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8 Types of Underwater Communication Systems for Scuba Divers

Underwater communication systems, doesn’t it seem like an incredible topic to you? It does to me.

They surprised me when they told me I had to write about underwater communication.

How much we have evolved!

Our ancestors never imagined learning about such a topic, yet they started the seed that makes it possible.

It is a cold, misty night when lightning strikes a tree and split it in two. One of our ancestors witnessed how it is burning and illuminated everything around it. I’m sure the person who discovered that fire could provide light and heat wanted to share it with others, and he did, without a doubt. Otherwise, we wouldn’t be here today.

Communication is what has allowed our evolution as a species. It’s as old as humans themselves: we invented gestures, sounds, smoke signals, drums, paintings, and symbols… We’ve thought of everything to inform, express feelings, stay in touch, persuade someone, and, above all, solve problems.

And now we’re underwater. But we still need to communicate. Sure, many of us dive to disconnect, but that doesn’t mean we don’t have things to share, do we?

So, we invented again gestures, sounds, signals, and paintings, for diving communication. This article discusses these underwater communication systems.

We know we can’t make you read this article, only make you interested in reading it. So please take a look at the table of contents, it will trigger your interest.

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1. Hand Signals Diver Communication System

For most divers, underwater communication is about gestures and manual signals.

In the initial OWD course, we already learn about underwater communication by signals code: “Are you ok?,” “Everything ok,” “I have problems,” ”I have little air, and I need air.”

These signs are the most important ones for diver underwater communication. However, they are usually complemented by others.

When through experience or training, you become an advanced diver, you do dives that require more complex communication.

An advanced diver does deeper dives and has to be more precise in indicating the gas remaining in his tank. For this, many advanced divers use technical diving communication signals.

They need to indicate how much pressure is in the tank by numbers just using the fingers of one hand. With the palm facing out and the fingers pointing upwards, they communicate underwater numbers from 1 to 5. Meanwhile, for numbers from 6 to 9, they use their palm facing in and the fingers pointing side.

A complete circle made using their fingers and thumb means 0. It is the underwater communication code they use to say to dive buddies the exact amount of air or gas left in the tank. With this communication system, they can also indicate depth or time.

There is an international underwater communication system standardized for cave diving as well. It has little variation from what we have explained. In cave diving communication, they need manual signals to express: “sediment,” “I have reached my return pressure,” “guideline”, etc.

Learn more about this topic in this article: 17 Scuba Diving Hand Signals You Should Know


2. Light Signals Dive Communication System

As an advanced diver, you cannot dive in overhead environments but do perform night dives with limited visibility that are similar in conditions to those of caves. It is why advanced divers use an underwater communication system adapted from cave diving.

Making a circle with the primary light beam is used to ask if you are ok and to answer that everything is ok. Moving the light beam from one side to the other is a way to communicate something is wrong and is used to get the buddy’s attention.

In any case, night diving communication should be done with signals using only one hand and pointing the light beam down or sideways at the signaling hand.

It is useless to raise a hand to signal during a night dive if, at the same time, we point the light beam on the buddy’s face, dazzling him. So, the hand signals dive communication system, in which the diver needs two hands, had to be modified for night diving.

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3. Sound-Making Devices for Diving Communications

Some divers and guides prefer to use sound-making devices to get the attention of their partners and other divers. These devices can be metal objects that hit the tank or gadgets that use the air in the tank to create sound when a button is pressed, connected to the BCD’s inflator.

While these underwater communication systems can be useful in good visibility, they have a significant disadvantage. They cannot indicate a direction, as sounds seem to come from all directions underwater. They can only be used to verify if the buddy is in the water.

Nonetheless, in limited visibility environments, these devices can help us locate the buddy, but we cannot follow the sound’s origin to find them.

Some of these underwater communication systems can emit powerful, sharp sounds at the surface that can reach up to 1 or 2 km away. They can attract the attention of the diving boat’s crew if a diver surfaces in trouble or gets swept away by a strong current.

Several commercial underwater communication systems incorporate both options, i.e., for use underwater and at the surface. These devices are essential when making drift dives, and the boat leaves divers in a location with a strong current. During these dives, divers allow themselves to be carried away by the current, and when their air gauge reaches reserve, they surface. The boat follows them and picks them up when they surface.

Any problem or error can cause a considerable distance between divers and the boat, making it challenging to locate them. For this reason, using acoustic dive communication systems that can reach a great distance, much more than shouting or using a whistle, is crucial.


4. Written Dive Communications

When it comes to diving communications systems, dive slates are a lifesaver. Dive slates are pieces of plastic similar to whiteboards that come with a wax pencil attached. These slates can be large enough to write complete sentences or compact enough to clip onto a wrist. Some dive slates even come with magnets, and there are variants that are like “dive notebooks” with multiple thin plastic sheets.


5. Diver Communication by Body Contact

It’s crucial to keep communication with your diving buddy, especially in environments with low visibility. When visibility is severely reduced, the only way to talk is through physical contact. Cave divers, in particular, have standardized scuba diving communications protocols useful in zero visibility situations. These protocols often involve holding your partner’s arm and using hand signals to communicate and give instructions for safely emerging from the cave.

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6. Underwater Tech Communication Systems

Underwater communication is very important for many activities like exploring the ocean, collecting data, and even coastal security.

There are different ways to send information, like using acoustic, optical, and electromagnetic waves.


6.1. Underwater Acoustic Communication

Technology has improved a lot, and now we use modems to send information wirelessly. Acoustic modems are a special kind of modem that turns digital information into sound signals that can travel underwater.

We use devices called transducers to pick up the sound signals and turn them back into digital information. This technology is used for things like monitoring the ocean, talking to divers, and controlling underwater robots.

One problem with underwater acoustic communication is that it can be hard to send information over long distances, receiver depth, and transmission range because the sound signals can get weaker. This means that the further the information has to travel, the more difficult it is to get it to where it needs to go.


6.2. Underwater Electromagnetic Communication

There’s a way to send signals through water called the “Underwater Electromagnetic Communication” method. In Underwater Electromagnetic Communication electromagnetic waves are used in radio frequency (RF).

Water can stop RF waves pretty easily, though, especially seawater. The higher the frequency of the waves, the more they get stopped by the water.

ELF or extremely low-frequency waves can travel really far through water, which is great for communication between submarines. But using electromagnetic waves like this needs a big antenna and the signal still gets weaker the farther it has to travel.


6.3. Underwater Optical Communication

Optical Communication is based on the transmission of electromagnetic waves in the visible spectrum. The attenuation of the signal depends on the absorption of water, much like the way colors are absorbed, as well as the turbidity of the water.

What the underwater telecommunications industry is currently working on is hybrid communication systems that combine technical underwater communication systems. This way, the signal is broken down into replicas of the original signal and transmitted through different channels to avoid fading.

Currently, underwater communication systems based on these technologies allow divers to talk to each other. However, they are mainly used in professional diving due to their price and the requirement of a full-face mask.

The question is, will we ever be able to communicate freely underwater? What do you think? Feel free to leave your comment on our Facebook thread.