SEAKEEPING I.T.T.C. COMPARATIVE TESTS on S175 Standard Model

This experimental research work is complementary to the previous theoretical SEAK1 research of the Programma Ricerche INSEAN 1984-85. Not only it becomes part of the international cooperative program promoted by the 17th ITTC (for comparative tests on a S175 container standard ship model, running at two Proude numbers in unidirectional, head and following, regular and irregular waves), but it also has the more general aim to answer three requirements, particularly urged: to make uniform the seakeeping model tests carried out in rectangular basins; to identify and characterize the input seas and ship responses most significant in order to define and assess seakeeping performance of classic surface displacement monohull ships operating in head and following sea; to identify some standard seakeeping predictions presentation formats mostly suitable to assess ship seakeeping operability related to a given mission. More in details, in the first part of the paper, a general survey is made to introduce to main factors affecting the results reliability degree of seakeeping model tests carried out in rectangular basins. In part 2, after model tests and their purposes have been described, some experimental troubles (as interference effects and waves reflection from damping beach) are discussed, in conjunction with implications that tank frontal and side walls presence brings either in handling model tests and in analizing experimental data, in the following sea case as well. In part 3, after a brief description of software framework (structured coherently to the pre-existent one devoted to still water model tests and designed to wholly automatize seakeeping tests data acquisition, analysis, processing and presentation), either model tests results and their analysis techniques are discussed and compared with those obtained by other towing tanks taking part to the ITTC cooperative program, either ship motions, accelerations and propulsion characteristics predictions, in rough seas, are debated as well. For specific signals measured during regular waves model tests, an originai analysis technique has been developed, which INSEAN decided to use as its standard technique, due to the doublé advantage, on one hand, to overcome the substantial drawback (signal energy distribution over multiple frequencies of only "presumed reaP fundamental harmonic) of techniques founded on the Fourier series expansion and to which most attention is given by ITTC, and, on the other hand, to resolve, with some degree of accuracy, the analysis problem for signals whose time histories are (because of their long encounter period and/or of excessive time needed to get the selfpropulsion condition) shorter than their encounter period and which we may be pressed to content ourselves with. In part 4, seakeeping ship predictions presentation formats, which are the most adequate to define and to assess both short and long-term seakeeping performance and operability indices, according to ship and mission kind, are discussed. In the last part, devoted to conclusions, after the positive outcome attained by INSEAN through this research work has been emphasized, the main problems, stili opened, are briefly recalled, on whose resolution increasing improvements in the already high (especially compared to that one so far attained by theoretical methods) utility and reliability degree of seakeeping model tests in rectangular basins depend.