The Global Maritime Distress and Safety System (GMDSS), introduced by the International Maritime Organization (IMO), ensures fast and effective communication in emergency situations. Standard GMDSS equipment includes VHF and MF/HF radios, satellite communication, EPIRBs, SARTs, and NAVTEX. However, additional equipment such as handheld VHF radios, ITU publications, emergency lighting, chargers, and batteries also plays a crucial role in enhancing the system’s functionality and reliability.

In this article, we will explore these additional components in detail, their importance, and their applications within the GMDSS framework.

Handheld VHF Radios in the GMDSS System

Importance of Handheld VHF Radios

Handheld VHF radios are one of the last-resort communication tools used in emergency situations such as evacuations. They enable communication between rescue teams, liferafts, ships, and rescue units. Due to their mobility, handheld VHF radios allow for quick and effective transmission of information in situations where access to other communication means is limited. However, they also come with several limitations.

SOLAS and IMO Requirements

According to Chapter IV of the SOLAS Convention, all ships covered by the GMDSS system must have:

  • At least two handheld VHF radios for vessels operating in area A1.
  • At least three handheld VHF radios for ships operating in areas A2, A3, and A4.

These devices must meet the following criteria:

  • Waterproofing: Minimum protection level of IP67 or higher.
  • Power supply: Equipped with rechargeable battery packs providing at least 8 hours of operation. Additionally, handheld VHF radios should include single-use, non-rechargeable backup batteries. The battery must be sealed, and its expiration date should be clearly marked. Once expired, the battery must be replaced with a new one.
  • Channels: Support for channel 16 (distress) and other emergency channels.
  • Labeling: Each radio should be marked with the vessel’s name, MMSI number, Call Sign, and IMO number.
  • Certification: Compliance with IMO and SOLAS standards.

Benefits of Use

  • Flexibility: Can be used anywhere on the ship and beyond.
  • Emergency backup: An alternative communication source in case of failure of fixed systems.
  • Evacuation support: Ensures communication during ship abandonment.

Disadvantages and Limitations

  • Low transmission power: Handheld radios typically have two operating modes—Low with 1W transmission power and High with 2W transmission power. It should also be noted that, like any battery-powered radio, transmission power decreases as the battery discharges.
  • Lack of DSC support: Due to the absence of a built-in GPS receiver, battery operation, and various other factors, handheld radios do not monitor DSC communication.
  • Short range: While a fixed VHF radio with a full-size mast-mounted antenna has a range of several dozen nautical miles, a handheld radio equipped with a short antenna has a very limited range, especially when communicating from a lifeboat. It is important to reduce the squelch level in an emergency to hear even weak or distorted signals.

ITU Publications within the GMDSS

Importance of ITU Publications

The International Telecommunication Union (ITU) develops and publishes documents that are crucial for the proper functioning of the GMDSS system. ITU publications contain standards, regulations, and information related to maritime radio communications.

Key ITU Documents for GMDSS That Must Be Available on Every Ship

  • ITU List IV – List of Coast Stations and Special Service Stations
  • ITU List V – List of Ship Stations and Maritime Mobile Service Identity Assignments
  • ITU Manual for Use by the Maritime Mobile and Maritime Mobile-Satellite Services

Current ITU Versions for GMDSS (as of 06-01-2025)

  • 2023 – ITU List IV – List of Coast Stations and Special Service Stations
  • 2024 – ITU List V – List of Ship Stations and Maritime Mobile Service Identity Assignments
  • 2024 – ITU Manual for Use by the Maritime Mobile and Maritime Mobile-Satellite Services (Maritime Manual)

Requirements for Publications on Ships

According to regulations, ships must have the latest editions of ITU publications available in either physical or electronic form. Ensuring access to these documents enables effective communication in emergency situations. You can always check the latest versions at the following link: ITU maritime publications

Emergency Lighting in the GMDSS System

Role of Emergency Lighting

Emergency lighting plays a crucial role in ensuring safety during evacuation and emergency situations. In the context of GMDSS, it includes the illumination of radionavigation systems. The power source for such lighting must be the GMDSS backup power supply. The emergency lighting switch should be clearly marked.

Power Sources

Importance of Reliable Power Supply

The GMDSS system relies on the continuous availability of electrical power. A power failure can result in the loss of communication capabilities, endangering the safety of the crew and the vessel. Therefore, chargers and batteries are key components of the GMDSS system.

Main Power Source

This is the primary power source for the entire vessel, consisting of at least two independent generator sets, each with sufficient capacity to cover the vessel’s energy demands for safe operation. These are typically generator units located in the engine room.

Emergency Power Source

The requirement for an emergency power source applies to all cargo ships, with the following exceptions: vessels with a gross tonnage of less than 500 and fishing vessels under 24 meters in length. The emergency power source can be either a generator or a battery bank.

Reserve Power Source

The reserve power source is intended to supply radio communication equipment for distress situations in case both the main and emergency power sources fail. The reserve source must be capable of simultaneously powering the VHF and MF/HF radio stations (or VHF radio station and INMARSAT/IRIDIUM terminal), AIS, and GPS receiver. If duplicate equipment is installed on the vessel, all such devices must be powered.

