Chart Symbols and Abbreviations — Reading the Chart's Own Vocabulary

To port, if you are following the preferred channel — green topmost makes it a port hand mark for that channel. Taking the other channel, the same buoy is a starboard hand mark. Consult the chart before committing: the mark may also be sitting on a wreck or obstruction you may pass on either side.</details>

How the symbols are drawn

The basic buoy symbol is a diamond with a small circle, or a dot on older charts. The diamond may sit above, below or alongside; it exists to draw the eye and to describe the aid. The small circle or dot denotes the approximate position of the buoy's mooring Boat Crew Seamanship Manual (M16114.5C) Ch. 14 — Nautical Charts ¶2. Those "position approximate" circles are used on floating aids because the aid has no exact position — it moves around its mooring, and the actual buoy may be displaced from the charted circle by the scope of that mooring .

Three details in the buoy symbol are worth reading deliberately. A horizontal line through the symbol means horizontal bands; a vertical line means vertical stripes; crossed lines mean a checked pattern. The letter C, N or S beside it means can, nun or spar, and any other buoy is assumed to be a pillar unless it is a special shape such as spherical or barrel. On NOS charts the number or letter designation appears in quotation marks. There is no significance whatever to the angle at which the symbol is drawn — it is placed to avoid other features. Lighted buoys show a purple flare, or a small purple disk centred on the position circle.

Beacons are drawn differently. Small triangles mark red daybeacons; small squares mark all others, and the centre of the triangle is the position of the aid. Outside Intracoastal Waterway and state waterway charts, Bn appears beside the symbol with a colour abbreviation if known, and all beacon abbreviations are in vertical lettering. Lighthouses and other fixed lights are black dots with purple disks or purple flares, the centre of the dot being the light's position; the flare gives the look of a large exclamation mark, with major lights named and described and minor lights described only .

Lettering is a fast test of what you are looking at. Slanted Roman lettering labels everything affected by tidal change or current, with the exception of bottom soundings, and all descriptive lettering for floating aids is slanted. Vertical Roman lettering labels what tide and current do not affect — lighthouses, ranges and other fixed aids. Magenta carries most information because it reads more easily under the red light used at night.

Beacons themselves are permanently fixed to the earth's surface, from large lighthouses down to single-pile structures. Lighted beacons are called lights; unlighted beacons are daybeacons. The daymark of a large lighthouse or tower is the structure itself, and those daymarks infer no lateral significance .

Areas, restrictions and hazards

Designated anchorages are outlined with a dashed magenta line and labelled with the anchorage type: general, prohibited, restricted or quarantine Light List — Anchorage Area. Individual anchorage berths appear as purple circles with the berth number or letter inscribed, and caution notes appear where specific anchoring regulations exist. Spoil areas are enclosed by short broken black lines, tinted blue on NOS charts and labelled; they contain no soundings and should be avoided. Traffic separation schemes are printed in magenta on charts of 1:600,000 and larger Bowditch Pub. 9 Ch. 4 §442.

A controlled area is marked in the water by a white buoy with orange bands around the top and bottom and a circle symbol on opposite sides — the words inside the circle state the restriction, such as no-wake or slow-speed Light List — Controlled Area Marker. A sunken wreck may be shown by a symbol or by an abbreviation plus a number giving its depth at mean low or lower low water, and a dotted line around any symbol calls special attention to its hazardous nature .

Two abbreviation conventions catch candidates on sight-reading questions: periods after abbreviations in water areas are omitted because a period could be taken for a rock, though a lower-case i or j is still dotted; and private aids, when charted, are marked Priv on NOS charts and should be used with caution . Private aids are often established for a specific user rather than for general navigation, and discrepancies to them tend to be found and corrected less promptly than on Coast Guard aids .

Western Rivers daymarks

Diamond-shaped non-lateral dayboards, checkered red-and-white or green-and-white, are the crossing dayboards, used where the river channel crosses from one bank to the other 33 CFR §62.51. They stand in place of the triangular or square lateral daymarks used elsewhere Bowditch Pub. 9 Ch. 7 §735. The mark telling you the channel parallels the bank it stands on is the passing daymark Light List — Passing Daymark (Western Rivers).

