Mooring Matters: Sustained Measurements of Crucial Ocean Currents

Mooring Matters: Sustained Measurements of Crucial Ocean Currents

For the next installment in our series of technical articles, Dr. Peter Spain of Teledyne RD Instruments discusses the development of ADCP technology and the use of syntactic foam buoyancy in subsea moorings for sustained measurements of ocean currents.

Sustained Measurements of Crucial Ocean Currents

Teledyne RDI ADCPs and DeepWater Buoyancy Deliver a Go-To Combo

By Peter Spain Ph.D., Teledyne RD Instruments

Current Profiling

ADCPs are sonar systems that measure motion underwater. Using sound waves, they work like hand-held radars used by police to catch speeding motorists. To measure motion, ADCPs emit sound bursts along beams angled upward or downward.

Echoes are returned due to scattering off particles. Because zooplankton and suspended sediments are carried by the moving water, echoes scattered off them carry a change in pitch; this is the Doppler Effect. It tells how fast the current is moving and in what direction.

Sound waves propagate through the water column so echoes are returned and processed from many depths. The vertical range of this collection of measurements—called a profile of ocean current velocities—is greater for lower frequency sound waves.

Introduction

Next to the eastern seaboard of continents stream the largest currents on the planet. They have been well-known to seafarers for centuries. Found around the globe, these major ocean currents are energetic, narrow and deep. They exist in all ocean basins, north and south of the equator: Gulf Stream, Kuroshio, and Brazil, Agulhas, East Australian Currents respectively.

These strong currents move much warm water poleward from low latitudes; thus, they redistribute heat for the earth’s climate system. On shorter time scales, they affect regional and local weather. These flows transfer organisms, nutrients, chemicals, debris, and pollutants – all affect life in and out of the sea and along coastlines. And strong currents affect routes selected by shipping.

Crucial ocean currents have been studied to measure their structure, transport, and fluxes—and, in recent times, their changes on seasonal and longer times scales. In ball-park numbers, these flows span 100 km, move faster than 100 cm/s, and carry 100 times the outflow of the world’s largest river.

Measuring these currents has been challenging. To capture their extent, measurements need to reach deep. To resolve changes over time, measurements need to be sustained. And to survive, persistent measurement methods need to withstand the energy of these powerful currents. For example, surface drifters, floats, and gliders are quickly swept away in strong upper-ocean currents.

Figure 1. Large ADCP Buoys with Teledyne RDI ADCPs off South Africa. Credit: SAEON Egagasini Node. http://asca.dirisa.org/

Programs making long-term measurements of important currents rely on resilient moorings. And for measuring strong currents in the upper ocean, these moorings carry ADCPs.

In this two-part report, we first review some background to moorings carrying Teledyne RDI ADCPs mounted in DeepWater Buoyancy buoys. Then we look at sustained measurements of crucial ocean currents in some less-familiar places.

Figure 2. William Richardson, pioneer of Buoy Group at WHOI. Credit: Nova Southeastern University. LINK

Background

Almost 60 years ago at WHOI [1], William. S. Richardson launched the modern era of ocean-current metering. For studying deep-sea currents—notably, the Gulf Stream—he identified and invented two essential tools: a recording current meter and an unattended mooring. Richardson’s intent for the mooring was to suspend current meters at several depths. The meters would record long time-series of currents simultaneously. For studying currents across large areas, Richardson deployed several moorings.

Over the next two decades, the Buoy Group at WHOI engineered this reality. Their impressive results were hard won in the harsh and unforgiving environment of the deep sea. You can read more at this link: 50-years-of-the-whoi-buoy-group. For the UK story, see this PDF: UK_moorings.pdf.

Along the way, one key problem was mooring loss. A leading culprit was large drag force caused by strong currents. The adjacent graphic shows a section of the Gulf Stream in the upper 2000 m. Speeds are directed along-stream. Notice the extreme current speeds in the upper ocean and the large spatial gradients.

[1] Woods Hole Oceanographic Institution. See Richardson et al. report (WHOI Ref: 63-1)

Figure 3. Gulf Stream currents and thermal structure. Distance: km, Current speeds: cm/s. Credit: Halkin + Rossby, 1985. LINK

For recording currents accurately, the meters need to hold position in three dimensions. The mooring must therefore be taut. To this end, sizable buoyancy is added to the mooring line. Yet, unavoidably, these elements increase drag forces exerted by strong currents.