Types of Batteries Used in GMDSS

  • Lead-acid batteries: A traditional type of battery used due to its low cost and easy availability.
  • Lithium-ion batteries: Increasingly chosen for their higher efficiency, longer lifespan, and lower environmental impact.
  • Nickel-cadmium (NiCd) batteries: Used in some systems due to their high resistance to extreme temperatures.

Requirements for Chargers and Batteries

  • Certification: Chargers must comply with SOLAS requirements and IMO regulations.
  • Charging time: The charging system must be capable of fully recharging the batteries within 10 hours while following proper charging procedures.
  • Status monitoring: GMDSS systems should be equipped with monitoring devices to track battery charge levels. The system must display at least the voltage, charging and discharging current, and include an audible and visual alarm for power failures.
  • Testing: The capacity of the batteries must be checked at intervals of less than 12 months.

Three Types of Battery Tests:

  1. Daily load/no-load test – Ensures that all connections are functional and that a loaded battery does not lose voltage too quickly.
  2. Annual capacity test – Measures the battery capacity in ampere-hours (Ah). The battery should be replaced if its capacity falls below 80% of its nominal value.
  3. General maintenance (performed daily) – Includes checking electrolyte levels and specific gravity.

Logbook Entries:

  • Battery charge and discharge times.
  • Results of required tests, including electrolyte density in lead-acid batteries and battery voltage readings.
  • For automatic charging systems, logging specific times is not required. Instead, a statement confirming the use of such a system is sufficient.
  • The requirement to measure specific gravity or battery voltage and record the result in the logbook remains unchanged.

Daily Battery Test

Daily Load Test
This test ensures that:
✓ All connections between the battery and the device are in normal condition and that the GMDSS equipment can be powered by the battery.
✓ The battery can supply power to operating equipment, meaning that the battery does not discharge too quickly under load.

How to Perform a Load Test?

  1. Turn off AC power to the GMDSS station by pressing the on/off button under the GMDSS panel (or by switching off the charger fuses). Turn off all other battery power sources if connected. If the battery is constantly being charged, you will not see a voltage drop. However, the purpose of this test is to measure the voltage drop precisely.

NOTE: GMDSS batteries are usually charged by automatic chargers powered by AC voltage. Turning off the AC power ensures that the batteries are not charging during the test. After switching the GMDSS equipment to battery power, record the battery voltage.

  1. Select a free VHF channel and set the power to high.
  2. Press the PTT button to transmit. Record the under-load voltage at the moment the PTT is pressed.
  3. Check that the voltage drop does not exceed 1.5V.
  4. Repeat the same step for the MF or MF/HF radio.

Annual Capacity Test

This test aims to measure battery capacity, which decreases over time. To do this, ensure the batteries are fully charged and then discharge them under a known load.

NOTE: Battery capacity is not measured by voltage! Battery capacity is expressed in ampere-hours (Ah). A 200 Ah battery means it can supply 200 A for one hour or 20 A for 10 hours, etc.

Preventing Deep Battery Discharge
One of the SOLAS requirements is to avoid deep battery discharge during the capacity test. Deep discharge refers to the minimum voltage a battery can reach. If a battery is discharged below this level, it may be irreversibly damaged.

Example: For nickel-based batteries, this level is 1.0V per cell. For a 24V set (1.2V x 20 cells), the minimum voltage is 20V. Therefore, during the test, the voltage should not drop below 20V or 1V per cell.

Test Procedure:
A GMDSS battery typically has a capacity of 200 Ah and supplies 24V. To check its capacity, we disconnect the battery from charging and from the GMDSS station, then connect a known load.

Example: 6 bulbs (600W) consume 25A of current.
Formula: Power = Voltage x Current
600W / 24V = 25A

During the test, voltage and current are measured at the terminals every hour.

When to End the Test?

  1. When one cell shows a significantly greater voltage drop.
  2. When the voltage reaches the deep discharge level (20V).
  3. When the test confirms 100% of the nominal capacity (e.g., after 8 hours at 25A current).

If the test was stopped due to point 3, the battery is in good condition. If it was stopped due to deep discharge, check whether it delivered at least 80% of its capacity. If not, the test is considered failed.

Theoretically, if the batteries discharge after 3 hours, and the requirement is for them to last at least one hour, there is no obligation to replace them. However, in practice, we know that such batteries will degrade rapidly, so we recommend replacing them with a new set.

Also, remember that a new battery should never be mixed with an old one. Even if the old battery is only a year old and passes the test, the battery bank must be balanced. This means that their capacity, voltage, and ability to supply current must be the same or at least similar.

GMDSS Equipment Battery Operation Time:

    • At least 1 hour if the ship has an emergency generator ready for immediate start-up and capable of continuous operation for 18 hours. In practice, this means an emergency generator in AUTO mode with a fuel reserve for at least 18 hours of operation.
    • At least 6 hours if the ship does not have a generator or if it cannot be immediately started.

NAVTEX – Automatic Navigational Information System

What is NAVTEX?

