A Radar SART and an AIS-SART are both search-and-rescue locating devices, but they reach the people searching for a casualty in different ways. Follow one imaginary distress situation from abandonment through search, locating and recovery to see where each technology fits.
Imagine the situation.
A vessel has suffered a serious casualty and the crew has entered a lifeboat or liferaft.
A distress alert may already have entered the search-and-rescue system. Rescue assets may know that assistance is required and may already be moving towards the casualty area.
But knowing that somebody is in distress is not the same as finding a small survival craft at sea.
As rescuers approach, the question becomes increasingly practical: where exactly are the survivors?
That is where a search-and-rescue locating device enters the story.
Radar SART vs AIS-SART — the answer in 30 seconds
A Radar SART is a radar transponder. Once activated, it responds when interrogated by compatible 9 GHz X-band radar and produces a recognisable response on the assisting radar display.
An AIS-SART obtains its position using GNSS and transmits search-and-rescue locating information on the AIS frequencies 161.975 MHz and 162.025 MHz.
The crew is in the survival craft — what is a SART?
In the radar context, SART means Search and Rescue Transponder.
An AIS-SART is an AIS Search and Rescue Transmitter.
Both are search-and-rescue locating devices. Their purpose is to help search units locate a casualty during a search-and-rescue operation.
The rescue process in four stages
The distress situation enters the applicable emergency and rescue system.
Search-and-rescue resources are directed towards the casualty area.
Search units work to locate the casualty.
Rescuers reach and recover the casualty.
For the wider maritime communications system, see What is GMDSS and how does it work?
A rescue vessel is approaching — how does a Radar SART work?
Imagine the survival craft is carrying an activated Radar SART.
Somewhere outside visual range, an assisting vessel is operating compatible X-band radar.
The Radar SART does not need to determine its own GNSS position to perform its radar-transponder locating function.
Instead, it waits for compatible radar interrogation.
The current Tron SART20 manual specifies operation in the 9.2–9.5 GHz X-band.
When compatible X-band radar interrogation is detected, the Radar SART responds across the radar band.
The response is received by the assisting radar and produces the characteristic SART presentation.
The assisting radar interrogates the area
A compatible X-band radar transmits radar pulses. An activated Radar SART within suitable conditions can detect the interrogation.
The transponder answers
The response is received by the assisting radar and creates the Radar SART locating presentation.
What the current IMO standard requires
IMO Resolution MSC.510(105) states that a Radar SART should indicate the location of a unit in distress on assisting radar by means of 12 equally spaced dots.
The standard also contains requirements for activation, deactivation, standby indication, correct-operation indication and survival-craft deployment.
Suitability and statutory acceptability must be confirmed for the vessel concerned.
The bridge team sees the response — what appears on radar?
The rescue vessel continues to close the distance.
The Radar SART has been interrogated and the response has become part of the radar picture.
This is where the familiar Radar SART presentation becomes important.
The current IMO performance standard specifies 12 equally spaced dots.
The current Tron SART20 manual also explains that the display changes with distance.
At close range the response can appear as rings. At greater separation the presentation reduces to the 12-dot pattern indicating the direction to the unit.
What does the 5 NM figure mean?
IMO MSC.510(105) requires correct operation when interrogated at up to at least 5 nautical miles by a compliant navigational radar under the test conditions specified in the standard, including a radar antenna height of 15 m above sea level.
The standard also specifies correct operation at up to 30 nautical miles under the specified airborne-radar test conditions.
These are performance-standard test conditions and should not be represented as guaranteed real-world detection ranges.
Now change the equipment — how does an AIS-SART work?
Rewind the story to the survival craft.
This time the locating device is an AIS-SART.
The objective remains to help rescuers locate the casualty.
The method is different.
The current Tron AIS-SART manual specifies GNSS positioning and transmission on the two international AIS frequencies.
161.975 MHz
162.025 MHz
The current manual specifies a radiated power of 1 W EIRP for the Tron AIS-SART.
It also specifies 96 hours continuous operating life at -20°C.
The rescue vessel does not need to interrogate the AIS-SART with X-band radar for the AIS locating function.
The AIS-SART has obtained a position and is transmitting search-and-rescue locating information through AIS.
That information can now reach suitable AIS receiving equipment.
