Then a vessel constrained by her draft, which exists only in the International rules. Then a vessel engaged in fishing, meaning fishing with gear that restricts maneuverability — trolling does not count. Then sailing. Then power-driven.
Two qualifications do most of the work in practice. First, the hierarchy is a keep out of the way ordering between different vessel types; it does not override the overtaking rule, and an overtaking sailing vessel still keeps clear of the power-driven vessel it is passing. Second, Rule 9 means a vessel of any type must not impede a vessel that can safely navigate only within a narrow channel — a rule that regularly surprises sailors.
Sailing vessels meeting each other have their own ordering, by tack and by windward position.
Concretely: a boat under sail and a container ship meet in a dredged channel the ship cannot leave. Rule 18 alone puts power below sail, but it opens "except where Rules 9, 10 and 13 otherwise require", and Rule 9(b) says a sailing vessel, or any vessel under 20 meters, shall not impede a vessel that can safely navigate only within a narrow channel. The sailboat keeps clear — and a ship in doubt about a crossing vessel's intentions sounds five short blasts.
Rule: check for overtaking and for a narrow channel before applying the hierarchy — both outrank it.
Narrow channels, traffic schemes, and what fog actually changes
~2 min
In a narrow channel, keep to the starboard side and do not impede a vessel that can only navigate there. In restricted visibility, the give-way and stand-on roles do not exist at all — that is the single most important thing fog changes.
In a narrow channel or fairway, keep as near to the outer limit on your starboard side as is safe. Small craft, sailing vessels and vessels engaged in fishing must not impede a vessel that can navigate safely only within the channel. Crossing it is permitted only if you do not impede such a vessel.
A traffic separation scheme — a routing system that separates opposing streams of traffic — is used by joining at its ends where practicable, and crossed, if you must cross, on a heading as nearly as possible at right angles to the traffic flow.
Restricted visibility changes the framework, not just the caution level. The steering rules that assign give-way and stand-on apply between vessels in sight of one another. Once you cannot see the other vessel, those roles are gone, and Rule 19 applies to both: proceed at a safe speed with engines ready for immediate maneuver, and take avoiding action in ample time.
Rule 19 also names two turns for you to avoid where possible: altering to port for a vessel forward of your beam (unless it is being overtaken), and altering toward a vessel abeam or abaft the beam.
Concretely: in fog with no radar contact you hear one prolonged blast about every two minutes somewhere forward of your beam — Rule 35's signal for a power-driven vessel making way. Rule 19(e) then applies: reduce to the minimum speed that keeps you on course, take all way off if you must, and navigate with extreme caution until the danger is over. If she shows on radar forward of the beam instead, Rule 19(d) forbids the instinctive turn to port for her.
Rule: in fog, stop looking for who is stand-on — nobody is, and acting as though you are the privileged vessel is the classic fog collision.
How to read a light: arcs, ranges, and when they are required
~2 min
Navigation lights are a language with fixed vocabulary. Each light has a defined color, a defined arc of visibility measured in degrees, and a minimum range set by vessel length — so the lights you can see tell you the aspect you are viewing from.
Lights are shown from sunset to sunrise, and also in restricted visibility by day. The arcs are the key to reading them.
Sidelights are red to port and green to starboard, each covering 112.5 degrees from dead ahead to 22.5 degrees abaft the beam. A sternlight is white over 135 degrees astern. Together those cover the full circle exactly: 112.5 + 112.5 + 135 = 360. A masthead light is white over 225 degrees, covering the forward arc.
That arithmetic is the practical trick. Seeing only a white sternlight means you are behind the vessel. You are overtaking, and the burden is yours. Seeing red and green together with a masthead light means you are nearly dead ahead of a power-driven vessel: a head-on situation. Seeing one sidelight tells you which side you are on.
Required ranges scale with vessel length, so a small craft's lights are legitimately dimmer and closer together, and are easy to lose against shore lights. Dayshapes — black balls, cones and diamonds — carry the equivalent information in daylight.
Rule: work the arcs, not the colors alone — the combination of lights you can see fixes your aspect, and your aspect determines your duty.
Reading a vessel's job from its lights
~2 min
Beyond the basic set, extra lights say what a vessel is doing — towing, fishing, dredging, restricted, aground, at anchor. These are the lights that tell you where the vessel sits in the Rule 18 hierarchy before it is close enough to see anything else.
The basic power-driven set is a masthead light, sidelights and a sternlight, with a second masthead light abaft and above the first on vessels of 50 meters or more. That second light also gives you the vessel's heading at a glance, because the two masthead lights line up when it is heading straight at you.
The status lights are the ones worth recognizing. A vessel not under command shows two all-round reds in a vertical line. Restricted in ability to maneuver shows red-white-red. Constrained by draft shows three all-round reds. A vessel at anchor shows an all-round white forward, and a second one aft if 50 meters or more. A vessel aground shows the anchor lights plus two all-round reds.
Towing changes the picture substantially: extra masthead lights in a vertical line indicate the tow's length, and a long tow astern is far larger than the towing vessel's lights suggest. The unlit water between a tug and its tow is a hazard that has sunk boats that passed between them.
Fishing vessels show green-over-white when trawling and red-over-white otherwise.
Concretely: ahead at night, red-white-red in a vertical line with a green sidelight below it — a vessel restricted in her ability to maneuver (Rule 27), showing you her starboard side and making way; under Rule 18 sail and power alike keep out of her way. Astern of a tug you would see two masthead lights in a vertical line, three if the tow exceeds 200 meters, and a yellow towing light above the sternlight (Rule 24); the towed vessel behind shows only sidelights and a sternlight, and the dark water between is the tow line.
