VHF and DSC

VHF (Very High Frequency) radios are a primary source of radio communications between vessels and shore installations. More importantly, crucial in fact, VHF radios are a primary source of communication during an emergency. Most maritime safety organizations monitor VHF radio signals – specifically channel 16, the international distress, safety, and calling channel.

Operating VHF radios is easy, but there are protocols to follow. One thing to keep in mind is that the sender and the receiver cannot talk at the same time. This is often difficult to remember in an emergency. Transmissions should be kept short and cover only vital issues.

If you put out a distress signal on channel 16, the chances of it being heard by someone who can rescue you is almost 100 percent. The “almost” lies in the distance VHF signals can travel and land mass obstructions in the way.

VHF Signal

VHF is essentially a line-of-sight system since radio waves don’t bend very much to follow the curvature of the Earth. Sometimes the signal can reflect and refract around land masses but mostly if there is a land mass in the way you cannot expect your signal to get through. For most reliable VHF communication, the VHF antenna must “see” the antenna of a distant station.

Therefore, antenna height is more important in determining the range than radio wattage. The effective useful range of a VHF radio is 20 to 25 miles for ship-to-shore and 10 to 15 miles for ship-to-ship. The distance a VHF signal can reach between ship and shore installations is usually a bit further since the ground-based antenna is higher.

Fixed-Mount VHF Radios

Fixed-mount units are just that—they are permanently fixed into your boat and are usually high wattage, up to 25 watts. They gain their power from the house battery system.

VHF Radio

Handheld VHF Radios

VHF handhelds also offer many of the same features found on fixed-mount units. They offer portability in the same way a cordless phone allows more mobility at home. A handheld radio may be just what you need for use in a dinghy, or small boat without electrical systems, or as an emergency backup for your boat’s radio. Handhelds have a maximum output of six watts. Due to their short antennas, they have a limited range of five miles.

Handheld VHF

You can achieve a significant increase in range by connecting an external antenna or using a telescoping antenna mounted to the handheld radio. Battery life varies with the size of the battery pack. Many models have optional battery packs with longer operating times, greater transmitting power, or both. Some have battery-saver circuits that turn off the receiver to save power. The battery life of a handheld can be increased by switching from full transmit power to one watt of transmit power.

If you have handheld VHF radios on board, make sure you also have a way to charge them.

Check out a handheld VHF/DSC radio product review video from West Marine.

Handheld VHR video

Channel 16

Channel 16 is the most important VHF channel for sailors. It is essential for all emergencies. The United States Coast Guard and most other country’s coast guard systems monitor channel 16, 24 hours a day, 7 days per week.

Channel 16 is designated as the single channel to be constantly used by all vessels at sea. This channel is a sailor’s best link for communicating problems with other vessels or ground-based stations.

You can find the proper procedure for using your VHF—Channel 16—radio in an emergency in Module 13.

General Calls to Other Ships or to Shore

You can refer to the Wikipedia marine VHF Channels website for a table of VHF Channels for the UK, USA, Canada, Australia, New Zealand, and Finland.

VHF Channels Wikipedia Article

Each channel has a specific use. Note carefully the channels you as a recreational non-commercial boater can use to communicate.

Each channel operates on a different VHF frequency. Here is a summary for the USA:

Channel 09—Boater Calling. Commercial and Non-Commercial.
Channel 13 — Ship to ship communications for organizing passing arrangements in waterways. Also used for bridge openings.
Channel 16—International Distress, Safety, and Calling. Any ships that are required to carry a VHF radio. Global Coast Guards and most coast stations maintain a listening watch on this channel.
Channel 68—Non-Commercial traffic
Channel 69—Non-Commercial traffic
Channel 71—Non-Commercial traffic
Channel 72 —Non-Commercial (Inter-ship only)
Channel 78A (aka 1078)—Non-Commercial traffic

All others are for port operations, commercial traffic government, and the like. They should not be used by recreational boaters. Note in particular that Channel 70 is for DSC distress signals. No voice is allowed on Channel 70. Sometimes you’ll see an A and B switch. A is typically used in the USA; B is used outside the USA (sometimes labeled as “international”).

