Lights and buoys

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Aids to navigation

Aids to navigation are special structures like lighthouses, lightships, beacons, buoys, etc that are used to enhance safety by providing more opportunities to obtain LOPs.

These lights and marks are prescribed across the world by the International Association of Lighthouse Authorities (IALA). In 1977 this IALA endorsed two maritime buoyage systems putting an end to the 30 odd systems existing at that time. Region A - IALA A covers all of Europe and most of the rest of the world, whereas region B - IALA B covers only the Americas, Japan, the Philippines and Korea. Fortunately, the differences between these two systems are few. The most striking difference is the direction of buoyage.
All marks within the IALA system are distinguished by:

Light identification

During daytime, the identification of aids to navigation is accomplished by observing: location, shape, colour scheme, auxiliary features (sound signals, RACON, RC, etc) or markings (name, number, etc).

During the night, we use the features of the aid to navigation's light to both identify it and ascertain its purpose. There are three features to describe the light:

Let's look at some examples using colour, period and phase characteristics. The arrows mark the periods:

All lighted aids to navigation are either major or minor lights, where major lights are used for key navigational points along sea-coasts, channels and harbour and river entrances. These lights are normally placed in lightships, lighthouses and other permanently installed structures, providing both high intensity and high reliability of the lights. Major lights are then subdivided in primary lights (very strong, long range lights used for the purpose of making landfalls or coastal passages) and secondary lights (shorter range lights found for example at harbour and river entrances). Important details of (especially) primary lights can be found in a reference called the Light List where information (about pedestals etc.) can be found which is not included in the chart.
Minor lights on the other hand are likely to be found within harbours, along channels and rivers. These have a low to moderate intensity and sometimes mark isolated dangers.

Six types of navigation buoys:

Lateral buoys and marks

The location of lateral buoys defines the borders of channels and indicates the direction.
Under IALA A red buoys mark the port side of the channel when returning from sea.
Under IALA B green buoys mark the port side of the channel when returning from sea.
See below for the directions of lateral buoys in IALA A and IALA B.

Red buoys have even numbers and red lights; green buoys have odd numbers and green lights. Lateral lights can have any calm phase characteristic except FL (2+1).
Lateral red buoy.Lateral green buoy.

Preferred channel to starboard: keep buoy to port (IALA A). Generally, when two channels meet, one will be designated the preferred channel (i.e. most important channel). The buoy depicted on the right indicates the preferred channel to starboard under IALA A. The light phase characteristic is R FL (2+1): Red buoy indicating a preferred channel to port (in USA, Japan.

Preferred channel to port: keep buoy to starboard (IALA A).The buoy depicted on the left indicates the preferred channel to port under IALA A. These buoys are marked with the names and numbers of both channels. The light phase characteristic is G FL (2+1):
Green buoy indicating a preferred channel to starboard (in USA, Japan).
For an example of lateral buoys used to mark a (preferred) channel, see direction of buoyage below.

Cardinal buoys

The four cardinal buoys indicate the safe side of a danger with an approximate bearing. For example, the West cardinal buoy has safe water on its West and the danger on its East side. Notice the “clockwise” resemblance of the light phase characteristics. The top marks consist of two black triangles placed in accordance with the black/yellow scheme of the buoy. When a new obstacle (not yet shown on charts) needs to be marked, two cardinal buoys - for instance a South buoy and an East buoy - will be used to indicate this “uncharted” danger. The cardinal system is identical in both the IALA A and IALA B buoyage systems.
Cardinal buoys around a selection of dangers.

Marks indicating isolated dangers

Marks indicating isolated dangers.This type of buoy indicates the position of an isolated danger, contrary to cardinal buoys which indicate a direction away from the danger. Body: black with red horizontal band(s); Topmark: 2 black spheres. The light (when present) consists of a white flash: Fl(2).
Marking of isolated dangers

Marks indicating safe water

Marks indicating safe water. Notice that whereas most horizontal striping spells “danger”, this safe water buoy is vertically striped. These marks are for example seaward of all other buoys (lateral and cardinal) and can be used to make landfall. Body: red and white vertical stripes; Topmark (if any): single red sphere. Lights are typically calm and white: Morse A, Iso, Occ or LFl 10s.

