Source: Wikipedia
At sea, every second counts when emergencies strike, especially in situations of global maritime distress. Locating a distressed vessel or survival craft in vast waters can be extremely challenging, especially in adverse weather conditions. That is why the SART was developed, a small but powerful device that saves lives. Required under GMDSS regulations, the SART is an essential part of the maritime safety system, supporting search and rescue operations by making ships, life rafts, and lifeboats clearly visible on radar screens.
What is SART?
A search and rescue transponder (SART) is a compact, waterproof, self-contained radio device that helps rescuers locate a distressed vessel or survival craft. It works by receiving a radar pulse from a nearby ship or aircraft and sending a distinctive reply that appears on the radar display. This response, unique to the SART, makes it easy for search and rescue units to identify the position of people in need.
There are two main categories: Radar SART and AIS SART. Both are bright orange, activated manually, and designed to float. They are mounted near bridge wing doors or packed in a life raft so they can be quickly deployed during rescue operations.
Why SART is Important
In an emergency, the SART acts as a digital lighthouse. Unlike a radar reflector, which only bounces back signals, the SART actively responds, producing a pattern of SART signals that pinpoint an emergency position. This makes it one of the most reliable rescue locating devices.
The International Maritime Organization requires cargo ships of 300–500 gross tons to carry at least one SART, while larger cargo ships and passenger ships must carry two. This carriage requirement ensures every vessel has a reliable rescue transponder available to aid rescue units if the worst happens.
How It Works
A SART has both a radar receiver and a radar transponder. When an interrogating radar on a ship or aircraft sweeps across it, the SART instantly responds. The radar transponder produces 12 dots or arcs on the radar display, spaced evenly apart. As the interrogating radar gets closer, these dots transform into concentric circles, making the active SART unmistakable.
This radar interrogation process ensures the SART only uses power when needed. In standby mode, the SART conserves battery but switches on immediately when it detects a radar signal.
Range, Distance, and Frequency
The radar SART frequency is in the X band radar range (9.2–9.5 GHz). Since this is line-of-sight, mounting height is key. On a life raft, the range might be only 2–3 nautical miles, but mounted higher, detection extends to 6–12 miles. Aircraft with marine radar can pick up SART signals more than 30 nautical miles away.
Manufacturers advise mariners to always check the instructions on each unit, as different models vary slightly in operating range and testing procedures. Following the manual ensures correct operation when every minute counts.
Types of SART
There are two main types of Search and Rescue Transponders. The Radar SART works with X-band radar to show survivors’ positions on the radar display, while the AIS SART sends updated position reports through the AIS system. Both play a vital role in guiding rescuers to a distressed vessel or survival craft.
Radar SART
The radar SART is the traditional and still the most widely used rescue transponder. It relies on X-band radar to function, making it compatible with virtually every ship’s radar set. When it receives a radar pulse, the radar receiver inside triggers the radar transponder to sweep across its starting frequency and emit replies. This process repeats as it sweeps rapidly through the band, creating the iconic 12 dots on the radar display.
As the interrogating radar approaches, these dots change into arcs and then circles, guiding search and rescue radarteams directly to the distressed vessel. This makes radar SARTs highly effective in low visibility, fog, or heavy seas.
A radar SART is manually activated by survivors and provides both audible and visual cues when responding. An LED light or buzzer confirms it is active, so survivors know the rescue radar transponder is working. With a battery life of 96 hours in standby mode and at least 8 hours in continuous response, the radar SART is a trusted companion in emergencies.
Despite newer alternatives, radar SART remains essential because it works with all types of rescue operations, regardless of whether ships are equipped with AIS.
AIS SART
Source: Wikipedia
An AIS SART is a newer type of rescue transmitter that integrates with the Automatic Identification System (AIS). Instead of creating dots on a radar display, the AIS SART transmits updated position reports directly to nearby ships. These sending updated position reports are derived from GPS, making the AIS SART a precise locator.