Procedure for Hailing a Ship by Radio

You may use channel 16 to hail a ship or shore station, but if you do so, you must, must be brief! We recommend this same procedure be used over channel 9 if channel 9 is used as a calling channel.

A hailing example:

Blue Duck: “Mary Jane, this is Blue Duck” (the name of the vessel being called may be said 2 or 3 times if conditions warrant).

Mary Jane: “Blue Duck, this is Mary Jane. Reply 68” (or some other proper working channel).

Blue Duck: “68” or “Roger”.

Both switch to channel 68 (as an example). Have the conversation. End each turn with “over.” End the conversation with your station name and “out.”

Operator’s License

Some countries in the Mediterranean require that you have a VHF operator’s license before entering their waters. If chartering a yacht, the charter company is required to ensure you have a VHF license before heading out.

DSC (Digital Selective Calling) and Distress Signals

View a quick introductory video on DSC:

DSC Introductory Video

Digital Selective Calling (DSC) is an automated radio communication technology used in maritime VHF and MF/HF radios for sending preformatted digital messages. In the context of distress signals, DSC plays a crucial role in enhancing maritime safety by providing a quick and reliable method for signaling emergencies.

The DSC is combined as part of all VHF units

How a DSC Distress Signal is Sent

A DSC distress signal can be activated by pressing the dedicated distress button on a DSC-equipped radio, typically held down for about five seconds to avoid accidental activation. This button is usually protected by a cover to prevent inadvertent use. The distress signal is a preformatted signal built into your DSC unit and will transmit the digital signal via VHF and be received by other VHF units including Coast Guard stations and other commercial traffic if in range.

Do note however that if you are in distress, you should not solely rely upon the DSC transmission. You should also broadcast in voice your emergency.

Information Included in a DSC Distress Signal

When a DSC distress signal is sent, it automatically transmits the following information:

Maritime Mobile Service Identity (MMSI) Number: This unique nine-digit identifier is assigned to each individual DSC/VHF Unit and thus the Vessel.
- The MMSI number must be personally requested for by the owner who supplies appropriate information such as the owner name, the vessel name and type, and emergency contacts. Thus when the SAR authorities receive a DSC message containing the MMSI number extremely helpful information is thus garnered quickly. If you have a DSC, you can request an MMSI number free of charge at this web address: http://www.boatus.com/mmsi.
Position Coordinates: If the DSC/VHF radio is connected to a GPS, the distress signal will include the vessel’s precise location coordinates. If not connected to a GPS, the user can manually input coordinates if time permits. If you have a GPS unit onboard, ensure it is connected to the DSC/VHF unit.
Nature of Distress: Some DSC radios allow the operator to specify the nature of the distress (such as sinking, fire, man overboard, etc.), providing additional information to rescue services.

Range of DSC Distress Signals

The range of a DSC distress signal depends on the type of radio and frequency used:

VHF Radios: The range of the DSC message is the same as VHF and is typically line-of-sight, which is usually up to 20-25 nautical miles, depending on the height of the antenna and the surrounding terrain.
MF/HF Radios: These radios can have a much longer range, even potentially global, depending on atmospheric conditions and the frequencies used.

Monitoring and Reception of DSC Distress Signals

Who Monitors DSC: Coast Guard stations and other maritime rescue coordination centers (MRCCs) continuously monitor DSC distress channels (Channel 70 for VHF and designated channels for MF/HF) for distress alerts.
Who Receives DSC Signals: All DSC-equipped vessels within range of the transmission will receive the distress signal. Nearby ships equipped with DSC radios will receive the distress alert and can assist in the rescue operation if they are able.
Channel 70: Channel 70 on VHF is solely designated to DSC therefore no voice transmissions are allowed on channel 70.

Why Use DSC Instead of Just a Voice Call on Channel 16?

