Diver communications
Diver communications are the methods used by divers to communicate with each other or with surface members of the dive team. In professional diving, diver communication is usually between a single working diver and the diving supervisor at the surface control point. This is considered important both for managing the diving work, and as a safety measure for monitoring the condition of the diver. The traditional method of communication was by line signals, but this has been superseded by voice communication, and line signals are now used in emergencies when voice communications have failed. Surface supplied divers often carry a closed circuit video camera on the helmet which allows the surface team to see what the diver is doing and to be involved in inspection tasks. This can also be used to transmit hand signals to the surface if voice communications fails. Underwater slates may be used to write text messages which can be shown to other divers, and there are some dive computers which allow a limited number of pre-programmed text messages to be sent through-water to other divers or surface personnel with compatible equipment.
Communication between divers and between surface personnel and divers is imperfect at best, and non-existent at worst, as a consequence of the physical characteristics of water. This prevents divers from performing at their full potential. Voice communication is the most generally useful format underwater, as visual forms are more affected by visibility, and written communication and signing are relatively slow and restricted by diving equipment.
Recreational divers do not usually have access to voice communication equipment, and it does not generally work with a standard scuba demand valve mouthpiece, so they use other signals. Hand signals are generally used when visibility allows, and there are a range of commonly used signals, with some variations. These signals are often also used by professional divers to communicate with other divers. There is also a range of other special purpose non-verbal signals, mostly used for safety and emergency communications.
Function
For safety and efficiency, divers may need to communicate with others diving with them, or with their surface support team. The interface between air and water is an effective barrier to direct sound transmission, and the natural water surface is also a barrier to visual communication across the interface due to internal reflection, particularly when not perfectly smooth. The equipment used by divers and the [|pressurised environment] are also hindrances to sound-based communication, and the encumbrance of diving equipment, relatively low light levels, and low visibility of many diving environments also hinders visual communication.Communication is most critical in an emergency, where high stress levels make effective communication more difficult, and the circumstances of the emergency may make the communication physically more difficult. Voice communication is natural and effective where it is practicable, and most people rely on it for fast and accurate communication in most circumstances.
The general requirements for an effective system for diver communication are that all the people who will use it have access to the system, that it functions effectively in the specific environment, that the people who wish to use it are familiar enough with it to communicate quickly, accurately and unambiguously with each other, and that the system has sufficient range to work when needed. A simple, logical and widely standardised system of signals is more effective at meeting these requirements. Several such systems have been developed using different equipment and suited for different circumstances. These include sound-based systems, visual systems and tactile systems.
History
The original communication between diver and surface attendant was by pulls on the diver's lifeline. Later, a speaking tube system, patented by Louis Denayrouze in 1874, was tried; this used a second hose with a diaphragm sealing each end to transmit sound, but it was not very successful. A small number were made by Siebe-Gorman, but the telephone system was introduced soon after this and since it worked better and was safer, the speaking tube was soon obsolete, and most helmets which had them were returned to the factory and converted. In the early 20th century electrical telephone systems were developed which improved the quality of voice communication. These used wires incorporated into the lifeline or air line, and used either headsets worn inside the helmet or speakers mounted inside the helmet. The microphone could be mounted in the front of the helmet or a contact throat-microphone could be used. At first it was only possible for the diver to talk to the surface telephonist, but later double telephone systems were introduced which allowed two-divers to speak directly to each other, while being monitored by the attendant. Diver telephones were manufactured by Siebe-Gorman, Heinke, Rene Piel, Morse, Eriksson, and Draeger among others. This system was well-established by the mid-20th century, has been improved several times as new technology became available, and is still in common use for surface-supplied divers using lightweight demand helmets and full-face masks. The introduction of closed circuit video to monitor the interior of diving bells, and to provide the supervisory team with direct feedback on the diver's work activities has expanded the capacity to provide useful advice to the working diver, and to keep track of the stand-by diver or 's activity in an emergency, making coordinated activity easier and more effective.More recently, through-water systems have been developed which do not use wires to transmit the signal. They were first developed for the U.S. Navy in the late 1960s. An early system for recreational scuba, the Wet Phone, was launched by Sound Wave Systems in 1977, but failed. By the mid-1980s miniaturized electronics made it possible to use single-sideband modulation, which greatly improved intelligibility in good conditions. By 1988 several systems using single side-band were found satisfactory by the US Navy for intelligibility and range, and mostly satisfactory for ergonomics, reliability and maintainability. Through-water systems allow communications over limited distances between divers and with the surface, usually using a push to talk system, which minimises power consumption by transmitting only on demand. They are not yet in general use by recreational divers due to cost and the need for a full-face mask.
