A review of Savitsky pre-planning method to the resistance of semi-displacement passenger ships

Abstract

Recent development of semi-displacement ships show their good performance to carry passengers particularly in connecting small islands. These ships operate at speed ranges of 19 to 25 knots (Froude Number, 0.55 to 0.80). At initial design stage, ship resistance of these ships may be determined from the statistical resistance prediction method derived by Mercier and Savitsky. This method was based on regression analysis data from previous series of model tests. In fact, recent semi-displacement ships show differences in hull configurations such as FrV, L/V1/3, V/B3, √2iE, and AT/AX ratio compared to the Savitsky method. This study reviews the resistance of recent semi-displacement ships obtained from Savitsky method which is compared to the resistance obtained from model test. Three ship models were developed and tested to fit full-scale ship speeds of 19 to 25 knots. The ship resistances obtained from the model tests and the computation method were compared. The comparison shows that at speed below 21 knots there is a good correlation between the resistance curves of the model tests and the Savitsky method with, less than 5% of difference. However, for speeds over 22 knots, there is a big deviation between the resistance curves, with a difference of 5% to 20% depending of the ship configuration. The study concludes that the application at early design stage of the Savitsky method for recent semi-displacement ships should be reconsidered and it is recommended to perform model tests to validate the computation results.