Using AIS on Your Sailboat

Simple Equipment to Avoid Collisions with Ships

AIS stands for Automatic Identification System, the international automated collision-avoidance system. While somewhat complex in all its variants and requirements, the concept is generally simple. Large ships and all commercial passenger vessels are required to have and use a special AIS transceiver that continually broadcasts key information about the ship via special VHF radio channels. This information includes:

  • Position
  • Course
  • Speed
  • Vessel name, ID, and radio call sign

This information can be received by all other ships within range (up to 46 miles or more) so that navigators can avoid collision.

The Value of AIS for Sailors

A large ship traveling at speed can within 20 minutes or so appear over the horizon and reach your sailboat - if you are on a collision course. Even in good visibility, that doesn't give you much time to observe and calculate its relative heading and then take evasive action - especially since most sailboats move so much more slowly than commercial ships. And if there is fog or rain or it's dark, then you are at greater risk for collision, even if you use radar, since the range of radar is usually less than AIS range. And if you don't have radar on your boat, then you really do need to think about AIS if you sail in open water at night or may experience reduced visibility.

Inexpensive AIS Options for Sailors

There is no legal requirement for recreational sailboats to have an AIS transceiver or transponder, so all most sailors need is an AIS receiver of some sort so that you get the information about an approaching ship that may pose a threat. AIS data or a warning alarm gives you time to alter course and avoid collision.

Depending on your budget, personal preferences, and other navigational equipment onboard, you have a number of options available for receiving and viewing AIS data about ships within range. Following is a summary of six different ways to receive AIS data as of the time of this writing. Some are new as of now but will likely become more widely used soon; other new systems may yet still emerge. Because of constantly changing prices and configurations I will not include particular model numbers and prices here; these are easily researched online once you've considered what type of unit is best for you and your boat. These systems range from about $200 for add-on components to equipment you likely already have up to about $700 or more for dedicated units at the higher end.

  • AIS receiver only. This type of device connects to a VHF antenna (either its own - or shares your VHF radio's antenna using a splitter) and power source. It outputs data that is displayed on a chartplotter, radar, or laptop computer. It costs less, but you need more other equipment to use it.
  • Dedicated AIS receiver. A dedicated receiver is an all-in-one unit with its own controls (usually the antenna is sold separately). Give it power and its own screen displays the AIS data.
  • Chartplotter with AIS built in. This is a new combination coming on the market. The antenna is connected to the chartplotter, which already has or is wired to a GPS, and AIS ship data can then be overlaid on the same chart screen. If you are already shopping for a new chartplotter, this may be your best option.
  • VHF radio with AIS built in. This is also a relatively new approach appearing with some new fixed-mount VHF radios. Obviously the VHF already needs an antenna, so that component is already in place. For full function you need to connect a GPS antenna, however, and the small VHF alphanumeric screen provides less visual data than a plotter, computer, or radar screen.
  • AIS "smart antenna." This new device is a simple, easy way to feed AIS data into a laptop computer (likely already running a chartplotter program). It's a small antenna (with more limited range) with built-in AIS receiver that plugs into a USB port. Available for Windows, Mac OS, and Linux.
  • Web site or app. If you sail close to the coast and have G3 or G4 connectivity for your laptop, smartphone, or tablet, you're in luck because you can get AIS data for free without needing any more hardware. (But you must have connectivity - so don't trust this method until you're sure!)

All this equipment can only give you data about other ships - you still need to make your own decisions about what action to take. Remember that most large ships cannot turn or stop easily, so even if you think you might have right of way as a sailboat, don't forget the rules of the road and take steps early to avoid collision when needed.

Look here for more ideas about how to stay safe on your sailboat.