The transmission reaches the bridge — what can rescuers see?
Suitable AIS equipment can receive information transmitted by an AIS-SART.
The precise presentation depends on the receiving equipment and whether its implementation is AIS-SART compliant.
These links identify related AIS products. This article does not claim that all listed products present an AIS-SART in the same way.
The same rescue problem — two different technologies
| Feature | Radar SART | AIS-SART |
|---|---|---|
| Operating principle | Radar transponder | AIS search-and-rescue transmitter using GNSS-derived position |
| Example discussed | Tron SART20 | Tron AIS-SART |
| Frequencies | 9.2–9.5 GHz | 161.975 MHz and 162.025 MHz |
| How locating information reaches rescuers | Response to compatible X-band radar interrogation | AIS search-and-rescue transmission |
| GNSS required for locating principle | No | Yes |
| Current Jotron endurance specification | 96 h standby followed by 8 h operation at -20°C | 96 h continuous operation at -20°C |
| Battery service life | 5 years | 5 years |
| Routine inspection | Monthly according to current manual | Monthly according to current manual |
Back in the liferaft — deployment matters
Correct deployment forms part of the intended operation of the equipment.
For Radar SART, IMO MSC.510(105) states that the installed antenna height should be at least 1 metre above sea level.
The current Tron SART20 instructions require the unit to be deployed vertically using the applicable survival-craft arrangement.
AIS-SART also needs a position that supports GNSS reception and its AIS transmission.
The illustration is not the operating manual
Deployment should follow the instructions supplied with the actual equipment and the vessel’s approved survival-craft arrangements.
How did rescuers know there was an emergency? EPIRB vs SART
A 406 MHz EPIRB and a search-and-rescue locating device do not perform the same function.
A 406 MHz EPIRB is primarily a satellite-based distress-alerting beacon operating through Cospas-Sarsat.
A Radar SART is a search-and-rescue radar transponder.
An AIS-SART is an AIS search-and-rescue transmitter.
Distress alerting
406 MHz satellite distress beacon.
Radar locating
Responds to compatible X-band radar.
AIS locating
Transmits GNSS-derived search-and-rescue information over AIS.
The rescue is bigger than one device — where does GMDSS fit?
Search-and-rescue locating devices form part of the wider maritime distress and safety framework.
IMO Resolution MSC.256(84 amended SOLAS terminology to recognise both Radar Search and Rescue Transponders and AIS Search and Rescue Transmitters as search-and-rescue locating devices.
A UK regulatory example
MCA Merchant Shipping Notice MSN 1903(M) states that, for vessels within its scope, the required search-and-rescue locating device may operate in the 9 GHz band or on frequencies dedicated for AIS.
The Notice has a defined scope and should not be treated as a universal carriage rule for every vessel.
How many SARTs does my vessel need?
That depends on the requirements applicable to the individual vessel, including its regulatory regime, voyage, survival-craft arrangements and applicable flag, survey or certification requirements.
Go back to the day before the emergency — where was the SART?
A SART may spend years waiting to be used.
That means storage, inspection, testing and battery management are part of the rescue story long before an emergency ever occurs.
Readiness is created before the vessel has to abandon ship.
Emergency locating equipment needs to remain available for emergency use and should be stowed according to the applicable vessel requirements and manufacturer’s instructions.
The equipment may wait for years — how do you know it is ready?
The current Tron SART20 and Tron AIS-SART manuals specify monthly inspection of the unit and bracket.
The unit should be removed and tested according to the procedure for the specific model.
Radar SART test
The current manual describes use of the TEST position while another person observes the radar.
For that described test procedure it specifies a 10 NM radar range setting.
The manual states that tests should be kept as short as possible.
AIS-SART test
The current manual specifies testing outdoors with a clear view of the sky.
The test includes acquisition of a GNSS position and status indications from the unit.
Follow the manual for the exact equipment and revision installed.
IMO caution for Radar SART testing
IMO MSC.510(105) states that when an onboard Radar SART test uses a shipborne 9 GHz radar, SART activation should be limited to a few seconds to reduce interference and excessive battery consumption.
The last thing to discover in an emergency: an expired battery
Manufacturer documentation distinguishes shelf life from service life.
