Sea Technology

NOV 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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www.sea-technology.com November 2017 / st 25 ous electrical and mechanical features to ensure that if one cell goes into thermal runaway, the event does not propa- gate to neighbors. A key benefit of this architecture is its graceful degradation—the rest of the battery remains on-line to complete a mission, with just a small loss of capacity. Another important aspect of this architecture is that there is a wide variety of cells available that can fit. This means the battery modules can be built to emphasize power or energy performance simply by changing the cells used in construction. Of course, appropriate retesting must be done for any change in materials or architecture. This capability was re- cently demonstrated when newer, higher-energy-density cells were used to build several new battery modules. At GA, testing at the individual cell and small subassembly lev- el indicated that the new cells, providing 18 percent greater energy density, would probably be able to pass system-level tests. System-level testing is still ongoing but initial results are encouraging. GA's LiFT batteries have been approved for use in un- dersea vessels and classified by DNV GL. At-sea testing in the U.S. Navy's S301 submersible was successfully completed in April 2016, and the batteries are now in a follow-on test program with the S351 submersible. Manufacturing was re- cently completed on the first shipset for the Dry Combat Submersible for the U.S. Special Operations Command. From a broader perspective, lithium-ion batteries will be a significant improvement for diesel submarines, and while testing of various configurations has occurred in several na- vies around the world, it is only a short matter of time before the first submarines go to sea with them. There are also benefits for smaller UUVs, and GA's LiFT architecture is currently being designed for testing in the U.S. Navy Semi-Autonomous Hydrographic Reconnais- sance Vessels (SAHRV), a 7.5-in.-diameter UUV. Fuel Cell Systems For use under the sea, some fuel cell technologies have the important advantage of no gaseous or toxic emissions. Fuel cells have long been a primary choice for missions where freedom from the atmosphere is required. The Apollo space program demonstrated both the promise and the peril of fuel cell power, when a liquid O 2 fuel tank blew up and (Photo Credit: Submergence Group LLC) (Left) The S301 submersible. (Right) ALPS aluminum beads.

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