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Bow seals evaluated in first-of-its-kind testing at NSWC Carderock's Large Cavitation Channel

Navy News Service

Story Number: NNS120830-25
8/30/2012

By William Palmer and Robert Etter, Naval Surface Warfare Center Carderock Division Public Affairs

MEMPHIS (NNS) -- Researchers conducted first-of-its-kind testing of the design and performance of bow seals on the Office of Naval Research's Transformable Craft Surface Effect Ship (SES) in early August.

Teams from Naval Surface Warfare Center (NSWC) Carderock Division, the University of Michigan, and Australia's University of New South Wales collaborated at the Large Cavitation Channel (LCC) to perform the testing.

The SES is an air cushion vehicle and is similar to the landing craft air cushion (LCAC). Like the LCAC, the SES rides on a pressurized cushion of air generated by on-board lift fans. While the LCAC is technically a hovercraft with flexible seals around the entire periphery of the vehicle, the SES has rigid walls on the port and starboard sides as well as two flexible seals, located at the bow and stern. The bow seal and the stern seal both help contain the air in the cushion.

"Numerous enabling technologies for the SES were identified as critical and requiring further technical understanding and development. One of these technologies was the design and performance of bow seals," said Bob Etter, a senior researcher in NSWCCD's Hydromechanics Department's Propulsion Branch.

The effort to measure bow seal effectiveness began five years ago. Now, the vast amount of new data generated from the testing is being analyzed and will provide critical insight on how future bow seals should be designed to reduce drag on a ship's hull, improve the bow seal structure and integrity, extend bow seal life, reduce life cycle costs and aid in the general understanding of the physics of bow seal behavior.

The testing took place at NSWC Carderock's LCC, one of the world's largest and most technically advanced high-speed, variable-pressure water channels. Generally, the LCC's sophisticated design enables the Navy to measure submarine and surface ship power, efficiency and propeller noise by testing models such as ship hulls, submarines and torpedoes in a controlled but realistic environment. Typically, models are fully submerged when testing is conducted in the LCC.

In order to measure bow seal effectiveness, the researchers needed to modify the LCC to collect "free surface" data (above, at and below the waterline). While past testing involving air cushion-supported craft was conducted in towing tanks or in open-water, the unique test condition in the LCC provided the benefit of large size, high speed, and exceptional visibility inside, outside and below the bow seals.

The modified LCC also had the capability of maintaining controlled test conditions over a long period of time, something tow tanks and open-water testing environments do not provide. Testing in the LCC also enabled the researchers to incorporate many innovative instrumentation suites, photographic capability and variance of the seal submergence into the free surface, independent of the cushion pressure.

NSWC Carderock Division's responsibilities span a broad range including science and technology, research and development, test and evaluation, product delivery and fleet support. Specifically, NSWC Carderock Division leads the Navy in hull, mechanical and electrical engineering expertise and delivers technical solutions in order to build and sustain a dominant, ready and affordable fleet. Headquartered in West Bethesda, Md., approximately 3,600 scientists, engineers, technicians and support personnel are located across the U.S., which includes the Large Cavitation Channel (LCC) located in Memphis, Tenn.