Boating Safety
 Two rulebooks

One short blast means
two different things.

The rules that decide who turns are shorter than people expect, older than people expect, and split into two versions that disagree in the places that matter most to a small boat. This page covers the steering and sailing rules, what the lights and shapes tell you, what the whistle signals mean and where they mean something else, what changes in fog, and how to read the aids. Rule numbers throughout are the shared numbering used by both the Inland Rules (33 CFR part 83) and the International Rules.

Read this part
This is a study and reference page about the US Navigation Rules. It is not the Rules. The Rules are federal law, they run to a hundred pages of text plus five annexes, and a summary cannot cover the case you are actually in. Carry the current Navigation Rules and Regulations Handbook and read the rule itself before you rely on it. Nothing here is legal advice, and it does not substitute for the state boating safety course your state may require by law.
ON THIS PAGE
There are two rulebooks, and you are always in one of them Look-out, safe speed, and how you know a collision is coming What a proper avoiding action looks like The three encounters: overtaking, head-on, crossing Give-way, stand-on, and the trap in the middle Responsibilities between vessels, and the myth about sail Narrow channels and traffic separation schemes Lights and shapes: what you must show Sound signals, and the one that means different things in different waters Restricted visibility, where the ordinary rules stop applying Aids to navigation: reading the water
START HERE

There are two rulebooks, and you are always in one of them

Most people learn "the rules of the road" as a single thing. It is two things. The International Rules (the 1972 COLREGS) apply on the high seas and in waters connected to them outside a line drawn along the coast. The Inland Rules apply landward of that line. The line itself is drawn in 33 CFR part 80, harbour by harbour, and it is called the COLREGS Demarcation Line.

The two sets share their numbering, which is a mercy: Rule 15 is the crossing rule in both. They also share most of their text word for word. But they diverge in exactly the places that matter most in a small boat — what a whistle signal means, who has right of way on a river, and what you do about an overtaking vessel. Learning one and assuming the other is the single most common way to be confidently wrong.

Where the two rulebooks actually disagree
Rule 9 and 14 Inland gives a downbound vessel on the Great Lakes, Western Rivers, or waters the Secretary specifies the right of way over an upbound vessel, and the downbound vessel initiates the signals. International has no such provision. rivers
Rule 15 Inland adds that a power-driven vessel crossing a river keeps out of the way of one ascending or descending it. International does not. rivers
Rule 34 The big one. International whistle signals announce what you are doing: one short blast means "I am altering my course to starboard". Inland signals announce what you intend: one short blast means "I intend to leave you on my port side", and they are exchanged when meeting or crossing within half a mile. everywhere
Rule 34(c) Overtaking. International uses two prolonged plus one or two short. Inland uses one or two short blasts alone, and the vessel being overtaken agrees by sounding the same signal back. everywhere
Rule 23 International lets a power-driven vessel under 7 metres making no more than 7 knots show an all-round white light and, if practicable, sidelights. Inland has no 7-metre exception of that kind. small boats

If you boat on a bay, a lake, a river or inside a harbour, you are almost certainly under the Inland Rules, and Inland Rule 34 is the version you need. Check 33 CFR 80 for the demarcation line at your own inlet before you assume.

A rule this page will keep coming back to
Rule 2 is the one nobody quotes and everybody is judged against. It says nothing in the Rules exonerates any vessel from the consequences of neglecting to comply with them, or of neglecting any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case. And it says that in construing the Rules, due regard shall be had to all dangers of navigation and collision, and to any special circumstances that may make a departure from the Rules necessary to avoid immediate danger. Rule 2 is why "I had right of way" has never once been a complete defence.
RULES 5 TO 7

Look-out, safe speed, and how you know a collision is coming

Rule 5 is twenty-nine words and is cited in more collision findings than any other: "Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision." Note hearing, and note all available means — if you have radar or AIS switched off, you are not using all available means.

Rule 6 defines safe speed functionally rather than numerically: a speed at which you "can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions." There is no number in it. The rule then lists what you must weigh — visibility, traffic density, your own manoeuvrability and stopping distance, background light at night, sea state, draught against depth — and adds a second list for vessels with operational radar.

