WARNING - What you are about to read DOES NOT take the place of qualified training!!
The arc search pattern is a very popular pattern amongst public safety divers. The reason for this is that the pattern is easy to set up and conduct. All it takes is a piece of rope, a diver, line tender and the two of them knowing what they are doing. Be careful, because some teams get attached to the arc search to the point where the arc search is the only pattern they really know how to conduct. Like all search patterns, the arc search has its strengths and its weaknesses. Knowing its limitations will allow you to use the pattern correctly and thus help you be more effective as an Underwater Criminal Investigator.
The arc search is designed to search for medium to large size objects. However, it can be used for smaller items if the conditions (visibility, hard bottom, etc.) are right, the pattern is kept tight and the diver and tender both know what they are doing. However, when I am searching for something small, and it is important that I find it, I will not waste time with the arc search. I'd get serious with a two man jackstay and with a one to two foot move.
As I mentioned before, the arc search is easy to set up and conduct. It's mainly used for locating items not very far from shore, no farther than someone could throw a rifle. However, you can get creative with the pattern and use it underwater to conduct arcs or even a complete circle known as (what else) a circle search, which will allow you to get away from shore and into deeper water. Both patterns come from the same family. Both require the same equipment, personnel and communication procedure. One simply makes half a circle, the other a full circle and the tender gets wet.
There seems to be some confusion as to who controls the arc search, the diver or the tender. Let me go on record as saying the line tender. The diver is a tool the tender uses to conduct the search. This does not mean the diver is not important; it means the tender is responsible for the area being searched and whether or not it was searched properly. The diver has the responsibility to conduct a thorough search underwater, to do his job and to go where the tender leads him.
There are several ways of conducting the arc search. Usually the difference is in the way the diver controls the search line. Some teams prefer the diver to hold onto the rope , others believe in mechanically tethering the diver (using locking carabineers, snap shackles and figure 8 knots). The instructions I will give are how I normally conduct the arc search. I prefer not to be mechanically locked into the system (unless I'm in an overhead environments, etc.) but to simply hold onto the rope (keeping it simple). I completely understand both sides of the argument.
Before beginning your search, make sure you have reviewed your on line communications. Once the tender and diver have reviewed their pull signals, get yourself one of your 75' or 100' ropes and make a loop in one of the ends by tying a figure 8 knot. The loop needs to be big enough for the diver to put a gloved hand through, but not so big that it will be hard for a diver to control. If the loop is too small, however, the diver will end up holding onto it with just a few fingers instead of the entire hand. This again makes the loop hard for the diver to control and hold onto.
Note: The instructions given are not for hazardous conditions such as those encountered in ice diving or other overhead or confined space situations. These conditions would of course require a lot more safety procedures and control.
It's also a good idea to practice your search patterns on land before getting in the water. This rehearsal is called a "Dirt Dive". You will be surprised how many potential problems you discover and how many misunderstandings of each other's role there are. Once everyone has understood their job, it's time to get changed and go diving.
Have the diver start in shallow water ten to 15 feet away from the tender. If the diver is to the left of the tender, the rope would be held in the diver's right hand and if the diver is to the right of the tender, the rope would be held in the diver's left hand. Keeping the rope tight, the tender would then signal the diver that he was ready (two pulls). If the diver was also ready, he would signal the tender accordingly (two pulls) and move out searching along the bottom.
The hand not holding the rope is called the searching hand. This free hand moves along the bottom in a grid pattern, patting side to side in front of the diver, feeling for whatever might be in the diver's path as he moves forward.
One of the many areas in which dead zones can be created in the arc search pattern is found in the diver's turn. With a little practice, you can become proficient in using the turning technique described below (which by the way was invented by UCI) and, by doing so, enhance your arc search performance. Many divers simply turn when the signal is given and move into deeper water, creating dead zones with every pass.
Unfortunately, this is the turning procedure that most teams use. The turn I prefer is equally simple but is easier and more thorough, and it takes away the dead zones. I first developed this turn years ago when I was trying to perfect my arc pattern by eliminating the dead zones I created in my turn.
First, when the signal to stop and turn is given (one pull), instead of turning around, continue to face the shore and move away from the tender, while remaining at the depth you were stopped in, while he gives you line.
