Buoyage and lights – DS & YM


Before reading this page grab a copy of the training almanac and chart (and a real one if possible).

Before reading this page you will need to know the basics of reading a chart.

Why is this important?

Although there are no signposts at sea, where there is a hazard there is often (not always) a buoy, pole or ever a lighthouse to mark it.

There are a number of different types of navigation marks which you need to be able to indentify both in the real world and on charts.

Cardinal Marks

Cardinal Marks mark the position of a hazard either above or more likely below the surface.

One of four different types of cardinal mark may be used, one for each cardinal point of the compass – North, East, South and West.

In each case the mark is laid on the corresponding side of the hazard ie. a North Cardinal is laid to the north of a hazard and it is safe to pass to the north of it.

cardinalmarksThe diagram and table below shows the different characteristics of the marks. Be aware that although the diagram above shows all four cardinal marks around one hazard this is not common, often marks are used on there own.

  Top Mark Colours Light
North Both point up (north) Black on top Continuous flash
East EASTer egg Black top and bottom 3 Flashes
South Both point down (south) Black at bottom 6 Flashes plus one long
West The cone have a Waist Back in middle 9 Flashes
Notes:   Cones of the top mark point to the black. 

Be aware that sometimes tide, weathering or even bird’s mess can effect the colours so double check with the top mark and chart.

Remember these by comparing to a clock face and check the chart for timings of flashes.

When approcahing a cartdinal marks (or any type of buoyage) the distance at which you first see the buoy will depend on a number of factors including, its size, visablity and sea state. However, as a rule of thumb in good conditions the buoy should be visable within 2Nm and the characteristics should become clear at around 1Nm (you will often see the colours before the topmark).

Lateral Marks (IALA A)

Lateral Marks are primarily used to mark channels. In the UK we can expect to see buoys laid out as the diagram shows below. Simply put, as youcome into a harbour, port or river, red on the port and green on the starboard.

  Shape Colours Light
Port Hand Square or square top mark Red Red Flashing
Starboard Hand Conical or conical top mark Green Green Flashing
Notes:     Check the chart for the exact characteristics.


directionofbuoyageIn some areas it is not obvious which way the buoyage should be going ie. around an island. In these cases the direction of buoyage will be indicated on the chart by the following symbol.



If you are doing the Yachtmaster Course (or planning to sail overseas) it is important for you to know that there are two systems of Lateral buoyage around the world known as IALA Area A and IALA Area B.



Lateral Marks (IALA B)

We live in Area A and our lateral buoyage works as above. However, if we sail in Area B the buoyage looks like this. Note that the colours are the other way around but the shapes are the same.


Isolated Danger

isodangerThis marks a danger to navigation which only covered a small area. The buoy or pole it often positioned on top of the main hazard. You should keep a good distance away.

If lit is will have a white light that flashes twice.

Safe Water Marks

safewatermarkThese are very rare and when used often mark the start of the channel into a port. In the past they would have aided navigators trying to find the entrance to a harbour but in the age of GPS are being slowly removed.

It is worth noting that regardless of their names the areas where they are positioned can rarely be described as safe water as it will likely be in an area busy with shipping.

If lit is will have a white light that flashes Morse A (. -), a single long flash or Isophase (see below).

Special Marks

specialmarkThese are used for many different purposes. Small versions of these marks may be used to mark a jet ski area, used a fixed yacht racing marks or mark a conservation area. Larger versions could be used to mark the centre of traffic separation scheme.

You need to check your chart to find out what any particular one is marking. If lit is will have a yellow light that flashes in a pattern that could not be confused with a white lights pattern ie it could not be 3 yellow flashes as this could be confused with an East Cardinal.


By night, some (but not all) navigational aids are lit. So that you can tell then difference between them they all have particular characterisics It is only by referencing a chart at you will be able to identify a lights exact purpose however.


Characteristic Short-hand Notes
Fixed F Always on
Flashing Fl Flashes once in a set time
Group Flashing Fl(3) Flashes a set number of times in a set time (number of flashes in brackets)
Isophase Iso On for the same time as off
Occulting Oc On most of the time and then flashes off
Morse Mo(A) Morse letter shown in brackets*

* Note: Morse Code that is commonly used on lights include:
A (dot dash), used sometimes for Safewater Marks
U (dot dot dash), meaning, you coming into danger ie. on a oil rig

Light can come in a number of different colours but if not referred to the colour will be white. Otherwise the following codes are used:

R – Red
G – Green
Y – Yellow
Bl – Blue


Lights will repeat there characterisics in a set time or period. This is shown after the other light details ie. 15s means it repeats every 15 seconds.

Some examples

Short-hand Meaning
Fl.R 5s Flashing red once every 5 seconds
Fl(4) 15s Flashing white four times every 15 seconds
Iso 10s White light on for 5 seconds off for 5 seconds
Oc 12s White light flashing off once every 12 seconds
Mo(U) 20s White light flashing Morse code U once every 20 seconds

Video: additional information

Sectored Lights

Some lights are sectored, that is to say they appear as a different colour and/or timing dependent on which way you appoach it.

For example, the lighthouse at Penzance displayed a white flashing light if viewed from the relatively deep water to the southeast of the harbour (B on the chart below). However, from the southwest the same lighthouse displays a flashing red light to warn of the dangers of The Gear and Lowlee in that sector (C on the chart). There is also a Red sector warning of the rocks on the northern shore of the bay (A on the chart).

The divisions between these different sectors as shown on the chart as dotted lines coming out from the lights position. The colour is then indicated on the arcs drawn between these lines. On Imray charts the colour is also displayed on the arcs as a coloured arc.




Buoyage – Quick Quiz
Use this slide show to remind yourself of the different types of buoyage and then test your knowledge.


British Canoeing: Buoyage
A quick online module coving Buoyage

Light Characteristics
A guide to light characteristics on Wikipedia

Sailtrain – Buoyage Guide
Sailtrain’s guide to buoyage including a multiple choose test.

Trinity House
The General Lighthouse Authority for England and Wales, maintains the major lights and buoys around much of the UK.

Check your understanding

Check your knowledge of the basics using this quick self-marking test.

Open the quiz


Practice reading a chart and finding these marks and hazards. This is particularly important in Passage Planning and Pilotage.


The content of these pages is put together in good faith and is constantly evolving. It is possible that errors exist within this content. If you spot an error or would like to add anything to these pages please contact use via email.

Reading the content of these pages is not a substitute for completing a RYA Shorebased course or similar.