Besides sweeping away moorings, strong drag forces caused mooring lines to pull apart (part way up) or to blow-over. The latter mooring motion carried instruments and mooring elements in large vertical excursions: 300-500 m in a tall mooring. See Fig. 4. These excursions confounded interpretation of measurements. Worse, the mooring could sink when in-line buoyancy was crushed by high pressure at unplanned depths.

Figure 4. Large vertical excursions of a mooring line in the Gulf Stream. Time series of two pressure sensors mounted in-line and separated by 200 m.  Credit: Hogg, 1986.  LINK

Mooring Changes

By the mid 1980’s, the design of both moorings and current meters had evolved substantially. Fig. 5 shows typical designs. Highlighted are important changes in mooring components. Notice the change in where buoyancy is added.

One strategy to decrease mooring losses was reducing drag. Major currents have strong near-surface speeds. To avoid these, moorings that terminated subsurface were developed. Many were topped with large spherical buoys. They provide the same buoyancy for less drag than smaller options. To solve the crushing problem during severe blow-over, these large spheres were made of syntactic foam.

Figure 5. Deep-sea moorings—pre ADCPs: Changes from early-1960’s to mid-1980’s. Credit: Richardson et al., 1963 WHOI Ref 63-1;  Molinari, 1986 LINK

Beginning with Hogg (1986), scientists introduced methods for correcting measurements confounded by blow-over of a mooring. As well, methods for evaluating the design and dynamics of moorings were more available. See Mooring Design and Dynamics

Figure 6. Spherical syntactic foam buoys housing Teledyne RDI ADCPs. Credit: NOAA. LINK

ADCPs

From the mid 1980’s, ADCPs provided a new solution for measuring strong surface currents. A mechanical current meter must be immersed in the flow it measures. In contrast, ADCPs are sonar systems; they can measure current velocity remotely. They emit an acoustic signal and then process the informational content of returning echoes.

Scientists realized that ADCPs looking upward could be used to measure strong surface currents while deployed in slower waters below. This helped reduce drag on the mooring. To this end, ADCPs were mounted in the flotation buoy atop subsurface moorings. Pioneering this approach was Friedrich A. Schott at University of Miami.

DeepWater Buoyancy’s antecedent, Flotation Technologies, developed these buoys as standard kit for ADCPs. Using syntactic foam for flotation elements permitted custom designs. Notably, a cylindrical instrument well was inserted along the vertical axis of the large spheres. Housing ADCPs in this sheltered location reduced current drag on the mooring. Since the late 1980’s, ADCPs have been commonly mounted atop a subsurface mooring within a collar of syntactic foam.

To further decrease drag on the mooring, new designs evolved for syntactic flotation buoys. An elliptical-shaped float that is more hydrodynamic became a common component on many deep sea moorings.

Figure 7. DeepWater Buoyancy Elliptical ADCP Buoy.  LINK

For measuring very strong currents, such as tidal streams, a torpedo-shaped buoy is now state-of-the-art. This approach reduces drag and increases stability in pursuit of moored nirvana—low tilt and minimal vertical excursions.

Figure 8. DeepWater Buoyancy StableMoor® Buoy holding Teledyne RDI ADCP. Credit: Bedford Institute of Oceanography. LINK

Moored ADCP Arrays

A mix of methods is needed to clarify the long-term effects of global warming. Moored arrays in major ocean currents provide an essential ingredient. Insights have come from researchers using computer models and satellite-based observations. And drifters, gliders, and floats can provide snapshots. Yet there is no substitute for hanging around in these deep and energetic flows.

For scientists to see long-term trends and large-scale connections, moored arrays must collect sustained time series. And for collecting this information Teledyne RDI ADCPs mounted in DeepWater Buoyancy flotation provide a go-to combination.

.   .   .   .   .   .   .  

 

In Part 2 of this report, we review some compelling examples of moored ADCP arrays measuring crucial ocean currents around the globe.

