User's Guide

Weatherdock AG Page 7
www.easyAIS.com
5 Introduction
5.1 General Information about AIS
AIS stands for Automatic Identification System. AIS increases navigational safety and collision avoidance by
transmitting vessel identification, helping to reduce the difficulty of identifying ships when not in sight (e.g. at
night, in radar blind arcs or shadows or at distance) by broadcasting navigational intentions to other vessels by
providing ID, position, course, speed and other ship data with all other nearby ships and land based stations.
According to IALA regulations, AIS is defined as follows:
AIS is a broadcast Transponder system, operating in the VHF maritime mobile band. It is capable of sending
ship information such as identification, position, course, speed and more, to other ships and to shore. It can
handle multiple reports at rapid update rates and to meet these high broadcast rates and ensure reliable and
robust ship to ship operation.
The IMO defines the performance standards as follows:
Ship to ship working, ship to shore working, including long range application, automatic and continuous
operation, provision of information messaging via PC and utilization of maritime VHF channels
The Modules:
GPS system, AIS Transponder, VHF Antenna, and the Data Power Cable and the appropriate application
software.
AIS are required to function flawlessly in a variety of modes.
The relevant regulations requirements:
The system shall be capable of
• An "autonomous and continuous" mode for operation in all areas. This mode shall be capable of being
switched to/from one of the following alternate modes by a competent authority;
• An "assigned" mode for operation in an area subject to a competent authority responsible for traffic
monitoring such that the data trans-mission interval and/or time slots may be set remotely by that
authority;
• A "polling or controlled" mode, where the data transfer occurs in response to interrogation from a ship or
competent authority.
This illustration depicts a typical AIS System, where two or more AIS equipped vessels (and shore based
systems) are automatically communicating with each other.
The following sketch shows a typical easyAtoN installation in a common environment. The easyAtoN is
connected to an external power supply, and in connection with the VHF antenna the minimal requirements for
Transponder operation are fulfilled.
Due to “Time – Synchronization” they use the same organization of free and allocated windows (Slots) in the
shared VHF Data Link to send and receive messages. Without the necessity of any operating interaction, both
vessels know exactly who or what is cruising nearby and where the individual object is heading.
• Class A transceivers
these transceivers are designed to be fitted to commercial vessels such as cargo ships and large passenger
vessels. Class A transceivers transmit at a higher VHF signal power than Class B transceivers and therefore
can be received by more distant vessels, they also transmit more frequently. Class A transceivers are
mandatory on all vessels over 300 gross tons on international voyages and certain types of passenger
vessels under the SOLAS mandate.