The widespread misuse of VHF channels at sea, especially the distress, safety and calling Channel 16 (156.8 MHz) and channels used for port operations, ship movement services and reporting systems, is giving concern.

Often the misuse of VHF channels causes serious interference to essential communications and becomes a potential danger to safety at sea.

The proper use of VHF channels at sea makes an important contribution to navigational safety. In accordance with the ITU Radio Regulations:

a. Channel 16 may only be used for distress, urgency and very brief safety communications and for calling to establish other communications which should then be conducted on a suitable working channel.

b. On VHF channels allocated to the port operations services the only messages permitted are restricted to those relating to the operational handling, the movement and safety of ships and, in emergency, to the safety of persons; as the use of these channels for ship-to-ship communications may cause serious interference to communications related to the movement and safety of shipping in congested port areas.

VHF equipment is frequently operated by persons not trained in its proper use though the ITU Radio Regulations requires that the service of every ship radio-telephone station shall be controlled by an operator holding a certificate issued or recognized by, the Government concerned.

The following guidelines have been prepared and, if followed, should ensure that VHF channels are used correctly.

Proper Use of VHF Channels at Sea

(An extract from the IMO Resolution A474 (XII))



1.1 Preparation

Before transmitting, think about the subjects which have to be communicated and, if necessary, prepare notes to avoid unnecessary interruptions and ensure that no valuable time is wasted on a busy channel.

1.2 Listening

Listen before commencing to transmit to make certain that the channel is not already in use. This will avoid the irritating interference.

1.3 Discipline

VHF equipment should be used correctly and in accordance with the Radio Regulations. The following in particular should be avoided:

1. calling on Channel 16 for purposes other than distress, urgency and very brief safety communications when another calling channel is available.

2. communications not related to safety and navigation on port operation channels;

3. non-essential transmission, e.g. needless and superfluous signals and correspondence;

4. transmitting without correct identification;

5. occupation of one particular channel under poor conditions;

6. use of offensive language.

1.4 Repetition

Repetition of words and phrases should be avoided unless specifically requested by the receiving station.

1.5 Power Reduction

When possible, the lowest transmitter power necessary for satisfactory communication should be used.

1.6 Automatic Identification Systems (AIS)

AIS is used for the exchange of data in ship-to-ship communications and also in communication with shore-based facilities. The purpose of AIS is to help identify vessels; assist in target tracking; simplify information exchange (e.g. reduce verbal reporting); and provide additional information to assist situation awareness. AIS may be used together with VHF voice communications. AIS should be operated in accordance with resolution A.917(22) – Guidelines for the onboard operational use of shipborne automatic identification systems (AIS).

1.7 Communications with Shore Stations

1.7.1 On VHF channels allocated to port operations service, the only messages

permitted are restricted to those relating to the operational handling, the movement and the safety of ships and, in emergency, the safety of persons; as the use of these channels for ship-to-ship communications may cause serious interference to communications related to the movement and safety of shipping in port areas.

1.7.2 Instructions given on communications matters by shore stations should be


1.7.3 Communications should be carried out on the channel indicated by the shore

station. When a change of channel is requested, this should be acknowledged by the ship.

1.7.4 On receiving instructions from a shore station to stop transmitting, no further

communications should be made until otherwise notified (the shore station may be receiving distress or safety messages and any other transmissions could cause interference).

1.8 Communications with Other Ships

1.8.1 VHF Channel 13 is designated by the Radio Regulations for bridge-to-bridge

communications. The ship called may indicated another Worthing channel on which further transmissions should take place. The calling ship should acknowledge acceptance before changing channels.

1.8.2 The listening procedure outlined in paragraph 1.2 should be followed before

communications are commenced on the chosen channel.

1.9 Distress Communications

1.9.1 Distress calls/messages have absolute priority over all other communications.

When hearing them all other transmissions should cease and a listening watch should be kept.

1.9.2 Any distress call/message should be recorded in the ship’s log and passed to the


1.9.3 On receipt of a distress message, if in the vicinity, immediately acknowledge receipt.

If not in the vicinity, allow a short interval of time to elapse before acknowledging receipt of the message in order to permit ships nearer to the distress to do so.

1.10 Calling

1.10.1 In accordance with the Radio Regulations channel 16 may only be used for distress,

urgency and very brief safety communications and for calling to establish other communications which should then be conducted on a suitable working channel.

1.10.2 Whenever possible, a working frequency should be used for calling if a working

frequency is not available, VHF Channel 16 may be used for calling, provided it is not occupied by distress call/message.

1.10.3 In case of difficulty to establish contact with a ship or shore station, allow adequate

time before repeating the call. Do not occupy the channel unnecessarily and try another channel.

1.11 Changing Channels

If communications on a channel are unsatisfactory, indicate change of channel and await confirmation.

1.12 Spelling

If spelling becomes necessary (e.g. descriptive names, call signs, words which could be misunderstood) use the spelling table contained in the international Code of Signals and the Radio Regulations and the IMO Standard Marine Communication Phrases (SMCP) (See Phonetic Alphabet and Figure Code on page 390).

1.13 Addressing

The words “I” and “You” should be used prudently. Indicate to whom they refer.


Seaship, this is Port Radar, do you have a pilot?

Port Radar, this is Seaship, yes I do have a pilot.

