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Preliminary
Research Design
The investigation of these shipwrecks has the potential to be one
of the most significant studies of shipwrecks to date. The investigations
have the possibility of adding to the archaeological record information
that has previously been inaccessible. Because these shipwrecks
lie in deepwater, they have not been subjected to the effects of
strong tidal currents, surface wave action, high dissolved oxygen
levels, or diver exploration. The structure of the vessel’s
as well as the artifacts associated with them, have only been subjected
to natural bacterial and chemical processes and artifact shifting
as the vulnerable portions of the shipwreck disintegrated. As a
result, it appears that the wreck sites are far more complete than
any others that have been extensively investigated.
While many shipwrecks have been thoroughly and scientifically investigated,
all of them lie in shallow water and are exposed to the environmental
characteristics associated with shallow water. In deep water, only
limited investigations and salvage projects have been carried out
to date.
The primary purpose of our investigations will be to confirm the
sonar targets believed to be additional vessels and conduct detailed
surveys of each of the known shipwrecks. All of the investigations
will recover as much data about the sites as is technically feasible
with the least destruction of the archaeological fabric of these
shipwrecks.
A second purpose of these investigations will be to collect data
that will support the theory that deepwater shipwrecks are archaeologically
more complete than their shallow water counterparts. This data will
be critical for continuing to make the argument that deepwater shipwrecks
are scientifically worth the added cost of their investigation.
This case has yet to be proven through scientifically collected
data. Almost all investigations in deepwater to date have been documentary
in nature.
Detailed Non-Intrusive Mapping
In order to accurately interpret each of the sites, and the possible
association that they may have with each other, it will be essential
to document the precise location and orientation of all objects
associated with each of the them before any artifacts are disturbed.
This applies to the wrecks themselves as well as artifacts lying
on the ocean floor in the vicinity. For each wreck site, a survey
area 500 feet by 500 feet will be established to encompass all artifacts
related to the wrecks and any geologic features that have been created
by the deposition of the shipwreck in the bottom.
To accomplish this task, an medium sized, heave compensated ROV
system will need to be specially outfitted. That ROV will need to
have a variety of remote sensing, navigation, and speciality tools
and equipment installed, integrated, and tested prior to executing
the expedition. The ROV will need a side scan sonar, multi-beam
bathymeter, stereo cameras with lighting, and a sub-bottom profiler.
The ROV will also need to have a complex navigation suite consisting
of a deep-ocean transponder system with an integrated Doppler Velocity
Log (DVL) and an IMU to accurately measure heading, pitch, and roll.
All sensor data will need to be precisely geo-located. To accomplish
this, a high frequency bottom mounted positioning system such as
Sonardyne’s Extra High Frequency (EHF) LBL system will be necessary.
Sonardyne’s (EHF) system operates at 50-110 kHz with an accuracy
of approximately 2-15cm. In addition, precise and high frequency
platform telemetry information will be needed to accurately reduce
and synthesize the sensor data. Platform telemetry information should
include heading, pitch, roll, and speed over ground.
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The telemetry information can be gathered using a combination of an
Inertial Measurement Unit and a Doppler Velocity Log. None of these
navigation sensors are usually found on an ROV, however this type
of navigation system while complex has been successfully deployed
on ROV’s and many AUV’s and other systems previously. The
topside control of the ROV will need to have autopilot functions integrated
into it, so that a series of planned track lines can be executed with
the various sensors over the wrecks sites. Those track-lines will
need to be navigated parallel, level, and straight.
Initially, a high-resolution
side scan sonar survey of each shipwreck will be conducted. Lane spacing
will be approximately 50 feet with range scale set to 50 meters to
allow for approximately 300 percent coverage of the bottom. This lane
spacing and coverage will support the generation of a detailed sonar
mosaic of each wreck site. That mosaic will map each of the shipwrecks
and all objects external to the hull remains. The sonar survey will
also map any scouring and sedimentation changes adjacent to the wrecks.
A sonar frequency of approximately 500 kHz with a resolution of approximately
3” in both the along track and across track orientations will
be sufficient to complete the job. The sonar mosaic will serve as
an initial base map for the investigation of the shipwrecks.
Second, generate a precise hydrographic map of each of the sites and
the areas surrounding each of them, approximately 500 feet by 500
feet. To accomplish this, a narrow multi-beam echo sounder such a
Reson 8125 should be employed. That sonar has a resolution of 1-2cm
vertical with a beam width of .5 degrees. The multi-beam echo sounder
should be run over each of the sites on appropriate lane spacing to
accomplish a minimum of 150% coverage. The bathymetric information
should be corrected to account for tidal variation in the area; this
can be accomplished mathematically using one of several algorithms.
