Final Report
Testing of Instrumentation for WISSARD
Lake Tahoe, August 20-30, 2012
Lidar bathymetry (US-ACE) + Landsat (provided by Gordon Seitz – CSGS)
Ross D. Powell
&
Reed P. Scherer
Department of Geology and Environmental Geosciences
Northern Illinois University
1. Summary
This report summarizes outcomes from testing of instrumentation for use in the
Antarctic field operations of WISSARD (Whillans Ice Stream Subglacial Access
research Drilling). The testing was carried out in Lake Tahoe, CA, in August
2012. Instrumentation that was tested included a suite from Northern Illinois
University (including Instrumentation Packages for Sub-Ice Exploration – IPSIEs,
a hydraulic percussion corer, a multicorer, and a multipurpose winch and smart
cable umbilical), and from University of California at Santa Cruz (including a
piston corer and geothermal probe).
Testing showed that most instrumentation and equipment is ready for shipping by
early October 2012 without further work. Some modifications are underway to
make equipment handling easier and more efficient and those should be
complete by shipping time. Some instruments require “tweaking” to either
enhance their operation for high quality data, or to improve their surface
communications; these too will be completed before shipment.
2. Objectives
Testing of instrumentation for use in the Antarctic field operations of WISSARD
(Whillans Ice Stream Subglacial Access research Drilling) this coming season
occurred during August 20-30, 2012 in Lake Tahoe, CA. Instrumentation included
a suite from Northern Illinois University (including Instrumentation Packages for
Sub-Ice Exploration – IPSIEs, a hydraulic percussion corer, a multicorer, and a
multipurpose winch and smart cable umbilical), and from University of California
at Santa Cruz (including a piston corer and geothermal probe).
The major reason for our testing was to assess and learn how: (i) to
modify/improve engineering design to ensure effective communication with, and
data streaming from, the scientific instrumentation, (ii) the equipment will meet
standards of the WISSARD project in terms of cleanliness and ease of handling
and cleaning; and (iii) the equipment will be best loaded/unloaded and
transferred for downhole operations in Antarctica. In addition, we wanted to test
the winches and smart cable/umbilical, assess instrumentation behavior and
sensitivity, including the operation of the Water Distribution System (WaDS) of
the IPSIEs, and the instrument communications and data-management systems,
and the effectiveness of the percussion coring system.
Ultimately our plan was to target some science goals, working in conjunction with
the California State Geological Survey and the Tahoe Environmental Research
Center. The science goals necessarily were ancillary to instrumentation testing,
but were possible once testing was complete and provided all equipment was
working well.
3. Background
Lake Tahoe is situated in a granite graben near the crest of the Sierra Nevada
Mountains on the CA-NV border, at 39oN, 120oW and 1895m amsl (see cover).
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The lake is 33km-long by 18km-wide with a surface area of 500km and total
volume of 156km3. It has an average depth of 330m and a maximum of 501m.
With these characteristics, Tahoe was thought to provide a good testing
environment for Antarctica in terms of its depth and water quality.
Major participants in the testing and their responsibilities were:
• DOER-Marine – contracted by NIU to design and build most of the
equipment to be tested. Prime control of test plan and operations in
consultation with NIU.
• Tahoe Marine and Excavating – contracted by DOER to operate the barge
platform used for all testing operations.
• Northern Illinois University (NIU) – owner and ultimately operator of much
of the instrumentation to be test. Scientists tested the scientific
instruments included in the equipment designed by DOER.
• University of California, Santa Cruz – included scientists and engineers to
test the instruments designed and built at UCSC. They also provided a
ferrying link to and from shore during barge operations.
• California State Geological Survey – included a scientist, Gordon Seitz
who was interested in earthquake activity and history of Lake Tahoe. He
will write-up scientific results from the testing.
• Tahoe Environmental Research Center – were not involved in testing
directly, but provided access to their Tahoe City facility for us to use
storage space and wet-lab access when we needed.
• Scripps Institution of Oceanography provided an ROV for observing
subsurface behavior of equipment.
