ABSTRACT 



The motions and hull-girder bending moments which a ship of the general 

 form and size of the AVPIO Class may be expected to experience over a wide range 

 of operating conditions are presented in statistical form. The data are based on 

 extensive measurements made on the USCGC UNIMAK during sea trials in the 

 J<forth Atlantic Ocean. The methods of statistics have been employed in the plan- 

 ning of the at-sea phases of the trials and in the collection, analysis, and presenta- 

 tion of the large amount of data. From the test results, data are derived for this 

 type of ship for use in design and operating problems involving bending moments, 

 hull motions, and slamming pressures. Formulas are given for use in estimating 

 probable maximum values of moments and motions. 



INTRODUCTION 



The Bureau of Ships initiated a long-range investigation of strains in ships at sea for 

 the purpose of evaluating and improving methods for the design of the ship girder and its 

 structural components.^ Instrumentation has been developed and installed on various types 

 of ships to collect information on the wave loads, stresses, and motions which ships exper- 

 ience in service. During the winter of 1954 and 1955, measurements were carried out on the 

 USCGC UNIMAK (formerly AVP31) during operation in the North Atlantic Ocean. One of the 

 main objectives of this work is the collection of sufficient data on ship motions and longitud- 

 inal hull-girder stresses to determine, by statistical methods, the frequency distributions of 

 these quantities for different combinations of sea conditions, ship speed, and ship heading 

 relative to the waves. For a complete background and general discussion of these trials, see 

 Reference 2. 



This report presents the distributions of the motions and bending moments* to be util- 

 ized for design purposes. To devise these distributions, it is necessary to specify the ship 

 operations for which the vessel is to be designed. The term "mission" will be used here to 

 define the ship's assigned operational pattern. One component of this mission is the aggre- 

 gate of sea conditions under which the vessel must operate. It will be assumed that the ship 

 will operate in the North Atlantic Ocean inasmuch as this probably represents more severe 

 sea conditions than the vessel will actually experience and thus is on the safe side. 



Accordingly, the probable speeds and headings at which these ships would be expected 

 to operate under wartime conditions and the fraction of time the ships would spend at each of 

 the various conditions were estimated by the skippers of a number of vessels of this class. 



References are listed on page 42. 



*The hull bending moments due to flexure in the longitudinal plane of the ship were deduced from the strain 

 measurements and the section modulus applicable to the strain-gage location. 