Three further variations decide questions. Buoys are not numbered. Numbers on beacons carry no odd/even lateral significance; they indicate mileage from a fixed point, normally the river mouth. Isolated danger marks are not used . Lights on the right descending bank show single flashing rhythms, green or white; lights on the left descending bank show group-flashing-two, red or white — and the conventional direction of buoyage here is upstream, even though local terminology names the left and right banks as seen from a vessel proceeding downstream .

Telling it apart

The single criterion is whether the shape is drawn on the paper or built into the aid.

• Diamond on the chart — a cartographic symbol for a buoy, any buoy. No lateral meaning of its own; the colour, the letter and the legend carry that.
• Diamond in the water, on the Western Rivers — a checkered crossing dayboard, non-lateral. Most often misfiled as a lateral mark to be left on one side.
• Triangle on the chart — a red daybeacon. Squares mark all the others, so a green daybeacon plots as a square.
• Triangle in the water — a red starboard hand daymark, right side of the channel in the Conventional Direction of Buoyage.
• Square in the water — a green port hand daymark. Also the daymark shape on a preferred channel mark with green uppermost.
• Octagon — safe water. Red and white vertical stripes, navigable water all round.
• Round or spherical buoy — also safe water, as is any buoy showing a red spherical topmark.

Working a question

You are inbound and the chart shows, at the entrance, a black dot with a purple flare, legend "6" Fl(2) R 10s 80m 19M in vertical lettering. Half a mile inside, a diamond with a small circle at its base, legend C "7" Fl G 4s in slanted lettering.

1. Fixed or floating. Vertical lettering and the dot-and-flare put the first symbol on a fixed light structure; its position is the centre of the dot. Slanted lettering and the diamond-and-circle make the second a buoy, and the circle is only the approximate position of its sinker.
2. Decode the legend in its charted order — designation, characteristic, colour, period, height, range. Light 6, group flashing two flashes, red, two flashes in 10 seconds, 80 metres, 19 nautical miles.
3. Account for what is absent. As scale decreases, elements are deleted in a set order: height first, then period, then the group repetition interval, then designation, then range. Characteristic and colour will almost always be shown. A legend without a height on a coastal chart tells you the chart is decluttered, not that the light is at sea level.
4. Read the buoy from its letter and colour. C is a can; green; therefore a port hand mark to be left to port proceeding in the Conventional Direction of Buoyage. N would be a nun, S a spar, and no letter at all means assume a pillar.
5. Confirm the direction of buoyage before you act on step 4. Inbound from seaward toward the head of navigation is the conventional direction. On the Intracoastal Waterway, or in Region A waters, resolve the reversal before deciding a side.
6. Take the fix off the light, not the buoy. Use bearings or angles from beacons or landmarks, soundings and electronic navigation. Buoy positions are approximate, the mooring length defines a watch circle the buoy will move within, and a buoy can be dragged off station, sunk or capsized 33 CFR §62.23.

Where candidates lose the point

• Picking the diamond as the position. The diamond is a pointer and a label; the small circle or dot is the charted position of the mooring, and the aid itself may be displaced by the scope of that mooring. Any option that treats a charted buoy as a precise position is wrong.
• Answering that the buoy's charted position was verified recently. Positions are checked at periodic maintenance visits; between visits, sea state, seabed slope and composition may have shifted the buoy off station 33 CFR §62.23.
• Reading the angle of the buoy symbol, or missing the line inside it. A distractor built on a horizontally-lined symbol is testing banded colouring — a preferred channel mark — while a vertical line is a striped safe water mark. The tilt of the symbol means nothing.
• Answering "triangle" for a green daybeacon on the chart sheet. Triangles are reserved for red daybeacons; squares cover everything else.
• Expecting odd and even numbers to give the side on the Western Rivers. They give mileage from a fixed point. The candidate who reasons from numbering there has already lost the question, and buoys in that system carry no numbers to reason from.
• Flipping the shapes along with the colours in Region A. Only colour significance reverses; can, nun, square and triangle mean exactly what they mean in Region B.
• Treating a Priv aid or a "Marker" circle as an equal to a Coast Guard aid. Its purpose may not be obvious to a casual user, and it may have been established for one specific operator 33 CFR §62.21.

Check yourself