Safe speed is not the posted speed limit
A state or local no-wake zone is a separate legal requirement. Rule 6 can require you to go slower than the posted limit and never permits you to go faster than is safe. In fog, at night, in traffic, or in a boat you cannot stop quickly, the safe speed can be a small fraction of what the boat will do. Excessive speed was the primary contributing factor in 279 accidents and 26 deaths in 2024.

Rule 7 is the test. "Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist." The operative technique is in 7(d): risk of collision shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change.

Constant bearing, decreasing range
Sight the other vessel across a fixed part of your own boat — a stanchion, the edge of the windscreen — while you hold your own course and speed. If she stays lined up with that mark and gets bigger, you are on a collision course. If she draws forward of the mark, she will pass ahead; if she draws aft, she will pass astern. This works because two vessels on steady courses that will collide form a closing triangle whose shape stays similar, so the bearing between them stays fixed. It is the same geometry a hand-bearing compass gives you, and it needs no instrument.

Rule 7(d)(ii) adds the exception that catches people out: risk may exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow, or when approaching at close range. A ship a thousand feet long can have a bearing that swings steadily and still run you down, because the bearing you are taking is to her bridge and the part that hits you is a quarter of a mile away from it.

RULE 8

What a proper avoiding action looks like

Rule 8 governs the quality of whatever manoeuvre you make. It requires that action be "positive, made in ample time and with due regard to the observance of good seamanship". Four specific requirements follow, and each of them exists because of a class of accident.

The give-way vessel does not get to pass close
Rule 8(d): "Action taken to avoid collision with another vessel shall be such as to result in passing at a safe distance." Threading a gap at fifty feet because you technically kept clear is not compliance. And Rule 8(f) adds that a vessel required not to impede another must take early action to allow enough sea room, and remains fully bound by the rest of the Rules if the two do end up approaching.
RULES 13 TO 15

The three encounters: overtaking, head-on, crossing

Between two power-driven vessels in sight of one another, there are only three geometries, and which one you are in is decided by where you are relative to the other vessel — not by who is bigger, faster, or under way first.

  1. 1
    Rule 13 — Overtaking. The overtaking vessel keeps clear, full stop.
    A vessel is overtaking when she is coming up on another from a direction more than 22.5 degrees abaft that vessel's beam — that is, from a position where at night she would see only the sternlight and neither sidelight. Rule 13 opens with "notwithstanding anything contained in Rules 4 to 18", so it overrides everything else in this section, including Rule 18. A sailing vessel overtaking a powerboat keeps clear of the powerboat. And 13(d) closes the argument door: any subsequent alteration of bearing does not make her a crossing vessel or relieve her of the duty until she is finally past and clear.
  2. 2
    Rule 14 — Head-on. Both turn to starboard and pass port to port.
    When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision, each shall alter course to starboard so that each passes on the port side of the other. Note that both vessels act — there is no give-way and stand-on in a head-on meeting. Rule 14(c) settles doubt in the safe direction: when in doubt whether such a situation exists, assume it does and act accordingly.
  3. 3
    Rule 15 — Crossing. The vessel that has the other on her own starboard side keeps out of the way.
    And, where the circumstances of the case admit, she shall avoid crossing ahead of the other vessel. The mnemonic is that green means go and red means stop: if you see her red sidelight she is on your starboard side and you give way; if you see her green she is on your port side, you are the stand-on vessel, and she should be keeping clear of you.
Both sidelights red green She is pointing at you. You are inside both 112.5 deg arcs, so you are within 22.5 deg of her bow. Rule 14 -- head-on. Both alter to starboard. One sidelight only green You are on one side of her. Green means you see her starboard bow: she is crossing from your left. Rule 15 -- crossing. She has you on her port side, so you give way. Sternlight only white You are behind her. No sidelight visible means you are more than 22.5 deg abaft her beam. Rule 13 -- overtaking. You keep out of her way, whatever she is.
The lights you can see decide which rule you are in. This is the same geometry as the arcs diagram further down, seen from the other vessel's position — which is the direction you actually have to reason in at night.
The 22.5-degree boundary decides which rule applies, and it is not obvious in daylight
Overtaking and crossing carry opposite duties in some geometries, and the line between them is 22.5 degrees abaft the beam — a bearing you cannot judge accurately by eye on a moving boat in daylight, when no lights are showing. Rule 13(c) is the answer: "When a vessel is in any doubt as to whether she is overtaking another, she shall assume that this is the case and act accordingly." Doubt resolves toward the duty to keep clear, every time.
RULES 16 AND 17

