Scaling of RV Athena’s Appendage Drag Using CFD

Abstract

The drag or the resistance contribution of appendages such as brackets, skegs, shafts, rudders and fin stabilizers fitted to R/V Athena were investigated. The issue in estimating the appendage drag is that laminar flows occurred at lower Reynolds number typically in ship model used for ship hydrodynamic testing in a towing tank. In full-scale ship, the flow is usually turbulent. Uncertainties when scaling the model result to full-scale may arise as the flow regime in both cases are not similar, hence the full-scale estimate will be inaccurate. One method to resolve this issue is to scale the appendage drag using a fixed fraction which is known as the ‘Beta’ approach. The aim of this investigation was to determine the value of beta. R/V Athena was chosen as the case study in this investigation. The results obtained from SHIPFLOW 6.3 shows that the drag in model scale increased at 14% when fully appended. The drag in full-scale increased at 11% when fully appended. It was observed that the skeg contributed to the highest percentage of drag at about 7–8% of the total drag. Finally, the value of beta was estimated to be in between 0.38 and 0.39.