Every AIS-equipped vessel in range receives the coordinates of the distressed vessel, displayed on electronic charts or AIS monitors. This allows search and rescue operations to home in with accuracy. The AIS SART is also a self-contained radio device, brightly colored, lightweight, and waterproof.
AIS SARTs are invaluable where many ships already use AIS, such as in coastal waters or busy shipping lanes. Their ability to send updated position reports means rescuers can track the drifting path of a life raft or survival craft in real time.
Although an AIS SART cannot replace a radar transponder, the combination of radar SART and AIS ensures maximum visibility during emergencies. For this reason, many modern vessels carry both.
Operating Principle
A search and rescue radar transponder works by conserving power until it detects an incoming radar pulse. Once triggered, the SART transmits a unique signal sequence. These SART signals stand out from clutter, even in poor visibility. In essence, the SART amplifies the chances that rescue units will see you first.
How to Use SART in Emergencies
- Remove the unit from its bracket near the bridge wing doors or in the life raft.
- Break the seal and switch it on, it is activated manually.
- Mount it as high as possible on the survival craft or extend its pole.
- Wait for the radar antenna of a nearby vessel to sweep across.
- Confirm the buzzer/light indicates correct operation.
What Not to Do / What to Avoid
- Never trigger a SART outside a true emergency, it creates a false distress signal.
- Do not store it near heat or puncture its lithium battery.
- Avoid blocking its line of sight; the higher it is mounted, the better SART detection will be.
- Do not use a RADAR reflector and a SART together
Risks and Errors
Improper testing or damage can render the SART ineffective. Failing to maintain batteries, confusing AIS SART with radar SART, or relying only on a radar reflector are common mistakes.
Justifying the Cost of a SART
For many mariners, the question is whether to invest in a SART in addition to EPIRBs. While EPIRBs alert authorities, a SART allows search and rescue units to pinpoint you quickly. Given the low price compared to the cost of losing lives at sea, carrying both is a wise choice.
Key Things to Keep in Mind
- Always check battery expiry
- Mount in accessible areas
- Familiarize yourself with both radar SART and AIS SART functions
Maintenance and Testing
SARTs should be visually checked monthly and tested annually. Use radio beacons or a marine radar for a quick check, keeping the test short to avoid confusion with genuine rescue operations. Batteries must be replaced every 5 years.
Warning and Safety Information
- For emergency use only
- False alarms waste resources
- Do not touch the antenna when transmitting, as it emits RF energy
Transportation and Handling
Lithium batteries make SARTs subject to shipping regulations. Always pack securely and comply with safety codes.
What to Do if SART Is Faulty
If self-tests fail, return the unit to an authorized service center. It has no user-serviceable parts.
Optimising Radar for SART Detection
To improve SART detection, rescuers should use radar displays on the 6–12 nautical mile range, allowing the 0.6-mile spacing between SART signals to show clearly. Adjust marine radar bandwidth for best clarity.
Conclusion
The search and rescue transponder is a key lifeline during emergencies. Whether it is a radar SART responding to an interrogating radar or an AIS SART sending updated position reports, the SART bridges the gap between a distress signal and a successful rescue. For cargo ships, passenger ships, and even recreational mariners, carrying a SART means being prepared for the worst while hoping for the best.
FAQs
Q1. Is a SART automatically activated?
No, most models are manually activated, though some can be automatically activated in survival systems.
Q2. How long does a SART operate?
It remains in standby mode for 96 hours and transmits for 8 hours once active.
Q3. Can a SART replace an EPIRB?
No. An EPIRB alerts authorities globally, while a SART helps search and rescue radar teams locate you locally. Both are vital.
Q4. Where should a SART be kept?
Near bridge wing doors or packed in a life raft or survival craft for quick access.
Q5. Why are there two types?
The radar SART works with X-band radar, while the AIS SART shares updated position reports with AIS-equipped vessels. Together, they maximize your chances of being found.
