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.
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.
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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