GMDSS study cards

Equipment Cards

One card per device or system: what it is, then the specs. Each card prints on its own A4 page.

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EPIRB

Emergency Position Indicating Radio Beacon

Alerts rescue centres anywhere in the world

406 MHzsatellite alert
121.5 MHzhoming
48 hmin. operation
Globalcoverage

Definition

An EPIRB is a satellite-based distress beacon used on vessels to signal a life-threatening emergency to search and rescue authorities. When activated manually or automatically upon submersion, it transmits a 406 MHz signal containing the ship's unique MMSI, allowing rescue centers to locate the vessel globally using the Cospas-Sarsat satellite system.

Specifications

Frequencies

  • 406.0–406.1 MHz: satellite distress alert
  • 121.5 MHz: local homing signal
  • Modern EPIRBs also incorporate GNSS/GPS frequencies

Battery / transmission

  • Minimum 48 hours of continuous operation once activated
  • Battery life: 5 years

Operating range

  • Global coverage via the Cospas-Sarsat satellite system (MEOSAR / LEOSAR / GEOSAR)

Key data

  • Transmits a 5 W signal burst every 50 seconds containing the vessel's MMSI
  • Activated automatically by water contact / hydrostatic release unit (HRU) at 1.5–4 m depth, or manually
MMSIShip's own MMSI
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SART

Search and Rescue Radar Transponder

Shows the liferaft on the rescuer's radar

9 GHzX-band radar
12 dotson radar
96 h + 8 hstandby + active
8–10 NMto ship radar

Definition

A SART is a localized homing device designed to assist search-and-rescue vessels and aircraft in pinpointing lifeboats or rafts. When painted by a 9 GHz X-band search radar, it automatically responds by generating a distinctive pattern of 12 dots (turning into arcs and concentric circles at close range) on the rescuer's radar display.

Specifications

Frequencies

  • 9.2 GHz to 9.5 GHz (X-band radar range)

Battery / transmission

  • Minimum 96 hours in standby, waiting for radar interrogation
  • Followed by at least 8 hours of active continuous transmission
  • Battery life: 5 years

Operating range

  • 8–10 NM to a ship's radar antenna (15 m high)
  • Up to 30–40 NM to an airborne radar

Key data

  • Responds to radar interrogation by sweeping back and forth, generating 12 distinct dots on the target ship's radar screen

How to check

  • Check the battery expiry date and look for damage to the case and bracket
  • Switch to test mode near your own ship's X-band (3 cm) radar
  • Radar should show concentric rings around own ship; the SART light flashes / beeper sounds when it is interrogated
  • Keep the test short (a few seconds) so other ships don't take it as a real distress
  • Switch off and stow correctly
MMSINo MMSI: it answers radar, it does not send data
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AIS-SART

AIS Search and Rescue Transmitter

Shows the liferaft on nearby AIS screens

970MMSI prefix
96 hmin. transmission
8 / minmessages
5–10 NMto vessel

Definition

An AIS SART is a modern locator device that replaces traditional radar SARTs by broadcasting emergency positioning data over VHF AIS channels. Operating on a 970-prefixed MMSI, it transmits the survival craft's exact GPS coordinates, UTC time, and an alert message directly to nearby AIS-equipped vessels up to 5 nautical miles away.

Specifications

Channels

  • AIS 1: Ch 87B
  • AIS 2: Ch 88B

Battery / transmission

  • Minimum 96 hours of continuous operational transmission
  • Battery life: 5 years

Operating range

  • Typically 5–10 NM to a vessel
  • Up to 30–40+ NM to SAR aircraft

Key data

  • Fixed MMSI prefix 970XXXXXX
  • Transmits 8 messages per minute, alternating channels every minute
  • Built-in GPS, ~10 m accuracy
  • Water resistant to 10 m, drop-tested to 20 m

How to check

  • Check the battery expiry date and look for damage to the case and lanyard
  • Press the test function: it sends a test message and checks its GPS
  • Your own AIS display / chart plotter should show the AIS-SART (970 MMSI) marked as a test, not a live alert
  • Check the indicator light shows a successful test, then switch off and stow
MMSI
970721234
Prefix 970, e.g. 970721234
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AIS

Automatic Identification System

Tracks ships to prevent collisions

Ch 87BAIS 1
Ch 88BAIS 2
2–10 sreport underway
3 minreport at anchor

Definition

AIS is an automated, VHF-based maritime tracking system used to prevent collisions and enhance situational awareness near ports and busy waterways. It automatically broadcasts and receives static and dynamic vessel data, such as position, course, speed over ground, heading, and MMSI, every few seconds to nearby ships and shore stations.

