Place one end of a straight edge at the geostro- 

 phic wind speed on the extreme left-hand scale 

 and the other end at the sea-air temperature 

 difference. Read the approximate surface wind 

 on the scale so labeled. Turn the straight edge 

 on this point to intersect the curvature correc- 

 tion scale in the upper right-hand corner. Read 

 the surface wind speed at the intersection of 

 the straight edge and the scale labeled Us. An 

 example is shown on the nomogram. 



Plate III shows minimum duration time for 

 any fetch. Enter with surface wind speed at 

 the left. Proceed horizontally to the appro- 

 priate curved line of fetch distance. Proceed 

 vertically and read minimum duration time 

 from the scale along the bottom of the graph. 



Plate IV gives the wave height and period 

 as functions of the wind speed and duration. 

 Enter at the left-hand side with wind speed 

 and proceed horizontally to the vertical repre- 

 senting duration time. At this intersection 

 read the wave height from the solid, curved 

 line and the period from the dashed, curved 

 line. 



Plate V is similar to plate IV and is used in 

 the same way when the duration time is less 

 than 12 hours. 



Plate VI is the decay diagram. Enter on the 

 left with the wave period at the end of the 

 fetch. Proceed horizontally to the vertical rep- 

 resenting decay distance. At this intersection 

 read the reduction factor Ho/Hp, the travel 

 time, and the period at the end of the decay. 

 The inset on this plate gives the wave speed 

 and wave length appropriate to the wave 

 period. 



Plate VII shows the distance from the gen- 

 erating area and the wind speed in this area as 

 functions of the height and period of an 

 observed swell. Enter on the left with the 

 observed height and proceed horizontally to 

 the intersection with the vertical representing 

 the observed period. At this intersection read 

 the distance to the generating area, the wind 

 speed in the generating area, and the travel 

 time of the waves. 



Plate VIII contains a nomographic repre- 

 sentation of the wave growth and decay rela- 

 tionships which has been fashioned to eliminate 

 certain readings of intermediate quantities and 

 slide rule operations. This plate also contains 

 an example. The following instructions are 

 for using the four sections of the plate : 



1. Enter 1 with the given value of the 

 wind and proceed along a horizontal line 

 from left to right to the given fetch or dura- 

 tion time, whichever occurs first. 



2. From this point proceed upward along 

 a vertical line into 2 to the intersection of 

 the vertical line with the curve correspond- 

 ing to the given value of wind speed. Read 

 the value of Hp (and Tp if desired) at this 

 point. 



3. Proceed along a horizontal line into 3 

 to the intersection of the horizontal with the 

 given value of the decay distance. Read To 

 or Toe and tu at this point. 



4. Proceed down along a vertical into 4 

 to the intersection of the vertical with given 

 Hp line corresponding to the value found in 

 2. Proceed along the horizontal to the scale 

 at the right, reading Hd or Hoe from that 

 scale. 



Plate IX contains an alignment chart for 

 wave generation with an example. An explana- 

 tion for the use of the duration scale follows: 



1. Copy the scale at the bottom of the dia- 

 gram on a tracing vellum strip for use as 

 an index line. 



2. Set the index line on given wind speed 

 on left-hand vertical scale and on given dura- 

 tion time on right-hand vertical scale. 



3. Slide index line so that the point of 

 intersection with turning line coincides with 

 wind on index line wind scale. 



4. Pivot index line about point of inter- 

 section until it is perpendicular to the turn- 

 ing line. 



5. Read wave height Hp at intersection of 

 height curve with index line, and wave 

 period Tp at intersection of period curve with 

 index line. The fetch scales are used in a 

 similar fashion. The values of wave height 

 and period determined by the fetch scales are 

 used only if the height is less than that deter- 



' mined from the duration scale. 



Plate III can also be used to determine 

 whether duration or fetch is critical, and the 

 fetch table on plate IX serves as a guide in this 

 respect. 



Plate X contains an alignment chart for wave 

 decay with an example. An explanation for 

 its use follows : 



1. Use an edge of a transparent ruler or 



a straight line ruled on a strip of tracing 



vellum as an index line. 



24 