1.14 Watchkeeping

Every ship, while at sea, is required to maintain watches (Regulations on Watches in Chapter IV of SOLAS, 1974, as amended). Continuous watchkeeping is required on VHF DSC Channel 70 and also when practicable, continuous listening watch on VHF Channel 16.


2.1 Calling

When calling a shore station or another ship, say the name of that shore station once (twice if considered necessary in heavy radio traffic conditions) followed by the phrase THIS IS and the ship’s name twice, indicating the channel in use.


Port City, this is Seastar, on Channel 14.

2.2 Exchange of Messages

2.2.1 When communicating with a ship, whose name in unknown but whose position is

known, that position may be used. In this case the call is addressed to all ships.


Hello all ships, this is Pastoria, Pastoria. Ship approaching number four buoy, I am passing Belinda Bank Light.

2.2.2 Where a message is received and only acknowledgement of receipt is needed, say

“received”. Where a message is received and acknowledgement of the correct message is required, say “received, understood”, and repeat message if considered necessary.


Message: Your berth will be clear at 08:30 hours.

Reply: Received, understood. Berth clear at 08:30 hours.

2.2.3 Where appropriate, the following message should be send:

“Please use/ I will use IMO Standard Marine Communication Phrases”.

When Language difficulties exist which cannot be resolved by use of IMO Standard Marine Communication Phrases, the International Code of Signals should be used.

In this case the word “INTERCO” should precede the groups of the International Code of Signals.


“Please use/ I will use the Internal Code of Signals.

2.2.4 Where the message contains instructions or advice, the substance should be repeated

in the reply.


Message: Advise you pass astern of me.

Reply: I will pass astern of you.

2.2.5 If a message is not properly received, ask for it to be repeated by saying “Say again”.

2.2.6 If a message is received but not understood, say “Message no understand”.

2.2.7 If it is necessary to change to a different channel say “Change to channel …..” and

wait for acknowledgement before carrying out the change.

2.2.8 During exchange of messages, a ship should invite a reply by saying “over”.

2.2.9 The end of a communication is indicated by the word “out”.


3.1 Since most ship-to-shore communications are exchanges of information, it is

advisable to use standard messages which will reduce transmission time.

3.2 Commonly used standard messages are given in the IMO Standard Marine

Communication Phrases (SMCP), which should be used whenever possible.


SOLAS Convention, 1974, as amended, Chapter IV on Radio communications.

Radio Regulations, Appendix 18 Table of Transmitting Frequencies in the VHF Maritime Mobile Band.

Resolution A.917(22) on guidelines for the Onboard Operational Use of Shipborne Automatic Identification Systems (AIS).

Resolution A.918(22) on IMO Standard Marine Communications Phrases (SMCP).



It is most important to realise that the transmitting and receiving range of VHF signals is limited, in theory, to line of sight. This is because the radio waves of VHF do not normally bend around the curvature of the earth. The range may be affected to some degree by barometric pressure and/or increased humidity which often gives greater ranges than normally attained.

This atmospheric refraction results in the radio waves tending to follow curved rather than straight line paths.

The bending or refraction arises from a change of wave speed as the waves propagate through the atmosphere, the waves changing direction towards the region of lower wave speed. The degree of bending or refraction depends upon the rate at which the wave speed changes. This is governed by the refractive index of the air and its variation with height which, in turn, depends upon the pressure, temperature and humidity of the air.

Another significant factor in determining range is, generally, the height above sea level of the transmitting and receiving aerials. It should also be noted that the fact that a transmitter and a receiver are within radio sight does not automatically guarantee that an acceptable signal will be received at that point. This will depend, amongst other things, on the power of the transmissions, the sensitivity of the receiver and the quality and position of the transmitting and receiving aerials. Figure 13 illustrates some typical VHF ranges that can be obtained from various transmitting and receiving stations.


The use of mobile telephones in the marine environment offshore is now well established, with users in all areas of the commercial, fishing and leisure communities.

A growing number of incidents have occurred where vessels requiring assistance from rescue services have used the inland emergency service, or alternatively telephoned direct to request assistance (e.g. Lifeboat services). This procedure through a mobile telephone is strongly discouraged.

Use of mobile telephones bypasses the existing dedicated well established international marine distress communication systems.

Mobile telephone coverage offshore is limited and does not afford the same extensive safety coverage as VHF Channel 16. Consequently a greater risk exists of communications difficulties or even a complete breakdown if an accident should occur at the edge of a cell coverage area.

Subsequently on-scene communications would be restricted and delayed if mobile telephone communications were exclusively maintained throughout. There is always a risk that elements of vital information could be lost or misinterpreted by the introduction of further relay links in the communication chain. Mobile telephones are also highly susceptible to failure during water ingress.

It is not possible to communicate direct to another vessel able to render assistance unless that vessel is also fitted with a mobile telephone and the telephone number is known. Requests for assistance cannot be monitored by other vessels in a position to render assistance. Valuable time would be lost whilst the relevant Coastguard Rescue Co-ordination Centre receives and then re-broadcasts the information to all ships on the appropriate distress channel(s).

In the interests of Safety of Life at Sea (SOLAS), owners of vessels are urged to carry MARINE communications equipment onboard and to use this medium as the primary means of Distress and Safety communications.