4. Daily Operations and Achievements
Nine daily field reports were circulated to interested personnel and are available
for reading at http://www.niu.edu/geology/news/submersible_testing.shtml.
5. Outcomes
Overall, most of our goals for the testing were achieved, even though there were
some frustrations with the operating platform and in losing some instrument
components. The major outcomes can be grouped into two categories: science
instrumentation, and engineering and operations.
5.1 NIU IPSIEs (Instrumentation Packages for Sub-Ice Exploration)
These units include a range of sensors that are designed for regular
oceanographic and limnological uses. However, they have been redesigned from
their common profiling deployment arrangement in a rosette, into a vertical array
to fit down an ice borehole. To achieve this and ensure they are all sampling the
same water, Tygon tubing connects them with an intake in the Bottom Stage
(Fig. 1) and a pump below the Power & Telemetry Stage to draw the water up
through each stage.
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Figure 1: Engineering schematic layout of the POP (Physical Oceanography Package) and the WIPSIE (Water chemistry
Instrument Package for Sub-Ice Exploration) of the IPSIE sensors: 1- Contros nutrient stage (HydroC - CO2, CH4), 2Envirotech nutrient stage (PO4, SiO4, NH4, NO 3), 3- Envirotech water-bag sampler stage, 4- Bottom stage (down- and sidelooking cameras with LED lights, Wetlab fluorometer and optical-backscatter (FLNTU), Contros electromagnetic current
meter, Tritech altimeter), 5- WaDS pump stage, 6- lifting power and telemetry stage, 7- Physical properties stage (Seabird
CTD and dissolve oxygen sensor, LISST Deep particle-size analyzer, Wetlab CStar transmissometer, Nortek Aquadopp
Doppler current meter).
The IPSIEs are designed in stages whose instruments can be connected
together through the WaDS and electrical whips using flanges (Figs. 2 and 3) to
bolt together their outer steel tube casings. All the instruments are mounted in
racks that then slide in the protective casings, which also have ports for those
that need to be open to the water (e.g., Aquadopp) or those to which we need
access.
Figure 2: Steel flange used to bolt IPSIE stages together.
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Figure 3: The WaDS system showing the Tygon tubing on the left, water flowing from the outflow at the end of the tubing
in the left center, and the pump on the right. The pump itself is located at the top of the IPSIE units to draw the water
upward from the bottom to enable all instruments to sample the “same water” and also to lower the chance of cavitation by
drawing water up rather than pushing it.
We are planning to use two configurations of stages and instrumentation in
Antarctica for WISSARD. One configuration is the Physical Oceanographic
Package (POP) and the other is Water chemistry Instrument Package for Sub-Ice
Exploration (WIPSIE) (Fig.4). All instruments within each configuration are listed
in Figure 1 caption and are shown in additional figures set in their racks.
IPSIEs are deployed on a strengthened fiber-optic umbilical or “smart cable” and
winch (Fig. 5), the cable being directly terminated to the top Power & Telemetry
Stage (Fig. 6). The other end of the fiber-optic cable is connected directly to the
topside data system that, processes, plots, and archives all of the instrument
data in real-time. Algorithms are built-in to the custom-designed data processing
software to synchronize the data from each instrument in time and depth by
using the known flow rate through the WaDS. These two stages are deployed
each time with the IPSIE.
The other stage that is always attached in IPSIEs is the Bottom Stage (Fig. 7).
That stage is important because it houses a Tritech altimeter to provide real-time
distance above bottom. The Bottom Stage also contains side-looking and
downward-looking cameras to help visually with any issues in the borehole and
as we descend through the water column and stop just above the sediment floor.
In addition, to these two critical components the other instruments in this stage
are the Wetlab fluorometer and optical-backscatter (FLNTU) and Contros
electromagnetic current meter that can determine velocity directly at the base of
IPSIE.
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Figure 4: Bottom center – IPSIE stages lying on the deck with connecting WaDS hoses and
electrical whips extending out through their flanges. IPSIEs are then hoisted vertically from the
horizontal by one end and then can be deployed vertically.
