Nautical terms
39 of 469 terms in Rules of the road. Show all
A
- All-round light (All-around light) Rules of the road
-
A light that shows all the way around the horizon (360 degrees). A white all-round light serves as an anchor light, and on power boats under 12 m it may replace the masthead light and sternlight.
- Anchor light (Riding light) Rules of the road
-
An all-round white light shown where it can best be seen by a vessel at anchor, from sunset to sunrise and in restricted visibility. Vessels under 50 m may show a single one.
On inland waters a vessel under 20 m anchored in a Coast Guard special anchorage area need not show one, and a vessel under 7 m anchored away from channels and fairways is also excused (Rule 30).
C
- Constrained by her draft (CBD, Vessel constrained by her draft) Rules of the road
-
International Rules only: a power-driven vessel so deep for the available depth and width of water that it can barely leave its track. It may show three all-round red lights in a vertical line or a cylinder, and others should avoid impeding it.
The Inland Rules have no such category; the definition is marked "reserved" there.
- Crossing situation Rules of the road
-
Two power-driven vessels crossing with risk of collision: the one that has the other on her own starboard side keeps out of the way and, if possible, avoids crossing ahead of her (Rule 15).
A quick check the Coast Guard gives: if you see another vessel's red sidelight on your starboard side at night, you are the give-way vessel.
D
- Danger signal (Doubt signal, Five short blasts) Rules of the road
-
At least five short, rapid blasts on the whistle, sounded when you do not understand another vessel's intentions or doubt it is doing enough to avoid a collision (Rule 34(d)). It may be backed up with five or more short, rapid flashes.
- Day shape (Shapes) Rules of the road
-
Black balls, cones, diamonds or cylinders hoisted by day to show a vessel's status, the daytime match for special lights. Examples: one ball forward at anchor, a cone point-down when motor-sailing, two balls when not under command.
- Demarcation line (COLREGS demarcation line) Rules of the road
-
A line, printed on charts and listed in 33 CFR 80, that divides the high seas from US harbors, rivers and other inland waters. It decides whether the Inland Rules or the International Rules apply where you are.
- Distress signals (Annex IV signals) Rules of the road
-
The signals listed in Annex IV of the Rules that mean "in distress and need help": a continuous fog signal, red flares, orange smoke, SOS, "Mayday" by radio, a DSC distress alert, an EPIRB signal, and slowly raising and lowering outstretched arms, among others.
Using any of these signals except in real distress is prohibited. Inland rules also recognize a high-intensity white light flashing 50 to 70 times a minute.
F
- Fog signals (Sound signals in restricted visibility) Rules of the road
-
Rule 35 signals in or near restricted visibility, at intervals of no more than 2 minutes: one prolonged blast for a power-driven vessel making way; two when stopped; one prolonged and two short for sailing, fishing, towing, NUC or RAM vessels.
At anchor, ring a bell rapidly for about 5 seconds each minute. Boats under 12 m need not use these exact signals but must make some other efficient sound signal at least every 2 minutes.
G
- Give-way vessel Rules of the road
-
The vessel the Rules require to keep out of the way of another. Rule 16 says it must act early and substantially so that it stays well clear.
The Coast Guard stresses that the Rules do not grant rights, they impose responsibilities, so it avoids the phrase "right of way".
H
- Head-on situation (Meeting situation) Rules of the road
-
Two power-driven vessels meeting on opposite or nearly opposite courses with risk of collision. Each turns to starboard so they pass port side to port side (Rule 14). At night you would see the other's masthead lights in line and both sidelights.
I
- In sight of one another Rules of the road
-
Two vessels are in sight of one another only when one can be seen by eye from the other. The crossing, meeting and overtaking rules (11 to 18) apply only then; a target seen only on radar in fog falls under Rule 19.
- Inland Rules (Inland Navigation Rules) Rules of the road
-
The US version of the Navigation Rules used on harbors, bays, rivers and the Great Lakes, shoreward of the demarcation lines. They match the International Rules in most places but differ in some whistle signals, lights and river right-of-way.
One practical difference: on inland waters, one- and two-blast whistle signals state what you intend to do and expect an answer; under the International Rules they announce a turn you are making.
L
- Lookout (Look-out) Rules of the road
-
Rule 5 requires every vessel to keep a proper lookout at all times, by sight, by hearing and by every other available means such as radar, so it can fully judge the situation and any risk of collision. It applies to small boats and single-handers too.
The Coast Guard says that on all but the smallest boats the lookout should ideally be someone other than the helmsman, placed where they can best see and hear.
M
- Making way Rules of the road
-
Moving through the water under power or sail. A vessel can be underway without making way, for example stopped and drifting, and the fog signals differ: one prolonged blast when making way, two when stopped.
- Maneuvering signals (Whistle signals) Rules of the road
-
Rule 34 whistle signals between power-driven vessels in sight of each other: one short blast for a turn to starboard (inland: "I intend to leave you on my port side"), two short for port, and three short for "operating astern propulsion".
Inland, a passing agreement made by VHF radio can replace the whistle signals; if no agreement is reached, sound them.
- Masthead light Rules of the road
-
A white light on the centerline showing forward over 225 degrees, from dead ahead to 22.5 degrees abaft the beam on each side. Power-driven vessels underway show one; vessels 50 m and longer add a second, higher one aft.
A power-driven boat under 12 m may show an all-round white light plus sidelights instead (Rule 23(d)).
