Types of Metal Detecting Activities, page 26:

Underwater Metal Detecting:
Shipwreck Diving, Types of Shipwrecks, Important Aspects of Shipwreck Treasure Hunting


ShipwreckAfter an approximate location of a shipwreck is derived from research (see details on page 27), a wide variety of search methods for pinpointing the exact shipwreck location can be used (see details below).

When a shipwreck is pinpointed, scuba divers with metal detectors search the seabed for valuable artifacts and recover them by hand. A special attention is paid to "rocks" and "black chunks," which may be the encrusted silver objects and coins.

Because most artifacts are encased by encrustation after being in marine environment for a few centuries, a treasure hunt becomes a "rock hunt." Gold objects are the only exception since gold is inert and maintains its shiny luster without oxidizing after being in water for ages. Oxidized iron artifacts look like orange lumps on the ocean bottom.

Besides metal detecting, other search and recovery methods are used. They may require powerful equipment (see details in "Equipment for Shipwreck Treasure Hunting" on page 31) and good operating skills.

Experienced underwater treasure hunters conduct the shipwreck penetration (see details below). This advanced form of shipwreck diving requires a substantial experience, knowledge of scuba gear and equipment, additional safety precautions, and many heavy tools and recovery equipment as well as practical knowledge of its usage.

Types of Shipwrecks

According to the Merchant Shipping Act 1995, shipwreck can be:

Flotsam are goods lost from a ship which has sunk or otherwise perished which are recoverable because they have floated.
Jetsam are goods cast overboard in order to lighten a vessel which is in danger of sinking, even if they ultimately perish.
Derelict is property which has been abandoned and deserted at sea by those who were in charge without any hope of recovering it. This includes vessels and cargo.
Lagan (or Ligan) are goods cast overboard from a ship, which afterwards perish, buoyed so that they can be recovered later.

Throughout the world, there are shipwrecks of all ages and types ranging from ancient Egyptian vessels and Spanish galleons, which now often look like just the piles of ballast stone, to luxury liners, oil tankers, airplanes, and barges, even small cabin cruisers. Because each of these wrecks will be unique, it will require an individual approach in diving style and search methods. The deeper wrecks are often more intact than the wrecks closer to shore which suffer from the constant pounding by the water currents and waves and become broken up and scattered over vast areas.

Important Aspects of Shipwreck Treasure Hunting

To master the skills of shipwreck diving, you should obtain the complete shipwreck diver's guide. The process of shipwreck diving consists of the following aspects that are given short descriptions here, but should be studied in details in other informative sources and fully understood:

Finding Shipwrecks
Shipwreck CoinsFinding a virgin shipwreck is a dream of all shipwreck treasure hunters. A wide variety of search methods exists. Many wrecks have been located by divers just exploring new areas or checking out new LORAN (Long Range Aid to Navigation) numbers supplied by local fisherman. In the northeast, most wrecks are also located with LORAN numbers.

In clear water locations, many wrecks are located with the aid of triangulating land ranges. After aligning these ranges, one looks for uncharacteristic straight lines on the sand or coral bottom, which indicate a wreck underneath. Shallow clear water search methods include "towing shark bait" - towing a diver on a sled while the boat does a grid of the area.

Shipwrecks can be located with devices such as side scan sonars, proton magnetometers, three dimensional sonars (see "Treasure Hunting Systems" on page 29) or less expensive equipment like a depth recorder. The search procedure usually starts with towing a side-scan sonar or magnetometer attached to a survey boat. Side-scan sonars help locate piles of ballast rock which used to be carried by ships in the past. And magnetometers are used to find large chunks of iron that may be present at the sites of decomposing ships.

Aerial surveys can also be very helpful when using aircraft, helicopters or even a hot air balloon. Aerial surveys should be done no higher than 500 feet, and polarized sunglasses should be used.

Shipwreck Identification
Identifying an unknown shipwreck is a difficult task and has no easy rules to follow. The most positive identification can be only made through the retrieval of artifacts from the wreck, but even this method can deceive the most experienced researcher.

Underwater Communication
Underwater communication is discussed in every basic diver's manual and in all certification classes. However all of the hand signals and the meaning behind each may not work in the real world of wreck diving as they become very hard to use and understand.