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Figure 5: Winch with level wind and HPU box spooled with the smart cable or armored umbilical with
strengthening steel wires around fiber-optics fibers and power wires all cased in non-polluting and cleanable
jacket.
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Figure 6: Motor and electronics stage with “telemetry brain” that is enlarged at the bottom left. The internal units of
this stage are being slipped into the casing and it is then hoisted vertically to be connected to the WaDS stage with
electronics and hydraulic hoses that are then primed before final set-up.
Figure 7: The bottom stage that includes cameras, altimeter, fluorometer and
optical-backscatter (FLNTU) and electromagnetic current meter.
The EnviroTech water bag sampler can collect six samples on one deployment
(Fig. 8) and is a stage in itself. It can be deployed with both the POP and WIPSIE
configurations.
Figure 8: The EnviroTech water bag sampler with 48 ports for 1L sample bags. Due to space we will be able
to collect six samples per deployment in bags that are housed within protective plastic sheet (left image) in the rack.
The POP configuration focuses on physical measurements of the water column
(Fig. 9). Instruments that complete this configuration in addition to the Water
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Sampler and the Bottom Stages, include a Seabird CTD and dissolve oxygen
sensor, a Wetlabs CStar transmissometer, a Sequoia Scientific’s LISST Deep
particle-size analyzer and a Nortek Aquadopp Doppler current meter (Fig. 10).
Figure 9: Engineering schematic layout of the POP (Physical Oceanography Package) and the WIPSIE (Water chemistry
Instrument Package for Sub-Ice Exploration) of the IPSIE sensors: 1- Contros nutrient stage (HydroC - CO2, CH4), 2Envirotech nutrient stage (PO4, SiO4, NH4, NO 3), 3- Envirotech water-bag sampler stage, 4- Bottom stage (down- and sidelooking cameras with LED lights, Wetlab fluorometer and optical-backscatter (FLNTU), Contros electromagnetic current
meter, Tritech altimeter), 5- WaDS pump stage, 6- lifting power and telemetry stage, 7- Physical properties stage (Seabird
CTD and dissolve oxygen sensor, LISST Deep particle-size analyzer, Wetlab CStar transmissometer, Nortek Aquadopp
Doppler current meter).
The WISPIE configuration (Fig. 9) includes chemical instrumentation for
measuring nutrients in the water column. It includes two stages: the Contros
Nutrient Stage that has HydroC sensors for CO2 and CH4, and an EnviroTech
Nutrient Stage with sensors for determining PO4, SiO4, NH4 and NO3. In-line
filters at the limits of sand, silt and clay are mounted before water enters these
nutrient sensors and can be used to quantify transmission (CStar) and
backscatter sensors (FLNTU) and to verify particle size estimates of the LISST
Deep (Fig. 11).
5.1.1 Engineering outcomes
Both the Power and Telemetry Stage performed well in our testing, as did the
WaDS pump stage, although the latter needs modification to fully integrate the
CTD and size analyzer (see 5.1.2).
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Figure 10: The POP Stage with a Seabird CTD and dissolve oxygen sensor, a Wetlabs CStar transmissometer,
a Sequoia Scientific’s LISST Deep particle-size analyzer and a Nortek Aquadopp Doppler current meter
Fitting the EnviroTech water sampler and its sample bags, WaDS tubing and
wiring whips within its rack and into the casing was very tight, and so some
modifications are being made by DOER to make that process easier in the field,
including new wiring and connectors and tubing. There was also an issue of
some water leakage into the unit and that is being addressed at DOER too.
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Figure 11: WIPSIE configuration that includes two stages: the Contros Nutrient Stage that has HydroC sensors for CO2 and CH 4
(center image), and an EnviroTech Nutrient Stage with sensors for determining PO4, SiO 4, NH4 and NO3 (outside two images).
5.1.2 Science outcomes
All of the instruments in the Bottom Stage worked well in their communications
with the surface and in data generation (Fig. 12). Communications with the
EnviroTech water sampler are good at the surface, but there were issues once
submerged. These issues are being worked on at DOER now so it can be
commanded to collect samples (up to 1L) where needed in the water column.