Marks for new wrecks

After the sinking of the “Tricolor” in the Pas de Calais (Dover Straits) in 2002, several other vessels hit the wreck despite standard radio warnings, three guard ships and a lighted buoy. This incident spawned a new type of buoy, the emergency wreck marking buoy, which is placed as close as possible to a new dangerous wreck.
Emergency wreck marking buoy for new wrecks

The emergency wreck marking buoy will remain in position until: a) the wreck is well known and has been promulgated in nautical publications; b) the wreck has been fully surveyed and exact details such as position and least depth above the wreck are known; and c) a permanent form of marking of the wreck has been carried out.

The buoy has the following characteristics:

It is important to realize - especially for the colour-blind - that this new buoy breaches the useful and crucial convention: vertical stripes equal safety, horizontal stripes equal danger.

Special buoys and marks

Marks used for special indication.
I have saved these buoys for last since they lack an actual navigational goal. Most of the time these yellow buoys indicate pipelines or areas used for special purposes.
I have drawn the five official IALA shapes, from left to right: conical, spar, cylindrical, pillar and spherical.

Chart symbols

The seafaring nations of the world - members of the International Hydrographic Organization - agreed in 1982 on an universal set of chart symbols, abbreviations, colours, etc to be used in the nautical chart, in order to obtain uniformity.

On regular charts a white, red, yellow or green lights will be indicated by Standard chart light colour, and on GPS displays and modern multi-coloured charts in specific colours: Lights in the multi-coloured nautical chart, with the yellow coloured lobe indicating a white light.
The precise position of a chart symbol is its center, or is indicated with a line and circle Position of chart symbol, the “position circle”.

Two distinct types of sea mark are drawn differently in the chart:

Major floating light (light-vessel, major light-float, LANBY) Major floating light (light-vessel, major light-float, LANBY)
Light-vessel Light-vessel
Major light, minor light Major light; minor light
Green or black buoys (symbols filled black) Green or black buoys (symbols filled black): G = Green ; B = Black
Green or black beacons (symbol filled black) Green or black beacon (symbol filled black). Note the upright G, instead of an oblique G
Single coloured buoys other than green and black Single coloured buoys other than green and black: Y = Yellow ; R = Red
Coloured beacon other than green and black Coloured beacon other than green and black, the symbol is again filled black so only the shape of the topmark is of navigational significance.
Multiple colours in horizontal bands, the colour sequence is from top to bottom Multiple colours in horizontal bands, the colour sequence is from top to bottom
Multiple colours in vertical or diagonal stripes, the darker colour is given first. Multiple colours in vertical or diagonal stripes, the darker colour is given first. W = White
Spar buoy - safe water mark. Spar buoy (here a safe water mark)
Lighted marks on multi-coloured charts, GPS displays and chart plotters. Lighted marks on multi-coloured charts, GPS displays and chart plotters.
Lighted beacon on standard charts Lighted red beacon on standard charts.
Radar reflector chart symbol Red beacon and green buoy with topmark, colour, radar reflector and designation. Red buoys and marks are given even numbers, green buoys and marks are given odd numbers.
Radar reflector magenta The black symbol indicates a true radar reflector. Other radar-conspicuous objects - natural or manmade - which are known to give an unexpectedly strong radar response may be distinguished by the magenta symbol.
Fog signals Wave-actuated bell buoy to the left, and to the right a Light buoy, with a horn giving a single blast every 15 seconds, in conjunction with a wave-actuated whistle. Other sounds include “Gong”, “Siren”, “Diaphone” (Dia).
The fog signal symbol Fog signal symbol may be omitted when a description of the signal is given.
Leading beacons Leading beacons - Leading line (firm line is the track to be followed)
Leading lights Leading lights (≠ : any two objects in line under each other). Bearing given in degrees and minutes. The lights are synchronized. The red light has a shorter nominal range (the distance from which the light can be seen): 10 nautical miles.
All-round light with obscured sector All-round light with obscured sector
Sector light Sector light on multi-coloured charts.
The elevation is 21 metres (height of the light structure above the chart datum used for elevations).
The nominal range of the white light is 18 nautical miles. The range of the green and red light is 12 nautical miles.
Main light visible all-round with red subsidiary
light seen over danger Main light visible all-round with red subsidiary light seen over danger. The fixed red light has an elevation of 55 metres and a nominal range of 12 nautical miles. The flashing light is white, with three flashes in a period of 10 seconds. The elevation is higher than the red light: 62 metres and the range of the white light is 25 nautical miles.
Symbol showing direction of buoyage (where not obvious) Symbol showing direction of buoyage (where not obvious)
Symbol showing direction of buoyage (where not
obvious), on multi-coloured charts (red and green circles coloured as appropriate) Symbol showing direction of buoyage (where not obvious), on multi-coloured charts (red and green circles coloured as appropriate), here IALA A
Full example of a light description in the chart:
Learn to sail Athens
Class of light: group flashing repeating a group of three flashes;
Colours: white, red, green, exhibiting the different colours in defined sectors;
Period: the time taken to exhibit one full sequence of 3 flashes and eclipses: 15 seconds;
Elevation of light : 21 metres;
Nominal range(s): white 15 M, green 11 M, red between 15 and 11 M, where “M” stands for nautical miles.

