Digital Selective Calling (DSC) – A Comprehensive Guide

Understanding the DSC Distress Alert and Calling System

Three main components of the DSC system work together to provide efficient and reliable communication at sea.

VHF and MF/HF radios

DSC is primarily used with VHF (Very High Frequency) radios, but it can also be used with MF (Medium Frequency) and HF (High Frequency) radios. These radios allow communication over different distances and are crucial for safety.

Global Maritime Distress and Safety System (GMDSS)

The GMDSS is an international system designed to improve maritime safety by ensuring effective communication between vessels and shore stations. DSC plays a vital role in the GMDSS by sending distress alerts and selective calling features.

Maritime Mobile Service Identity (MMSI)

An MMSI is a unique nine-digit number assigned to each boat. It acts like a phone number, allowing DSC-equipped radios to directly contact specific ships or groups of ships. MMSIs are crucial for efficient communication and safety at sea.

DSC frequency bands

DSC operates on specific bands, which are used to transmit and receive digital information. 

VHF (156.525 MHz) and Channel 70

VHF is the primary method used for DSC communication. Channel 70 (156.525 MHz) is dedicated exclusively to DSC, ensuring reliable and interference-free communication.

MF (2187.5 kHz)

MF is another used for DSC, particularly for longer-range communication. It can be beneficial in areas where VHF coverage is limited.

HF (4207.5, 6312, 8414.5, 12577, and 16804.5 kHz)

HF is used for long-range communication and is essential for boats sailing in remote areas. Several frequencies within the HF band are dedicated to DSC, ensuring that communication remains clear and reliable.

Features of DSC (Digital Selective Calling)

DSC provides several advanced communication features that help streamline and improve communication:

1. Selective calling: With DSC, you can directly call specific boats using their MMSI numbers, just like dialling a phone number. This feature allows for efficient, private communication between boats.
2. Group calling: DSC also enables group calling, allowing you to communicate with multiple vessels simultaneously. This is particularly useful for coordinating activities or sharing information with a fleet of boats.
3. All ships calling: An all-ships call is a broadcast message sent to all boats within range. This can be used to share important safety or navigational information with nearby boats.
4. Geographical calling: DSC allows you to target boats within a specific geographical area. This is useful for sharing local information or coordinating activities with nearby boats.

Automated DSC Distress Alerting

One of the key benefits of DSC is its automated distress alerting system, which significantly improves safety at sea:

1. Distress button and priority handling: When pressed, the radios have a dedicated distress button that sends an automated alert. This alert is given priority, ensuring a rapid response from nearby boats and coast guard shore stations.
2. Distress call format and content: The automated alert includes crucial information such as the boat’s MMSI, position, and nature of distress. This helps responders assess the situation and provide appropriate assistance.
3. GPS integration and location data: The radios can be integrated with the craft’s GPS, ensuring accurate location data is included in the alerts. This allows for faster and more precise responses in emergencies.

Improved safety and efficiency

DSC offers several benefits that contribute to a safer and more efficient marine environment:

1. Reduction in false alarms: DSC’s digital communication system reduces the risk of false alarms, ensuring that resources are focused on genuine emergencies.
2. Faster response to distress situations: With automated alerts and accurate location data, DSC enables faster responses to emergencies, potentially saving lives and property.
3. Better coordination among vessels: DSC’s selective calling and group calling features improve vessel coordination, enhancing safety and efficiency during boating activities.

MMSI (Maritime Mobile Service Identity)

How to obtain an MMSI

An MMSI is a unique nine-digit number assigned to your vessel. To obtain one, you can register through either a national authority or a private organisation:

National authority registration

1. In the United States, the Federal Communications Commission (FCC) issues MMSIs. You must apply for a Ship Radio Station License through the FCC’s Universal Licensing System (ULS) to obtain one. Once your application is approved, you’ll receive your number.
2. In the United Kingdom, the Office of Communications (Ofcom) issues MMSIs. You can apply by registering your vessel’s radio equipment on the Ofcom website. After submitting your application, you’ll receive your number.
3. In Australia, the Australian Maritime Safety Authority (AMSA) issues MMSIs. You’ll need to complete an application form on the AMSA website to obtain one. Once your application is processed, you’ll receive your number.

Private Organisation registration

Alternatively, you can obtain an MMSI through private organisations such as BoatUS, Sea Tow, or the U.S. Power Squadrons. These organisations can issue MMSIs for recreational vessels that do not require an FCC-issued Ship Radio Station License. Remember that MMSIs obtained through private organisations may not be valid for international travel.