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About Teledyne RD Instruments

With well over 30,000 Doppler products delivered worldwide, Teledyne RD Instruments is the industry’s leading manufacturer of Acoustic Doppler Current Profilers (ADCPs) for current profiling and wave measurement applications; and Doppler Velocity Logs (DVLs) for precision underwater navigation applications. Teledyne RDI also supplies Citadel CTD sensors for a variety of oceanographic applications.

Learn more at www.teledynemarine.com/rdi/

2018 European Teledyne Marine Users Conference

2018 European Teledyne Marine Users Conference

Sponsors and Exhibitors

DeepWater Buoyancy is co-sponsoring and exhibiting at the first European Teledyne Marine Users Conference .  The event is being held in Cannes France, October 9-11.

We will be represented at the event by Dan Cote, our Sales Manager.  If attending, please be sure to stop by our exhibit table and visit with him.

 

About the Event

TMTW offers a packed, non-stop schedule that truly offers something for every level of users, from novice to seasoned pro.​

Morning sessions will be comprised of three concurrent tracks dedicated to presentations given by Teledyne users from around the globe, who will share their experiences, challenges and solutions using Teledyne products in a wide array of application areas, including:

  • Oceanographic Research
  • Hydrography
  • Offshore Energy
  • Civil Engineering / Infrastructure
  • River/Stream Monitoring
  • Security / Defense
  • Aquaculture / Fisheries​

Attendees are sure to learn new and helpful information from these sessions, not only from the speakers, but from the questions and answer, and interaction with their industry peers in these sessions.

Afternoon sessions are comprised of Teledyne Marine product / software training, new product and application introductions, Q&As with Teledyne’s technical teams, dockside and on-water demonstrations, one-on-one meetings, and an opportunity to visit with our top-tier co-spons​​ors to discuss their third party solutions and services.

Questions?  Please contact Margo Newcombe at margo.newcombe@teledyne.com.​

For more details about the conference: ClickHere

To register: ClickHere

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About Teledyne Marine

Beginning as a small collection of unique marine solution providers and expanding to a powerhouse of highly engineered, high performance solutions for a broad range of markets, Teledyne Marine now offers the largest breadth of marine technology in the industry.

With technologies divided into 5 core segments; Imaging, Instruments, Interconnect, Seismic and Vehicles, Teledyne Marine sales staff can address not only brand level solutions, but turn-key, customized systems that leverage our full range of technology. Our goal is to provide one-stop purchasing capability, world-wide customer support, and the technical expertise to solve your toughest challenges.

A Sea of Solutions…..One Supplier.

Learn more at teledynemarine.com

NEW Pop-Up Buoy for EdgeTech PORT LF-SD.

NEW Pop-Up Buoy for EdgeTech PORT LF-SD.

Announcement

DeepWater Buoyancy, Inc. announces that it has developed a new Pop-Up Buoy Recovery System (PUB) for the EdgeTech PORT LF SD Acoustic Release.  Like the original product, the new PUB allows for direct retrieval of seabed packages, such as anchors, anchor lines, and bottom-mounted frames and instruments.

The new product was developed with EdgeTech’s product development team at the request of Woods Hole Oceanographic Institute.

Pop-Up Buoy Product Details

Easily mounted to any framework, the assembly sits on the seafloor until the acoustic release is activated. Once the release completes its disconnection, the buoy lifts free from the canister and rises to the surface. A synthetic line connects the buoy directly to the framework of the seabed item and allows for retrieval.

The buoy is outfitted with an electropolished 316 stainless steel frame.  The canister holds 75 meters of 1/4″ synthetic line. (Other line lengths are available upon request.) The recovery buoy is made from high-strength DeepTec® solid syntactic foam. The foam is finished with an abrasion-resistant, polyurethane elastomer coating.

The canister is made from PVC and 316SS plate. It has a rugged design and has attachment features to permit various mounting configurations, including easy mounting to our BTM-AL50 tripod bottom mounts.

To learn more about the PUB – CLICK HERE

Acoustic Release Product Details

The PORT Push Off Release Transponder is ideal for deployments in coastal environments. The mechanical drive off system is the best choice for deployments where acoustic release mechanisms can experience growth or sediment build up. Its unique push-off mechanism provides reliable release every time.