Figure 12: Topside
computer command
center with display and
archiving of all
instrument data in realtime.
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Figure 12: Descent profiles of different variables measured by the IPSIE instruments in Lake Tahoe. These data show that the
instrumentation was working appropriately with one major issue that is being modified. The CTD/DO data were obtained with
the instruments outside of the WaDS system and thus were affected by a delay time for water mixing into the casing during
descent. The strange “kicks” in T, O and turbidity (~30m depth in top profile and ~50m depth in bottom profile) are due to
turbulent mixing and bubble creation in the water as the barge was being moved (noted on our event log records and seen on
the video from the downward-looking camera). Kicks in the plots at the bottom show where IPSIE came close to the lake floor.
These data are comparable to those collected over many years by the TERC group.
Each of the sensors in the POP configuration performed well with surface
communications and in generating appropriate data (Fig. 13). However, two units
require modification in the POP configuration to integrate them completely into
the WaDS – the Seabird CTD/DO and the LISST Deep, and DOER is currently
carrying out these modifications.
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The Contros sensors in the WIPSIE configuration are communicating well and
providing data, but the EnviroTech units have had communications issues that
have been a combination of the units themselves and the telemetry system of the
IPSIEs. DOER is in the process of trouble shooting this problem. Like the water
sampler, these EnviroTech units are a tight squeeze in the casings and we are
modifying the WaDS hosing, whips and chemistry bags within the racks for
easier handling in the field.
Two descent profiles of different variables measured by the IPSIE instruments in
Lake Tahoe are shown in Figure 13. These data show that the instrumentation
was working appropriately with one major issue mentioned just above, that is, the
CTD/DO data were obtained with the instruments outside of the WaDS system
and thus were affected by a delay time for water mixing into the casing during
descent. The strange “kicks” in T, O and turbidity (~30m depth in top profile and
~50m depth in bottom profile in Fig. 13) are due to turbulent mixing and bubble
creation in the water as the barge was being moved (noted on our event log
records and seen on the video from the downward-looking camera). Kicks in the
plots at the bottom show where IPSIE came close to the lake floor and caused
slight disturbance. These data are comparable to those collected over many
years by the TERC.
5.2 NIU Percussion Corer
The percussion corer (Fig. 14) is designed to be lowered to the lake or sea floor
on the smart cable of the multipurpose winch, and then to hammer a core barrel
up to 5m-long into stiff over-consolidated sediment such as subglacial till. As the
corer is deployed, a 2000lb mass is released within its casing by unbolting an
Figure 14: DOER engineering CAD of the NIU Percussion Corer
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extension section from inside the casing (Figs 15 and 16; refer to pink section in
Fig. 14). Once deployed on the sediment surface, the hydraulic motor is
commanded to drive a piston that raises the mass to its maximum height within
its casing, and then is tripped to be released in a free-fall, to then strike a plate
on the top of the core barrel. This process is automatically repeated every 20-30
seconds until commanded to stop.
Figure 15. Upper stages of the percussion corer including the power and hydraulic motor stage and
the telemetry stage. Below these is the drop-weight stage (the weight can be seen through the holes
at the bottom of the stage in image on the left.
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Figure 16: Unbolting the extension section to release the drop-weight before deploying the
percussion corer. On the right, the corer is at its full extent with the 5m core barrel being the
lowest stage.
A linear position sensor is used to measure the penetration distance with each
strike. Coring is stopped when there is either a lack of further penetration or the
5m-barrel is fully buried in the bottom sediment. To avoid large pullout strains
beyond the capacity of the cable, which is 10,000lb, the hydraulic system is
designed to help extract the core barrel. The hydraulics can be commanded to
force pressurized-water down between the core liner and core barrel; the water
exiting via jets through holes in the core cutter head (Fig. 17). The water is then
forced up the outside of the core barrel to decrease friction between it and the
sediment.
