AIS was developed as an identification and tracking system for ship to ship and shore to ship use. The primary and founding purpose is for collision avoidance and vessel safety. It is designed to allow vessels to visualize, identify and under- stand the intentions of other vessels navigating in the same and sometimes con- gested waterways. Because it is reliant on VHF broadcast and reception, transmission is limited to a possible maximum of 30 to 40 miles. Despite its limited range, AIS
augments and can surpass radar detection for collision avoidance. Large waves and swells
along with bad weather do not affect AIS the way they do radar. Also, a vessel within VHF
range (running close to land or behind an island or peninsular) can still be detected. AIS
identifies what vessels are nearby by name, type and can indicate rate of turn and navigation intentions instantly.
Equipment required for an onboard AIS system includes an appropriate transponder,
receiver and display, along with an AIS antenna or VHF splitter. All but the antenna and/or
splitter are integral with some models, and some have their own built-in display. Many
units also have the ability of interfacing their information with other displays and equipment. They are no longer limited to displaying data on radar screens but can be viewed
on compatible equipment, including multi-function displays through NMEA protocols
and to smart devices though WiFi. AIS transmits on two VHF frequencies (161.975 and
162.025, channels 87 and 88) in the upper end of the marine VHF range. Each vessel with
AIS needs to have a Maritime Mobile Service Identity (MMSI) number, which is broadcast
along with GPS data giving navigation status information.
A life-saving technology
expands and evolves
Not too many years ago,
AIS (Automatic Identification System)
was thought by some to be just another
mandated burdensome expense on commercial shipping and an unnecessary
technology requirement. Since then AIS
has proved its value in a number of
ways and is a key component
in new applications.
AIS displays on smart phones and tablets are increasingly popular. The technology could also be an important component on automomous
self-propelled platforms called “wave gliders” (at top) that transmit data about ocean conditions and more.
BY GLENN HAYES