Rule: identify the status lights first — they tell you the hierarchy position, and therefore your duty, at maximum range.
Sound signals say intention, not warning
~2 min
Short blasts announce maneuvers. In International waters they state what you are doing; in Inland waters they propose it and require agreement. That difference — action versus proposal — is the most consequential divergence between the two rule sets.
A short blast is about one second; a prolonged blast four to six.
Under the International rules, maneuvering signals are declarations of fact: one short blast means "I am altering my course to starboard", two means to port, three means "I am operating astern propulsion". You sound them as you act.
Under the Inland rules the same blasts are a proposal, and the other vessel is required to answer with the same signal to agree — or with the danger signal to disagree. Failing to answer is not consent. This is the divergence to remember, because the same two blasts mean "I am turning" offshore and "may I turn?" inshore.
Five or more short rapid blasts is the danger or doubt signal, used when you do not understand another vessel's intentions or doubt it is taking sufficient action. It is under-used: it exists precisely for the moment when you are unsure, and sounding it early is cheap.
In restricted visibility the signals change entirely to prolonged blasts on a timed cycle — a power-driven vessel making way sounds one prolonged blast every two minutes; a vessel not under command, restricted, sailing, fishing or towing sounds one prolonged plus two short.
Concretely, Inland: two power-driven vessels meeting inside half a mile. You sound one short blast — "I intend to leave you on my port side". If she agrees she sounds one short blast back and both pass port-to-port; if she doubts the safety of it she sounds at least five short rapid blasts, and both take precautionary action until a passing agreement is made. Silence is neither. Offshore the same single blast would mean you are already turning to starboard.
Rule: know which rule set you are in before you sound two blasts — offshore it announces, inshore it asks.
Buoyage: the lateral system and what it assumes
~2 min
United States buoyage follows the International Association of Marine Aids to Navigation and Lighthouse Authorities Region B convention: red to the right when returning from sea. Everything else in the system is a modifier on that one rule, and it is the opposite of the convention used across much of the world.
The lateral system marks the sides of a channel relative to a direction of travel. In Region B, which covers the Americas, red marks are kept to starboard when returning from seaward — the mnemonic is "red, right, returning". Region A, covering most of Europe, Africa and Asia, reverses it, so a chart's region is not a detail.
Red marks are even-numbered and often nun-shaped; green marks are odd-numbered and can-shaped. Numbers increase as you proceed from seaward, so they double as a progress check.
"Returning from seaward" is the assumption that carries the whole system, and it is not always obvious on a river or an intracoastal route, where a conventional direction of travel is defined rather than physical. Getting the direction wrong inverts every mark you see.
Beyond the lateral marks: preferred-channel marks are banded red and green, with the top band showing the preferred side; safe-water marks are red and white vertically striped and can be passed on either side; isolated-danger marks are black with red bands. Special marks are yellow and carry no lateral meaning at all.
Concretely: heading up a channel from the sea at night, a flashing red light lies to your right and a flashing green to your left — red lights mark the starboard side in the conventional direction, red nuns carry even numbers, green cans odd — so you are in the channel. Meet a mark banded red and green and the topmost band names the preferred channel: red on top is a starboard-hand mark for the preferred channel and a port-hand mark for the other. Red-and-white vertical stripes is safe water all round. Certain Intracoastal Waterway marks carry reversed lateral significance, which is why the direction, not the color, is the thing to check.
Rule: fix the direction of "returning from seaward" before reading a single buoy — every mark's meaning depends on it.
Bridges, regulated areas, and the rules that are local
~2 min
Beyond the Navigation Rules sit federal regulations for specific waters: bridge signals and clearances, safety and security zones, speed-restricted areas and vessel traffic services. These are local by nature, so the operative skill is knowing they exist and where to look.
Drawbridges have their own signaling and their own schedules, and many open only at fixed times or on advance notice. A bridge that does not answer is not necessarily ignoring you; it may be operating on a published schedule that a chart supplement lists.
Regulated navigation areas, safety zones and security zones are established for specific waters and carry specific prohibitions — often a minimum standoff distance from naval vessels or critical infrastructure, sometimes a speed limit, sometimes a seasonal closure. They appear on charts and in local notices rather than in the Rules themselves.
Vessel traffic services operate in busy ports, monitoring and organizing traffic on a designated radio channel. Participation is mandatory for some classes of vessel and advisory for others, but listening is useful for everyone: it tells you what the large vessels around you intend before you can see it.
Manatee zones, no-wake zones and similar restrictions are state or local, which is the general shape of this material — the further you get from collision avoidance, the more the applicable rule depends on exactly where you are.
Concretely: a recreational boat entering a port with a vessel traffic service is a "VTS User" only if it falls under the Bridge-to-Bridge Radiotelephone Act, must take part in the reporting system, or carries a required AIS — three conditions, none of them size. If it does, it keeps a listening watch on the VTS frequency and follows the VTS's directions. At the drawbridge upstream the request is one prolonged blast followed within three seconds by one short; the same signal back means the draw will open, and the federal drawbridge regulation says to repeat the request until it is acknowledged.
Rule: treat this category as a checklist to run before departure — unlike the steering rules, none of it can be derived from first principles on the water.
Written by Keentune. We are not affiliated with or endorsed by the organizations whose documentation informs this guide, and any linked sources belong to their respective owners.
All exam, test, and product names and trademarks are the property of their respective owners and are used here for identification and reference only. Keentune is independent study practice — not affiliated with, authorized, or endorsed by any of these organizations.