AIS Flashcards
What is AIS
Automated Identiftcation System
What does SOTDMA stand for
Self-Organising Time Division Multiple Access
How does SOTDMA work?
autonomous and default mode of AIS
2250 time slots, with 2 channels, allows 4500 transmissions per minute
What is ‘assigned’ Mode of operation?
Shore stations appropriately equipped can take over SOTDMA to prioritise high risk vessels etc
What is ‘polling’ mode of operation
Information / data sent by transponder when interrogated by another transponder.
Can be used to obtain information earlier than required, such as by a shore station.
Has potential use for Long Range AIS in the future
Difference between class A and class B AIS Vessel?
Class A is a mandatory fit vessel (commercial vessels over 300gt)
Class B is a non mandatory fit vessel (fishing and leisure craft)
Static Information
Set manually on instillation
Information about the ship that does not change (size etc)
Transmitted every 6 minutes or on request
Dynamic information
Set automatically by the ships sensors
Information about the ship that DOES change, Course, Speed etc which changes quickly
Transmitted depending on the ship speed and whether altering course
Voyage information
Set Manually by the OOW/Master
(only on authority of the master)
What it says on the tin. Cargo, Passengers, destination and crew
Transmitted every 6 minutes or on request
Advantages of AIS over radar
It can see around corners
It gives immediate indication of a vessel altering course
Targets do not get lost in clutter
Information about vessel is in depth
Why not use AIS for Collision avoidance?
It relies on ships instruments which cannot check to be correct
ColRegs are BASED on visual and radar information
Describe the three types of ATONS
(aids to navigation)
Real / physical
Synthetic
Virtual
Real / Physical: A physical navigation mark with an AIS transmitter affixed and data transmitted
Synthetic: A physical navigation mark without an AIS transmitter fitted instead relying on a shore based transmitter to project the information
Virtual: No physical navigation mark and the data is transmitted by a shore based station
Radio: Operational Guidance on the Use Of VHF Radio and Automatic Identification Systems (AIS) at Sea
MGN 324
What vessels are required to carry AIS type A?
Vessels engaged on international voyages >300GT
Vessels not engaged in international voyages, over 500GT, and passenger vessels
Range of AIS
Dependant on Antenna height, but roughly 20-30nm (VHF range)
What is AIS?
AIS is a maritime mobile VHF broadcast system that sends dynamic and static ship
information, such as MMSI, call sign, position, course and speed, to other AIS transponders
and base stations.
Limitations of AIS
It is not mandatory for all vessels
Can display intentionally wrong info
Can be switched off
Is fed with SOG
NOT for collision avoidance
What is LRIT?
The Long-Range Identification and Tracking (LRIT) system provides for the global
identification and tracking of ships to enhance security of shipping and for the purposes of
safety and marine environment protection.
Minimum requirements for LRIT?
- Be capable of automatically, and without human intervention on board the ship,
transmitting the ship’s LRIT information at 6-hour intervals to an LRIT Data Centre; - Be capable of being configured remotely to transmit LRIT information at variable
intervals; - Be capable of transmitting LRIT information following receipt of polling commands;
- Interfaces directly to the shipborne global navigation satellite system equipment, or
have internal positioning capability; - Be supplied with energy from the main and emergency source of electrical power.
What is BNWAS?
Bridge Navigational Watch Alarm System
Three modes of operation of BNWAS
Auto, as soon as auto pilot is switched on
Manual on
Manual off
How does BNWAS work?
- Once operational, stays dormant for a user set period of 3-12 minutes
- Visual alarm on Bridge
- 1st stage audible alarm in Bridge 15 seconds after visual Alarm
- If not reset, 2nd stage alarm in Master/Back up officers cabin 15 seconds after 1st stage audible alarm
- If not reset, the BNWAS should additionally sound a third-stage remote audible alarm
at the locations of further crew members capable of taking corrective actions 90 s
after the second-stage remote audible alarm is initiated.
What other function does BNWAS have?
Manual call for assistance