The low frequency acoustic command structure is proven to be very reliable and is unsurpassed in multi-path environments.

Features:

  • All Aluminum components
  • Simple and easy maintenance
  • Small lightweight package
  • Medium load acoustic release
  • Full transponder capability
  • 1.25 years on alkaline batteries
  • Reliable and secure command coding
  • including Enable, Disable and Release commands
  • Purge Port
  • Auto Disable
  • Tilt & Release indication

To learn more about the PORT LF SD – CLICK HERE

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About EdgeTech

EdgeTech is a leading manufacturer of underwater technology solutions. The company is known worldwide for its high quality products which include: side scan sonars, sub-bottom profilers, bathymetry systems, AUV and ROV-based sonar systems, combined and customized solutions. In addition to the full line of underwater survey products, EdgeTech provides reliable USBL systems, transponder beacons, deep sea acoustic releases, shallow water and long life acoustic releases, MRUs and customized underwater acoustic command and control systems.

Learn more at www.edgetech.com

StableMoor® Buoys Support Ice Studies

StableMoor® Buoys Support Ice Studies

The Right Design

DeepWater Buoyancy’s StableMoor® Mooring Buoys have been chosen to support the “Stratified Ocean Dynamics in the Artic” (SODA) initiative headed by the Office of Naval Research.

The buoys were custom-designed and built to specifications provided by the University of Washington Applied Physics Lab and the University of New Hampshire.  These buoys will support instrumentation that will map the underside of sea ice in support of the research project.

 

About the StableMoor® Buoys

The pair of StableMoor® buoys were over 12 feet (3.5 meters) long in order to house the instruments required for the deployment.  Each unit was equipped with features to allow for an upward-facing ADCP, upward facing sonar, a velocimeter, and three battery housings.  Each unit provides 475 lbs (215 kgs) of buoyancy and is rated for 750 msw.

This product was chosen by the research team because of its unique performance characteristics. Specifically engineered for high current applications, the StableMoor® is designed to reduce drag and increase mooring stability in extreme flow regimes. By decreasing frontal area (compared to a standard spherical buoy) and increasing dynamic stability in high current areas, the StableMoor® minimizes mooring inclination and excursions.

Learn more about the comparison of buoy shapes in differing flow regimes HERE

Learn more about our StableMoor® buoys HERE

The University of Washington team is well acquainted with the value of the StableMoor® design.  These two buoys add to their existing units that they have been working with for the past three years.  Some of these buoys previously supported a challenging NREL project studying high flow/turbulence sites for subsea turbines.

Learn about the NREL application HERE

About the Research Project

From the research paper “Stratified Ocean Dynamics of the Arctic: Science and Experiment Plan – Technical Report APL-UW 1601”, September 2016, by Craig M. Lee et al.

Vertical and lateral water properties and density structure within the Arctic Ocean are intimately related to the ocean circulation, and have profound consequences for sea ice growth and retreat as well as for propagation of acoustic energy at all scales. Our current understanding of the dynamics governing arctic upper ocean stratification and circulation derives largely from a period when extensive ice cover modulated the oceanic response to atmospheric forcing, resulting in weak seasonality, at least within the deep basins.

Recently, however, there has been significant arctic warming (Overland et al., 2016), accompanied by changes in the extent, thickness distribution, and properties of the arctic sea ice cover. Summertime sea ice extent has been declining since at least 1979 (when satellite-borne passive microwave sensors began providing comprehensive ice maps; Perovich et al., 2012), with a trend of –13.4% per decade relative to the 1981–2010 average (Figure 1; Perovich et al., 2015; Thomson et al., 2016). September sea ice minimum extents from 2007–2015 are the lowest in the 1979–2015 period, with a record minimum of 3.39 million sq km in 2012.

Figure 1. Time series of Northern Hemisphere sea ice extent anomalies in March (the month of maximum ice extent) and September (the month of minimum ice extent). The anomaly value for each year is the difference (in %) in ice extent relative to the mean values for the period 1981–2010. The black and red dashed lines are least squares linear regression lines. The slopes of these lines indicate ice losses of –2.6% and –13.4% per decade in March and September, respectively. Both trends are significant at the 99% confidence level. From Perovich et al. (2015).

