Performance Prediction of Planing Hulls With Propeller Tunnels

In order to study the performance of planing hulls with propeller tunnels, the resistance tests have been conducted on two models with and without tunnels in a towing tank for different forward speeds in calm water condition. Two models were provided with tunnels of different tunnel area ratios (The ratio of projected area of tunnels to the projected water-plane area of the model) of 0.07 and 0.12 by keeping the propeller immersion constant. Wetted surface area, trim angle and CG rise were measured at three different drafts as a part of the study. Pressure measurements were also conducted for a chosen case for a design draft. The extrapolation of resistance from model to prototype has been done using modified Froude’s extrapolation method, which takes the average bottom velocity and trim angle into account. The resistance was also calculated using the method given by Savitsky (1964). The results show that the resistance of the model with tunnel is less when compared to that without tunnel for the same model irrespective of the drafts in case of the model with larger tunnel area ratio. Such variation was not exhibited in the case of the model with lesser tunnel area ratio. Hence, it is observed that the model having the larger tunnel area ratio has beneficial effect due to tunnels. The Savitsky method based results have been compared with experimental results. Pressure distribution along the length of the model shows that the maximum pressure peaks occur near the forward region and reduces towards aft with undulations.