Page 59: of Maritime Reporter Magazine (February 1999)

MARINE ENGINEERING

Stern Flap System Dubbed Technical Breakthrough

Proven 14% fuel savings helps nab prestigious EPA Award

Technical innovation in the name of saving money and maintenance has become somewhat of a cliche in many industries, leaving many with the impression that the message is more marketing hype than real world results.

An innovation which is solidly in the latter category was recently honored by the U.S.

Environmental Protection Agency for its role in conserving fuel, thus reducing pollutants.

Specifically, the U.S. Navy's CG-47/DD-963

Stern Flap R&D Team has received one of the

EPA's 1998 Climate Protection

Awards, as it was singled out for "Technical Breakthroughs in Ship

Energy Efficiency" demonstrating powering improvements and signifi- cant fuel savings deriving from installation of new stern flaps on

Navy ships.

The modification is an extension of a hull bottom surface at the rear of a vessel. The Carderock Division team determined the appropriate shape via model ship tests in the

David Taylor Model Basin. Trials on USS Arthur W. Radford (DD- 968) (pictured), a Spruance Class destroyer, have shown a reduction in required power up to 14 per- cent resulting in a projected annu- al fuel savings of 4,400 barrels per ship. This equates to approximately $240,000 per year in fuel savings, as well as a .75 knot increase in speed. Radford is the destroyer also being used to demonstrate the new composite mast recently announced.

While the flap has been trialed on a num- ber of different ship types, both real and model simulated, and the performance of the stern flap varies based on hull form and

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Above & Left: Stern flap on USS Arthur W. Radford speed, it has proven itself as an invaluable aid to propulsion power and efficiency.

An Evolving Revolution

The advent of the stern flap solution to fuel savings and performance enhancing can hardly be termed a new development, at least in terms of publicity surrounding the system. For the past decade, the U.S. Navy have been investi- gating, at model scale, the potential powering improvements due to stern flaps, as low cost retrofits on many ship designs. It is interesting to note here that flap performance is opti- mized where the ship expends the most power.

While the fuel savings and power enhancing aspects of the stern flaps are truly amazing, from a business stand point they are outstanding performers as well, as predicted annual fuel savings will repay the flap retrofit costs in less than a year.

A stern flap is simply an appendage which reduces the power required to propel a ship through the water. It is a relative- ly small extension of the hull bot- tom surface aft of the transom.

The critical parameters for stern flap design geometry are the flap angle, referenced to an extension of the local centerline buttock angle, flap chord length and flap span across the transom.

Flap design is dictated, ulti- mately, by the hullform design and the mission requirements of the ship. The stern flap's critical para- 56 Circle 313 on Reader Service Card Maritime Reporter/Engineering News