176 



iiVDRonvx XNfK.s i\ Mill' orsicv 



Srr. tS.n 



TABLE -IS.k — AvKR-VGK KKt-ATinvsiiii' Bktwkks N Alt rm. Winhs and \\ avks 

 For the source of those diita, see tho arcompimying text. The Beaufort si-ale numbers and wind velocities do not 

 conform to tho latest U. S. Navy values as given along the top edge of Fig. 48.J. For this tabic it is assumed that the 

 waves travel at the same spocd as the vrind. 



direction for the duration specified, and that the 

 fetch i.s long enough to eUminate the effect of 

 nejirby land. 



Data relating to .statistical method.s for charac- 

 terizing the pattern of natural waves in a .seaway 

 and for foreca.sting waves on a basis of known 

 meteorological data are given by W. J. Pierson, 

 Jr., G. Neumann, and R. W. James in a publica- 

 tion entitled "Practical Methods for Observing 

 and Forecasting Ocean Waves by Cleans of 

 Wave Spectra and Statistics," prepared as 

 Technical Report 1 under Contract Nl89s-8G743, 

 liuAer Project AROWA, July 1953. On pages 320 

 and 321 there is a bibliograjjliy of 39 items. These 

 methods arc described in some detail in Part (j of 

 Volume III. 



48.13 The Zimmermami Wave. In the earlj- 

 1920's Erich Zimniormann published the results 

 of an extensive analysis made by him on the 

 natural waves previously reported by many 

 observers ["Aufsuchung von Mittelwerten fur die 

 Formen ausgewachscner Meereswellen auf Grund 

 alter und neuer Beobachtungen (Search for 

 Average Values for the Form of Fully Developed 

 Ocean Waves, Bjised on Old and New Ob.serva- 

 tion.s)," ScliilTljau, 28 Apr 1920, pp. ()33-G40; 

 .') May 1920, pp. ri(;3-{i70]. On pages (KiS, md, 

 and 070 of this paper there are given 72 references 

 from a wide variety of .sources, covering the 

 periwJ from 1779 to 1914. 



While recognizing the relation.ship i)etween 

 length, periixl, and wave velocity in the trochoidal- 

 wavc HyHt<;m, Zimmermann set out to find the best 

 poHoiblo empirical relution.sliijis of tiie natural 

 waves of tho sea between: 



Length Celerity 



Height Period 



Breadth (length of crest) Wind velocity. 



He succeeded in developing what he felt was a 

 good average relationship between these values 

 for a wide range of variables. He published a 

 single curve, reproduced with some adaptations in 

 Fig. 48. J, which gives two sets of relationships 

 between three \'ariables in each set. This he did 

 on the basis, admittedly arbitrary, that there is a 

 unique combination in nature between these 

 variables throughout this large range. Never- 

 theless, Zimmermann's wave can be taken as a 

 sort of statistical average for any point on the 

 range. It does at least give the marine architect 

 an idea of the combinations of variables to be 

 expected at any selected point of the range. The 

 graph of Fig. 48. J contains a workcd-out example 

 of its use. 



Incidentally, Fig. 1 on page G34 of the 28 April 

 1920 SciiilTbau reference gives a plot made by 

 Zimmermann of thirteen sets of wind-velocity 

 values corr('s])on(ling to the wind-force nvunbers 

 of the Beaufort scale; every set is different from 

 every other. The authorities quoted in the refer- 

 ence published their data over the period I8()G- 

 1911. To the Zinunermann plot was appended a 

 .set of values by Kocpix-n, Shaw, and Palazzo, 

 from the International .MetiMirological Conference 

 at Rome in 1913. 



.\fter considering them all it was finally decided 

 to adopt for the lop-edge .scale of Fig. 4S.J the 

 values given in "Instructions for Keeping Ship's 

 Deck Log," NavPers l.")87() of July 19.')."), '\ss\wi\ 

 bv thf Bureau nf Naval Personn<'l of the Xavy 



