WAVE REFRACTION PLOTTER 



by 

 R, Q. Palmer, Chief, Civil Works Branch 

 Honolulu Area, San Francisco District 

 U, S, Army Corps of Engineers 



The Honolulu Area of the San Francisco District, Corps of 

 Engineers, recently prepared design analyses for several projects, each 

 requiring a series of refraction diagrams. These diagrams were con- 

 structed in accordance with instructions contained in Technical Report 

 No. 4 of the Beach Erosion Board entitled "Shore Protection Planning 

 and Design, 



The first series of refraction diagrams was constructed using a 

 template, iJ illustrated on figure 17 of Technical Report No. 4. The 

 template is a great improvement over previous devices used and it can 

 be used with charts of any scale. Nevertheless, the work was time 

 consuming -nd occasional errors were made due to slippage of the template 

 or triangles used to orient the template. To overcome these problems, 

 the template was adapted to a wave refraction plotter which could be 

 attached to an ordinary drafting machine^] (see Figure 1), Time trials 

 by technicians trained on an equal period of time with both the template 

 and the plotter showed that the production rate when using the plotter 

 was more than twice that when using the template and fewer errors were 

 made. Plotters can be fabricated for about $15 each in quantities of 

 2 or 3, but could be produced for about $10 each in amounts of 50 to 100, 



Hydrographic work charts are prepared in the same manner as when 

 using the template. The plotter is oriented for the selected deep water 

 wave direction and the azimuth on the drafting machine is set at zero. 

 The lower motion is then locked. 



The upper motion of the drafting machine is freed and deflections 

 are turned with the plotter. At all other times both motions are locked 

 to fix the orientation of the plotter. The built-in pivot point is de- 

 pressed with the palm of the hand when turning the deflection angles. A 

 spring raises the pivot point viien released. After each deflection angle 

 is turned, the plotter is shifted slightly to bring the right angle- 

 straightedge into position for extending the orthogonal. In the event 

 that the orthogonal intersects the contours at angles less than 10 de- 

 grees, this fact is shown by angle markings on the plotter. Thus, 

 guesswork or continual checking to determine when it is necessary to 

 change either to or from the R/J method is eliminated. When a change to 

 the R/J method is required, it is only necessary to read the azimuth 

 on the drafting machine and by ready reference to the chart attached 



Ij After Arthur, Munk & Issacs, 1952 



2\ When a drafting machine is used which has "stops" at 15-degree incre- 

 ments, the trigger on the "stop" should be depressed by placing a 

 number of rubber bands around the control knob. 



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