Text and Photography by David Finnern
Most people have heard the stories of divers reaching into a hole for a lobster and retrieving an ornate gold plate or divers discovering antiquated coins carpeting the ocean bottom after a storm. While these particular treasures may be a bit difficult to find, treasure still abounds and it may in the very dive spots frequented by sport divers. The key thing to keep in mind is that treasure is in the eyes of the beholder.
Curiously, I learned this quite by accident. I had purchased an underwater metal detector primarily for use on shipwreck sites. I chose to test the unit at a local beach for no particular reason other than it was close to my home. I was soon on the bottom fiddling with the tuning control. The detector was ready to go within a few minutes and I began sweeping the coil across the sand. The headphones soon rang out and the little red light flashed, indicating the presence of metal. A few sweeps of my hand to remove the sand exposed a newer quarter. Okay, I thought, it's not much of a treasure, but the detector does what it's supposed to do.
After digging up a couple of fishing weights and several pop tops, I zeroed-in on a target that seemed slightly deeper than the previous ones. As I fanned a little more sand from my mini-excavation, gold suddenly radiated from the bottom of the hole. I reached down and, to my utter amazement, retrieved a spectacular gold cocktail ring with 11 diamonds forming a heart design on top.
I stared at the hefty ring and thoughts of retiring soon came to mind. I mean, this first discovery only took about 10 minutes and I wasn't even too sure how to operate this metal detecting contraption. A ring every 10 minutes-that equates to about five gold rings a dive. Three tanks equals 15 rings. Yep, there was no doubt about it, I figured. I'd be rich!
Well, it didn't quite turn out that way. But that first dive with an underwater metal detector did indeed open a whole new realm of underwater exploration. The subsequent years provided the introduction of a wide array of advanced, economical and user-friendly underwater metal detectors making treasure hunting even easier.
There are two types of metal detectors commonly used underwater: pulse induction (PI) and very low frequency/transmitter receiver (VLF/TR). PI detectors have a distinct advantage over other types of circuitry since they ignore black sand, salt and other minerals commonly found underwater. This translates into a fairly deep detection depth, which is no doubt the reason PI metal detectors are the choice of so many professional salvors.
Most PI machines are non-motion detectors. In other words, the coil need not be moving to detect a target. This makes pinpointing a target relatively easy and makes them a viable option for detecting uneven areas, such as rock reefs, where swinging a coil is difficult. PI detectors are also easy to operate and generally utilize only one or two controls for ground balancing, volume and on/off.
The primary disadvantage to PI metal detectors is that they usually don't offer discrimination circuitry, which can block out junk targets. The PI machines which do offer a discrimination option utilize a pulse delay process, which can drastically reduce detection depth.
VLF/TR metal detectors use technology similar to that of the common radio. While more sensitive to mineralization in the water than PI detectors, they are extremely practical for all-around treasure hunting and most machines offer discrimination circuitry, which helps out considerably in areas cluttered with small pieces of trash.
The multiple frequency detector is the new kid on the block and solves a metal detecting dilemma. In most detectors, using too much discrimination will also remove some good targets from their detecting range. The concept behind multiple frequency technology is the machine can adequately discriminate out iron and other junk targets while maintaining good depth and detection ability on nonferrous objects. Another advantage of multiple frequency detectors is they can even identify certain categories of targets via a variety of different sound signals in the headphones.
Coil size is another consideration when selecting a metal detector. Most searchcoils have a cone-shaped detection pattern. In other words, an 11 inch coil may detect an 11 inch swath on the surface, but it may only detect a three inch area a foot down. Since the larger the coil diameter, the wider the search area and the deeper it penetrates, a large searchcoil has definite advantages when hunting a sandy swimming beach with little trash. However, this larger coil can be detrimental in areas blanketed with countless pieces of buried junk since the coil will detect several targets concurrently, making it difficult to discern what is junk and which targets are worth digging.
I have field-tested virtually all types of underwater metal detectors and have discovered one consistent fact: they all find treasure. Thus, it would seem the type of detector that an individual diver should purchase is relative to the particular type of hunting he'll be pursuing, his personal budget and where he'll be using the machine.
Where to Search
The ocean coasts of the U.S. have no shortage of swimming beaches and these can be extremely lucrative sites to hunt since a popular beach has an endless supply of bathers and swimmers replenishing it with goodies. Modern coins are among the most common types of treasures discovered at swimming beaches. But there is the reasonable expectation of finding lost jewelry and even older coins may be present if the beach has been in use for many years.
I didn't think too much about other areas to detect until the day I overheard two college students discuss their vacation adventures. While they excitedly relived their feat of leaping from a cliff into a lake, all I could think about was what might have been removed during impact. My interest piqued as they continued their dialogue and I learned that one of the men felt he had drank at least 24 cans of beer a day and the other still didn't know what had happened to his swimming trunks. But in the midst of such intriguing facts I also learned the mysterious identity and location of the cove in which such beer drinking/cliff leaping/trunk losing adventures took place. And within a month I was pulling my boat into the cove.
I no more than hit the bottom when it was easy to see I was in the right place; bathing suits and beer cans were everywhere. In fact, I have never seen such a collection of bathing suits and beer cans. And, after a few swings of the detector, it was also apparent numerous other items, besides trunks, were lost in the cove. The searchcoil first registered a few coins and then an entire crevice filled with coins. I soon discovered a silver ring, then a thick, solid gold wedding band. Before long, I had found just about everything one could possibly lose, including countless sets of keys.
Since that first freshwater exploit, I have found that many lakes have at least as many possible detecting sites as the ocean. Just about any place where swimmers have congregated, boats have anchored and campers have camped has proven a good site for a treasure dive. There are even some distinct advantages to lake sites since most swimming areas are small when compared to ocean beaches and the goodies tend to be relatively concentrated.
You do have to figure out how to protect yourself from personal watercraft and speed boats, whose operators may not know what a divers down flag means. If diving in a small cove, I try to block the entrance with my boat. In this way, I'm relatively confident no one can enter the area where I'm diving. If that's not possible, I often use a wreck/cave diving reel attached to the anchor chain so that I can surface in the area right next to the boat. In roped swimming areas, there should be no problem, but I wouldn't bet my fins on it.
While metal detecting a swimming beach may not produce a solid gold plate, it still offers the same thrill of exploration and discovery. And there are indeed few thrills that compare to unearthing a shiny piece of gold jewelry or a long lost coin.
Eager to try your hand at metal detecting? Although not all dive stores offer this specialty, it is available from some. Check with your local dive store or one of the certification agencies.