Speed and Accuracy: DSC distress signals can be sent quickly with the press of a button, ensuring immediate transmission of critical information like MMSI and location without needing to speak. This is especially useful in urgent situations where time is critical, and there may be no time for a voice call.
Automatic Alerts: DSC signals are digital and automatically alert all nearby DSC-equipped radios and shore stations. This ensures that the distress call is received by as many potential rescuers as possible, even if they are not actively listening to Channel 16.
Reduced Human Error: The digital nature of DSC reduces the chance of misunderstandings or errors in communication that can occur with voice transmissions, particularly in stressful situations or poor radio conditions.

DSC Transmission Conclusion

DSC distress signals provide a reliable, fast, and effective way to signal emergencies at sea. It can be as simple as holding the Red DSC button for 5 seconds. By automatically including vital information and reaching all DSC-equipped vessels and shore stations within range, DSC ensures a swift response in life-threatening situations, complementing traditional voice calls on Channel 16.

Relaying a Received Distress DSC Message

To relay a received Digital Selective Calling (DSC) distress signal, you need to follow specific procedures to ensure that the distress information is communicated effectively to other vessels and authorities. Here’s how you can do it:

Steps to Relay a DSC Distress Signal

The reason to relay a received DSC message is because of relative ranges. Let’s say the vessel in danger is 50 miles offshore. Its message may not be received by a land station because of its distance offshore. If you are only 25 miles off shore then by you relaying the message to an available land station, you may be saving a life.

Acknowledge the DSC Alert:

Do Not Acknowledge Directly via DSC: When you receive a DSC distress signal, you should not acknowledge it directly via your DSC radio, as this could prevent the distress signal from being rebroadcast by other stations or prevent it from reaching the coast station.

Instead, take note of the details provided by the DSC alert, such as the MMSI number, location (if available), and nature of distress if indicated.

Verify the Situation:

Visual or Radio Verification: If possible, try to visually verify the distress situation or establish voice communication with the distressed vessel using VHF Channel 16 to confirm the emergency and gather additional details.

Relay the Distress Alert:

Manual Relay via VHF Voice Communication:

Switch your VHF radio to Channel 16 (the international distress and calling channel).
Broadcast a MAYDAY RELAY message to alert other vessels and shore stations about the received distress signal.
The format for a MAYDAY RELAY message typically includes:
- MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY
- This is [Your Vessel’s Name and MMSI Number]
- Received DSC distress alert from vessel [Distressed Vessel’s Name or MMSI Number]
- Location [Distressed Vessel’s Location Coordinates, if known]
- Nature of distress [if known]
- Requesting immediate assistance

Contact the Nearest Coast Station:

Direct Communication: If you are close to shore or within range of a coast station, contact them directly to relay the distress information. Provide all the details you have about the distress signal to ensure they can coordinate a proper response.

Monitor and Assist if Possible:

Maintain Communication: Keep your radio tuned to Channel 16 to listen for further instructions or updates from the distressed vessel, other vessels, or rescue authorities.
Offer Assistance: If you are able to safely assist, coordinate with the distressed vessel and authorities to provide help.

DSC Relay Conclusion

Relaying a DSC distress signal involves manually broadcasting a MAYDAY RELAY message on VHF Channel 16 to alert nearby vessels and shore stations. It’s important not to directly acknowledge the DSC alert via the DSC system, as this can interfere with the distress signal’s transmission. Always ensure to communicate clearly and provide as much information as possible to facilitate a prompt and effective rescue response.

Telephones

Ordinary cell phones do work well so long as the unit is in approximately line of sight of a receiving tower. However while it is imperative that you get your distress signal out as quickly and efficiently as possible with any and all mean, Maritime Rescue centers do not recommend relying on cellular phones as a means of communication during an emergency.

In regards to using the phone for emergencies; first, who are you going to call, and do you have their phone number? You can’t speak to the helicopter to coordinate the rescue via cell phone. The best you might manage is to call your mother-in-law (why she is on speed dial we don’t know) and tell her to call the authorities. Then you’re expecting her to write down a latitude and longitude number? Is her daughter on board? Does she really like you? Is this her chance?

Bottom line: Make sure your vessel has an up-to-date VHF unit with DSC.