While in the water, the task of establishing efficient communications during any aquatic operation is difficult, to say the least. Topside, various types of radio communications can be used, as necessary, by surface support personnel. However, radios are not appropriate for communicating with divers while positioning themselves on the surface in preparation for an underwater search. Communications from surface support personnel to divers at the surface and vice versa can be accomplished through a series of prearranged signals, which must be understood by all personnel involved in the search. Methods of communications can involve prearranged hand or whistle signals or a system where each diver is assigned a separate number corresponding to a number painted on a card or board large enough to be easily seen at distance. A second board displaying a large arrow is used to indicate the direction in which the diver should move for correct positioning (e.g., away from shore, toward shore, right, left, etc.). The availability of a large easel or a vehicle, which can be used to hold these boards, will serve to alleviate fatigue in support personnel on shore, who otherwise must hold up such signs.
To facilitate communications from the diver at the surface to shore personnel, prearranged hand signals and/or signals using a piece of equipment are effective. Such a communication system has been developed by using a mast capable of being attached to or detached from the diver's surface float (mini-mother). Should the number of personnel in the dive team warrant, each individual diver can identify his or her mast according to an assigned number by use of the binary system. In addition, the diver's number can be prominently displayed on his or her float.
While underwater, communication can be accomplished by rope pulls, or in the case of very low visibility, and where divers are positioned close together, communcation can be accomplished by hand squeezes. For example: 2 pulls (squeezes)= Stop; 3 pulls = Go; 2 pulls twice - Stop/Up; constant pulls = Help! One problem divers encounter with using both, rope pulls and hand squeezes, is that the communication process is slow. To effectively communicate a message, all signals must travel down the line from diver-to-diver and then be returned to the source, to indicate that the signal was received. Only then can the mechanical act called for by the signal be performed.
Another problem with such signals is that they are not by any means standardized. Should anyone choose to investigate different publications covering this topic, that will become obvious. For example, one nationally known organization in the field of underwater search and recovery teaches that one pull on a line means, "Are you O.K!" Our experience has taught, however, that one pull on a line means nothing specific. For example, a diver may find it necessary to tug the line in order to free a snag; he may inadvertently tug the line when getting into position or repositioning himself; etc. Where visibility allows, rope pulls are best utilized as an attention getter between divers and followed up with appropriate hand signals, which are standardized in the diving community.
Several underwater communications systems have been developed and may be useful in an underwater search. These systems are not without limitations, however, and vary in effectiveness due to inherent deficiencies or environmental difficulties. A "hardwire" communications system may be of value when conducting a search using one searcher in a straight sweep or semicircular sweep or when it is desirable to communicate with only one of a number of searches on a line. Rope pulls can be used as backup communications for the hardwire.
There are a variety of systems that will allow underwater communications amongst a number of divers, however, these too have their limitations. Some are directional, meaning that the transducer on the diver must be in direct line with the transmitter/receiver. This can be a problem when the diver has his back to the transmitter or where underwater obstacles are present. Some are affected by the engines of watercraft in the area. Some are affected by thermoclines.
Regardless of the communications system selected, the intelligibility of transmitted messages improves significantly if divers are trained to talk properly when using the equipment. The basic rule is to K I S S (Keep It Slow & Simple). Divers must also understand that just like in the bygone days of telephone party lines - everyone cannot talk at once!