N
- Narrow channel (Fairway) Rules of the road
-
Rule 9: in a narrow channel or fairway keep as near its starboard edge as is safe. Boats under 20 m and sailing vessels must not impede a vessel that can only navigate inside the channel, and no one should cross in a way that does. Avoid anchoring in one.
What counts as "narrow" depends on the vessels involved; the Coast Guard advises erring on the side of following Rule 9.
- Not under command (NUC, Vessel not under command) Rules of the road
-
A vessel that, through some exceptional circumstance such as a steering failure, cannot maneuver as the Rules require and so cannot keep out of the way. It shows two all-round red lights in a vertical line, or two black balls by day.
These are not distress signals (Rule 27(h)); a vessel that needs help uses the distress signals of Annex IV.
O
- Overtaking (Overtaking situation) Rules of the road
-
Coming up on another vessel from more than 22.5 degrees abaft her beam, where at night you would see only her sternlight. The overtaking vessel must keep clear until finally past and clear, whatever kind of vessels are involved (Rule 13).
If in doubt whether you are overtaking, the Rules say assume you are.
P
- Power-driven vessel Rules of the road
-
Any vessel moved by machinery. A sailboat with its engine in gear is a power-driven vessel under the Rules, even with its sails up.
When motor-sailing by day, Rule 25(e) calls for a cone, point down, hoisted forward; on inland waters a boat under 12 m may skip it.
- Prolonged blast Rules of the road
-
A whistle or horn blast lasting four to six seconds (Rule 32). One prolonged blast is sounded when nearing a blind bend in a channel and, on inland waters, when a power-driven vessel leaves a dock or berth.
R
- Restricted in ability to maneuver (RAM, Vessel restricted in her ability to maneuver) Rules of the road
-
A vessel whose work, such as dredging, surveying, diving, laying cable, servicing a buoy or certain towing, keeps it from getting out of the way. It shows red-white-red all-round lights in a vertical line, or ball-diamond-ball shapes by day.
- Restricted visibility Rules of the road
-
Any condition in which fog, mist, falling snow, heavy rain, sandstorms or something similar limits how far you can see. Rule 19 (conduct in restricted visibility) and the fog signals of Rule 35 then apply.
- Right of way (Right-of-way) Rules of the road
-
A common phrase the Rules mostly avoid: they give vessels duties to keep clear or to stand on, not privileges. The main exception is Inland Rule 9, which gives right-of-way to a downbound power-driven vessel with a following current in narrow channels on the Great Lakes and Western Rivers.
- Risk of collision Rules of the road
-
Rule 7: use every available means to judge whether you might collide, and if in doubt assume you might. If an approaching vessel's compass bearing does not change noticeably, risk of collision is deemed to exist.
The bearing can still change while risk remains, especially near a large ship, a tow, or a vessel at close range.
S
- Safe speed Rules of the road
-
Rule 6: always travel at a speed that lets you act effectively to avoid a collision and stop within a suitable distance. Visibility, traffic, your boat's stopping and turning ability, wind, sea, current, nearby hazards and depth all count.
The Rules set no number for safe speed or passing distance; it depends on the conditions at the time.
- Sailing vessel Rules of the road
-
Any vessel under sail, provided that any engine it has is not being used to drive it. Start the engine and put it in gear, and the boat counts as a power-driven vessel.
- Short blast Rules of the road
-
A blast of about one second on the whistle or horn (Rule 32).
- Sidelights Rules of the road
-
A green light on the starboard side and a red light on the port side, each shining from dead ahead to 22.5 degrees abaft the beam (112.5 degrees). On vessels under 20 m they may be combined in one lantern on the centerline.
- Stand-on vessel (Privileged vessel) Rules of the road
-
The vessel that must hold its course and speed while the other keeps clear (Rule 17). If the give-way vessel is plainly not acting, it may maneuver to avoid collision, and it must act if collision can no longer be avoided by the other alone.
In a crossing situation a stand-on power-driven vessel that does act should, if it can, avoid turning to port for a vessel on its own port side (Rule 17(c)).
- Sternlight (Stern light) Rules of the road
-
A white light at the stern shining aft over 135 degrees, 67.5 degrees either side of dead astern. If a vessel's sternlight is the only light of hers you can see, you are overtaking her.
T
- Traffic separation scheme (TSS) Rules of the road
-
A charted set of one-way lanes for ships approaching busy ports. Rule 10: cross a lane as close to a right angle as practicable, avoid anchoring in or near one, and if you are under 20 m or under sail do not impede ships following a lane.
U
- Underway (Under way) Rules of the road
-
In the Rules, a vessel is underway whenever it is not anchored, not made fast to the shore and not aground. A boat drifting with its engine stopped is still underway.
V
- Vessel Rules of the road
-
In the Navigation Rules, any watercraft used or able to be used to travel on water, including seaplanes and hovering or wing-in-ground craft. A dinghy, a kayak and a 50-foot trawler are all vessels with duties under the Rules.
- Vessel engaged in fishing Rules of the road
-
A vessel fishing with nets, lines, trawls or other gear that limits its ability to maneuver. A boat trolling lines that do not hamper its maneuvering is not "engaged in fishing" under the Rules.
Power-driven and sailing vessels underway must keep out of the way of a vessel engaged in fishing (Rule 18), but a fishing vessel must not impede traffic in a narrow channel (Rule 9).
W
- Western Rivers Rules of the road
-
An Inland Rules term for the Mississippi River and its tributaries, South and Southwest Passes, and parts of the Atchafalaya and Red Rivers. Some special rules apply there, such as right-of-way for power-driven vessels heading downstream with the current.
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.