AIS SARTs and Radar SARTs Under GMDSS: Key Differences

Maritime distress alerting has evolved significantly over the past several decades. Under the International Maritime Organization’s Global Maritime Distress and Safety System (GMDSS), vessels are required to carry specific survival craft equipment to aid in location and rescue during emergencies.

Two critical pieces of such equipment are AIS SARTs and Radar SARTs. While both serve the same ultimate purpose, helping rescuers locate survivors, they operate in very different ways. Let’s break down the key differences and help you understand which technology does what, and why both still matter today.

What Is a SART?

A Search and Rescue Transponder (SART) is a self-contained, battery-powered device used to assist in locating survival craft or distressed vessels. When activated, it transmits signals that guide rescuers directly to the emergency location.

Under GMDSS carriage requirements, certain SOLAS-class vessels must carry a SART on board, typically stored near the bridge or survival craft for quick deployment. There are two approved types: Radar SARTs and AIS SARTs.

Radar SARTs

A Radar SART operates on the 9 GHz (X-band) marine radar frequency. It remains in standby mode until it detects an incoming radar signal from a searching vessel or aircraft. Once triggered, it responds by transmitting a series of pulses. On the rescuer’s radar display, this appears as a line of 12 dots, eventually forming concentric arcs as the rescue unit gets closer. Key characteristics of Radar SARTs are as follows:

• Passive until interrogated by radar
• Requires nearby vessel or aircraft radar to activate
• Range: Typically up to 8 nautical miles (from liferaft antenna height)
• SOLAS / GMDSS compliant

AIS SARTs

An AIS SART transmits a distress message using Automatic Identification System (AIS) functionality on VHF frequencies. Instead of waiting for radar interrogation, it actively broadcasts its GPS position at regular intervals. AIS-equipped ships/vessels within VHF range receive a distress alert which includes a clearly marked target on their chartplotter or ECDIS with precise latitude and longitude. The target is clearly identified as a SART. Key characteristics of AIS SARTs are as follows:

• Actively transmits position data
• Provides real-time GPS coordinates
• Range: Typically 5–10 nautical miles depending on antenna height
• SOLAS / GMDSS compliant

Both AIS SARTs and Radar SARTs serve the same critical mission: helping rescuers find survivors quickly and accurately. The primary differences come down to:

• How they transmit
• How they are displayed
• How precisely they communicate location

Under GMDSS regulations set by the International Maritime Organization, both technologies are approved, but AIS SARTs represent the modern evolution of search and rescue location technology. Although AIS SARTs are a more modern solution, Radar SARTs still matter because not every vessel worldwide operates with fully functional AIS or ECDIS systems at all times. Radar remains universal and independent and in some search scenarios, especially involving aircraft, radar SART responses can still be highly effective.

Given that AIS SARTs and Radar SARTs each possess their own unique merits, an operator that values redundancy could choose a carriage configuration comprised of both SART types in order to ensure compatibility across various rescue scenarios.