SOLAS VHF Radio Requirements: What Every Vessel Operator Actually Needs to Know
SOLAS VHF Radio Requirements: What Every Vessel Operator Actually Needs to Know
There is a piece of equipment on the bridge that everyone takes for granted until the port state control officer asks for the type approval certificate. The VHF radio. It sits there, channel 16 always on, quietly doing its job. But when the inspection happens, suddenly everyone remembers that SOLAS has very specific things to say about what that radio must be, what it must do, and how it must perform.
We design and manufacture our own navigation and communication equipment. VHF radios, AIS, GNSS compasses, the whole stack. And over the years, we have watched too many vessel operators discover too late that their "compliant" VHF radio was never actually compliant at all.
The Legal Foundation: SOLAS Chapter IV
The carriage requirements for VHF radio equipment live in SOLAS Chapter IV, which covers radiocommunications. This is the chapter that tells you what radio equipment your ship must carry, based on the GMDSS sea areas in which it operates.
The GMDSS divides the world into four sea areas:
- Sea Area A1: Within range of a VHF DSC coast station (typically about 20-30 nautical miles)
- Sea Area A2: Beyond A1 but within range of an MF DSC coast station (about 100-150 nautical miles)
- Sea Area A3: Beyond A1 and A2 but within Inmarsat satellite coverage
- Sea Area A4: The polar regions outside A3
The equipment you must carry depends on which of these areas your vessel operates in. But the baseline VHF requirements apply to virtually every SOLAS ship.
The Minimum VHF Equipment Requirement
SOLAS Chapter IV, Regulation 7, sets the baseline. Every GMDSS ship must carry a VHF radio installation capable of two things. First, transmitting and receiving Digital Selective Calling (DSC) on channel 70, which operates on 156.525 MHz. Second, radiotelephony on channels 16, 13, and 6.
Channel 16 is the international distress, safety, and calling frequency. Channel 13 is for ship-to-ship safety communications, primarily for navigational purposes. Channel 6 is for ship-to-ship search and rescue communications.
But the requirements do not stop at the main installation. SOLAS also mandates portable two-way VHF radiotelephones for survival craft. Passenger ships and cargo ships of 500 gross tonnage and above must carry at least three of these portable units. Cargo ships between 300 and 500 gross tonnage must carry at least two.
These portable units must be stowed so they can be rapidly placed into survival craft when needed. They are not optional extras. They are part of the mandatory equipment.
The DSC Watchkeeping Requirement
Here is where many operators get confused. Having a VHF DSC radio is not enough. You must also maintain a continuous watch on DSC channel 70. Every ship, while at sea, must maintain a continuous listening watch on VHF DSC channel 70.
That watch can be maintained by a separate DSC watch receiver, or it can be combined with the main VHF installation. But the watch receiver must not be muted or interrupted when other radio equipment is in use. It must run continuously.
This is a functional requirement, not just a paper exercise. When a distress alert comes in on DSC, the watch receiver must be able to receive it and alert the bridge crew.
The Performance Standards Behind the Equipment
Carriage is one thing. Performance is another. SOLAS Regulation IV/14 requires that all radio equipment must meet the performance standards adopted by the IMO.
For VHF radio installations, the key performance standard is IMO Resolution A.803(19), adopted on 23 November 1995. This resolution covers "Performance Standards for Shipborne VHF Radio Installations Capable of Voice Communication and Digital Selective Calling".
The technical details matter. The transmitter output power must be between 6 and 25 watts. There must be provision for reducing the power to between 0.1 and 1 watt for short-range communications. That low-power setting is useful when you are working close to another vessel or a shore station and do not want to overpower the receiver.
The equipment must operate on specific frequency bands. The radiotelephone facility must work in the band from 156.3 MHz to 156.875 MHz on single-frequency channels, as specified in Appendix 18 of the ITU Radio Regulations. For two-frequency channels, the transmission band is 156.025 MHz to 157.425 MHz, and the receiving band is 160.625 MHz to 162.025 MHz.
The DSC facility must operate on channel 70, which is 156.525 MHz. The class of emission must comply with Appendix 19 of the Radio Regulations.
Channel changing must be rapid. The time taken to change channels should not exceed five seconds. That sounds trivial, but when you are in a distress situation, five seconds of fumbling with controls is an eternity.
The Antenna System
The antenna requirements in A.803(19) are specific. The VHF antenna must be vertically polarized and, as far as practicable, omnidirectional in the horizontal plane. The installation must be suitable for efficient radiation and reception of signals at the operating frequencies.
This matters because a poorly installed antenna degrades performance. If the antenna is not vertically polarized, you lose signal strength. If it is not omnidirectional, you create blind spots. If the installation is inefficient, your range suffers.
The Power Supply Requirements
SOLAS Regulation IV/13 covers sources of energy for radio installations. The reserve source of energy must be capable of simultaneously operating the VHF radio installation.
The battery capacity must be checked at intervals not exceeding 12 months when the ship is not at sea. For portable two-way VHF radios used in survival craft, the primary battery must have sufficient capacity to operate the radio for eight hours based on a 1:9 duty cycle. That means one part transmitting to nine parts receiving.
The batteries must be recharged to required minimums within a 10-hour period. The changeover between the ship's main supply and the radio reserve source should not require any equipment to be re-initialized manually, and it should not result in loss of stored data.
The 2028 Channel Update That Changes Everything
Here is something that will catch many operators off guard. In January 2025, the IMO issued MSC.1/Circ.1460/Rev.5, which sets a hard deadline for VHF equipment upgrades.
All VHF communication equipment installed under SOLAS Chapter IV, Regulations 7.1.1, 7.1.2, and 7.1.6-including backup equipment-must be upgraded to comply with the latest channel arrangements in Appendix 18 of the ITU Radio Regulations. The deadline is the first radio inspection after 1 January 2028.
What does that mean in practice? The ITU made significant revisions to Appendix 18 at the 2012, 2015, and 2019 World Radiocommunication Conferences. The key changes include the full implementation of 12.5 kHz narrowband channelization, protection of AIS channels 87B and 88B for data transmission only, and the clear designation of channel 70 as DSC-only with no voice traffic allowed.
If your existing VHF equipment does not support these new channel arrangements, it will need a software or hardware upgrade. Some older units may not be upgradeable at all and will need replacement. The deadline is not optional. Fail to comply, and your vessel could face detention during port state control inspections.
The Practical Reality
When you are selecting VHF equipment for a SOLAS vessel, the requirements are not suggestions. The equipment must carry type approval from a recognized notified body. It must meet the performance standards of A.803(19). It must support DSC on channel 70. It must operate on the correct frequencies. It must have the correct power output. It must have a properly installed antenna. It must have adequate battery backup. And from 2028 onward, it must support the latest channel arrangements.
We design our VHF equipment because we have seen too many shortcuts. We have watched equipment that passed the bench test fail the real-world inspection because the antenna installation was wrong. We have seen DSC watch receivers that were supposed to be continuous but dropped out whenever the main radio transmitted. We have seen batteries that tested fine on paper but failed when actually needed.
The SOLAS requirements exist for a reason. The VHF radio is not just a convenience. It is the primary means of distress alerting and safety communications for most vessels. When something goes wrong at sea, that radio is what brings help. The manufacturers who actually meet the requirements will be glad to show you the certificates. The ones who do not will talk about everything except the type approval.
