Line Signals

By: Mark Phillips

Underwater communication is vital for diver safety and successful searches. It should be a goal for all PSD teams to eventually own and utilize an electronic underwater communication system. The ability for divers and surface personnel to talk directly to one another not only improves safety but efficiency. When plain speech is used to direct the diver and give the diver the ability to talk to the surface, efficiency, safety improves. Some electronic communication systems are wireless. They depend on separate receivers and transmitters. Because any electronic system may fail, teams need a backup.

We teach students to use voice communications sparingly. This does not imply that the communication system is or could be the primary communication method between divers underwater or a diver to shore support personnel at the surface. Relying on any single system is not wise.

Since our divers use search lines. This provides physical contact with a surface line tender. It also means the tools for a tug or pull line signal must be in place. Divers can use this as a backup to electronic communication system.

Where electronics fail 

Some teams make line signals their primary communication method. Electronic communication system used as a backup. While this seems to be backward thinking. A diver dependent on an electronic communication system must stop and press a microphone button each time they need to:

  • Speak
  • Ask directions
  • Acknowledge a message
  • Answer a question

To avoid missing a search area, divers will usually:

  • Stop forward momentum
  • Respond
  • Then begin again

This takes time and burns air needlessly. It’s inefficient.

Some teams may not be able to afford expensive electronics. This is often true of newly formed teams. These teams must rely solely on line signals.

Since this means of communication is dependent on diver-to-tender and tender to diver contact, the tender must pay constant attention to:

  • The diver’s position
  • Any signals sent
  • Changes in movement
  • Uncharacteristic events.

Tenders will be near the water’s edge. This means they must wear personal floatation devices (PFD)s. Tenders must also be able to:

  • Change the diver’s direction
  • Recall the diver
  • Stop the diver at a moment’s notice

A history of line pull signals 

Divers used line signals as early as the 5th Century BCE. Early Persian writings report divers salvaging sunken treasure. By this time, underwater salvage was a known skill. Breath-hold divers were in constant demand.

Food, treasure, salvage or profit motivated these early divers. As early as the 3rd Century BCE, Greek laws regulated treasure divers.

In the early days, a rope and a rock for weight were all divers needed to get to the bottom. The trick was getting back to the surface.

We can safely assume divers used line signals to communicate with the surface. Even if it was as simple as, “One tug means pull me up.”

In 1998, Historical Diving Times published an article titled, For the Moment, Let’s Forget the Diver. In it, the author writes:

“The diver-surface link is one that we would, therefore, do well to explore further, when considering information on diving from any period. Having noted equipment, exploits, depths or times in the usual logbook fashion, forget the diver for a moment. Go over things again, from the viewpoint of those on the surface. This is a simple analytical technique, which often helps to explain so much more about what really went on.

“To illustrate this, take Oppian, the second century AD Greek poet from Cilicia, and the only ancient source to mention directly those on the surface.

“This occurs in the fifth book of his Halieutica (on hunting and fishing). His text is particularly important, as it provides the best details we have of the diving technique used by ancient breath-hold ‘sponge cutters’. Naturally, the narrative contains high drama, which starts underwater but ends on the surface.

“Shaking repeatedly the rope he bids his comrades pull him up. And the mighty sea-monster and the companions of the fisher pull at his body rent in twain, a pitiful sight to see, still yearning for ship and shipmates. And they in sorrow speedily leave to land, weeping over the remains of the unhappy comrade.”

In 1535, Guglielmo de Lorena designed one of the first diving bells. Divers used this to work on sunken barges in Lake Nemi, Italy. Though it may not have been the first recorded use of a diving bell, it was among the earliest.

Things get better with time… 

Diver motivations have not significantly changed. However, with improved equipment and technology, divers now stay underwater longer.

When divers in suits began using surface-supplied air, line signals remained the only way to communicate with the surface. Underwater communications were dependent on line tug or pull signals and as the need progressed, a variety of complex systems of line signals were developed.

The US Navy uses a variety of modern communication technologies. It still employs line signals as well. (See Table 8-3 from the US Navy Diving Manual, Revision 4.)

The scientific diving community uses a different set of signals. These were developed by the Scientific Committee of the World Underwater Federation (CMAS). The signals appear in their manual, Scientific Diving: A General Code of Practice. The CMAS signals are much simpler than the Navy’s. Most public safety divers recognize them.

The NOAA Diving Manual details a much more complex set of signals. These more closely resemble the Navy’s. NOAA also includes hand-squeeze signals. These signals resemble the much less complex line signals public safety divers use.