Give-way, stand-on, and the trap in the middle

Rule 16 is one sentence: every vessel directed to keep out of the way of another shall, so far as possible, take early and substantial action to keep well clear. Early, substantial, well clear. Three words, three separate failures available.

Rule 17 is the harder one, because it changes the stand-on vessel's duty twice as the situation deteriorates. Most people learn only the first stage.

  1. 1
    Stage one: hold course and speed.
    Rule 17(a)(i). The stand-on vessel keeps her course and speed. This is a duty, not a privilege — the give-way vessel is making her plan on the assumption that you will do the predictable thing, and a helpful early turn by the stand-on vessel is how a large fraction of collisions begin.
  2. 2
    Stage two: you may act, and there is one thing you must not do.
    Rule 17(a)(ii). As soon as it becomes apparent that the give-way vessel is not taking appropriate action, the stand-on vessel may take action by her manoeuvre alone. But 17(c) forbids one specific manoeuvre: a power-driven vessel taking action under this paragraph in a crossing situation shall, if the circumstances admit, not alter course to port for a vessel on her own port side. Turning left into a vessel that is about to turn right is how the near miss becomes the collision.
  3. 3
    Stage three: you must act, and everything is on the table.
    Rule 17(b). When collision cannot be avoided by the give-way vessel's action alone, the stand-on vessel shall take such action as will best aid to avoid collision. "Shall", not "may". At this point the port-turn restriction gives way to whatever actually works.
Being the stand-on vessel does not make a collision the other party's fault
Rule 17(d) preserves the give-way vessel's obligation, so she is not excused. But Rule 2 makes the stand-on vessel answerable for failing to act when acting was plainly required. In practice, marine casualty findings routinely apportion fault to both vessels: one for not giving way, one for standing on into a collision it could see coming. There is no rule that protects you from the consequences of watching it happen.
RULE 18

Responsibilities between vessels, and the myth about sail

Rule 18 sets a hierarchy for vessels of different kinds meeting each other. Read downward: each type keeps out of the way of every type above it.

Rank Vessel Keeps clear of
1 Not under command — unable to manoeuvre through some exceptional circumstance, e.g. a breakdown Nothing, in this rule
2 Restricted in her ability to manoeuvre — dredging, laying cable, launching aircraft, replenishing under way Not under command
3 Engaged in fishing — with nets, lines or trawls that restrict manoeuvrability. Not trolling. The two above
4 Under sail The three above
5 Power-driven Everything above
6 Seaplane and WIG craft All vessels; keep well clear and avoid impeding
Where "constrained by her draught" went
She is not a rung on this ladder, which is how she is usually taught. International Rule 18(d)(i) says that any vessel other than one not under command or restricted in her ability to manoeuvre shall avoid impeding the safe passage of a vessel constrained by her draught — and, as Rule 8(f) makes clear, not impeding is a weaker and earlier duty than keeping out of the way. The category does not exist in the Inland Rules at all, so on inland waters a deep-draught ship claims nothing under this head and you fall back on Rule 9(b) instead.
"Sail has right of way over power" is wrong in at least five ways
Rule 18 puts sail above power, and then the exceptions swallow a great deal of it. One: a sailing vessel with her engine running is a power-driven vessel, whether or not the sails are up. Two: Rule 13 overrides Rule 18, so a sailing vessel overtaking a powerboat keeps clear. Three: Rule 9(b) says a vessel under 20 metres, or a sailing vessel, shall not impede a vessel that can navigate safely only within a narrow channel — which is most of the commercial traffic you will meet. Four: Rule 10(j) says the same for a traffic separation scheme. Five: two sailing vessels meeting each other are governed by Rule 12, not Rule 18, and the wind decides.

