Vassilopoulos and Mandel 



paper rests heavily on the results reported in Part I of Ref. [6] which includes 

 an extensive correlation of results of strip theory calculations with model re- 

 sults for a wide range of hull forms. The present paper also reports on the 

 further analysis made and experience gained since the publication of Ref. [6]. 



In contrast to the more rigorous thin-ship, raft and slender body theories, 

 strip theory is undoubtedly the crudest and relies on the most limiting assump- 

 tions. However, in advocating a less rigorous approach, the proponents of strip 

 theory were presenting to the profession a procedure for immediate practical 

 application, something which more rigorous approaches to the ship motion prob- 

 lem have still failed to fulfill adequately. In the words of the quotation selected 

 by Korvin-Kroukovsky [9], the advocates of strip theory have had to truly sacri- 

 fice rigor in favor of vigor. 



Strip theory has reached its present state through a series of distinct stages 

 during which significant contributions and corrections were advanced from time 

 to time. In fact, a perusal of its evolution indicates that the method was built on 

 a series of estimations, adjustments, and tedious accounting. Too many approx- 

 imations which were neglected for "obvious" reasons in the beginning had to be 

 incorporated at a later stage and many "essential" truths had to be finally neg- 

 lected. 



The fact that the strip theory procedure was not initially developed on a 

 rigorous physical and analytical basis caused, and still causes, much doubt as 

 to its validity in practical applications. For example, Cummins has referred to 

 it [7] as a "shoe that doesn't really fit." On the other hand, at this stage of 

 progress in seakeeping research, we cannot yet afford to reject a useful device 

 which simulates nature fairly effectively, albeit, by force. 



In support of the previous statement, one of the objectives of the work re- 

 ported in Ref. [6] was to assess the degree of correlation between strip theory 

 and experiment. It is mandatory to note that since both experimental and theo- 

 retical approaches contain sources of systematic errors, this comparison at- 

 tempt was characterized by the absence of a distinct norm. Thus, it is only to 

 be interpreted as beir^ an attempt to match the products of strip theory and ex- 

 periment in the hope that further light will be shed. 



After a brief historical review, this paper presents the results of the broad 

 comparison between experimentally measured and theoretically computed ship 

 motions and phase angles first reported in Ref. [6]. Tank data for a wide range 

 of Series 60 models in regular waves were extracted from N.S.M.B. publications 

 and correlated with model responses calculated by a digital computer program 

 which is based on the Korvin-Kroukovsky linear theory of ship motions in con- 

 junction with Grim's latest results on added mass and damping. Seas from both 

 directly ahead and astern are considered and emphasis is paid to the effects of 

 variations in hull form shape and weight distribution. 



Methods which will improve the applicability of strip theory and advantages 

 to be gained by modifying its analytical description are next presented in antici- 

 pation of further development of the theory. New theoretical data on added mass 

 and damping are also discussed. Although no definite statements are as yet 



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