Once the line is tight, back up slowly while searching backwards. The hand that was holding on the search line continues to hold the line and the hand that was searching continues to search. When you get into deeper water (2 feet or so deeper), make your turn and switch hands, back up a little (just to be sure), and start out searching. I find this technique is actually easier for the diver to perform as well as more thorough.
With every successive pass the diver wants to go back over some of the same area already covered to eliminate the dead zone that would otherwise be created between passes. Keep in mind the diver's "search zone" ( the area he is responsible for) is approximately 3-5 feet directly in front of him. Three feet of rope is about the most you want to give out as the tender unless conditions dictate otherwise.
The amount of rope the tender lets out depends on visibility, bottom composition (sandy. rocky, etc.) and the size of the item you are searching for. In Virginia, for example, there are rivers in certain seasons when it hasn't rained in a while that have great visibility. These rivers, away from the embankment, have hard bottoms and ten-foot, sometimes twenty-foot, visibility. If I'm lucky enough to catch these conditions when I'm searching for a body, my passes might cover a width of anywhere from 5 to 10 feet at a time.
Unfortunately, I don't see these conditions too often. It seems people don't like to drown in nice calm, clear water where I can make a quick recovery. If it's a stolen item, the bad guy usually knows the good locations in the area to throw it where it's not going to be easy to find.
Now getting back to the search. After the diver has turned around, he then moves away from the tender in a direction parallel to the search line, until the line becomes tight.
Personally, when I'm the diver or tender I do not like to signal OK each time a pass is made. When the diver makes his turn and is ready, he simply moves out searching while keeping the rope tight. His moving out in effect sends his OK back to the tender. But some teams like to signal OK to each other each time they make a pass or each time the diver stops to check something. The tender asks, "Are you OK?" The diver says, "Yes, I am OK. Are you OK?" The tender says, "Yes of course I'm OK." To me that gets to be too many OK's. They become confusing. Then, when an OK is really needed, you're OK'd out. Anyway, whatever works for you is fine as long as you have clearly understood signals throughout the search, OK? Oops, sorry!
If you find the item using the arc search
If the item is located while on an arc, the diver would signal the tender that the item has been found (four pulls). The tender would then advise the diver that he understood (two pulls) and tie a "marking" loop in the rope to mark the distance between where the tender was standing and where the item was found.
Tying knots on every pass
I do not teach or believe in tying a knot every time the diver makes a pass. This practice only takes up a lot of needed rope, causes more entanglements (the loops catch obstructions) and serves no useful purpose. You don't need to know the number of passes that were made and the only measurement you need is from the tender to the diver when the item is found. If you think you need to make a knot in order to hold on to the rope, you might not be strong enough for this type of work. So, hold the rope tighter and quit making those useless knots.
Once the tender has been given the signal that the diver has found something and after the tender has tied his marking loop, (the only knot tied) the tender needs to give the diver about 3 to 5 feet of slack line so the diver may move around freely. The diver would then send up a buoy, marking the location of the recovery. After releasing the buoy, the diver should follow the buoy line to the surface to ensure the buoy reached the surface.
The search line should be laid on the bottom next to the item or even tied off to the item, taking into consideration possible loss of physical evidence. This way the diver has a choice. When returning to package the item, he can either follow his buoy line down to the item or follow the search line to the item. This second option gives him a back-up in case the buoy line has been moved off the item. Accordingly, the line tender lays his end of the search line down after making his marking loop. The search line will be pulled in only after the evidence has been packaged and the area cleared.
What procedures are used next depends on the item found and the preplanned procedures agreed upon prior to the diver entering the water.
If the item is not found
If you have searched the primary area and have not found what you're searching for, move the search pattern over to the right or left of your primary location and perform another arc search. This requires the tender to move over to the right or to the left of where he was originally standing. Make sure your arcs overlap each other to ensure you are covering the entire search area. If you believe the item you're searching for has gone farther out than the arc can cover, its time to switch to another pattern or another variation of the arc.
Is there more to say about the arc search pattern? You be there is! Unfortunately, I don't have the time or the space here to write it all down. I hope this little bit helps you in some way. Good luck in your search and recovery diving!