Selection of the most suitable method to split the resistance increment into components related to individual propellers of double-ended ferry

The resistance incrementΔRD+R measured in model propulsion tests of a double-ended ferry with the pushing aft propeller SR and the pulling fore propeller SD is to be split into two components: ΔRR and DRD related to each of the propellers. The splitting procedure based on the measured magnitudes is possible only when additional assumptions are made. Two procedures are presented in this paper. The first procedure, i = 1, is directly related to the components of resistance increment ΔRR and ΔRD. The second procedure, i = 2, is related to the components (R0 -FD)R and (R0 -FD)D attributed to individual propellers. In both procedures the same assumptions are used for splitting. Proposed assumptions are based on the proportion of propeller thrust TR and TD, or on the proportion of the delivered power PDR and PDD. Procedures combined with assumptions define the methods and are denoted Kj where subscript j refers to the assumption. Two prerequisites were formulated. Both have to be satisfied by methods of practical importance: 1. ΔRR + ΔRD = ΔRD+R, 2. ΔRR1j = ΔRR2j and ΔRDlj= ΔRD2j. Above prerequisites are satisfied only by theK11 and K21 methods. The methods K13 and K23 satisfy only the first prerequisite.