Table VI 



Summary of Quantities to be Determined when Forecasting Swell 

 In the Presence of Following or Opposing Winds 



No. 



21 



Term 



Distance to beginning of second 

 wind area 



Symbol Units 

 D' 



Source 



Naut. m. Current and prognostic synoptic 

 charts 



22 



Distance to end of second wind 

 area 



D" 



Naut. m. 



Current and prognostic synoptic 

 charts 



23 Wind velocity In second wind 

 area (D" - D' ) 



Knots Estimated from current and 

 prognostic synoptic charts 



24 Sign to be applied to U' 



25 Reduction factor for wave 

 height for distance D' (U' = 0) 



26 Wave height at distance D' 

 (U' - 0) 



27 Factor of period increase for 

 distance D' 



28 Period at distance D' 



29 Reduction factor for wave height B.j.„/E„ 

 for distance D" (U' =0) ^ " 



Follov.dng or opposing wind 



Plate VI, using (12) from 

 Table IV and (21) 



(11) , Table IV, times (25) 

 Plate VI, Inset II, using (25) 

 (12) , Table IV, times (27) 



Plate VI, using (12), Table 

 IV, and (22) 



30 Wave height at distance D" 

 (U' = 0) 



31 Factor of period increase for 

 distance D" 



H. 



D" 



'^D"''^F 



(11), Table IV, times (29) 

 Plate VI, Inset II, using (29) 



32 Period at distance D" 



33 Average period for distance 

 (D" - D') 



■•D" 



Seconds (12), Table IV, times (31) 

 Seconds Average of (28) and (32) 



34 

 35 



Ratio wind velocity to wave U'/ T 

 period in second wind area 



Ratio of wave heights in second H_„/H_, 

 wind area (U' =0) u u 



Knots/sec (23), considering (24), divided 

 by (33) 



(30) divided by (26) 



36 Correction factor to (35) 



37 Wave height at end of second 

 wind area 



^D",U'^" 

 V',U' 



Plate VIII, using (34) and (35) 

 (30) times (36) 



38 Reduction factor of wave 

 height for distance (D - D" ) 



39 Wave height near coast 



^D,U'/%',U' 



^,1 



Feet 



Plate VI, using (32) and (D - D") 

 (37) times (38) 



a 



