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

Abstract

The resistance incrementΔ R D + 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: Δ R R and DR D 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 Δ R R and Δ R D . The second procedure, i = 2, is related to the components ( R 0 - F D ) R and ( R 0 -F D ) 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 T R and T D , or on the proportion of the delivered power P DR and P DD . 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. ΔR R + ΔRD = ΔR D+R , 2. Δ R R1j = Δ R R2j and Δ R Dlj = Δ R D2j . Above prerequisites are satisfied only by the K 11 and K 21 methods. The methods K 13 and K 23 satisfy only the first prerequisite.