Not just for divers 

Line signals are not just for divers. Line signals can be used anytime a rope separates two people. From rescue to exploration, line signals have developed as one of the simplest means of communication.

Many public safety dive teams use the acronym OATH to identify line signals.

  • 1 Tug: Okay (can be a question or answer)
  • 2 Tugs: Advance or Give me rope
  • 3 Tugs: Take up rope or I’m coming back
  • 4 Tugs: Help!

Civil Defense uses similar lifeline signals as a method of communication for rescue workers working off a lifeline. They identify a lifeline as “A means of communication for members of a rescue party who must enter hazardous enclosures or toxic atmosphere. It enables them to keep in contact with persons outside by sending rope signals.” Their standard lifeline signals include:

  • One pull: Stop (if moving), Okay (If at rest)
  • Two pulls: Advance
  • Three Pulls: Come out at once
  • Four Pulls: Distress – come at once

Tethered Diving 

There are two approaches dive teams use when tending divers from the surface.

  • One is to attach divers to the line using a quick release. This allows divers to self-rescue if the line becomes fouled.
  • With the other approach, divers stay connected to the line, even if it fouls.

If using a quick release, it’s essential the release cannot open accidentally. If it does, backup or rescue divers will have no direct path to the missing diver. This is true whether the release opens accidentally or intentionally. Teams that use quick releases must train for this contingency.

Teams who avoid using quick releases do so because it all but eliminates the possibility of separation from the line. A diver who becomes fouled always has the option to cut the line to release himself. As with quick releases, this is something for which teams should train.

Most public safety diving takes place in low or zero visibility. Here search lines are critical for safety and communication. Common sense applies, too. Do you have 30 m/100 ft visibility in a 6 m/20 ft-deep lake? You probably do not need to be tethered.

Hand loops 

There are things tenders can do while divers suit up. Among these is making sure the line has a hand loop for each diver. The loop must be just out of reach of the diver’s fingertips. This allows for a little slack. It also helps divers maintain their orientation to the shore without being skewed.

Effective line signals require taut lines. Tenders must keep the search line tight enough to “feel” the diver. At the same time, they cannot apply so much force they pull divers off pattern.

To signal over a taut line, divers need not grab a handful of slack and yank as hard as possible. Doing so is unnecessary and can cause a wide variety of problems.

Imagine you are a diver who just became entangled in a trot line. One of the treble hook barbs has pierced your mask skirt. The tender sees your bubbles become stationary. He wants to ask if you are okay.  Would you prefer he:

  • A: Yank the search line as hard as possible, pulling the hook through the skirt and into your eye?
  • B: Hold the search line in one hand and, while keeping the line taut, rock his hand slightly, sending a single tug down the line?

We are sure you would choose option B.

Acknowledging signals 

Divers don’t always need to acknowledge their tender’s command signals. However, tenders must know beyond doubt their commands were received and followed.

If a tender signals to stop and turn, he should see bubbles change direction. This way he knows the diver followed his command. If the bubbles don’t change direction, the tender should re-send the command signal. If the diver fails to respond a second time, it’s time to alert the backup diver.

A single tug asking if the diver is okay is one the diver must acknowledge. A stationary diver who fails to acknowledge a single tug requires sending in a backup diver.

Backup divers 

Equip backup divers with a short tag line or strap. Teams sometimes call this a contingency strap. It is relatively short, typically 1 m/3 ft in length. There are two brass snaps, one on each end. The backup diver attaches one snap to his harness. He stows the remaining strap in a pocket until needed.

If the backup diver must enter the water, he clips one end of the strap to the search line. The other end of the strap remains clipped to his harness. Doing so helps ensure the backup diver never becomes separated from the line.

Contingency straps allow backups to go directly to the affected diver while keeping both hands free. This may be critical in zero visibility. It further allows surface personnel to know where both divers are.

Backup diver smay be moving fast. This creates a risk of running into the primary diver. To avoid this, add a stopper knot to the search line.

A stopper knot can be a single or double overhand knot in the search line itself. It can also be a separate knot tied on top of the search line. You can secure this knot by weaving heavy monofilament line through it and the search line.

The knot where you attach the hand loop can further act as a stopper. Train your backup divers to slow or stop their forward momentum when encountering the stopper.

Search line signals can be simple or complex. Consider your needs and experiments with different types. Just remember, the less complex the system, the better the communication.

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