AIS

Question 1

What does AIS mean?

Answer 1

Automatic Identification System

Question 2

What is AIS?

Answer 2

AIS is an autonomous VHF transceiver navigation aid that transmits static, dynamic and voyage between ships and ship to shore. Works on two VHF channels, 87b simplex for ship to ship and 88b duplex for ship to shore. Range around 30-40nm

Question 3

Who is required to have an AIS class A? (3 factors)

Answer 3

Class A receivers required for all SOLAS vessels:
1. All vessels over 300GT on international voyages.
2. Cargo vessels over 500GT
3. All passenger vessels regardless of size

Question 4

What is the difference between Class A and Class B?

Answer 4

Question 5

What are the AIS components?

Answer 5

Antennas
VHF Transmitter
2x Multichannel VHF receivers
Heading Input
Speed Input
Rate of Turn info
Position Input
MKD (Multikey display keyboard)

Question 6

Where can you have an AIS overlay?

Answer 6

ECDIS, Radar, ARPA, IBS (Integrated bridge system)

Question 7

What is dynamic data and how often does it transmit? (10 factors)

Answer 7

Every 2s - 3min
1. Navigational status
2. Rate of turn
3. S.O.G
4. Position accuracy
5. Position
6. C.O.G
7. True Heading & Bearing
8. Time (in UTC)
9. CPA
10. TCPA

Question 8

Why is navigational status a dynamic data?

Answer 8

Because if you for example go aground (and you change in AIS) that information need to be sent out faster and dynamic data has priority over voyage data

Question 9

What is voyage data and how often does it transmit? (5 factors)

Answer 9

Every 6 minutes
1. Destination
2. ETA
3. Draught
4. Cargo type / class
5. P.O.B (persons onboard)

Question 10

What is static data and how often does it transmit? (7 factors)

Answer 10

Every 6 minutes
1. IMO Ship Identity / MMSI
2. International Radio call sign
3. Name
4. Type of ship
5. Principal dimensions
6. Location of Positioning system
7. Type of positioning system

Question 11

What does SOTDMA stand for?

Answer 11

Self Organising Time Division Multiple Access

Question 12

Explain SOTDMA

Answer 12

In SOTDMA, the VHF channel (87b) is divided into time slots, and each AIS is assigned one or more time slots in which it is allowed to transmit data.
2250 time slots in minute, (4500 over two frequencies). This allows for three different modes of transmission.

Question 13

What modes of transmission (operation) are there? (3)

Answer 13

1. Autonomous / Continuous mode
2. Assigned mode
3. Polling mode

Question 14

How does AIS symbols look like?

Answer 14

Question 15

Should AIS be used for collision avoidance?

Answer 15

It shouldn’t be the determining factor for collision avoidance due to reliance on other users input of data and sensors, however it is a great tool for overall situational awareness “all available means”. AIS has longer range than radar which means we can get an heads up of an upcoming target, it can also see around headlands. It can give information about target size and type which is beneficial.

Question 16

What are the three AIS bouys and what would they look like on a chart?

Answer 16

1. Real / physical bouys
   A physical navigation mark with an AIS transmitter affixed and data transmitted
2. Synthetic bouys
   A physical navigation mark without an AIS transmitter fitted instead relying on a shore based transmitter to project the information
3. Virtual
   No physical navigation mark and the data is transmitted by a shore based station

Question 17

Why can’t you use AIS for collision avoidance?

Answer 17

There is no provision for it in the COLREGS

Question 18

What affects AIS accuracy?

Answer 18

Amount of vessels and therefore the reporting rate in SOTDMA