In bad visibility, as treasure divers carry equipment and holding a line reel, using hands becomes unpractical, especially when both divers are kneeling on the silt bottom, and the rising sediment is covering them in complete darkness.

In such cases, the underwater communication is conducted by staying close to each other, talking very slowly into each other's regulator, and keeping the sentences short. Thus, the treasure divers can continue exploring the shipwreck without having to stop or putdown any of their equipment.

Diving Navigation
Most shipwreck dives are done from a boat, anchored above the site. Depending on currents and visibility, it may be sometimes difficult to find the anchor line upon returning to the boat after the hunt is over. This can result in a long surface swim back to the boat or in a free floating hang if the diver has exceeded the "no decompression" limits.

Navigation methods include using tether line, conducting the perimeter search, or attaching a small strobe light to the anchor line about 20 or 30 feet off the bottom. While shipwreck diving in shallow waters, you can use the compass and land ranges visible on the shore.

Wreck Penetration
Wreck penetration is an advanced form of shipwreck diving. In fact, recreational shipwreck diving does not typically include penetration. It should only be done by those with adequate experience, training and equipment.

Basic rules used in shipwreck penetration are the same as cave penetration rules: 1) be trained and dive within your own limitations, 2) use a tether line and secure it in at least two places, 3) reserve at least two thirds of your beginning air supply for the swim out, 4) carry at least three dependable dive lights.

The diver who penetrates a wreck must also be disciplined and have a good mental attitude. Wreck penetration is not something you can easily learn from any book or article or even from years of open water experience.

Shipwreck Mapping
A drawing of the wreck can be used for various purposes such as displaying along with a valuable find, planning future dives, or benefiting others - divers, photographers and shipwreck archaeologists. You can draw a rough outline of the wreck after only diving it once, and then add and change details as you become more familiar with the wreck. Taking pictures and videos of the wreck may be very helpful.

Artifact Location
Increasing odds at finding nice artifacts inside the shipwreck solely depends on the number of dives performed by the treasure diver. Experience gives any diver trained eyes and knowledge of good productive spots to which he/she constantly returns and recover valuable finds time after time.

If you do not have a substantial experience in locating artifacts, you can still better your results if you use these simple tips: 1) always pay close attention to the stories other treasure hunters tell, especially if they are willing to give away a location, 2) be very observant of shapes as you swim over or through a shipwreck, 3) do not expect to be able to pick up and swim off with every great artifact you spot; many artifacts will require several dives, specialized tools, and determination to recover them.

Artifact Recovery
Finding an artifact is only half of the challenging process. Getting heavy objects off the sea bed and onto the boat safely can be actually an even greater challenge.

Artifact Conservation & Preservation
Preservation of artifacts is extremely important and requires not only time but often a little elbow grease as well. The process usually starts on the boat immediately after an artifact is found. The first rule is to keep the artifact wet and not exposed to air until the preservation process can begin. This is extremely important with steel artifacts which start to rust immediately upon contact with air.

If you do not have the required skills for particular conservation and preservation jobs, find people who do, and employ a conservator as a member of your team (very expensive), or find the services of a subcontractor with suitable facilities and experience.

Mental Attitude
Here are important rules used by shipwreck divers:
1) If any diver in the team does not feel comfortable with a dive, then that dive should be immediately ended.
2) To prevent stress, stay calm, move slowly throughout your dive, know your equipment and the location of your back up lights and alternate air source. Preventing stress can also come from diving frequently, not being over loaded with equipment, making sure all of your equipment operates correctly, and familiarizing yourself with the shipwreck.
3) Never let peer pressure or greed for an artifact compel you to do a dive beyond your own capabilities or the initial dive plan.

Metal Detecting & Target Recovery Techniques

Metal detecting and SMALL TARGET recovery techniques used in shipwreck diving are the same as the ones described in the "Snorkeling With A Metal Detector" section on page 23 and in "Scuba Detecting" section on page 25. Larger and heavier artifacts will require special tools and methods for their recovery.

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Sources: "Shipwreck Diving", "New Jersey Beach Diver", and "Tropical Shipwrecks" By Capt. Dan Berg, en.wikipedia.org