This page was printed from https://www.ifai.com

Tackling heavy duty projects

March 1st, 2013 / By: / Advanced Textiles, Projects

IAA award-winning safety and protective projects tackle unique challenges and succeed.

Imagine a 41,000-ton U.S. Navy vessel traveling at seven knots in choppy three-meter-high seas. It is carrying a heavy load of vehicles and container freight. Because of an emergency, the vehicles and containers need to be transferred from this vessel to a supply ship, also traveling at seven knots.

To do this, the vessels have to be slowed to three knots, but with the propeller thrust on both remaining at seven knots to maintain steerage—and they need to be held on course, seven meters apart, for several hours while freight is transferred by crane.

The solution

W.A. Coppins Ltd., Motueka, New Zealand, was engaged to design, test and manufacture a para sea anchor (PSA) system for the U.S. Navy fleet to hold container ships in position while at sea. With the vessels abreast, the PSA was to be released electronically from its own deployment bag, holding the ships seven meters apart, and at safe speed, for several hours while the transfer took place.

The client had been seeking solutions for several years; it was a key component of the U.S. Navy’s STLVAST (Small to Large Vessel at-Sea Transfer) plan, which supports the Navy’s vision of supplying humanitarian aid or projecting military power without the use of a traditional port or shore-based facility. Therefore, transfers needed to occur between large vessels at sea. The system had to work flawlessly every time.

The company determined what was needed:

  • a strong, light, fabric sea anchor;
  • an electronic release system;
  • a reliable deployment system;
  • a robust fabric buoy to hold the anchor at the right depth under the surface, in changing conditions;
  • a compact shell to hold and protect all the components for easy handling and use.

The company was also faced with a tight deadline: less than 12 months to achieve their goal—and prove that it would work. Specifically, the company had to overcome a variety of challenges to complete the work within the deadline.

Logistics. W.A. Coppins Ltd. is a small business in coastal New Zealand. The system it was asked to create was for the U.S. Navy, half a world away: designed, built, tested, and modified in New Zealand, and then tested in the U.S., based on available ships. Tidal flows at a wharf near the company were used to develop and modify the PSA and show it the client, at close quarters and from the comfort of a dry wharf.

Design. The load size that needed to be accommodated—200 tons—created design challenges: effective connections to ropes and shrouds; designing a deployment bag of limp fabric that would stay upright and release without tangling; and a buoy shaped like a grader blade that could be driven into the sea to drag the PSA from the bag.

Components. Worldwide searches for the strongest rope, fabric, webbing and thread were undertaken to provide strength previously considered unachievable. The company sourced extra-high-tenacity nylon to take more than six tons per square meter. Dyneema® webbing from DSM, headquartered in the Netherlands, was chosen, because it’s strong but able to be sewn with several layers of reinforced fabric. Custom fabric was supplied by W. Wiggins Ltd., Wellington, New Zealand.

Construction. Extra care and tests were needed so the nylon and sewing were not stretched to the breaking point, and with no bobbin changes in any panel join. Sewing the 80-panel PSA had to be accurate, and absorbing exactly 85 millimeters of fabric in each seam required skill.

Status. W.A. Coppins is a relatively small, family-owned company; it needed confidence in its knowledge and expertise to complete the work—often using low-tech methods—for its very large client, the U.S. government, whose respect was inspirational for the company.

Passing the test

The system was taken to sea out from San Diego, Calif., for full-scale tests, where it was deployed from the R/V Robert Gordon Sproul, a 125-yard research vessel. The dragline was transferred from the newly launched 229-yard, 41,000-ton vessel, the USNS Washington Chambers, which towed the PSA for release, drag and steerage tests. The system performed 100 percent in every area, and was pronounced a success.

The U.S. Government has since compiled a list of 43 potential uses for the company’s new PSA product, including possible contracts with oil companies. Additional projects are in process with the U.S. Navy, based on the success of this one.

In addition, the design of the super-strength PSA has led to a new range of lighter and stronger PSAs for larger vessels beyond what was previously thought possible.

Controlling methane gas

Biogas storage is a fundamental part of all anaerobic digestion systems and is used to regulate the supply of methane gas produced from the decomposition of slurry and organic waste. A membrane gas holder is designed to work like a flexible lung, increasing in size to accommodate extra gas when the anaerobic digester plant is producing more than required and accurately supplementing the supply when the plant is not providing enough.

The triple membrane biogas holder by Base Structures Ltd., Bristol, United Kingdom, is, in effect, two balloons that are held squeezed together in a tight constricting space. One balloon is filled with biogas, the other with air. Instead of losing money by burning off the excess gas—or worse, venting it into the atmosphere—it is pumped into the storage balloon for later use. To accommodate this added volume of biogas, air is simultaneously removed from the balloon. When more biogas is required than is being produced by the plant, air is pumped into the air balloon, forcing biogas out of the gas balloon at a finely controlled pressure and flow rate.

Because changes in volume are traded between gas and air balloons, the total pressure contained by the outer skin is constant. By fixing the structure to the ground via the outer skin, this constant internal pressure is converted into a tension in the skin, giving it a rigidity to resist external loads.

Modular systems

The client, one of the U.K.’s largest suppliers of civil engineering and building materials, had recently developed its own high-tech anaerobic digestion plant. They recognized the benefits of Base Structures’ modular biogas storage unit because it fitted perfectly the ethos behind the design of their new plant, where each component of the system is an individual “plug-and-play” unit. Base Structures added its 25-meter, cubed Biogas Storage Sphere to the Burdens trial plant in Llangadog, South Wales.

In combining small modular components to build complete anaerobic digestion systems, the business proposition is eminently scalable. This is important because one of the major issues confronted by all potential anaerobic digestion investors is the magnitude of the initial outlay, with a questionable return on the investment.

To help investors overcome this first hurdle, the client designed a plant that can be built incrementally. Every part of each subassembly can be bought off the shelf and bolted together to grow larger systems. For this project, a 25-meter cubed capacity biogas holder was required, constructed using three layers of fabric: a PVC polyester outer material and PVC-laminated/calendered inner materials.

The company’s gas holder can be installed directly on top of the ground as a temporary structure. To avoid the need for a concrete base, a ring of concrete or steel ballast weights can be supplied. This improves the flexibility of the system and opens up the opportunity to use the gas holder as a temporary storage device or additional (or emergency) storage, if an existing system fails or is being shut down for maintenance.

The complete installation process, from arrival on site to having the gas holder ready for customer connection, took a two-man install team only three hours.

Base Structures Ltd. received the 2012 IAA Outstanding Achievement Award for this project.

Leave a Reply

Your email address will not be published. Required fields are marked *

Comments are moderated and will show up after being approved.