Rule 12, sail against sail: when each has the wind on a different side, the vessel with the wind on her port side keeps out of the way of the other. When both have the wind on the same side, the vessel to windward keeps out of the way of the vessel to leeward. And if a vessel with the wind on her port side sees a vessel to windward and cannot tell with certainty which tack she is on, she keeps out of the way. The windward side is the side opposite that on which the mainsail is carried.

RULES 9 AND 10

Narrow channels and traffic separation schemes

Rule 9(a): a vessel proceeding along the course of a narrow channel or fairway shall keep as near to the outer limit of the channel or fairway which lies on her starboard side as is safe and practicable. Keep right, in other words, which is the opposite of the instinct to take the deepest water in the middle.

"Shall not impede" is not the same as "give way"
Rule 8(f) defines it: a vessel required not to impede another must take early action to allow sufficient sea room for the safe passage of the other vessel. The duty is to stay out of the situation entirely, before any risk of collision arises. But if the two vessels do end up approaching each other, the ordinary steering and sailing rules apply in full — not impeding does not cancel them, and being the vessel not to be impeded does not exempt anyone from Rule 5 or Rule 8.

Rule 10 governs traffic separation schemes adopted by the IMO — the shipping lanes off major ports. A vessel using one proceeds in the appropriate lane in the general direction of traffic flow, keeps clear of the separation line or zone, and joins or leaves at the ends where possible; if joining from the side she does so at as small an angle as practicable. A vessel crossing a lane shall cross on a heading as nearly as practicable at right angles to the direction of traffic flow — heading, not course made good, so you do not crab across to compensate for the current. And Rule 10(j): a vessel of less than 20 metres, or a sailing vessel, shall not impede the safe passage of a power-driven vessel following a traffic lane.

RULES 20 TO 31

Lights and shapes: what you must show

Rule 20 sets the scope, and two things in it get missed. The lights must be exhibited from sunset to sunrise, and during that time no other lights may be shown that could be mistaken for them, impair their visibility, or interfere with keeping a proper look-out — which is what makes deck floodlights and blue accent lighting a rule violation rather than a style choice. And the lights shall also be exhibited from sunrise to sunset in restricted visibility, and may be exhibited in all other circumstances when it is deemed necessary.

