What is AIS?
AIS (Automatic Identification System) is an automatic tracking system that makes vessels visible to each other and to traffic control centers via VHF radio. An AIS transponder continuously transmits data such as position, speed, course, MMSI , and vessel name, so other vessels can see you directly on their chartplotter. An AIS transponder also receives this data from other objects equipped with an AIS transponder. An AIS receiver receives only vessel data.
Why should you use AIS?
AIS helps you sail more safely. You see other vessels, and they see you on their screens early on. This is especially useful in bad weather, when visibility is limited. Moreover, AIS provides better situational awareness: you also see their course and speed, and (if you use an AIS transponder) other vessels can see yours. This is useful in busier waterways. In some cases, the use of an AIS transponder is also mandatory for recreational boating, such as in the port of Antwerp.
Three types of AIS
Initially, there was AIS Class A for commercial vessels and AIS Class B for recreational craft. In 2019, the first AIS Class B+ AIS transponders appeared. The main differences are in transmission power, transmission protocol, update frequency, and regulations.
|
Feature |
AIS Class B |
AIS Class B+ (SOTDMA) |
AIS Class A |
|
Transmit power |
2 W |
5 W |
12.5 W |
|
Reach (practice) |
5–10 NM |
15–20 NM (higher priority) |
20–30 NM |
|
Shipping protocol |
CSTDMA/RATDMA (listens to free slots) |
SOTDMA (reserved slots) |
SOTDMA |
|
Update frequency when sailing |
Every 30 sec |
5–15 sec (depending on speed) |
2–10 sec |
|
Update when standing still |
3 min |
3 min |
3 min |
|
Additional data (e.g. destination) |
No |
No |
Yes |
|
Price indication |
€400–€800 |
€700–€1,200* |
€3,000–€5,000 |
|
Obliged? |
Waterway dependent |
Waterway dependent |
Yes (IMO/SOLAS) |
|
Installation |
Simple |
Simple |
Complex, professional installation required |
* The ONWA KS-200A+ Class B+ (5W, SOTDMA) AIS transponder costs € 325 incl. VAT.
Which AIS is right for me?
Sail Trade always recommends choosing an AIS transponder over an AIS receiver. On the water, it's all about "seeing and being seen." Sharing your vessel information via AIS gives other vessels more time to avoid your vessel or contact you.
In summary, a Class B (2W) transponder is the basic transponder, a Class B+ (5W) transponder is the modern and much better mid-range, and Class A is the professional standard for commercial shipping. For recreational boating, AIS Class B is often sufficient, especially if you only share the waterway with other slow-moving vessels.
It is wise to use a Class B+ transponder if one or more of the following situations apply:
- You share the waterway with other fast-moving vessels, just like at sea.
- You have a faster (motor)ship.
- You regularly sail in busy waters (such as port areas).
- You also sail in bad weather conditions and/or darkness, when visual perception of distance, course and speed is limited.
ONWA sets new price benchmark
You don't have to choose a Class B AIS transponder for price reasons. The ONWA KS-200A+ is a reliable Class B+ (5W, SOTDMA) AIS transponder for less than the price of a Class B (2W) AIS transponder. And it's equipped with Wi-Fi!