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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