Deep-Six Underwater Systems, Inc.
"Add Depth to Your Life"
Contents

Table of Contents

Introduction
1 Pressure and Gases
2 The Face Mask
3 The Snorkel
4 The Fins
5 Weight Systems
6 The Knife
7 The Wetsuit
8 Pressure and Water
9 The Ear and Pressure
10 The Sinus and Pressure
11 The Stomach/Intestine and Pressure
12 The Lung and Pressure
13 Barotrauma caused by External Air Spaces
14 The Buoyancy Compesation Device (BCD)
15 The Scuba Cylinder
16 The Scuba Cylinder Valve
17 The Regulator
18 Density and the Diver
19 The 4 Gas Laws
20 Hand Signals
21 Carbon Monoxide Poisoning
22 Hyperventilation
23 Nitrogen Narcosis
24 Diver's Flags
25 Sound Underwater
26 Color Underwater
27 Decompression Sickness
28 Breathing Oxygen
29 Deep Diving
30 Thermoclines
31 Thunderstorms
32 Underwater Life
33 Open Water Dives
34 The Final Examination
35 The Environment
36 Advanced Course



36 - Advanced Course

     PADI's Advanced Scuba Course should be seriously considered by every certified diver. The various components are designed to extend the knowledge and experience that an Open-Water Scuba diver has. At Deep-Six it is an inexpensive way to continue diving, as well as a way for a diver that has not been diving for a while to get back into it.

     As explained elsewhere, there are just 5 dives that have to be completed for a diver to become Advanced. Two of them are core dives and are required. The other 3 are elected by the diver.

     The following information is used for specific dives. A diver working on Advanced Scuba may be referred to this chapter to enhance their knowledge about a specific dive.

SEARCH AND RECOVERY DIVE: 

METAL DETECTORS:

     It is quite simple to understand how a metal locator or detector works. Most use electromagnetic fields to locate metallic objects. Electromagnetism comes in a variety of forms such as light, x-rays, radio waves, etc. Some electromagnetic energy is at a very low frequency such as radio waves, and some is at a very high frequency such as gamma radiation. There is an even lower frequency than radio waves and that is electrical radiation. It travels at the speed of light, as do all of the types of electromagnetism, but it should not be confused with electricity. However, when electricity travels through a wire it emits electrical radiation. That is why your radio emits static when you drive under a high voltage wire.

     The very low frequency metal detectors (VLF Detectors) have an outer coil of wire that has alternating electrical current traveling through it. Electrical radiation is emitted from that coil of wire at right angles to it. If that radiation hits a piece of metal a pulse of electrical radiation is emitted by the metal but has an opposite polarity. A second smaller coil in the detector detects that pulse and registers it on a meter, with sound, or by light. Different metals change the electrical field in different ways so some metal detectors are manufactured to tell one metal, such as iron, from another, such as gold. They are discriminators.

     The Beat Frequency Oscillators (BFO Detectors) emit higher frequency radio waves. They also have a receiver for radio echos. Metals change the frequency of the radio waves and the metal locator detects those changes.

     Pulse Induction Detectors: These metal detectors have a single coil of wire. Direct current is pulsed out at rapid intervals. So, the very low frequency electrical radiation is emitted in pulses and is distorted by metals. This distortion is picked up between pulses and that is why only one coil is needed. The detection depth is greater but the ability to discriminate is usually less.

     Magnetometers: These have a great detection range sometimes measured in thousands of feet. Also, they are quite expensive when compared to the other types of detectors. They are able to detect only iron and steel objects. Magnetometers are able to measure the magnetic field of the earth. That field is distorted by iron or steel.  Just as a compass detects and lines up with the earth's magnetic field, if you bring a piece of iron near that compass it will deflect because of the change in the magnetic field. A steel shipwreck will deflect the magnetic field of the earth and that can be measure quite effectively by a magnetometer from quite a distance. 




Copyright Information about this text, DIVING WITH DEEP-SIX is as follows: Copyright 1996 - 2007 by George D. Campbell, III; President. All Rights Reserved. This file may be posted on Electronic Bulletin Boards for download, but may not be modified, printed for distribution, or used for any commercial purpose without the author's written permission.
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