VHF radio GMDSS requirements
VHF radio GMDSS requirements
There is a certificate that every GMDSS vessel carries. It lists the radio equipment on board and confirms that the installation meets the requirements of SOLAS Chapter IV. It is signed, stamped, and filed away. And for most of the time, nobody looks at it.
Then a surveyor arrives, or a distress situation develops, or a VHF radio that has worked for years suddenly stops doing what the certificate says it can do. That is when the difference between an installation that meets the regulatory minimum and one that actually performs under pressure becomes the only thing that matters.
We build VHF equipment. Not by assembling modules from other manufacturers, but by designing the radio, the DSC controller, and the interface from the ground up. And the more we work with GMDSS requirements, the clearer it becomes that the regulation is not a checklist. It is a description of how a radio installation is supposed to behave when the vessel is in trouble.
The Two-Frequency Baseline That Every GMDSS Vessel Must Meet
SOLAS Chapter IV, Regulation 7 is the starting point. Every ship must carry a VHF radio installation capable of transmitting and receiving DSC on 156.525 MHz-channel 70-and radiotelephony on channels 6, 13, and 16. That is the minimum. But the regulation does not stop at listing frequencies. It specifies how those frequencies must be available and where the controls must be located.
The distress alert must be capable of being initiated from the position from which the ship is normally navigated. That means the conning position. Not a radio room down the corridor. Not a secondary station on the bridge wing. The person steering the vessel must be able to press the distress button without leaving the helm.
This is where installation decisions start to have consequences. A VHF transceiver mounted in a cabinet behind the chart table may satisfy the frequency requirement on paper. It does not satisfy the operational requirement. The regulation assumes that in an emergency, the person who needs to transmit the alert is already at the conning position. If the radio is not there, the alert is delayed. And in a distress situation, delay is measured in consequences.
The DSC controller can be remote, but the bridge must have priority. The equipment may be connected to remote control units on the bridge wings, but the navigating bridge retains control. That architecture is not a convenience. It is a recognition that the distress alert originates from the bridge, and the equipment must be designed around that reality.
The Watch That Cannot Be Interrupted
Continuous watch on DSC channel 70 is not optional. Every ship, while at sea, must maintain a continuous watch on VHF channel 70 by use of a DSC receiver. The regulation does not say "a watch when convenient." It does not say "a watch during working hours." It says continuous.
The practical interpretation matters. A separate VHF channel 70 watch receiver satisfies the requirement, provided it is not muted or interrupted when other radio equipment is in use. A dedicated watch receiver combined with the VHF transceiver also satisfies the requirement, provided it is installed so that the watch is maintained even when the VHF equipment is used for telephony. A VHF with DSC permanently locked on channel 70 for DSC reception and transmission also meets the requirement, with an additional VHF transceiver for other correspondence.
What does not satisfy the requirement is a radio that ceases to watch channel 70 when the operator switches to channel 16 or channel 6. That is not a compliant installation, regardless of what the certificate says.
The Performance Standard Behind the Button
IMO Resolution A.803(19) is the performance standard that defines what a GMDSS VHF installation must do. It requires the equipment to provide for distress, urgency, and safety calls using both voice and DSC, along with ship operational requirements and public correspondence. It requires a dedicated DSC watchkeeping facility to maintain a continuous watch on channel 70. And it requires the distress alert to be activated only by a dedicated distress button that is not a key on a standard keyboard or digital input panel.
That last point deserves attention. The distress button must be clearly identified and protected against inadvertent operation. The alert initiation must require at least two independent actions. These are not bureaucratic niceties. They are design requirements that prevent accidental transmissions while ensuring that a genuine distress alert can be sent quickly by someone who knows what they are doing.
The equipment must also provide radiotelephony on the frequencies required for navigational safety. That includes channel 16 for distress and calling, channel 13 for ship-to-ship safety communications, and channel 6 for search and rescue communications. The radio installation must be capable of operating on single-frequency channels and on single- and two-frequency channels.
The Installation Requirements That the Certificate Does Not Cover
The type approval certificate confirms that the equipment passed the bench tests. It does not confirm that the equipment was installed correctly. And the installation is where many otherwise compliant systems fall short.
The VHF antenna must be vertically polarized and, as far as practicable, omnidirectional in the horizontal plane. It must be mounted in an elevated position that is as unobstructed as possible, with a minimum of two metres of horizontal separation from conductive structures. The AIS VHF antenna, if one is fitted, should be mounted directly above or below the primary VHF antenna, with no horizontal separation and a minimum of two metres of vertical separation.
The cable route matters as much as the antenna location. Coaxial cables should be kept as short as possible. They should be routed away from power cables and not subjected to sharp bends that change the characteristic impedance. The coaxial screen should be connected to ground at one end.
The power supply is another installation detail that the certificate does not address. SOLAS Regulation IV/13 requires a reserve source of energy capable of simultaneously operating the VHF radio installation. The duration depends on the vessel's emergency power arrangements. For ships with a fully compliant emergency source, the reserve must supply the radio installations for at least one hour. For ships without such a source, the requirement extends to six hours.
The 2028 Deadline That Is Closer Than It Looks
There is a regulatory change on the horizon that will affect every GMDSS VHF installation. The IMO circular MSC.1/Circ.1460/Rev.5 requires that all VHF radiocommunication equipment installed under SOLAS regulations IV/7.1.1, IV/7.1.2, and IV/7.1.6-including duplicated equipment-must comply with the latest channel arrangements in Appendix 18 of the ITU Radio Regulations. The compliance deadline is the first radio survey scheduled on or after 1 January 2028.
The changes to Appendix 18 affect the frequencies used for Vessel Traffic Services, port operations, and VHF meteorological and navigational broadcasts. They do not affect the core GMDSS distress and safety functions, but they do affect the working channels that vessels use to communicate with shore authorities. A VHF radio that cannot access the revised channel plan may be unable to communicate with a VTS centre or a port authority in a region that has already adopted the new frequencies.
The circular advises operators to liaise with manufacturers well in advance of the deadline to arrange for timely upgrades, which may be software, firmware, or hardware based. And it notes that some administrations and VTS centres may transition to the new frequencies before 2028. Waiting until the deadline is a gamble that a vessel's working channels will remain compatible with the shore infrastructure it depends on.
We build our VHF equipment with the 2028 change in mind. The channel plan is not a fixed table burned into the firmware. It is a configurable element that can be updated when the regulatory framework changes. That is not a feature we added because it was fashionable. It is a recognition that a GMDSS radio has to stay valid for the life of the vessel, not just until the next survey.
The Part That Cannot Be Certified
The regulation and the type approval certificate define the equipment. They do not define the operator. A VHF radio that meets every requirement in SOLAS Chapter IV is useless if the person on the bridge does not know how to use the DSC functions. A distress button that requires two independent actions is a safety feature only if the operator knows what those actions are.
This is where the installation and the training intersect. The certificate on the bulkhead confirms that the equipment is capable. The crew confirms that the capability is actually available. And the gap between those two things is where the real work of GMDSS compliance lives.
We design our VHF equipment to make that gap as small as possible. The controls are laid out so that the distress function is unmistakable and the routine functions are intuitive. The interface outputs the NMEA sentences that the bridge systems expect, so the radio is not an isolated box. It is part of the bridge network. And the documentation and the support are built around the reality that the radio will be used by people who are tired, busy, and dealing with a situation that is developing faster than they would like.
The GMDSS requirements exist because the sea does not forgive assumptions. A radio that meets the regulation is the starting point. A radio that works when the regulation is tested is the goal.
