How Do Ships Talk To Each Other? Explained By A Real Officer

With almost 100,000 merchant ships sailing the world’s waterways, it is obvious that there must be some way for ships to communicate with each other.

The maritime industry is slow to embrace new technology. This is exemplified by the fact that communication regarding collision avoidance is still done by using the ship’s whistle to sound out a series of coded signals.

Did You Know: Merchant Navy officers are still required to learn Morse code.

While there are several ways for ships to communicate with each other, there is only one common method of actually talking to another person on another ship, and this is done via radio – usually VHF DSC.

What is VHF DSC?

Very High Frequency (VHF) radios are required to be carried by just about every merchant ship. VHF radios transmit in the 30-300 MHz frequency range. The area of the world a ship is sailing in determines the type of radio equipment it must carry.

Sailing areaDescriptionRequired equipmentCoverage
A1In range of a coast station monitoring VHF DSC radioVHF radio30-40 miles from coastal radio station
A2In range of a coast station MF DSC radioVHF & MF radios150-180 miles from coastal radio station
A3Outside A2 but still between 70°N/S latitudeVHF & MF radios, plus either HF radio or satellite communications equipmentComplete coverage between 70°N/S
A4Polar regions >70° latitudeVHF, MF, & HF radiosPolar regions
Safety of Life at Sea (SOLAS) Chapter IV details what radio equipment ships must carry based on their sailing area

The range of VHF radio depends on a number of factors, the most important of which is the height of the antenna. Therefore, the taller the ship, the higher the radio antenna and therefore the greater its VHF range.

A good rule of thumb for VHF is this: If you can see it, you can talk to it!

A photograph showing a SAILOR brand VHF DSC radio
VHF radios are installed on just about every vessel in the world

Using a VHF radio is very simple, but it can be difficult to ensure that you are communicating with the correct ship. One way to ensure that you are talking to the correct vessel is by using Digital Selective Calling (DSC).

DSC is usually connected to the ship’s GPS and can be used on several different frequency ranges. It is used as a paging system to speak to one ship or a group of ships. The only thing you need is the Maritime Mobile Service Identity (MMSI) number of the other ship, which can be easily found online.

DSC is very useful for making sure you are talking to the correct ship. The introduction of DSC also made distress communications significantly easier and quicker.

To learn how to make a MAYDAY broadcast on both handheld and fixed VHF sets, check out our video below:

But did you know that it is actually not advised for ships to communicate with each other via radio in a collision avoidance situation?

How talking on VHF caused a serious collision

There have been a number of collisions between ships where, upon investigation, it has been found that the use of VHF radio communications potentially worsened the situation and contributed to the collision.

One such incident was the collision between the bulk carrier Huayang Endeavour and the oil tanker Seafrontier, which occurred in the Dover Strait on 1st July 2017. 

An investigation by the Marine Accident Investigation Branch (MAIB) found that because of poor communication on the VHF, the Bridge teams on each ship had a completely different understanding of the situation.

Huayang Endeavour tried to arrange a safe passing with the Seafrontier by calling her up on the VHF radio. A conversation was held between the two ships in English, as is international protocol, but English was the first language for nobody involved. This is very common as merchant shipping is an international industry, but it can occasionally lead to some misunderstandings, particularly in radio communications, which can be difficult to understand at the best of times.

A complete misunderstanding occurred and, as a result, the two vessels collided. Thankfully, nobody was hurt and no pollution occurred, although both ships sustained significant damage.

You can read the entire accident investigation report here: Collision between Huayang Endeavour and Seafrontier approximately 5nm west of Sandettie Bank, English Channel

The collision between Huayang Endeavour and Seafrontier is just one of many examples of why trying to arrange collision avoidance over the radio is a bad idea.

Why using radio to arrange collision avoidance is a bad idea
Language barriers
Radio communication can be unclear at the best of times
You may not be talking to the right ship
You do not know the passage plan or manoeuvring capabilities of the other ship
It can distract you from other traffic situations
Using VHF can make a collision avoidance situation much harder than it needs to be

How do ships avoid each other without talking?

All merchant ships must abide by the Convention on the International Regulations for Preventing Collisions at Sea, more commonly known as the COLREGS or Rules of the Road.

Every deck officer should have a thorough knowledge of the COLREGS as they define what each ship must do in any situation where there might be a risk of collision. The COLREGS are written in such a way as to remove ambiguity, and had they been followed in the case of Huayang Endeavour/Seafrontier the collision would not have occurred.

The best way to resolve any collision situation is for all vessels involved to simply follow the COLREGS. Introducing radio communications can add an extra layer of confusion and significantly delay any action by either ship.

That is not to say that the COLREGS do not prescribe for communication between ships.

An image showing the sound signals and their meanings as prescribed by the COLREGS
The COLREGS prescribe a number of whistle signals that are used in collision avoidance

Additional sound signals are also prescribed for identifying vessels in fog, and there is a separate set of signals to be used by vessels overtaking in narrow channels. Sound signals are meant to be unambiguous and most of the time are a one-way communication method used to inform other vessels of a ship’s actions.

Morse code and semaphore – are they still used?

Morse code is in fact still taught to all Merchant Navy officers in the UK and most of the rest of the world. 

Morse code is a method of encoding text as sequences of two different signal durations, called dots and dashes, or dits and dahs. Although it is no longer used as a primary means of communication at sea, many whistle signals that are still used today are based on Morse code, so it is useful for any deck officer to know.

Flag Semaphore is a more abstract system than Morse code. Visual rather than aural in form, semaphore was used to convey information at a distance using visual signals, with different combinations of hand placements representing different letters of the alphabet.

Flag Semaphore is no longer used on merchant ships, although it does retain some use during replenishment at sea on US naval vessels.