This section should give a short
introduction to general technical
description and description of main
components in general and onboard a is
consists of and ten i won VHF
transmitter to multi-channel VHF
receivers one channel 70 VHF receiver
for channel management a central
processing unit an electronic position
fixing system interface to heading and
speed devices be IIT built-in integrity
test
mkd minimum keyboard and display unit in
addition the following optional
interfaces may be provided interface to
radar and arpa automatic radar plotting
aid interface to electronic chart system
ecs or practice electronic navigation
chart display information system
interface to my NS integrated navigation
system our OT rate turn indicator VD our
voyage data recorder long-range
communication system ais graphical
display with the integral minimum
display and keyboard unit the AIS would
be able to operate as a standalone unit
a standalone graphical display for the
integration of the AIS data display with
other devices such as I NS ecs activist
radar or arpa would significantly
increase the effectiveness of a is a is
operates primarily on two dedicated VHF
channel
hey is one at 160 1.97 five megahertz
and a is to at 162 point 0 25 megahertz
where these channels are not available
regionally the AIS is capable of
automatically switching to alternate
designated channels the required ship
reporting capacity according to IMO
performance standards amounts to a
minimum of two thousand time slots per
minute the international
telecommunication union itu technical
standard for a is provides 4500 time
slots per minute the AIS broadcast mode
is based on a principle called
self-organized time division multiple
access abbreviated s.o.t.b ma this
technology allows the system to be
overloaded by four hundred to five
hundred percent and still provide nearly
one hundred percent throughput for ships
closer than eight to 10 nautical miles
to each other in ship-to-ship mode
SOT dma uses the extremely accurate
standard time references supplied via
GPS signals to synchronize data
transmissions from multiple users thus
preventing interference and loss of
information GBS provides both the
universal time reference and the
positioning data for each vessel in the
event of system overload only targets
far away will be subject to drop out in
order to give preference to targets
closed by that are the primary concern
of ship-to-ship operation of a is in
practice the capacity of the system is
unlimited allowing for a great number of
ships to be accommodated at the same
time
dynamic information update rate depends
mainly on the ship's speed that is slow
speed equals low updating rate and high
speed equals hi updating rate the
following table gives updating intervals
for a is dynamic information
static information such as call sign and
name type of ship etc will automatically
be updated every six minutes or on
request voyage related information such
as ships draft destination etc are
updated every six minutes when data has
been amended and on request from a
technical point of view a is is an
advanced piece of equipment from the
operators point of view a is is just
another black box simple and
straightforward to operate
however the operational aspect may turn
out to be a bigger challenge than
anticipated the reasons for this
statement will be discussed in more
detail in the next chapter the AIS is
normally connected to the ship's main
power source as well as to the ship's
emergency power source is connected to
the emergency power supply a new
calculation of consumption has to be
made the location of the AIS VHF antenna
should be weighed carefully digital
communication is more sensitive than
analog and voice communication to
interference created by reflections and
obstructions like masks and boons the
gps antenna must be installed where it
has a clear view of the sky
the objective is to see the horizon
freely through 360 degrees with a
vertical observation of five to ninety
degrees about the horizon small-diameter
obstructions such as masks and booms do
not seriously degrade signal reception
but such objects must not eclipse more
than a few degrees of any given bearing
the functionality of the minimum
keyboard and display she'll be available
to the Mariner this can be by means of
the AIS internal mkd integrated or
remote
or through the equivalent functionality
on a separate display system in case of
a separate display the internal mkd does
not need to be installed a pilot input
and output port is part of an AIS
station a plug connected to this port
should be installed on the bridge near
the pilots coning position so that the
pilot can connect a personal pilot unit
if there is navigational equipment
capable of processing and displaying a
is information such as activist arpa or
a dedicated system available on board
the ship the AIS mobile system may be
connected to that system via the AIS
presentation interface the AIS requires
an alarm output to be connected to an
audible alarm device or to the ship's
alarm system if available
installing a is does not establish a
need to install additional sensors over
and above carriage requirements