How Divers Find Anything in Water They Cannot See Through

By Gus Marchetti, Salvage master. Reviewed by Amanda McCallister, editor.

Marine Salvage & Recovery | Hull & Bottom Cleaning In February of 2011, I stood on the end of a crusted pier in Long Beach, smelling creosote and low tide while an insurance adjuster pointed at a slick patch of water. A forty-foot refrigerated container had been toppled off the stern of a cargo vessel the night before. We had his GPS mark and a depth sounder, but the water was the color of strong tea. He said, 'It's right there. I know it is.' I said, 'That doesn't help me.' He was right. It was twenty feet below us. But I still rigged the lift bag wrong on the first try, because I assumed the container was sitting upright on the silt. It had toppled over and was lying on its side, half buried. The line slipped, and the bag shot to the surface. Four hours later we were still fighting it. I've been a salvage master for twenty-two years. I've pulled cars out of rivers, anchor chain off reefs, and once a full-sized forklift out of a lagoon where visibility was four inches. Every time, the lesson is the same: you don't find things in murky water by looking. You find them by method. What follows is how.

Your hands are the flashlight

When you're in zero visibility, the first tool is your sense of touch. We sweep the bottom by crawling on our knees, hands extended, fingers slightly curled. You don't rake; you brush. A buried cable or a rusted edge can feel like a rock until you're right on top of it. You learn to read texture through thick gloves. The difference between a pipe and a timber is a matter of a few fibers. You also learn to use your knuckles, the back of your hand, even your cheek. Some old hands say they can 'smell' steel through their feet. They're lying. But you do feel the current change when you approach a big object. Your body pushes water ahead of it, and the object pushes back. That's real. The mistake is to swim fast. Go slow. The bottom is a page you have to read with your skin.

Strings and lines make you honest

In clear water, you can see where you've been. In muddy water, you leave no trail. So we use lines as boundaries. A jackstay is a heavy line stretched along the bottom between two anchors. Two divers face each other on opposite sides and move along the line, searching a lane about six feet wide. When they hit the end, they shift the line over and come back. It's boring. It works. A circle search is when you anchor a line to the seabed and swim a spiral around that anchor, holding the line. It's excellent for finding something near a known point. The line is your memory. It keeps you from checking the same patch twice and ignoring the next one. A tender on the surface holds the other end and pays out slack. That tender is your lifeline. Trust them more than you trust your sense of direction.

Let sound do the heavy lifting

From the surface, we use side-scan sonar to light up the seabed. A good side-scan image can show a target the size of a fuel drum a hundred meters away. Then we drop a shot line—a weighted line with a lead at the bottom—right onto the target. The sonar got you to the right zip code. Your hands find the door. For smaller or specific objects, we attach a pinger—a small acoustic beacon—to the object before it goes overboard. Then you use a handheld receiver to zero in. The pinger is the only way to find something like a computer box on a sunken hull that your hands could never cover. The trick is to put the pinger somewhere that will survive the sink. One time we placed it inside a steel case with a switch that shut it off underwater. That was a long day.

Magnets, but know their limits

A magnetometer towed behind a boat can detect ferrous metal in the sediment. But it gives you a map of anomalies, not an object. Once you have an anomaly, you send a diver down to see what's there. Underwater metal detectors are useful for small things—a wrench, a gun, a piece of machinery—but they don't work on aluminum or composite. And they don't help if the object is buried under silt. In practice, I've found that a simple magnet on a stick is my go-to when I'm looking for steel in open water. You drag it along the bottom and feel it click. Magnets don't get tired. But they will snap to a shipwreck and never come loose. Always carry a release line.

The grid is your conscience

You can find anything if you cover the ground. But you have to prove you covered it. So we lay out a grid of transits—lines from shore or from buoys—and we swim search lanes. We use a GPS recorder on the surface to track the diver's path. When you're down there, you can't see your own tracks. The grid is what you trust. It's not about being clever. It's about being boring and thorough. The worst search is the one you do quickly because you're tired of looking. The best search is the one where you go over the same lane three times because you're not sure. There's no prize for speed. The only prize is the object.

Frequently Asked Questions

Do divers use special lights in murky water? Lights are only useful if there's something to illuminate. In a foot of visibility, a dive light just makes a bright wall of silt. We use them mostly for signaling or for working after dark, not for seeing ahead. How long does a search take? It depends entirely on the area and the object. A 50x50 yard section can take a day if it's deep. A smaller search around a known anchor might be an hour. Plan for more time than you think, and bring patience. Can you really feel something through gloves? You don't feel sharp edges, but you feel shapes and textures. When you find a chain or a cable, it moves differently against the silt. With a bit of practice, gloves become fine instruments. The real problem is when the water is so cold you can't feel anything anyway. That's when you're in trouble.