ADDED RESISTANCE DETERMINATION IN REGULAR SEA ACCORDING TO ITTC RECOMMENDATION

Resistance tests in calm water conditions provide performance predictions of ships in an ideal and unrealic sea state, which can be found only in sea trials under particular condition. Focus has to be made on effects of various environment conditions, in particular rough sea. Evaluation of added resistance in waves and determination of additional power to install above the calm water power requirements are assuming an increasing importance in displacement ship's design and a growing interest is focused on them. The purpose of this paper is to present towing tank methodologies and procedures for assessment of ship's behavior in regular sea with particular attention on added resistance. The aim is to allow towing tank to test ships in regular seaway and then to evaluate motions and resistance in rough sea.  ITTC guidelines and procedures are considered in hull outfitting and in setup of the wave-making system. A tanker hull model is considered in experiments and preliminary calm water resistance and self-propulsion tests are carried out before the tests in regular waves. An experimental program in regular sea state is presented, developed under ITTC guidelines and procedures. Discussion on the towing tank instruments, towing experiments and error propagation due to the different experimental set up is given.