NAVTEX (Navigational Telex) is an automatic system for broadcasting navigational, meteorological, and hazard warnings. It is a key component of the GMDSS system, designed for ships operating in coastal areas. NAVTEX devices automatically receive text messages, eliminating the need for continuous monitoring by the crew.

How Does NAVTEX Work?

  • Operating Frequencies: NAVTEX operates on dedicated frequencies, such as 518 kHz (international messages in English) and 490 kHz (local messages in national languages).
  • Message Content: Includes navigational warnings, weather forecasts, SAR (Search and Rescue) alerts, and port information.
  • Range: Covers an area up to 400 nautical miles from the transmitting station.

NAVTEX Functions

  1. Navigational Warnings: Information on obstacles, drifting wrecks, or changes in navigational markings.
  2. Weather Forecasts: Detailed meteorological messages that facilitate route planning and operations.
  3. Operational Efficiency: Automatic reception reduces the crew’s workload, allowing them to focus on other tasks.

Testing NAVTEX

  1. Daily Receiver Check:
    • Ensure that the NAVTEX receiver is turned on and set to the appropriate frequency range.
    • Check whether the latest messages are displayed on the screen or printed out.
  2. Periodic Test:
    • Ensure that the receiver can receive transmissions from all stations for which it has been programmed.
    • Verify the signal quality, check for interference, and perform a test according to the manufacturer’s procedure.

When Must NAVTEX Be Equipped with a Printer?

According to RESOLUTION MSC.508(105) (28.04.2022) – PERFORMANCE STANDARDS FOR THE RECEPTION OF MARITIME SAFETY INFORMATION AND SEARCH AND RESCUE RELATED INFORMATION BY MF (NAVTEX) AND HF, reception systems for maritime safety information and search and rescue-related information via MF (NAVTEX) and HF must meet specific performance standards, including requirements for the presentation of received messages.

NAVTEX must have a printer if the only method of presenting received messages is automatic printing (integrated printing device).

When Does NAVTEX Not Require a Printer?

NAVTEX does not need a printer if it meets one of the following conditions:

  1. Has a dedicated display, an output port for connecting a printer, and non-volatile message storage – In this case, all received messages can be viewed on the screen, and a printer can be connected optionally. The display must be located in a place from which the ship is normally navigated.
  2. Is connected to an integrated navigation system and has non-volatile message storage – This means that information is stored digitally and can be viewed on other bridge devices, typically on ECDIS.

Additional Requirements

If the device does not have an integrated printer, it must be equipped with a standard interface for connecting an external printer.

In summary, NAVTEX does not always need to be equipped with a printer, but if it does not have one, it must provide an alternative method for displaying and archiving messages in compliance with MSC.508(105) requirements.

HF-MSI – High-Frequency Maritime Safety Information

What is HF-MSI?

HF-MSI (High-Frequency Maritime Safety Information) is a system for transmitting navigational and meteorological information over long distances, essential for ships operating in open waters beyond the range of NAVTEX. HF-MSI enables the global dissemination of critical messages within the GMDSS framework.

How Does HF-MSI Work?

  • Frequency Range: The system utilizes MF/HF (Medium Frequency and High Frequency) bands for long-distance communication. Typical HF-MSI frequencies range between 4 and 22 MHz.
  • Type of Information: Includes weather forecasts, navigational warnings, hazard information, and SAR alerts.
  • Coverage: Global, ensuring communication between ships and coastal stations in any oceanic region.

Testing HF-MSI

  1. Daily Monitoring:
    • Ensure the HF receiver is turned on and set to the appropriate frequencies.
    • Check the quality of received messages.
  2. Signal Tests:
    • Perform a reception test using a coastal station transmitting test HF messages.
    • Verify signal stability and transmission quality.

Conclusion

The GMDSS (Global Maritime Distress and Safety System) is designed to ensure maritime safety by providing fast and effective communication in emergency situations. Standard GMDSS equipment includes devices such as VHF radios, EPIRBs, SARTs, and NAVTEX. In addition to these core components, several additional accessories significantly enhance the system’s reliability and functionality. These accessories include handheld VHF radios, ITU publications, emergency lighting, chargers, and batteries.

Handheld VHF radios play a crucial role in ensuring communication during emergencies, especially during evacuations. SOLAS and IMO regulations require GMDSS-equipped vessels to have an adequate number of handheld VHF radios that meet waterproofing, power supply, and certification standards. Additionally, ITU publications serve as essential technical literature, mandated for proper GMDSS operation.

Emergency lighting provides safety during evacuations, while power sources are critical for maintaining continuous system functionality. Emergency and reserve power sources (lead-acid, lithium-ion, and nickel-cadmium batteries) must meet strict requirements regarding charging time, charge status monitoring, and capacity testing.

Furthermore, NAVTEX and HF-MSI systems deliver navigational and meteorological information, allowing for faster responses to potential hazards.

In conclusion, additional GMDSS equipment, combined with core systems, forms an integral part of maritime safety, enabling effective communication, emergency management, and efficient evacuation of crew and passengers.

We invite you to explore our previous articles on GMDSS: Blog