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Navigation aids 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 America's, Japan, the Philippines and Korea.
Fortunately, the differences between these two systems are few. The
most striking difference is the direction of buoyage (see Lateral buoys below).
All marks within the IALA system are distinguished by:
During daytime identification of navigation aids is accomplished by observing: location, shape, colour scheme, auxiliary features (sound signals, RACON(responds to special signals).");
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}" src="http://www.sailingissues.com/i7smal.gif" />, etc) or markings (name, number, etc).
During the night, we use the features of the navigation aid'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) 10 s'.
- Phase characteristic: The particular pattern of changes within one complete cycle (hence, within one period). Below are the most common types:
- 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):
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):
Light has equal duration between light and darkness. A period consists
of both a light and a dark interval. Also called Equal Interval (E
- Group Flashing (Gp Fl(x+x)):
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):
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
- 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.
Let's look at some examples using colour, period and phase characteristics. The arrows mark the periods:
- Fl (4) 8 s
- Oc (2+3) 10 s
- Iso G 4 s
All lighted navigation aids are either major or minor lights,
where major lights are used for key navigational points along
seacoasts, 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.
Five types of navigation buoys:
- Isolated danger
- Safe water
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, whereas under IALA B green
buoys mark the port side of the channel when sailing towards land. Red
buoys have even numeration plus red lights and green buoys have odd
numeration plus 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 starboardThe other channel requires a green buoy there.");
}" src="http://www.sailingissues.com/i7.gif" /> under IALA A. The light phase characteristic is R FL (2+1):
The buoy depicted on the left indicates the preferred channel to portThe other channel requires a red buoy there.");
}" src="http://www.sailingissues.com/i7.gif" /> under IALA A. These buoys are marked with the numerations of both channels.
The light phase characteristic is G FL (2+1):
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 topmarks 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 will be used to indicate this 'uncharted' danger. The
cardinal system is identical in both the IALA A and IALA B buoyage
Marks indicating Isolated dangers
type of buoy indicates the position of an isolated danger, contrary to
cardinal buoys which indicate a direction away from the danger. The
light (when present) consists of a white group 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. Lights are usually calm and white.
Special Buoys and Marks
saved these buoys for last since they have not an actual navigation
purpose. Most of the time these yellow buoys indicate areas used by
navies or pipelines or surfing.
It is important to know at what distance (range) we may see a
certain light, and when we can expect to lose sight of it, especially
when making landfall. This range can be defined in several ways:
- 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