Sea ice has become younger alongside the decreases in extent (Figure 2). Sea ice thickness typically increases with age, such that the combined trends toward decreasing extent and younger mean age point to a persistent loss of sea ice volume (Kwok et al., 2009; Schweiger et al., 2011). Thinner, younger ice tends to be weaker, more subject to deformation and fracturing, and thus more mobile and more likely to provide efficient coupling between the atmosphere and upper ocean. Furthermore, the growing summertime expanses of open water provide periods when the dynamics might more closely resemble those that govern the upper ocean at lower latitudes.

The need to understand these changes and their impact on arctic stratification and circulation, sea ice evolution, and the acoustic environment motivate the Office of Naval Research (ONR) Stratified Ocean Dynamics of the Arctic Departmental Research Initiative (SODA DRI).

Figure 2. A time series of sea ice age in March from 1985 to the present (top) and maps of sea ice age in March 1985 (lower left) and March 2015 (lower right). From Perovich et al. (2015).

Download the full technical report HERE

Learn more at the research project website HERE

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

IN PRINT – Don’t Let the Ocean Knock You Down

IN PRINT – Don’t Let the Ocean Knock You Down

Article

DeepWater Buoyancy was found In Print in the December Issue of the Marine Technology Reporter.  The article was called “Don’t Let the Ocean Knock You Down”.  Written by Dean Steinke of DSA, the article is a print version of the DeepWater Buoyancy Mooring Matters article, Mooring System Numerical Modeling.

In the article, Dean discusses the role of finite element-based simulation and visualization software in mooring design.

See a PDF of the printed article HERE

See the Mooring Matters post HERE

Watch the simulation video HERE

 

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

NEW Mooring Line Cable Fairing

NEW Mooring Line Cable Fairing

Introduction

DeepWater Buoyancy, Inc. has added a new product to their successful line of Mooring Line Cable Fairings.  The new fairing is designed to accommodate 1/4″ jacketed wire rope.  It is the latest item in the company’s portfolio of products for subsea mooring systems.

Vortex-induced Vibration

Under certain flow conditions, taut mooring lines can vibrate or “strum”. The strumming is caused by vortices that result from the water passing over the line diameter. Strumming not only creates cable fatigue, it can have a detrimental effect on instruments in the mooring string.

Mooring Line Cable Fairing

DeepWater Buoyancy’s mooring line cable fairings reduce strumming by eliminating this vortex action.  Less strumming means less fatigue on the line. Additionally, the fairing design reduces drag on the mooring line resulting in less mooring layover. As an example, the drag coefficient for a 3/8” jacketed wire cable is 1.20, whereas the mooring line fairing is 0.17. This is an improvement of over 85%.

Fairings are made of durable ABS plastic. They are easily loaded onto the mooring line during deployment simply by separating the ends of the fins and installing over the line.

Unlike other solutions, this product can be installed over select portions of the line, requires no maintenance, does not suffer from tangling problems, and resists biofouling.

The standard units are designed for 1/4″ and 3/8″ jacketed wire rope and are 12” in length. Other diameters and lengths can be produced upon request. End clamps are also available to limit the vertical movement of the fairing on the line.

Learn More

Learn more about mooring line cable fairings HERE

Download a datasheet HERE

See all our product types HERE

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

For further sales information:  Dan Cote, Sales Manager  |  sales@deepwb.com  |  +1 207 502 1400

For further company information:  David A. Capotosto |  davidcap@deepwb.com  |  +1 207 468 8545

Mooring Matters:  Mooring System Numerical Modeling

Mooring Matters: Mooring System Numerical Modeling

For the next installment in our series of technical articles, Dean Steinke of Dynamic Systems Analysis Ltd., discusses the role of finite element-based simulation and visualization software in mooring design. 

He demonstrates this capability with a video of the simulation showing an analysis of our three different ADCP buoy geometries – spherical, elliptical and the unique StableMoor® design.

 


Mooring System Numerical Modeling

“Don’t let the ocean knock you down.”