the beam the beam DEAD AHEAD masthead arc, 225 deg DEAD ASTERN RULE 21 -- THE ARCS, TO SCALE Port sidelight 112.5 deg red, ahead to 22.5 deg abaft the port beam Starboard sidelight 112.5 deg green, the mirror image to starboard Sternlight 135 deg white, 67.5 deg either side of right aft Masthead light 225 deg white, exactly the two sidelight arcs together All-round light 360 deg white, red, green or yellow depending on the job The three lateral arcs add to exactly 360 degrees 112.5 + 112.5 + 135 = 360. No gap, no overlap: from any bearing you see one and only one of them.
Rule 21, drawn from its own numbers. The two sidelight arcs and the sternlight arc add to exactly 360 degrees, which is why the lights tell you the aspect: from any bearing you see one and only one of them. The masthead arc is the two sidelight arcs put together.
Vessel What she shows under way Rule
Power-driven, under 12 m An all-round white light and sidelights, in lieu of the full set. This is the exception most small powerboats use. 23(d)
Power-driven, 12 m to under 50 m Masthead light forward, sidelights, sternlight. A second masthead light abaft and higher is optional under 50 m. 23(a)
Power-driven, 50 m and over The same, but the second masthead light is required. 23(a)
Sailing, under way Sidelights and a sternlight. No masthead light — a white light forward means she is under power. 25(a)
Sailing, under 20 m May combine the sidelights and sternlight in one tricolour lantern at or near the top of the mast. It replaces them rather than supplementing them, and is not permitted at 20 m and over. 25(b)
Sailing, under 7 m If she cannot show the above, she shall exhibit an all-round white light (Inland only) or have ready at hand an electric torch or lighted lantern showing a white light, exhibited in sufficient time to prevent collision. 25(d)(i)
Under sail and power at once A conical shape, apex downward, forward where it can best be seen — though the Inland text exempts vessels under 12 m. She is a power-driven vessel and must light as one. 25(e)
Vessel under oars May show the lights for a sailing vessel, or shall have ready at hand an electric torch or lighted lantern showing a white light. 25(d)(ii)
At anchor Two all-round white lights, one forward and one lower at the stern. A vessel under 50 m may instead show a single all-round white light where it can best be seen. By day, one black ball forward. 30(a), 30(b)
At anchor, under 7 m Not required to show the anchor light or ball unless anchored in or near a narrow channel, fairway, anchorage, or where other vessels normally navigate. 30(e)
Aground The anchor light plus two all-round red lights in a vertical line. By day, three black balls in a vertical line. 30(d)
Fishing, trawling Two all-round lights in a vertical line, the upper green and the lower white. By day, two cones apex to apex. 26(b)
Fishing, other than trawling Two all-round lights in a vertical line, the upper red and the lower white. 26(c)
Not under command Two all-round red lights in a vertical line. By day, two black balls. Sidelights and sternlight only when making way. 27(a)
Restricted in ability to manoeuvre Red, white, red in a vertical line. By day, ball, diamond, ball. 27(b)
Two mnemonics that actually hold up
"Red over red, the captain is dead" — two all-round reds in a vertical line is a vessel not under command. "Red, white, red, restricted she said" — red over white over red is restricted in her ability to manoeuvre. Both mean the same thing to you: she cannot get out of your way, so you get out of hers. The one to be careful with is "red over white, fishing tonight", which is only half the story: red over white is fishing other than trawling, and green over white is trawling.

Rule 22 sets how far the lights must be visible, and the numbers are minimum ranges, not what you will actually see. For a vessel under 12 metres: masthead 2 miles, sidelights 1 mile, sternlight 2 miles, all-round 2 miles. For 12 to under 50 metres: masthead 5 miles, or 3 miles if the vessel is under 20 metres, and the rest 2 miles. For 50 metres and over: masthead 6 miles, the rest 3 miles. A one-mile sidelight against a lit shoreline is close to invisible, which is a good reason to carry more light than the minimum.

RULES 32 TO 34

Sound signals, and the one that means different things in different waters

Rule 32 defines the vocabulary and there are only two words in it. A short blast is a blast of about one second's duration. A prolonged blast is a blast of from four to six seconds' duration. Everything else in Rules 34 and 35 is built from those two.

Rule 34 — the same blast, two meanings
One short blast INTERNATIONAL: "I am altering my course to starboard."   INLAND: "I intend to leave you on my port side." Rule 34(a)
Two short blasts INTERNATIONAL: "I am altering my course to port."   INLAND: "I intend to leave you on my starboard side." Rule 34(a)
Three short blasts "I am operating astern propulsion." The same in both, and note that it means the engines are going astern — not that the vessel is moving backwards yet. Rule 34(a)
Overtaking INTERNATIONAL: two prolonged plus one short to overtake on her starboard side; two prolonged plus two short for her port side; she agrees with prolonged, short, prolonged, short.   INLAND: one short blast to pass on her starboard side, two short to pass on her port side, and she sounds the same signal back if she agrees. Rule 34(c)
Five or more short and rapid blasts The doubt or danger signal, and the same in both. It means "I do not understand your intentions" or "I doubt whether you are taking sufficient action to avoid collision." It may be supplemented by five or more short and rapid flashes. Rule 34(d)
One prolonged blast Nearing a bend or an obstruction where approaching vessels may be obscured. Also sounded by a vessel leaving a berth in Inland waters. Rule 34(e), 34(g)

The Inland signals are an exchange of intentions and are required when power-driven vessels in sight of one another are meeting or crossing within half a mile. The International signals are an announcement of a manoeuvre being made, with no distance threshold. If you sound one short blast in inland waters meaning "I am turning right", you have told the other skipper you intend to pass port to port — which may be the opposite of what you are about to do.

