Lights and buoys
Skip over navigation
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:
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:
- Colour: Either white, red, green or yellow. If no colour is stated in the chart, default is white.
- Period: The time in seconds needed for one complete cycle of changes.
The arrow indicates the 10 second period of this flashing light “Fl(3) 10s”.
- Phase characteristic: The particular pattern of changes within one complete cycle (hence, within one period). Below are the most common types:
Let's look at some examples using colour, period and phase characteristics. The arrows mark the periods:
- Fixed F
This light shines with an unblinking and steady intensity and is always on. In this example a yellow fixed light is shown.
- Flashing Fl:
The duration of the light is always less than the duration of the darkness. The frequency does not exceed 30 times per minute.
- Quick Flashing Q:
Again, the duration of quick flash is less than the darkness. The frequency is at least 60 times per minute.
- Very Quick Flashing VQ:
Also here, the duration of very quick flash is less than the darkness. The frequency is at least 100 times per minute.
- Interrupted Quick Flashing IQ:
Like Quick Flashing with one moment of darkness in one period.
- Isophase Iso:
This Light has equal duration between light and darkness. A period consists of both a light and a dark interval. Also called Equal Interval (E Int).
- Group Flashing Gp Fl(x+x):
This is actually a combination of two patterns in one period. In this example the first 2 flashes followed by the pattern of 3 flashes result in: Gp Fl(2+3).
- Occulting Occ:
Occulting is the opposite of flashing, the light is more on then off.
- Alternating AL:
An alternating light changes colour. This special purpose light is typically used for special applications requiring the exercise of great caution. In this example ALT.WG is shown, alternating between green and white.
- Morse U Mo (U):
This light shows two flashes and a longflash, which is equivalent to the letter “U” in Morse code.
- Long-Flashing LFl:
This light has one long flash in a period. A long flash is at least 2 seconds long.
- Fl (4) 8s
- Oc (2+3) 10s
- Iso G 4s
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).
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):
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):
For an example of lateral buoys used to mark a (preferred) channel, see direction of buoyage below.
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.
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).
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.
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.
- A pillar or spar buoy, with size dependant on location.
- Coloured in equal number and dimensions of blue and yellow vertical stripes
(minimum of 4 stripes and maximum of 8 stripes).
- Fitted with an alternating blue and yellow flashing light with a nominal range
of 4 nautical miles where the blue and yellow 1 second flashes are alternated with an interval
of 0.5 seconds.
B1.0s + 0.5s + Y1.0s + 0.5s = 3.0s
- If multiple buoys are deployed then the lights will be synchronized.
- A racon Morse Code “D” and/or
AIS transponder can be used.
- The top mark, if fitted, is a standing/upright yellow cross.
Special buoys and marks
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.
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 , and on GPS displays and modern multi-coloured charts in specific colours: , 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 , the “position circle”.
Two distinct types of sea mark are drawn differently in the chart:
- beacons - fixed to the seabed; drawn upright;
- buoys - consisting of a floating object that is usually anchored to a specific location on the sea floor; drawn at an oblique angle and with oblique numbering, descriptions of colours and light characteristics.
Full example of a light description in the chart:
||Major floating light (light-vessel, major light-float, LANBY)
||Major light; minor light
||Green or black buoys (symbols filled black): G = Green ; B = 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: Y = Yellow ; R = Red
||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 vertical or diagonal stripes, the darker colour is given first. W = White
||Spar buoy (here a safe water mark)
||Lighted marks on multi-coloured charts, GPS displays and chart plotters.
||Lighted red beacon on standard charts.
||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.
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 may be omitted when a description of the signal is given.
||Leading beacons - Leading line (firm line is the track to be followed)
||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
||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. 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), on multi-coloured charts (red and green
circles coloured as appropriate), here IALA A
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) , conical , spherical , pillar and spar , but variations may occur, for example: minor light-floats . In the illustrations below, only the standard buoy shapes are used.
In the case
of fixed beacons - lit or unlit - only the shape of the topmark is of navigational significance.
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:
- The meteorological range is based on the current atmospheric conditions. The table below shows that the atmosphere immensely influences the visibility of light travelling through it.
|Meteorological Optical Range Table
||Less than 50
||1.0 - 2.0
||50 - 200
||2.0 - 5.5
||200 - 500
||5.5 - 11.0
||500 - 1000
||11.0 - 27.0
||1000 - 2000
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
- The geographic range is based on the elevation of the light. A higher light means that its horizon is farther away, see distance of horizon.
Moreover, if the observer's height of eye is higher than sea level the light can been seen beyond its geographic range, the dipping range. However, on sailing yachts this potential is limited.
