Experimental Evaluation of Spray Reduction Technologies

Abstract: This report concerns the efficiency of a novel spray deflector design. The novel design is analyzed and compared to a bare hull and a bare hull fitted with spray rails by experimental testing in a towing tank. The bespoke hull has a modular design where different inserts can be installed to make the parent hull into a bare hull, spray rail, low speed or high speed deflector. The hulls are analyzed in two environments, calm water and irregular waves, where the hulls are compared in drag resistance, running trim and heave for calm water and in bow and center of gravity accelerations for waves. The calm water results show that the deflectors lower the total resistance with up to 25% compared to the bare hull and by over 15% compared to the spray rail configuration, while also affecting the running trim of the hull, raising it by about 1°compared to both spray rail and bare hull. The heave is also affected but not to the same degree, the low speed deflector and the spray rail hull show a similar increase in heave compared to the bare hull as long as the deflector is at its design speed or lower. Because of this change in running position no conclusion about the specific removal of spray resistance on the part of the deflector compared to spray rails can be stated. The deflector design used in these tests change the running trim which has significant influence on the resistance. The irregular wave tests indicate that the current deflectors have a small influence on the vertical accelerations compared to the bare hull. The difference is similar to the spray rail setup where the accelerations at center of gravity for both designs show an increase while the spray deflector exhibited lower accelerations in the bow area. Several improvements have been stated that would improve the current design for the next series of experiments.