Figure 17: Specifics of the core barrel of the percussion corer. Clockwise the images are: water jet holes at the base of the
drop-weight stage that attaches to the top of the core barrel; top flange of the core barrel with water jet holes; linking the base
of the drop-weight stage to the core barrel (two images); core cutting head; looking up the core cutting head at the core catcher;
the core liner exposed without the core barrel attached to the core cutter with custom sealing ring with water jet holes.
Also for added safety if the hydraulic flushing process fails to extract the barrel,
weak-link bolts that fail in tension will break away at the top of the barrel so that
the rest of the corer assembly can be recovered and only the barrel is lost.
5.2.1 Engineering outcomes
Initially there were issues with having enough hydraulic pressure to drive the
drop-weight vertically at its designed speed. Adjustments to the hydraulic system
were made and then the weight behaved as expected. DOER is making
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modifications to the hydraulic system design to permanently accommodate the
adjustments made for efficient operation of the drop-weight.
The other main issue was that the weak-link tension bolts were shown to fail in
shear in addition to the tension for which they were designed. On one of its
deployments, the core barrel penetrated the lake floor sediment, but when it was
resting at a ~15o angle, the weak bolts failed under the strain and sheared off,
releasing the core barrel. All of this was observed with the ROV and DOER is
redesigning the bolts to accommodate more shear force. The bolts are being
slightly modified so they are stronger in shear, but will still fail under high tension.
The hydraulic water flushing system worked as expected.
5.2.2 Science outcomes
We selected sites on the bottom of Lake Tahoe that have highly consolidated
sediment that we consider to be till from the last glacial maximum underlying a
thin cover of very gravel-rich (granules to boulders) biogenic mud (Fig. 18). This
type of setting could well be what we will need to be sampling in Antarctica. The
corer performed as designed except for the initial slowness of the hammering
process as described above. Only short cores were recovered due to the slow
hammering process until the bolts sheared and we lost the core barrel. Even
though the cores were short, the corer showed that it is easily capable of
penetrating these types of sediment.
Figure 18: ROV images of the percussion corer penetrating coarse sediment on the lake floor. Upper middle image shows
the drop-weight stage at the top of the core barrel. Top right image is the base of a stiff till sample within the core cutter.
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5.3 Uwitec Multicorer
The multicorer is a lightly modified off-the-shelf system designed by the Swiss
Uwitech Company (Fig. 19) that is well-tried in many lakes around the world. It is
designed to take three replicate cores at the one time after self-triggering on
striking the bottom sediment during descent. It recovers undisturbed top-most
sediment, the sediment-water interface and the bottom water in contact with the
sediment in each of the tree core liners. Thus it is also an effective bottom water
sampler. It also comes with a custom sediment slicer with which you can extrude
sediment in discrete intervals for sequential sampling through the top-most lake
floor sediment.
Figure 19: Uwitech multicorer that takes three replicate cores at once preserving the top-most sediment, the sediment-water interface
and the water column. Two bottom right images show a sample being recovered.
5.3.1 Engineering Outcomes
There were no engineering/design issues with the Uwitech corer.
5.3.2 Science Outcomes
The Uwitech corer provided the upper-most lake floor sediment, the undisturbed
sediment-water interface, and the bottom lake water and performed very well, as
per its specifications (Fig. 19).
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5.4 Top-side Data Management and Instrument Communications
Initially there were issues in communicating with several instruments via the
telemetry system in the IPSIEs and then through the 3km of fiber optics in the
smart cable. Modifications of the customized software quickly improved
communications, although there still appears to be some issues with the
EnviroTech instruments that are currently being worked on.
We are now in a situation where all of the instruments are under direct command
from the surface through the customized software, which has been modified from
each of the packages that come with the instruments. In this way, each
instrument can be commanded from an integrated interface running on a single
workstation. Likewise data streaming up to the surface are also being collected in
a customized software package and being displayed real-time through that
package and simultaneously being stored as raw ASCII data files (Figs. 12 and
13), including back-ups. This includes video streams from the cameras. Where
appropriate, we will also recover any binary data, logged in each instrument’s
original proprietary format.