Using dynamic analysis software to assess mooring deployment, recovery, and performance in current and waves.
By Dean Steinke, PEng – April 5, 2017

Introduction

For many years moorings have been designed using basic mass-drag-buoyancy calculations, spreadsheets, rules-of-thumb, black magic scripts, and a dose of ‘salty-sea-dog’ experience. With these methods, we can frequently estimate a line size to use or an approximate anchor weight. But sometimes despite our experience we still have questions. This article looks at increasing the precision of mooring analyses using numerical modeling software designed for ocean engineers.

Software for single point moorings has come a long way in recent years. Finite element-based cable analysis programs have been tested and developed by oceanographic institutions and ocean engineers for various purposes (towed bodies, ROVs, moorings, etc.). However, their use has been typically limited to a few advanced numerical modelling specialists who had both the expertise and patience to wade through the complex analysis process. In recent years, increasingly-refined software has been developed. This software has benefited from increased computational power and advances in 3D graphics. We can now get a much clearer picture as to what is happening with our moorings subsurface through simulation and visualization.

The video below demonstrates an analysis carried out by my firm, Dynamic Systems Analysis Ltd, using our ProteusDS software. Based in Canada, we have cut our teeth over the last decade simulating many different types of ocean technologies, including single point moorings.

Analyzing Buoy Pitch and Knockdown in Current

The video shows four buoys of various styles (spherical, ellipsoid, and streamlined) being loaded by current. As the current ramps up to 3.6 knots, the knockdown and pitch of the buoys increase. There are two key forces at play – buoyancy and drag. The buoyancy provides a vertical restoring force that keeps the buoy from pitching. Conversely, hydrodynamic drag pitches the buoys about their mooring connection point.

A pitch of greater than 20 degrees is not recommended for ADCPs, as the inclinometers which allow for compensation of buoy pitch typically only have a range of 20 degrees. Mooring designers would try to limit ADCP buoy pitch to only a few degrees if possible. In addition to uplift and drag, buoy pitch also depends on the length of the mooring and weight of mooring equipment (chain, shackles, line, etc.).

The example shows that increased buoyancy is effective in preventing knockdown and limiting pitch, as the AF49-750 buoy has the lowest pitch and knockdown of the elliptical and spherical buoys. However, this buoy still pitches significantly at the higher currents, whereas the streamlined StableMoor® buoy, with its reduced drag and configurable connection point, is effective at maintaining low pitch and knockdown.

The ProteusDS model uses 6 degrees of freedom for the buoys (heave, sway, surge, roll, pitch, and yaw). Although this case is essentially 2D, the solver solves for the position in 3D. The effect of the attachment point and location of drag loading affect the pitch calculated by the software.

Figure 1 The ProteusDS software pre-processor is shown. This software allows users to add mooring elements such as shackles and swivels from a central library. Line types such as Amsteel Blue or wire rope can likewise be selected.

Transient Loading and Acoustic Release Damage During Mooring Deployment

One aspect not often considered by mooring designers is what happens during deployment. As shown in the video, the simulation allows for prediction of launch transients, which ensures that shackles and lines are properly selected to handle the deployment loads.

We’ve observed that acoustic releases get damaged during deployment when they are placed too close to the anchor. ProteusDS can be used to check that the acoustic release’s downward momentum will not cause it to crash into the seabed or anchor.

Mooring Systems ADCP Simulation

Figure 2 Mooring deployment analysis showing launch transient loading.

Mooring System Recovery

A few questions I’m asked from time to time are: How long will it take for the mooring to come to the surface? and, How far might the mooring drift as it comes to the surface? The mooring recovery section of the video shows how you can assess this.

In the case considered, the AF36-750 mooring rises at about 2.7 meters per second. If this mooring was deployed at 750 meters, it would take between 4 and 5 minutes to surface!

Although no current was applied in the example, current can be applied in the simulation to determine how far it might drift in the time it takes to get to the surface.

Mooring Systems ADCP Simulation

Figure 3 ProteusDS post-processing software showing rendered view of the mooring systems being tested.

