What is AIS and how does it work?

Throughout history, sailors and adventurers have utilized various methods to determine their location and direction at sea, as well as identify potential hazards like shoals and rocks, which they marked on nautical charts. To communicate from afar, they developed a specific signaling system. Nowadays, sailors have access to a wide range of sophisticated and dependable tools and systems for navigation, communication, and information gathering. These tools include radar, radios, analog and digital navigation instruments, and the advanced AIS system. With these tools at their disposal, modern-day sailors and captains no longer have to rely solely on the stars, compass, and lighthouse signals. How exactly does the AIS system work to prevent collisions, and what benefits does it offer?

In maritime navigation, AIS stands for Automatic Identification System and is a tool for locating, identifying, and aiding navigation. Although it has some features in common with radar and is often linked to it, it differs in many ways and the two should not be confused with radar. Radar is more expensive, more complex and works on the principle of sending out waves that bounce off nearby ships, obstacles and other objects. The reflected waves are then displayed on a radar monitor.

In basic terms, AIS is a system that regularly transmits and receives information about a vessel's position, speed, heading, and identification data. Its main purpose is to establish an identification network between vessels, between vessels and land, and between land stations to prevent collisions at sea. The information is shared through satellite or internet links and can be received by all ships equipped with AIS. While larger ships are required to have AIS under the Law of the Sea, it is not mandatory for smaller vessels, such as charter boats. Nonetheless, using AIS can significantly enhance navigation safety for all vessels.

The AIS system uses a VHF radio to transmit in the MARINE band, which is reserved for shipping. The data is updated between 2 and 10 seconds if the ship is moving, every 3 minutes when at anchor and once every six minutes other secondary data is updated.

There are two classes within ASI. AIS Class A is used by large transport and commercial ships (specifically ships of more than 300 GT, commercial ferries and fishing boats over 15 metres). These are expensive and sophisticated instruments capable of processing large amounts of data that cannot even be specified for smaller ships. AIS Class B are cheaper, simpler and suitable for private yachts and charter boats. The second class transmits less data, which is updated every half minute, and the signal range is about 10 nautical miles. The only exception is if the boat exceeds 14 knots, at which point the vessel's position information is updated more quickly.

All positioning and navigation systems are a very good way to prevent a collision with another vessel or other collision. However, in practice, it is always important to rely on your own common sense, experience and observation of the actual situation. Particularly when offshore and in busy waters, you cannot assume that all boats are equipped with AIS, as it is not mandatory for smaller and recreational vessels. It may also be the case that large ships equipped with Class A AIS filter out the transmissions of Class B AIS instruments. If the situation is in any way unclear or you are unsure, you are always obligated to try to avoid a collision. In addition to on-board instruments and positioning or navigation systems, continuous monitoring of your surroundings will serve you well. We have prepared a handy guide for you on how to judge distance at sea.