Using Underwater Metal Detectors

The use of underwater metal detector gives as much, if not more, excitement as other types of metal detectors. With recreational diving increasingly becoming popular, so grows the demand for underwater metal detectors. Its users are either those who were into metal detecting first and then decided they want to expand their search for treasures underwater. Or they may be divers first and then felt it was such a waste of an opportunity to pass possible treasures they could find while they are under the water.

Whether they belong to the first or the second category, underwater metal detector is certainly a must-have for their exploration. A great portion of lakes, rivers and oceans remain relatively untouched. It has been said that more than 75% of shipwrecks had occurred before the last century and many of these have gone unexplored.

A few years back, for example, a metal detectorist discovered a five-carat canary diamond ring set in platinum. The ring, which was believed to have lost in 1954 when Hurricane Hazel hit Northern Carolina, was later appraised at over $84,000.

With underwater metal detectors, it has become much easier to explore sunken treasures. Fortunately, manufacturers have risen to the challenge by coming out with lightweight underwater metal detectors that can go to great depths.

Metal detectors use five different types of electronic circuitry for metal detection. These are beat frequency oscillator (BFO), transmitter-receiver (TR), very low frequency (VLF), automatic VLF and pulse induction (PI). Automatic VLF or pulse induction circuitries are used mostly in underwater metal detectors. These types are ideal for divers since they easier to operate because they do not require manual adjustments to compensate for ground mineralization and salt water.

Automatic VLF metal detectors work well both on land or underwater. These kinds of metal detectors can automatically tune to changing ground conditions and salt water. Pulse induction metal detectors, on the other hand, are used mainly for their deep seeking capabilities. They perform well even under difficult conditions and its signals are not affected by black sand and salt water. Pulse induction metal detectors, however, need more battery power.

When choosing an underwater metal detector, you should get one that has good target elimination feature to effectively eliminate “trash” targets and identify real treasures. With target elimination, detectors can quickly survey a site and locate coins, jewelries, and other non-ferrous objects. Automatic VLF metal detectors would normally have fully adjustable target elimination capabilities.

Successful use of underwater metal detectors also depends on having good search coils. Normally, underwater metal detectors come with 8- to 10.5-inch diameter search coils, which could sufficiently provide good ground coverage and depth and can detect various range of target sizes. More specialized operations would require larger or smaller searchcoils depending on the requirements.

With larger search coils, the underwater metal detector can search much deeper but they may not be good for detecting smaller objects such as coins. Large search coils can also scan a wider area with each sweep but they would have more difficulty in pinpointing targets precisely.

Smaller search coils are best used for detecting small objects because of their strong magnetic field. However, they cannot go too deeply. Smaller search coils have narrow detection pattern and can isolate and pinpoint targets more precisely. They can also scan other nearby metal objects.

Aside from having the right search coils, underwater metal detectors should also have audio and visual target indication. Special headphones or bone conductors can provide audio target indication while visual indication is possible with a meter, LCD bar graph and/or a LED (Light Emitting Diode).  Most underwater metal detectors are sold with submersible headphones.

It is important to examine closely the features of underwater metal detectors before deciding to buy. See what best works best for you. Who knows how soon you will be going out of the water with a great treasure in your hands.