- The nominal range of a light is based on its candlepower, and is typically the range mentioned in the chart. The nominal range is the maximum
distance at which a light can be seen in weather conditions where visibility is 10 nm. If not stated in the chart, consult the List of Lights or a nautical almanac.
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.
- if the nominal range is just 5 nm.
- if the meteorological range is just 5 nm due to a light haze.
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”.
Dipping distance or range
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
Use the logo to navigate through this course,
- Navigation aid: An onboard instrument, device, chart, method, etc., intended to assist in the navigation.
- Aid to navigation: A device or structure external to the ship, designed to assist in determination of position, to define a safe course, or to warn of dangers or obstructions.
- Mark, seamark, navigation mark: An artificial or natural object of easily recognizable shape or colour, or both, situated in such a position that it may be identified on a chart. A fixed artificial navigation mark is often called a Beacon.
- Light characteristics: The sequence and length of light and dark periods and the colour or colours by which a navigational light is identified.
- Topmark: One of more objects of characteristic shape placed on top of a buoy or beacon to aid in its identification.
- Lateral Mark: An aid to navigation intended to mark the sides of a channel or waterway.
- Cardinal Marks: An IALA aid to navigation intended to show the location of a danger to navigation based on its position relative to the danger using the “cardinal point”: north, east, south, west.
- Isolated danger Marks: An IALA aid to navigation marking a danger with clear water all around it; it has a double ball topmark and is black with at least one red band. If lighted its characteristic is Fl(2).
- Sector light: A light having sectors of different colours or the same colour in specific sectors separated by dark sectors.
- Light sector: As defined by bearings from seaward, the sector in which a navigational light is visible or in which it has a distinctive colour difference from that of adjoining sectors, or in which it is obscured.
- Lighthouse: A distinctive structure exhibiting a major navigation light.
- Light List: A publication giving detailed information regarding lighted navigational aids and fog signals.
- Landfall: The first sighting (even by radar) of land when approached from seaward.
- Range: Two or more objects in line. Such objects are said to be in range. An observer having them in range is said to be on the range. Two beacons are frequently located for the specific purpose of forming a range to indicate a safe route or the centerline of a channel.
- Leading line: On a nautical chart, a straight line, drawn through leading marks. A ship moving along such line will clear certain dangers or remain in the best channel.
- Range lights, leading lights: Two or more lights at different elevations so situated to form a range (leading line) when brought into transit. The one nearest to the observer is the from light and the one farthest from the observer is the rear light. The front light is at a lower elevation than the rear light.
- Lights in line: Two or more lights so situated that when observed in transit they define a position: the limit of an area, an alignment used for anchoring, etc. Not to be confused with range lights, which mark a direction to be followed.
- Light-float : A buoy having a boat-shaped body. Light-floats are nearly always unmanned and are used instead of smaller lighted buoys in waters where strong currents are experienced.
- Primary (sea-coast) light: A light established for purpose of making landfall or coastwise past from headland to headland.
- Secondary light: A major light, other than a primary (sea-coast) light, established at harbour entrances and other locations where high intensity and reliability are required.
- Major light: A light of high intensity and reliability exhibited from a fixed structure (lighthouse) or on marine site (except range lights). Major lights include primary sea-coast and secondary lights.
- Minor light: An automatic unmanned light on a fixed structure usually showing low to moderate intensity. Minor lights are established in harbours, along channels, along rivers, and in isolated dangers.
- Visual range: The extreme distance at which an object of light can be seen.
- Geographic range: The extreme distance limited by the curvature of the earth and both the heights of the object and the observer.
- Bobbing a light: Quickly lowering the height of eye and raising it again when a navigational light is first sighted to determine if the observer is at the geographic range of the light.
- Luminous range: The extreme distance limited only by the intensity of the light, clearness of the atmosphere and the sensitiveness of the observer's eye.
- Luminous range diagram: A diagram used to convert the nominal range of a light to its luminous range under existing conditions.
- Charted or Nominal Range: The nominal range is indicated in the chart next to the light or can be found in the Light List. This is the maximum distance at which a light may be seen at night based upon intensity and 10 nautical miles of visibility.
- Meteorological Range: The meteorological range is based on the current atmospheric conditions. Weather in the form of haze, mist or rain is often a limiting factor in the visibility of the light travelling through it.
The meteorological optical range table ranks from 0 (dense fog : less than 50 metres of visibility) to 9 (exceptionally clear : more than 27 kilometres of visibility).
...or go to the next chapter,
or download the complete navigation course as PDF - including practice materials, exercises and answers.