AIS is a ship transponder system that is used by most of the commercial shipping industry. Each ship equipped with an AIS transponder sends out a packet every few seconds with information about the ship such as its name, dimensions, where it is, where it’s going and how fast it’s moving. With an AIS receiver connected to your PC, Coastal Explorer can show the locations of other ships in your area right on your chart!
While AIS transponders still cost thousands of dollars, AIS receivers are now available for only a couple hundred dollars. Many boaters find that seeing exactly where the nearby tankers, container ships, and cruise ships are relative to their own vessel is far more valuable than transmitting their own position to those ships.
AIS uses two VHF channels to transmit information and transponders switch channels with each position report they send. This is done to make sure the signal gets through even if there is a lot of noise on one of the channels. However some AIS receivers only have one channel and will receive only about half as many position reports as a dual channel receiver. This can result in a slower update of the positions of vessels on your charts, or in extreme cases some vessels might not appear at all.
In order to install an AIS receiver on your boat, you just need to connect a VHF antenna and power to the receiver and then connect the receiver to your PC either through a standard serial port or via a USB Serial Adapter. It is possible to share a VHF antenna between a VHF radio and an AIS receiver if a special splitter is used to switch off the AIS antenna connection when the VHF radio is transmitting (to prevent overloading the receiver).
Coastal Explorer will interpret the information from your AIS receiver and display vessel symbols on the chart wherever a ship is transmitting. It will also calculate your closest point of approach (CPA) and warn you if you will get closer than you want within a certain amount of time (the time to closest point of approach or TCPA).
When looking for an AIS receiver, you will be confronted with several options including all-in-one designs that include an antenna, single vs. dual channel receivers, and various price levels. Keep in mind that -- as with most marine electronics – the cost of the “box” is only part of the total cost and that installation and other accessories can add up. All-in-one units might cost more than other units, but they are easy to install and don’t require a separate VHF antenna. On the other hand, a splitter might cost the same or more than a second antenna, but might cost less than installing that second antenna.