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Light Signals




As well as their shape, colour, and top mark, it is possible to identify a particular type of buoy by it's light signal.

Light signals are essential for night navigation where it is not possible to identify the buoy by any other means. Every buoy can be identified on a shipping chart along with it's unique light characteristic.

When we talk about light signals we look at several different aspects of it characteristic. These are:


Phase & speed

The phase of a light signal can be described as:

Fixed (F)
Flashing (Fl)
Occulting (Occ)
Isophase (Iso)

Fixed = Uninterrupted light source
Flashing = OFF time is greater than the ON time
Occulting = ON time is greater than the OFF time
Isophase = Equal on and off times

see demonstration


The standard speeds or rates of flashing are:

- Flashing (Fl) 30ppm

- Quick Flashing (QF) 60ppm

- Very Quick Flashing (VQF) 120ppm

[ppm = pulses-per-minute, equivalent to flashes-per-minute]


1. Lateral markers

PORT hand markers display a RED light whilst STARBOARD hand markers display a GREEN light.

These light signals can have any phase characteristic other than that used for preferred channels.

Some possible examples are:


Preferred channel markers display a unique light signal which is always composite group flashing. That is a group of two followed by a single flash.

The colour of the light corresponds to the majority colour of the buoy. i.e. a preferred channel to PORT is predominantly GREEN , therefore a GREEN light is used and should be kept to the STARBOARD beam of the approaching vessel; hence taking the PORT channel.



2. Cardinal marks

A Northerly cardinal displays a continuous quick flashing or very quick flashing WHITE light.


An Easterly cardinal displays a quick flashing or very quick flashing WHITE light in groups of 3 .


A Southerly cardinal displays a quick flashing or very quick flashing WHITE light in groups of 6 followed by a long flash .


A Westerly cardinal displays a quick flashing or very quick flashing WHITE light in groups of 9 .


One way to remember these is to visualise the face of a clock with North being 12 O'clock, East 3 O'clock, South 6 O'clock, and West 9 O'clock. The time then gives the number of flashes in the sequence.


3. Other markers

An isolated danger mark always has a light which is WHITE and group flashing.


A safe water mark will always show a WHITE light but can be Isophase, Occulting, Morse 'A' or long flashing. Indeed, any combination can be used provided it doesn't get confused with a cardinal mark or isolated danger.


Special marks are the only buoys to be fitted with YELLOW lights and can have any phase characteristic not already used by WHITE lights.



Chart abbreviations

Chart abbreviations are a simple way of depicting the light signal of buoys in a descriptive written form.

The essential components of a chart abbreviation are:

[Colour. Phase. (flashes) + extra component. Period(s)]

E.g. a Southerly cardinal has the abbreviation

Q.(9) + LFl. 15s. It is white, quick flashing in groups
of 9 followed by a long flash. This repeats every 15s.


Some practical examples are:

R. QF. General port hand marker
G. Fl.(2) 5s General starboard hand marker
R. Fl.(2+1) Preferred channel to starboard
VQ. Northerly cardinal mark
Q.(3) 10s Easterly cardinal
VQ.(6) + LFl. 10s Southerly cardinal
Q.(9) 15s Westerly cardinal
Fl.(2) Isolated danger mark
LFl. 10s Safe water mark
Mo. (A) Safe water mark

N.B. If a WHITE light alone is used then the colour abbreviation is omitted.

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