This narrow multi-beam echo sounder will provide initial three-dimensional
spatial mapping of the sites.
Third, collect digital sub-bottom data throughout the same 500 foot
area to accurately map the geologic environment on which the airplane
rests. Lane spacing should be set at intervals appropriate to map
small sub-seafloor geologic features in the area. The sub-bottom profiler
survey will provide information related to sedimentation in the area
and the overall site formation processes.
Fourth a stereo photo-mosaic should be created of the entire site
with a minimum resolution of 1/16th of an inch. This mosaic will serve
to document the overall condition of each of the shipwrecks and the
location of all objects external to their hulls. The stereo imagery
will also provide very accurate three-dimensional spatial information
of the hulls and related artifacts. The photo-mosaics generated from
this data will serve as the overall plan view of each of the site.
Environmental Information
Core samples should be collected throughout the 500 foot survey area
centered on each shipwreck in order to document the geomorphology
of the area and for later analysis of the site formation processes.
Chemical analysis of the sediments collected during the coring, will
provide information relative to the formation of the shipwreck sites
and the historical interaction of the shipwreck and artifacts with
the seawater and the bottom sediments. Distribution maps generated
from these samples will indicate historical current patterns and deviations
caused by the deposition of the shipwrecks and associated remains.
Additionally, the chemical analysis of the sediments will provide
information that will be significant during the conservation of any
recovered artifacts.
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Water samples should also be collected on, in, and around each of
the sites. A sampling plan should be devised that will capture chemical
and biological information for each of the shipwreck sites as well
as the area around each of them. Analysis of this information will
be significant during the conservation of any artifacts recovered
from the sites.
Diagnostic Archaeological Sampling
A detailed conservation plan will need to be drafted prior to the
recovery of any objects. That conservation plan should address methods
to be employed, funding sources, the conservation laboratory to be
used, and the ultimate disposition and storage of the artifacts. The
services of a qualified conservator, familiar with the conservation
of artifacts from a submerged ancient shipwreck, will be sought out
to draft the conservation plan.
Diagnostic artifacts should be recovered from each of the shipwrecks
to determine their age and provide preliminary information related
to the ships’ origin and last port of call. Those artifacts should
not be recovered until their precise geographic position and location
within the wreck are mapped in detail. A properly prepared recovery
basket with an emergency acoustic locating device that would provide
a method to relocate the objects should they be lost during recovery,
should be used to recover all artifacts from the seafloor.
In order to build the case for continuing to go to the trouble and
expense of investigating deepwater shipwrecks, it will be essential
to recover data from one of the shipwrecks that captures a cross section
of the information that is contained in these vessel remains. To capture
this data, it will be necessary to completely excavate a portion of
one of the vessels, recover all the artifacts from the excavated area,
and collect a series of biologic and chemical samples from the area
designated for excavation. It will be necessary to record locational
data related to the position of all artifacts in the designated area
to a precision where the area could theoretically be reconstructed.
The test excavation will consist of a meter wide trench that will
be excavated across one of the shipwrecks. The trench will be excavated
in approximately 10 centimeter vertical levels and divided into 1
meter long subsections. At the beginning and end of the excavation
of each level, stereo photographs will be taken of each 1 meter square.
As artifacts are completely uncovered during the excavation, they
will be tagged with a unique identifier indicating both their horizontally
and vertically locations, a stereo photograph taken, and then they
will be placed in the recovery basket. Once the entire trench is excavated
a photo-mosaic run will be made along the entire trench and all artifacts
remaining in the trench recovered. It is not anticipated at this time
that the ship’s structure in the test trench will be recovered.
Once the excavation is complete, the test excavation will be back
filled with sediments from the surrounding area.
In terms of excavating the test trench, it is envisioned that in order
for the ROV system to gain the stability that will be required to
accomplish the complex tasks that will conducted, a light weight scaffold
or bridge will need to be constructed that will span the width of
the wreck. This bridge will provide a stable platform that the ROV
can attach itself to while it is excavating the test trench and recovering
the artifacts. A variable suction water pump that will drive a venturi
dredge of 3-4 inch diameter and a highly dexterous set of 7 function
manipulators will be necessary to conduct the excavation. The dredge
will need to have an outflow hose long enough for the outflow end
to be secured a short distance down current of the excavation site.
At the end of the dredge outflow hose will be attached a mesh net
to capture any small artifacts that are accidentally ingested.
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