GMDSS 

The Global Maritime Distress and Safety System (GMDSS) is an internationally agreed framework designed to ensure that vessels in distress can alert shore authorities and nearby ships quickly and reliably, regardless of location.

For deck cadets, understanding GMDSS is essential not only for legal compliance, but for effective decision-making during emergencies. Correct use of distress, urgency, and safety communications directly affects response time, coordination with Search and Rescue (SAR), and ultimately survival.

Purpose of GMDSS

GMDSS is designed to ensure that the following functions can always be carried out, appropriate to the vessel’s operating area:

• Transmission of ship-to-shore distress alerts using at least two independent systems

• Reception of distress alerts from other vessels or shore authorities

• Transmission and reception of ship-to-ship distress alerts

• Coordination with SAR authorities

• On-scene communications during rescue operations

• Reception of Maritime Safety Information (MSI)

• General radiocommunications with shore-based stations

These requirements are set out under SOLAS Chapter IV.

Digital Selective Calling (DSC)

Digital Selective Calling (DSC) is the primary alerting method under GMDSS.
It allows distress, urgency, and safety alerts to be transmitted digitally on VHF, MF, and HF.

A DSC distress alert automatically transmits:

• Vessel identity (MMSI)

• Position and time (from GPS)

• Nature of distress (if entered)

• Type of assistance required

DSC ensures rapid alerting even when voice communication is not immediately possible.

SÉCURITÉ is used to broadcast important navigational or meteorological safety information.

Examples include:

• Navigation warnings

• Severe weather warnings

• Unlit or drifting hazards

• Changes to aids to navigation

These messages do not indicate distress but are vital for voyage safety.

PAN-PAN is used when there is an urgent situation affecting the vessel or a person but not immediately life-threatening.

Typical uses include:

• Engine failure without immediate danger

• Steering problems

• Medical emergencies not yet critical

• Lost or overdue vessels

• Person overboard with visual contact maintained

It demands attention but does not override MAYDAY traffic.

MAYDAY is used only when a vessel or person is in grave and imminent danger and immediate assistance is required.

This includes situations such as:

• Fire or explosion on board

• Flooding or sinking

• Collision or grounding with immediate danger

• Abandoning ship

• Person overboard in life-threatening conditions

A MAYDAY triggers the highest priority across all GMDSS systems. All other traffic must cease.