Interaction of Waves with Subsurface Moorings

Much like current, waves can cause an ADCP mooring to pitch and move. The example in the video shows the impact of the subsurface orbital wave motion on the mooring line and buoy. A JONSWAP wave spectrum is simulated to check how much the buoy will pitch. Clearly, in this case, a bottom mounted ADCP frame would be preferred – but we don’t always have the equipment we need on hand. It’s good to have tools to check the impact of waves on our moorings.

Conclusions

DSA has carried out a series of simulations in consultation with DeepWater Buoyancy using our ProteusDS software. The software is designed to help mooring designers and builders to answer practical questions about mooring performance. Most would agree that the software’s 3D visualization capabilities shown in the video are really cool, but I believe that the real value of the software is that we don’t have to speculate what is happening subsea. We can now get a clear picture.


About Dynamic Systems Analysis Ltd.

Dynamic Systems Analysis Ltd. is an ocean engineering consultancy and software company based in Canada. DSA provides progressive and accessible dynamic analysis expertise and software to enable those working with vessels, structures, lines and technologies in harsh marine environments to reduce risk. DSA provides software and services to the aquaculture & fisheries, defence, marine renewable energy, naval architecture, ocean technology, and offshore sectors.

Learn more at www.dsa-ltd.ca

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

 

ADCP Bottom Mounts for Aquaculture

ADCP Bottom Mounts for Aquaculture

DeepWater Buoyancy, Inc. announced the delivery of a significant follow-on order of diver-serviceable bottom mounts for one of the world’s largest fish farming companies.  The bottom mounts are set on the seafloor at a depth of 50 to 100 meters and allow for the proper deployment of ADCPs to monitor the environment around the fish farm cages.

ADCP’s are used in aquaculture applications in order to monitor currents and waves for the following main purposes:

  • Investigate new fish farming areas
  • Monitor currents when feeding in order to minimize feed loss
  • Monitor fish waste for pollution plumes

The order was secured by DeepWater Buoyancy’s UK representative, Saderet Ltd.  Saderet is the exclusive distributor of DeepWater Buoyancy products in the UK.  Saderet also represents Teledyne RD Instruments, makers of the Sentinel V50 ADCP, which was chosen for this application.

DeepWater Buoyancy, Inc.’s recently retooled BTM-AL50 diver-serviceable bottom mount line is equipped with a two-axis gimbal to mount an ADCP, clamps for a remote battery housing, and zinc anodes for corrosion resistance.  The three articulating footpads are provided with standard urethane-coated ballast, with additional ballasting provided for this application.

The client was pleased with the performance, delivery, and quality of the equipment supplied in the first order, as well as the ongoing technical support provided by Saderet, DeepWater Buoyancy and Teledyne RDI.

 

About Saderet Ltd.

Saderet Ltd. specialize in the supply of survey and positioning equipment and services to a wide variety of markets including marine and land survey, GIS, oceanography, precision agriculture, and OEM. Presenting some of the best manufacturers of survey related equipment in the world, we deliver products worldwide.

www.saderet.co.uk

 

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

www.DeepWaterBuoyancy.com

 

ADCP Bottom Mount Fish Farm ADCP Bottom Mount Fish Farm

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Mooring Matters: How Fast Does a Buoy Ascend?

Mooring Matters: How Fast Does a Buoy Ascend?

For the next installment in our series of technical articles, ocean engineer Jon Wood addresses an interesting question related to deployment and recovery of subsea mooring systems. Jon has decades of experience working with DeepWater Buoyancy’s oceanographic buoys.


 

How Fast Does a Buoy Ascend?

I’ve been asked that question frequently, since the ascent (or descent) rate of a buoy can be a consideration when planning for offshore operations.  Especially for projects in very deep water, it can take a long time for a mooring to reach the seabed, and an equally long, if not longer, time for it to float back to the surface.  In this article we will look at the forces involved, methodology for tracking the rate during deployment or recovery, and an example that might help you estimate.

So, “How long will it take?”  The true answer is, of course, “It depends!” It depends on the buoyancy of the buoys in the mooring and the weight of the line, instruments and anchor, as well as the drag forces imposed by all of the components.

We have measured these rates during several past mooring deployment and recovery operations.  By setting a hydrophone over the rail and ranging repeatedly on the mooring’s acoustic releases (4 or 10 second repetition rate, typically), we have been able to quantify both descent (deployment) and ascent (recovery) speeds for different mooring configurations.   Not all scenarios are the same but these data provide some ballpark estimates that may be helpful in planning future operations.