Specifications

Channels

  • AIS 1: Ch 87B
  • AIS 2: Ch 88B

Power / range

  • Class A (commercial, 12.5 W): ~20–30 NM
  • Class B (recreational, 2–5 W): ~10–15 NM line-of-sight

Reporting intervals

  • Underway: position every 2 to 10 seconds (depending on speed and rate of turn)
  • At anchor: every 3 minutes

Key data

  • Powered by vessel mains power (no emergency battery limitations)
  • Static: MMSI, vessel name, call sign
  • Dynamic: GPS position, SOG, COG, heading
  • Voyage: destination, ETA
MMSIShip's own MMSI
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AIS EPIRB

EPIRB with built-in AIS

Global satellite alert plus local AIS homing

406 MHzsatellite alert
974MMSI prefix (AIS)
48 hmin. operation
2022SOLAS mandate

Definition

An AIS EPIRB is an advanced distress beacon that combines long-range 406 MHz satellite alerting with a localized VHF AIS transmitter. It alerts global Rescue Coordination Centers via satellite while simultaneously transmitting real-time AIS positioning signals to all nearby vessels, providing both wide-area rescue dispatch and immediate local vessel homing.

Specifications

Frequencies & channels

  • 406 MHz: satellite distress
  • 121.5 MHz: homing
  • AIS channels: Ch 87B (AIS 1) and Ch 88B (AIS 2)

Battery / transmission

  • Minimum 48 hours of continuous operation across all frequencies
  • Battery life: 5 years

Operating range

  • Global satellite coverage (406 MHz)
  • Plus local VHF line-of-sight range of 4–10 NM to surrounding vessels via AIS

Key data

  • MMSI prefix 974XXXXXX for the AIS component
  • Mandated for new SOLAS installations after 1 July 2022
  • Integrates long-range SAR dispatch with instant local-vessel collision avoidance and homing
MMSI
974721234
Prefix 974, e.g. 974721234
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Portable VHF

Portable (handheld) GMDSS VHF radio

Survival-craft and on-board voice radio

Ch 16must have
+1other channel minimum
8 hspare lithium battery
IPX7/8waterproof

Definition

A portable GMDSS VHF is a handheld marine radio for survival craft and on-board use. It must work on Channel 16 and at least one other channel, runs on a rechargeable NiCd battery, carries a sealed spare lithium battery for emergencies, and must be waterproof and tough.

Specifications

Channels

  • Must operate on Ch 16 (distress, safety, calling)
  • Plus at least one other channel, e.g. Ch 6 (inter-ship / SAR coordination)
  • Modern devices include all international VHF channels

Output power & modulation

  • Low power: 0.25 W (or 1 W)
  • High power: 1 W to 2.5 W
  • Frequency Modulation (FM): G3E / F3E for voice

Batteries

  • Primary: rechargeable NiCd battery
  • Spare: sealed, non-rechargeable lithium battery for emergency use
  • Spare gives a minimum 8 hours at 10% transmit / 10% receive / 80% standby (many give 12–16+ h)
  • Spare storage life: 4 to 5 years

Communication ranges

  • Handheld to handheld: ~3–5 NM
  • Handheld to vessel (antenna ~9 m): ~5–8 NM
  • Handheld to coast station / SAR aircraft: ~10–30+ NM

IMO construction standards

  • Waterproof to IPX7 / IPX8: 1 m depth for at least 5 minutes
  • Survives a 1 m drop onto a hard surface