5.5 University of California Santa Cruz Instrumentation
UCSC instrumentation to be tested included a piston corer with its own winch
and cable that is modeled on the previous CalTech corer (Fig. 20), and a
geothermal probe modeled on those used by IODP.
Figure 20: Preparing and deploying the UCSC piston corer. Bottom right image is from
the ROV of the protruding bent core barrel with its lower section being stuff in stiff till.
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The piston corer was deployed and appeared to work appropriately; however, it
was not recovered and remains on the floor of Lake Tahoe. As it was deployed
and struck bottom, the barge platform started drifting in the wind and waves. The
movement placed a strain on the cable because, as we found later, the core
barrel was embedded and stuck in the stiff till sediment sampled during
percussion coring.
The piston core winch was not strong enough to extract the core barrel,
especially with the angle on the cable due to barge drift. The cable was cut and a
buoy placed on the surface to mark its location. The ROV was then deployed
from the barge and the corer was found and seen to be stuck, with a bent core
barrel, in the sediment (Fig. 20). The ROV with manipulator arm made several
attempts to recover the corer, but unfortunately they all failed.
Due to a significant amount of operational time being lost to problems of
anchoring and stabilizing the barge for operations in wind and waves, there was
no time during the Tahoe testing to deploy and test the geothermal probe. Ian
Griffith of DOER offered to assist the testing of the probe at their facility, which
was completed on September 17 and is described in a separate report by Ken
Mankoff.
5.6 Additional Engineering & Operations
Other components to be used in Antarctica beyond the direct instrumentation
were also operationally assessed in their performances.
5.6.1 Hydraulic motor and Telemetry Stages
Both the Power and Telemetry Stages performed well in our testing after some
adjustments were made in the hydraulics and in the Ethernet cans used in
communications between the surface and the instruments. Due to some
leakages, pressures in the hydraulic system were adjusted in the field to improve
operations of the whole hydraulic system. DOER is making modifications to the
hydraulic system design to permanently accommodate the adjustments made for
efficient operation. Minor adjustments were made in the field to the “telemetry
brain” and it worked well afterward; no more adjustments are required.
5.6.2 Casings, Flanges, Racks, WaDS, Whips/wiring
Casing and flanges showed appropriate structural integrity and strength to stand
up to handling required in the field. More access holes will be cut in the casings
for easier access to the instruments and for cleaning. Bolting of the flanges in the
field may be a slow part of the operation. Fitting of the racks, with WaDS tubing
and instrument telemetry whips, was an issue and are being modified before
shipping for easier use in the field. Whips and tubing will be fitted and customized
for each stage so once in, can be joined through the flanges to the next stage.
More room will be made by relocating them within the problem racks so as not to
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get hung up on the casing. The WaDS system also needs modification to fully
integrate the CTD and size analyzer (see 5.1.2).
5.6.3 Smart winch and umbilical operation and handling
The smart winch worked well. Its gearing and computer control is being adjusted
so it can descend at faster rates to increase the speed of penetration of the
geothermal probe as it enters the sea floor. There was a minor issue with the
level wind that will also be adjusted before shipping.
The smart cable behaved well and met expectations. It needs to be re-terminated
to the Power Stage after a stressful bending at the connection during the learning
process of how best to handle the equipment.
5.6.4 Load transfer
The load transfer stanchion constructed at the side of the barge worked well in
operations Fig. 21). It is a helpful template for design of the load transfer cage to
be used at the moon-pool above the ice borehole.
6. Conclusions
This testing in Lake Tahoe of instruments and equipment for the WISSARD
project in Antarctica has shown that the bulk of them are ready to ship to
Antarctica. Some issues with the instruments and equipment were highlighted
during the testing process and NIU, DOER and UCSC are currently dealing with
these in order to meet the shipping deadline of early October and to be further
tested near McMurdo Station.
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Figure 21: Load transfer procedure from the crane to the smart cable and winch,
and then over a sheave and load-transfer stanchion on the side of the barge.