Programming your DSC radio with your MMSI

Once you obtain an MMSI, you must program it into your radio. This process may vary slightly depending on your radio’s specific make and model, so always refer to the manufacturer’s instructions.

Entering MMSI and other information

To program your MMSI, access the radio’s menu system and look for an option related to MMSI or DSC setup. Enter your nine-digit number and any other required information, such as vessel name, call sign, or GPS data. Save the information and exit the menu.

Updating and changing MMSI information

If you need to update or change your MMSI information, you may be able to do so through your radio’s menu system. However, some radios may require a factory reset or a visit to a service centre to update the number. Always consult your radio’s manual or contact the manufacturer for guidance on updating your information.

Proper Use of the DSC Radio in Various Situations

In this section, we’ll discuss the appropriate use of Digital Selective Calling (DSC) in various situations, including routine communication, urgent and safety communication, and distress communication. Understanding the proper use of DSC will help ensure efficient and effective communication on the water.

Routine communication

For day-to-day communication, DSC provides several features to facilitate effective communication between vessels:

1. Individual calling: Selective calling lets you contact a specific vessel directly by entering its MMSI number. This is useful for private conversations between two boats.
2. Group calling: Group calling enables you to communicate with multiple vessels simultaneously by entering their MMSI numbers or a designated group ID. This is particularly helpful for coordinating activities or sharing information among a fleet of boats.
3. Working channel and listening watch: Remember to switch to a working channel after establishing contact when using DSC for routine communication. This ensures the DSC channel (Channel 70) remains available for other users. Also, maintain a listening watch on the VHF to monitor incoming calls or important announcements.

Urgent and safety communication

For urgent or safety-related communication, DSC offers specific features to ensure that important information is communicated efficiently:

1. Safety announcements: Safety announcements can be made using the “All Ships” call feature, which broadcasts a message to all vessels within range. This is useful for sharing important safety or navigational information with nearby boats.
2. Urgency and routine calls: For less urgent situations that still require prompt attention, use the “Urgency” call feature. This sends a message to a specific vessel or group of boats, indicating the need for immediate assistance or action.

Distress communication

In emergencies, DSC provides a streamlined method for initiating and responding to emergency  alerts:

1. Initiating an alert: Press the dedicated distress button on your DSC radio to create a distress alert. This sends an automated transmission, which includes your vessel’s MMSI, position, and the nature of the distress, to nearby ships and shore stations.
2. Responding to a distress alert: If you receive a distress alert, ensure you are not in immediate danger. Then, if you can assist, acknowledge the alert and communicate with the vessel in distress using the working channels.
3. Cancelling a false alert: If you accidentally send a false distress signal, you must cancel it immediately. Send a “Distress Acknowledgment” or “Distress Relay Cancellation” message on the DSC channel. Follow up with a voice announcement on the appropriate working channel to inform nearby vessels and shore stations that the distress alert was sent in error.

DSC Compatible Equipment and Integration

Radios with built-in DSC

Two main types of radios come with built-in DSC functionality:

1. VHF: These are popular among recreational and small commercial boats due to their relatively short range and ease of use. As mentioned, Channel 70 is designated for DSC use in VHF communication.
2. MF/HF: Larger ships operating in more remote areas use these radios, which have a greater range than VHF radios and are suitable for communication in more challenging environments.

DSC integration with other marine equipment

DSC can be integrated with various equipment to enhance safety and communication capabilities:

1. GPS systems and receiver interconnect: Connecting your radio to your GPS ensures accurate location data is included in distress alerts and other DSC messages. This allows for faster and more precise responses in emergencies.
2. Chartplotters: Integration with electronic chart systems allows you to visualise DSC calls on a digital map, providing a more intuitive way to manage communications and navigate complex situations.
3. Automatic Identification System (AIS): When integrated with an AIS system, DSC can display nearby boats’ positions, speeds, and other information, enhancing situational awareness and helping to prevent collisions.
4. Radiotelephone and antenna systems: These radios can be connected to existing radiotelephone and antenna systems, allowing you to use your communication infrastructure more efficiently. This can help reduce equipment clutter and simplify onboard communication systems.

Final Thoughts

DSC is a crucial communication system that plays a significant role in improving maritime safety and efficiency. You can take full advantage of this powerful communication tool by understanding its features and capabilities and how to use and integrate it with other equipment properly.

With DSC, you can streamline routine communication, enhance vessel coordination, and ensure a safer and more efficient marine environment.