Rules of the Road: by Capt. Jake DesVergers
During a recent accident investigation, a vessel was lost at sea in poor weather conditions. Thankfully, no one was injured in the emergency. However, due to uncontrollable flooding, the yacht was abandoned by the crew. She subsequently stayed semi-afloat and was recovered by a towing company hired by the insurance underwriters.
It was noted that several types of equipment were utilized to locate, track, and salvage the yacht.
Automatic Identification System (AIS)
Following the terrorist events of September 11th, the member-states of the International Maritime Organization (IMO) enacted a series of safety and security regulations with a revision to the International Convention for the Safety of Life at Sea (SOLAS). These new rules included the requirement for all international trading vessels of 300 gross tons and greater to be equipped with AIS.
AIS works through a transponder. The unit automatically broadcasts information, such as a vessel’s position, speed, and navigational status. This data is sent at regular intervals via a VHF transmitter that is built into the transponder. The yacht’s info originates from navigational sensors, typically a GPS unit and gyrocompass or satellite compass. Other important information, such as the yacht’s name, MMSI, and call sign, is programmed into the AIS unit. The signals are received by AIS transponders fitted on other ships, yachts, or on land based systems, such as those used by Vessel Traffic Services. The received information is displayed on a screen or chart plotter, showing the other vessels’ positions in a format similar to that observed on a radar screen.
AIS provides many positive benefits. These include collision avoidance, search and rescue, and accident investigation.
Emergency Position-Indicating Radio Beacon (EPIRB)
EPIRBs are tracking devices, which aid in the detection and location of vessels in distress. In simplest terms, they are radio beacons that interface with the worldwide system known as COSPAS-SARSAT. This service is a satellite-based search and rescue (SAR) distress alert system. It was established in 1979 by the governments of Canada, France, the United States, and the former Soviet Union. When manually activated, or automatically activated upon immersion, EPIRBs actively send out a distress signal. The signals are monitored worldwide at dedicated rescue centers. Non-geostationary satellites detect the location of the distress.
Search and Rescue Transponder (SART)
A Search and Rescue Transponder (SART) is a self-contained, waterproof transponder intended for emergency use at sea. The device may be one of two types. It will be either a Radar-SART or a GPS-based AIS-SART.
The Radar-SART is used to locate a survival craft, life raft, or distressed vessel. It does this by creating a series of dots on a rescuing ship’s radar display. The radar observer will see a distinct pattern on the radar screen that provides a bearing towards the distress location. Unlike an EPIRB, a Radar-SART will only respond to a 9 GHz X-band (3 cm) radar. It will not be seen on the S-band (10 cm) or any other type of radar.
The AIS-SART calculates position and time from a built in GPS receiver. At an interval of once per minute, the position is actively sent as a series of eight identical position report messages. This scheme creates a high probability that at least one of the messages is sent on the highest point of a wave. The receiving rescue ship or aircraft is then provided an exact position, in addition to the visual bearing exhibited on the radar display.
Long Range Identification and Tracking (LRIT)
LRIT equipment must carried by internationally trading ships of 300 gross tons or greater. This includes commercial yachts.
The LRIT information that is transmitted includes the vessel’s identity, location and date, and time of the position. Unlike AIS, which is limited to VHF-type of range, LRIT signals are received via satellite. While similar in function, there is no interface between LRIT and AIS equipment. They are independent of each other.
One of the more important distinctions between the two systems, apart from the obvious one of range, is that, where AIS is an open broadcast system, data derived through LRIT is available only to the recipients who are entitled to receive such information. In most cases, this is the government of a sovereign nation. Safeguards concerning the confidentiality of this data are built into the regulatory provisions. Governments are entitled to receive information about ships and yachts navigating within a distance not exceeding 1000 nautical miles off their coast.
Much of the above equipment can be considered intrusive, especially when dealing with the privacy issues of a yacht. However, knowing that these systems are active, functioning, and transmitting to get you help, can be crucial if an emergency were to develop.
Capt. Jake DesVergers is chief surveyor for International Yacht Bureau (yachtbureau.org). Comments are welcome below.