Abstract

The added resistance in waves is a mean value of non-linear, second order reaction of a ship to incoming waves. In the beginning of the 20th century, the experimental methods for investigation of ship hydrodynamics at model scale were developed. They allowed the evaluation of added resistance by measurements in irregular waves (directly) or by measurements in regular waves (in-direct method). The main goal was to find more precise information about the margin for on-board installed engine power to fulfill operational demands of designed vessel. In the early sixties of the 20th century, numerical methods appeared, enabling the seakeeping analyses in frequency domain, and including the methods for determination of added resistance due to head waves. These computational methods, based on gravity character of added resistance, applied the potential flow theory and were mainly determined to cope with head waves. However, the issue of route optimization as well as the phenomena of broaching and surf-riding of vessels going through following and aft-quartering waves gained more attention recently, what demands accurate prediction methods applicable also for these conditions. To avoid dangerous behavior of a vessel, it is necessary to increase the speed, which means that the ship has to maintain a power margin for this operation. The level of added power can be assessed basing on computations of added resistance in waves coming from mentioned directions. The following paper presents the comparison of the results obtained from selected computational methods, including potential methods, semi-empirical formulae and RANS-CFD, with results of dedicated model experiments.

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