Stern Flaps for Enhanced Powering Performance

The U.S. Navy has been investigating the potential for improved powering performance by the installation of stern flaps on many recent ship designs. Stern flaps have been retrofitted to two FFG-7 Class frigates and they will be featured on the new LPD-17 and D00-51 flight 2A ships. In addition, the Navy has fit PC-13 with a flap in order to demonstrate performance prior to the retrofit of the entire PC-1 class. Full scale trials on the PC-13 are presently being conducted. An intensive investigation is underway to quantify the energy savings with stern flaps on the DD-963 and CG-47 class ships. Numerous model tests have been performed to explore the benefits of stern flaps on larger, sealift type ships. The physical mechanisms that account for the improved performance due to a flap are discussed. Powering reductions on the order of 6 to 8 % at cruise and maximum speeds have been measured at model scale. Limited full scale trials indicate that the improvement due to the flap on the full scale ship is greater than the improvement measured at model scale. Results from twelve different model test programs are presented, including predictions of overall energy savings, increased maximum speed, and decreased power at cruise speed. General guidance for evaluating the potential benefit of a stern flap on a new design is provided.