Lateral Marks - direction of buoyage

Lateral marks are generally for well-defined channels and there are two international Buoyage Regions - A and B - where these Lateral marks differ. Where in force, the IALA System applies to all fixed and floating marks except landfall lights, leading lights and marks, sectored lights and major floating lights.

The standard buoy shapes are cylindrical (can) Cylindrical buoy - Can , conical Conical buoy , spherical Spherical buoy , pillar Pillar buoy and spar Spar buoy - Spindle buoy , but variations may occur, for example: minor light-floats Light float. In the illustrations below, only the standard buoy shapes are used.
In the case of fixed beacons Green and red Beacons - lit or unlit - only the shape of the topmark is of navigational significance.
Region A

New Zealand
Middle East
Preferred channels - Lateral marks in IALA A
Region B

Preferred channels - Lateral marks in IALA B

Visibility of lights

It is important to know at what distance we may (begin to) see a certain light, and when we can expect to lose sight of it, especially when making landfall. Several practical ranges are used to the describe the visibility of lights in navigation:
Meteorological Optical Range Table
Code No. Weather Distance (m)       Code No. Weather Distance (nm)
 0 Dense fog Less than 50  5 Haze 1.0 - 2.0
 1 Thick fog 50 - 200  6 Light haze 2.0 - 5.5
 2 Moderate 200 - 500  7 Clear 5.5 - 11.0
 3 Light fog 500 - 1000  8 Very clear 11.0 - 27.0
 4 Thin fog 1000 - 2000  9 Exceptionally clear Over 27.0
So, a minor light - perched on a 70m high cliff - with a geographic range of 20 nm will not be detectable by the human eye at a distance of 6 nm
  1. if the nominal range is just 5 nm.
  2. if the meteorological range is just 5 nm due to a light haze.
Because of the limiting factor of the geographic range, most major lights will never be seen from a sailing yacht 20 nm away. Yet, it is sometimes possible to take a bearing on the loom of the light: its reflection against the clouds.


Dipping distance or range
Different coloured lights with equal candlepower have different ranges. White light is the most visible followed by yellow, green and then red. Therefore, at extreme ranges an “AL WG” can resemble a “Fl W”.

The range of a lit buoy is never indicated - with the exception of a LANBY - but on a clear night the maximum range is 3 nm, yet often considerably less.

There are 2 visual clues to determine your distance from a buoy: at about 0.5 nm, the light will rise up from the horizon, and at about 200m, the light will reflect in the surface.
Buoy at less than 3 nm
Buoy at less than 0.5 nm
Buoy at less than 200m


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2 April 2019
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