Rule 33 decides who has to carry what. A vessel of 12 metres or more shall be provided with a whistle. A vessel of 20 metres or more shall be provided with a bell in addition. A vessel of 100 metres or more shall in addition be provided with a gong, whose tone cannot be confused with the bell. A vessel of less than 12 metres is not obliged to carry these, but "shall be provided with some other means of making an efficient sound signal" — which is why a small boat still needs a horn or whistle aboard, and why an unaided human voice does not qualify.

RULES 19 AND 35

Restricted visibility, where the ordinary rules stop applying

In fog there is no stand-on vessel
Rule 19 applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. The steering and sailing rules in Section II — head-on, crossing, overtaking, stand-on and give-way — apply only to vessels in sight of one another. The moment you lose sight of her, none of that is operative. There is no right of way in fog for anybody.
Vessel Signal in or near restricted visibility Interval
Power-driven, making way One prolonged blast At least every 2 minutes
Power-driven, under way but stopped and making no way Two prolonged blasts, with about 2 seconds between them At least every 2 minutes
Sailing vessel; fishing; not under command; restricted in manoeuvrability; constrained by draught; towing or pushing One prolonged followed by two short blasts At least every 2 minutes
Vessel towed, if manned One prolonged followed by three short blasts, sounded immediately after the towing vessel's signal where practicable At least every 2 minutes
Pilot vessel on duty The applicable signal above, plus an identity signal of four short blasts At least every 2 minutes
At anchor, under 100 m Rapid ringing of the bell for about 5 seconds. May also sound one short, one prolonged, one short blast to warn an approaching vessel. At least every minute
At anchor, 100 m and over The bell rung forward for 5 seconds, immediately followed by the gong rung aft for 5 seconds At least every minute
Aground Three distinct strokes of the bell before and after the rapid ringing, plus any appropriate whistle signal At least every minute
Under 12 m Not obliged to give the above signals, but if she does not she shall make some other efficient sound signal At least every 2 minutes
Two minutes is a long time in fog
The interval is a maximum, not a target — "at intervals of not more than 2 minutes". Two vessels closing at a combined 20 knots cover two-thirds of a mile between one signal and the next. Sound more often than the minimum, and remember Rule 5: a proper look-out is by hearing as well as sight, which means somebody has to be somewhere they can hear, with the engine noise and the stereo accounted for.
33 CFR 62

Aids to navigation: reading the water

The United States uses IALA System B, in which red marks are kept to starboard when returning from seaward. Most of the world uses System A, where it is the other way round, which is why the mnemonic is a US mnemonic. The reference point is the conventional direction of buoyage, defined in 33 CFR 62.21 as the direction in which a vessel enters navigable channels from seaward and proceeds toward the head of navigation.

Aid Appearance Light
Starboard-hand lateral Red. Nun buoys — conical top — or red beacons. Even numbers, increasing as you go upstream. Red, regularly flashing or occulting
Port-hand lateral Green. Can buoys — flat cylindrical top — or green beacons. Odd numbers, increasing upstream. Green, regularly flashing or occulting
Preferred channel (junction) Red and green horizontal bands. The colour of the topmost band tells you which channel is preferred: treat the aid as though it were entirely that colour. Composite group flashing (2 + 1), in the colour of the top band
Safe water Red and white vertical stripes, with a red spherical topmark if any. Marks mid-channel or a fairway with navigable water all round. White Morse code A: short flash, long flash
Isolated danger Black with one or more broad red horizontal bands, and a topmark of two black spheres. Marks a danger with navigable water all round it. White group flashing 2
Special mark All yellow. Anchorages, traffic separation, dredging, fishnet areas, cables, pipelines. It marks a feature, not a channel side. Yellow, if lighted
Information and regulatory White with orange geometry. Open diamond = danger. Diamond with a cross = boats keep out. Circle = controlled area, such as a no-wake or speed limit zone. Square or rectangle = information, such as directions or distances. White, if lighted