Types of Metal Detecting Activities, page 29:
SHIPWRECK DIVING & METAL DETECTING
UNDERWATER METAL DETECTORS & TREASURE HUNTING SYSTEMS REQUIRED
Just like in any type of metal detecting, the same simple rule applies to underwater treasure hunting: the better quality of your metal detector or treasure hunting system, the better your chances of finding something valuable are.
Underwater Metal Detectors
Like the surf wading metal detectors, detectors used for shipwreck treasure hunting are also designed to overcome the effects of highly mineralized salt water and magnetic black sand and can be used on beaches and in shallow waters. They only differ from other underwater metal detectors by their ability to withstand the higher water pressure at greater depths.
These detectors are depth-rated down to 200 feet and normally have better volume control for hearing through a neoprene hood. Most of these underwater metal detectors have the search coil permanently attached (hard-wired) to the control box. Search coils designed for deep underwater search have an extra weight. Since underwater metal detecting is impossible without headphones, most underwater metal detectors have the headphones hard-wired to the control box as well.
Pulse induction detectors and Multi- detectors with Multiple Tone ID have an advantage over other machines. However, any metal detectors of a conventional design play only a secondary role in the shipwreck hunting process because the success of the entire enterprise depends on successful accomplishment of its first phase - locating a shipwreck. A different type of detecting devices - treasure hunting systems, are utilized during this initial phase.
To see what metal detectors for this metal detecting activity are available on the market today and read their reviews, you might want to visit my Metal Detectors for Beach/Surf/Underwater Treasure Hunting page.
Treasure Hunting Systems
Boat-Towed Underwater Proton Magnetometers, Underwater Side-scan Sonars, Three-Dimensional Sonars and Underwater Remotely Operated Vehicles (ROV's), play a major role in shipwreck diving because they are essential for pinpointing the location of the sunken ship. However, because these units are very expensive, they are not common place in the sport diving community.
As I mentioned above, less expensive devices such as depth recorders, or other inexpensive means for locating shipwrecks such as "towing shark bait" and simple area exploration may be used. Expensive treasure hunting systems can be effective only in the hands of an experienced operator. That is why such systems are owned and operated by professional treasure hunters who can use these devices with maximum efficiency and make them pay off many times.
• Side Scan Sonars use a tow fish which is towed behind the boat at a determined depth. The fish contains transmitting circuitry that sends high frequency bursts of acoustic energy down to the sea bed on both sides of the boat. Any object that is not buried, like a shipwreck or a topographic feature on the sea floor, produces echoes which are received by a transducer. This information is often computer enhanced to give a detailed image of the wreck.
• 3-D Sonars provide a complete 3D picture of what is ahead of the vessel and display a new 3D underwater map every 2 seconds. These devices are not affected by poor visibility and can be deployed by ROV.
• Underwater Remotely Operated Vehicles (ROV's) is a tethered underwater robot that is unoccupied, highly maneuverable and operated by a person aboard a vessel. ROV is linked to the ship by a tether - a group of cables that carry electrical power, video and data signals back and forth between the operator and the vehicle.
High power applications often use hydraulics in addition to electrical cabling. Most ROV's are equipped with at least a video camera and lights. Additional equipment may include sonars, magnetometers, a still camera, a manipulator or cutting arm, water samplers, and instruments that measure water clarity, light penetration and temperature.
• Proton Magnetometers are less expensive and also utilize a tow fish. They measure the strength of the area's magnetic field instead of registering the shapes of topographic features. The earth's magnetic field is changed at the location of any ferrous object such as a large chunk of iron at the spot of decomposing shipwreck. The amount of change in magnetic field is proportional to the amount of iron.
Magnetometers are capable to find any ferrous objects such as cannons, hull plates, and anchors, even when they are buried beneath the ocean floor. Magnetometers can detect wrecks, depending on the amount of ferrous content, up to 1,000 feet away.
To see features, characteristics and specifications of these systems and to read their reviews, please visit "Reviews for Treasure Hunting Systems" page.
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To see what metal detectors for this metal detecting activity are available on the market today and read their reviews, you might want to visit my page on Metal Detectors for Beach/Surf/Underwater Treasure Hunting.
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