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Shipwreck EXCAVATION
By Capt. Dan Berg
Many artifacts lie buried under sand or mud. These can be found
through excavation. Here are a few affordable methods that sport
divers can use to work a site.
HAND FAN
 The first is my favorite method because it's cheap, easy to make,
can be carried on every dive and without too much effort produces
fine results. It's a hand digger or hand fan. Divers can use any
number of designs from a ping pong paddle that was first used by
treasure hunter, Teddy Tucker, in the 1950's to my own design. My
digger is made from a curved piece of 1/8 plate steel, stainless if
it's available. Then a piece of 1 inch pipe has a hack saw slot cut
through one side. The steel, which can be curved by bending it
around a 4 inch diameter pipe, is pressed into the slot. A spot weld
assures security between the two components but is not necessary.
The finished item can be clipped onto a BC weight belt or carried in
a mesh bag. It's held in the palm and can be used to dig or gently
fan silt or sand. By always digging in the same direction the
current will usually carry any sediment away, leaving decent
visibility in the hole. The curvature of the digger's blade allows
more material to be moved with less effort and reduces drag on the
back swing.
AIR LIFT
An Air Lift is one of the nicest excavation tools. It can be made
with pvc, stainless or aluminum pipe and hooked to a suitable
compressor will move large volumes of sand with minimal loss of
visibility, that is, of course, if it's set up and used correctly.
The components of an air lift are simple: a high volume air
compressor, a length of pipe, a nuzzle and a hose. The unit is built
so that a hose connected to the compressor is connected to the
bottom of a twenty foot long 6 inch diameter pipe. Other pipe
diameters and lengths can also be used, but the example used would
require 75 psi and 100 cfm of air to work efficiently at 65 feet. A
valve is usually located at the bottom of the pipe and allows the
operator to control the volume or air being pushed into the pipe.
The air lift works because air is forced through a hose to the lower
end of the pipe. This air then rushes up the pipe towards the
surface, causing a vacuum effect which causes sand, mud or small
rocks to be sucked up the pipe. If the lift is set up correctly, the
debris will fall down current and heavy objects will not fall on top
of the diver working the lift. To better avoid the dumping of lifted
materials back onto the divers, a long horizontal pipe can be
floated at the surface. Depending on its length, a water jet may
have to be used to facilitate the movement of material.
Above Photo: Teddy Tucker uses a air lift to salvage the
San Pedro shipwreck
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Photos: Treasure Hunter Carl Fismer uses a air lift in the
Bahamas
Water dredge image
courtesy http://www.techdivetools.com/index.html
WATER DREDGE
 A water dredge can be useful if an airlift is not available. It's
made from a high volume water pump, a length of tubing, and hose.
The design is similar to an airlift except water is forced into the
bottom and directed back up the pipe, thus causing the suction
needed to vacuum the bottom. The water dredge may not be quite as
effective as an air lift, but, in shallow water up to 35 feet, it
works quite well and is easily controllable. Treasure hunter, Carl
Fismer, recommends facing into the current when working a water
dredge, this way the current carries suspended particles away and
allows good visibility for the diver.
Photos: Pump used to
power Capt. Dan Bergs water dredge. Fred Belise with engine room
bell recovered from the Lizzie D with a water dredge.
WATER
JET
 Using
the same pump as a water dredge and just changing the underwater
attachment to blow rather then vacuum. This type of unit works well
when its balanced properly. This means that the force of the water
jet will not turn into a propulsion vehicle and push the diver. The
benefit of using a water jet is for clay and other hard bottoms that
are just not easy to suck up with a dredge. The down side is
visibility is often reduced greatly and therefore its much harder to
find small items. We will often did through the hard clay with a jet
and then switch to a dredge for the majority of artifact recovery.
Enrique Alverez from techdivetools.com made both my jet and water
dredge. He makes a great product for anyone who is serious about
underwater excavation.
PROPULSION VEHICLE
 Using an
underwater propulsion vehicle as a excavation tool is not
exactly a scientific or manufacturer approved method, but since
these devices have become affordable, they have not only helped
divers to get to where they want to go but also fan away the sand in
order to search for artifacts. By turning a propulsion device away
from you while holding its front end against your chest and the
propeller pointed down, a diver or team of divers can dig a large
hole very rapidly. I prefer to use a model with an adjustable pitch
propeller. This way I can run on a low speed. Otherwise, as learned
from experience, instead of digging a hole, the diver is simply
propelled backwards. Two divers working as a team is the best way to
use this method. As a word of caution, this equipment was never
designed for this function. Mud, sand and dirt could get caught in
the trigger mechanism, causing the unit to stay on. Install a pin
that can be used to pull the trigger out in case of binding. If the
unit does jam in the on position, you can aim it downward so that it
runs itself into the bottom, allowing time to pull the trigger to
the off position. Another good idea is to secure the propulsion unit
to the wreck, so it can't swim away if the trigger does get stuck.
If the unit is secured correctly, it will also reduce the effort of
holding it in place and, therefore, reduce your air consumption.
MAIL BOX
The Mail Box or Prop Wash method of excavation is best left to
professional salvage divers. Home built units used on small boats
will work in shallow water of ten to 20feet or so, but the time and
effort of construction matched with immobility usually make other
methods more appealing to the average wreck diver. If, however, you
are doing a large excavation on a shallow site, a prop wash can be
built by constructing a large tube with a 90 degree elbow. This tube
has to be firmly mounted to the dive boat to capture her prop wash
and divert the force downward. The boat is usually anchored or
moored at four points to assure location integrity. The two stern
anchors take the most strain. When the engine is put into forward,
the bottom is dusted away. According to treasure hunter, Carl Fismer,
a safety cage can be mounted to the Prop Wash to allow divers to
work while the unit is being used. Divers should stay clear of the
boat when a Mail Box is in operation. According to THE
 UNDERWATER
DIG by Robert Marx, a simple but ingenious signal system was
achieved by using a weighted line attached to a horn on the boat.
Divers could then quickly signal the surface to turn off or start up
the Mail Box.
Photo: Treasure Hunter
Carl Fismers air lift for shipwreck salvage.
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The Shipwreck Diving E-Book
Instant Downloadable E-Book
Shipwreck Diving,
by Capt. Dan Berg is a complete how to book about the sport of
wreck diving. This book is packed with information and heavily
illustrated with over 80 sensational color photographs. |
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