Jotron Technical Bulletin TB05-2024-1 Rev.1 lists the following for the current Tron SART20 and Tron AIS-SART:
Tron SART20
Shelf life: 18 months
Service life: 5 years
Tron AIS-SART
Shelf life: 18 months
Service life: 5 years
The current manuals specify five-year battery-module replacement for these products.
The expiry marking on the actual unit should be checked rather than calculating the date from the remembered purchase date.
Radar SART or AIS-SART — which should you choose?
Neither technology should be described as universally better for every vessel.
They use different locating methods and the equipment permitted or required for a particular vessel depends on the requirements applicable to that vessel.
Radar-based locating
Responds to compatible X-band radar interrogation.
AIS position-based locating
Obtains GNSS position and transmits locating information through AIS.
Replacing statutory equipment?
Confirm the vessel’s applicable carriage requirements, approved arrangements, survival-craft provision and any relevant flag, class or survey requirements before changing locating technology.
Related F&C Marine equipment
These are related F&C Marine catalogue pages for the technologies discussed above. Inclusion does not mean that every product is required or suitable for every vessel.
Radar SART and AIS-SART FAQs
What does SART stand for?
In the radar context, SART means Search and Rescue Transponder. AIS-SART means AIS Search and Rescue Transmitter.
What frequency does a Radar SART use?
The current Tron SART20 manual specifies operation across 9.2–9.5 GHz in the X-band.
What frequencies does the Tron AIS-SART use?
161.975 MHz and 162.025 MHz.
Does an AIS-SART use GNSS?
Yes. AIS-SART uses GNSS-derived position for its locating transmissions.
Does a Radar SART require GNSS?
No GNSS position is required for the conventional Radar SART radar-transponder locating principle.
Why are there 12 dots on the radar?
The current IMO Radar SART performance standard requires a series of 12 equally spaced dots to indicate the distress unit on assisting radar.
How high should a Radar SART be deployed?
IMO MSC.510(105) states that the installed Radar SART antenna should be at least 1 metre above sea level.
How often should these Jotron SART units be inspected?
The current Tron SART20 and Tron AIS-SART manuals specify monthly inspection and testing according to the applicable manual.
Is a SART the same as an EPIRB?
No. A 406 MHz EPIRB is primarily a satellite distress-alerting beacon. Radar SART and AIS-SART are search-and-rescue locating devices.
Can AIS-SART replace Radar SART?
Whether AIS-SART can be used for a particular vessel or replace existing statutory equipment depends on the requirements and approved arrangements applicable to that vessel.
Continue through the F&C Marine Knowledge Base
What is GMDSS and how does it work?
Marine emergency beacons and survival equipment explained
How an EPIRB alert travels from your boat to a Rescue Coordination Centre
406 MHz EPIRB / PLB Hex ID Decoder
What is AIS and how does it work on a boat?
Marine VHF radio systems explained
The story ends where good preparation begins.
A Radar SART or AIS-SART may spend most of its working life waiting in its designated location.
If it is ever required during an emergency, that is not the time to discover how it works, find an expired battery, locate a missing mounting arrangement or learn the correct test and operating procedure.
Correct equipment selection matters.
So do storage, familiarisation, inspection, testing and maintenance.
If the day ever comes when the unit is taken into a survival craft, the preparation for that moment should already have been completed.
Need help selecting or replacing search-and-rescue equipment?
F&C Marine supplies marine communications, GMDSS, navigation and safety equipment.
For statutory equipment, the correct starting point is the actual vessel, its existing arrangement and the requirements that apply to that vessel.
Contact F&C Marine Sales Technical SupportTechnical sources
Technical statements in this guide have been based on manufacturer documentation and applicable regulatory material including:
Performance Standards for Search and Rescue Radar Transponders.
IMO source
SOLAS amendments including Radar SART and AIS-SART terminology.
IMO source
MCA source
Part No. 84145, Rev. M.
Part No. 85355, Rev. K.
Battery Lifetime on Battery-Powered GMDSS Products.
Important technical and regulatory note
This article is general technical information and does not replace the current manufacturer’s instructions, approved vessel arrangements, statutory requirements, flag-state requirements, class requirements or survey instructions.
Requirements for the specific vessel should be confirmed before purchasing, replacing, relocating or altering statutory safety equipment.