Stern End Bulb for Energy Enhancement and Speed Improvement

Unlike the bow bulb, the Stern End Bulb (SEB) has been used on just a few ships to improve performance. In one of these rare, full scale applications, a maximum resistance reduction in the 5% to 7 % range is claimed. A few applications of SEB’s are shown along with some model test data for a Naval Auxiliary ship. The rationale for SEB is discussed along with the hydrodynamic mechanism associated with a stern end bulb. In addition to wave making reduction the SEB can reduce eddy making and possibly improve course keeping. The results of several fluid flow computations with initial stern end bulb designs are shown for two ship classes; the TAKE LEWIS and CLARK dry cargo ship and the DDG 51 ARLEIGH BURKE destroyer. The calculations use the Ship Wave Inviscid Flow Theory (SWIFT) potential flow computer code and the FreeRans viscous flow free surface computer code. Several Stern End Bulbs were designed and investigated analytically for the T-AKE class ships, and the best of these is predicted to reduce resistance by 4.5 % at 20 knots. In addition, several initial SEB / Stern Flap configurations were designed for the DDG 51 Class Flight IIa destroyers, and five configurations, some with just an SEB added to the hull and others with a combined SEB-Stern Flap configuration were model tested. The examination of these initial efforts led to the design of several new style combined SEB-Stern flap configurations, the best of which is predicted to save at least 745 Bbls. of fuel per ship per year. NOTATION