The two main factors that affect the descent rate of a mooring are the weight of the anchor (magnitude of the downward force) and the restraining effect of buoys and other mooring components (buoyancy and drag).  Within these restraining effects, the largest components are typically buoys as they have the most immediate influence.

The mooring reaches terminal velocity when the downward gravitational force equals the upward restraining force.  This seems to happen quickly once all components are submerged.   Upon release, the ascent rates are also governed by the magnitude of the upward forces (i.e. buoyancy), as well as the drag-imposed restraints of all mooring components.

As an example, we had a mooring consisting of a 49” spherical buoy (reserve buoyancy about 900 lbs). The buoy was connected to the anchor via approximately 1000m of wire rope.  The mooring also included two smaller (35” spherical) intermediate buoys plus assorted current meters.  The anchor was a 4800-pound pile of old scrap chain cobbled together from a local salvage yard.  After streaming out the mooring line from the vessel and free-falling the anchor (i.e. the anchor-last technique), the acoustic releases descended to the seabed at an average rate of about 3.0 meters/second.  In 1500m water depth, that translates to 500 seconds, or just over 8 minutes, for the mooring to settle.  On recovery, after the mooring was released from its anchor to float freely to the surface, we found the ascent rate was quite similar, about 2.8 meters/second.   Since the top buoy was positioned roughly 500m deep, it took about 3 minutes for the buoy to appear at the surface.

Here’s wishing that your next mooring deployment sees a soft landing!

Jon Wood

Ocean Data Technologies, Inc.

 


 

About Ocean Data Technologies, Inc.

Ocean Data Technologies, Inc. is a Massachusetts (United States) corporation providing oceanographic data acquisition services and support to the global offshore marine industry. Ocean Data designs and installs simple, reliable systems that collect information critical to our customer’s needs in deep-water, continental shelf, as well as nearshore and estuary regions.

Contact us at www.oceandatatech.com

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Contact us at www.DeepWaterBuoyancy.com

 

ADCP Spherical Buoy Deployment

Ocean Data Technologies recovering a spherical ADCP buoy 8 miles outside of Port Everglades, Florida, in the Florida Current (Gulf Stream), aboard the M/V Richard L. Becker. The ADCP mooring was for Dr. Alexander Soloviev of Nova Southeastern University. It was deployed for nearly 4 years, with regular 6-month turnaround operations (like this one), recording an impressive data set of Gulf Stream variability.

ONR/MTS Buoy Workshop 2016

ONR/MTS Buoy Workshop 2016

DeepWater Buoyancy is co-sponsoring and exhibiting at the 11th MTS Buoy Workshop sponsored by the Marine Technology Society (MTS).

The Workshop will be held at the Woods Hole Oceanographic Institution (WHOI), Woods Hole, Massachusetts, on Quissett Campus.  The workshop will run from April 18-21, 2016.

To learn more about the event,  CLICK HERE

On Friday the 22nd, participants have been invited to make the trip north to Maine for lunch and a tour of DeepWater Buoyancy’s Biddeford facility.  Afterwards, participants can continue on and take a tour of the Yale Cordage facility in the neighboring town of Saco.

To sign up for the lunch and tour simply send an email to sales@deepwb.com.

To learn more about Yale Cordage, go to www.YaleCordage.com.

To learn more about DeepWater Buoyancy, go to www.DeepWaterBuoyancy.com.

DeepWater Buoyancy Sponsors ADCPs in Action in Australia

DeepWater Buoyancy Sponsors ADCPs in Action in Australia

DeepWater Buoyancy is co-sponsoring ADCPs in Action in Australia (AiAiA) on May 12-14.  The event is being hosted by UVS Pty Ltd.  UVS is a long term partner of DeepWater Buoyancy and represents us in Australia.

ADCPs in Action events are Teledyne RDI programs that are held in San Diego, India, Australia and the Netherlands.

Learn more about the event here… http://www.uvs.com.au/AiAiA

Download the event program here… AiAiA-2015-Program

 

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