Scope
Surface supplied diving uses the widest range of equipment and methods. As of 2021, hard wired voice communications are still the primary method, supported in major commercial applications by one-way closed circuit video but line pull signals are also used as an emergency backup, and through-water voice systems may be used as emergency backup for closed diving bells. Local communication between divers includes hand signals and text written on slates.Scuba diving can be done with cable voice communications, but the restriction on mobility makes this an unusual choice as it negates the primary reason for using scuba. Through-water voice communications do not have the same restriction on diver mobility, which is often the reason for choosing scuba for professional diving, but are more complex, more expensive, and less reliable than the hard-wired systems. There are some recreational applications for through-water voice communications for scuba, but this method is usually used for professional applications such as military and scientific diving, and almost all recreational diving relies on hand signals, light signals and writing slates for diver-to-diver communications, with the very few communications between diver and surface restricted to pre-arranged emergency signals. Breath-hold divers use a subset of the recreational diving hand signals where applicable, and have some additional hand-signals specific to freediving.
The presence of divers in the water during a diving operation exposes the divers to risks from passing waterborne traffic, and there are internationally standardised shape, light and flag signals to indicate that the diving support vessel is restricted in its ability to maneuver and that there are divers in the water.
Voice communications
Equipment
Both hard-wired and through-water electronic voice communications systems may be used with surface supplied diving. Wired systems are more popular as there is a physical connection to the diver for gas supply in any case, and adding a cable does not make the system any different to handle. Wired communications systems are still more reliable and simpler to maintain than through-water systems, and do not require the diver to carry a power source. The communications equipment is relatively straightforward and may be of the two-wire or four-wire type. Two wire systems use the same wires for surface to diver and diver to surface messages, whereas four wire systems allow the diver's messages and the surface operator's messages to use separate wire pairs, allowing simultaneous speech in both directions. A standard arrangement with wired diver communications is to have the diver's side normally on, so that the surface team can hear anything from the diver at all times except when the surface is sending a message on a two-wire system. This is considered an important safety feature, as the surface team can monitor the diver's breathing sounds, which can give early warning of problems developing, and confirms that the diver is alive.Through-water communications systems are more suitable for scuba as the diver is not encumbered by a communications cable, but they can be fitted to surface supplied equipment if desired. Most through-water systems have a push to talk system, so that high power is only used to transmit the signal when the diver has something to say. For commercial diving applications this is a disadvantage, in that the supervisor cannot monitor the condition of the divers by hearing them breathe.
Through-water communication systems are of two basic types. Acoustic systems provide one-way communications from the surface to divers. An audio signal emitted by a submerged transducer travels through the water to the divers, who can hear the sound directly, without signal receiving equipment. Amplitude modulated and single sideband systems provide two-way communications between divers and between the surface and divers. Both the AM and SSB systems require electronic transmitting and receiving equipment worn by the divers, and an immersed transducer connected to the surface unit. SSB systems perform better around obstacles, and AM systems give a stronger and often clearer signal for the same power, but are restricted to line-of-sight use.
The diver's speech is picked up by the microphone and converted into a high frequency sound signal transmitted to the water by the omnidirectional transducer. The signal can bounce off the bottom and surface and other obstructions, which can extend the range around obstructions, but will also degrade the signal due to interference effects caused by varying path lengths of different routes. When a receiving transducer picks up the signal, the ultrasonic signal is converted to an amplitude modulated electrical signal, amplified and converted to sound by the earphone. The through-water communications sets carried by the divers are battery powered.
The push-to-talk method is the most widely available system for through-water communications, but some equipment allows continuous transmission, or voice activated mode.
Push-to-talk is simple, efficient, and the preferred mode of many divers. It transmits only when the button is pressed, and saves power by not transmitting when the diver has nothing to say, but requires the diver to use a hand to transmit. Users take turns to speak and listen. This is normal communications protocol, and encourages clear communication, but does not allow audio monitoring of the diver between communications.
Voice activated means that the unit is intended to transmit when the diver's voice activates the microphone. If there is sufficient sound level generated at the microphone, the unit will transmit. This would run the battery down more rapidly when the background noise level is sufficient to activate transmission, but it allows hands-free communications.
Continuous transmission is a mode where one diver transmits continuously. This is hands free, but all audible noise will be heard by others on the same channel and within range. Open circuit breathing apparatus generally produces considerable exhalation bubble noise.
Through-water systems are also used for back-up to the wired communications via the umbilical generally used in closed diving bells. These systems are used in case of failure of the wired system, and do not rely on the integrity of the bell umbilical, so will work if the umbilical is severed and the bell lost. They operate between a battery powered transducer on the bell and a surface unit using a similar acoustic signal to those used for wireless diver communications. Single side-band suppressed carrier systems may be used, and a 27 kHz frequency with 4.2 kHz bandwidth is typical. Divers breathing helium may need a decoder system, which reduces the frequency of the sound to make it more intelligible.