280 



THEORY OF SEAKEEPING 



^4 

 ID 



O 



CD 



C 



(J 



.. 



- c 



5 



o 



5 



o 



CO 



(mm) (kg-m) 

 80_ 160 



GO 



> 



cn 



c 



> 



o 



a' 



20 



.. 



c 

 o 



D 

 > 



20 



40 



. :i: 60 



80 



lOOL 



100 



200 300 



Wave Height (mm) 



400 



500 



Wave Length 7.GG7m 

 Loca+ion of Strain Meter S5 

 (150 mm Forward from Midship) 



Bending Moment 



Heaving 



Pitclning 



o On Upper Deck (Center Line) 



D On Upper Deck CStarboard) 



A On Keel (Right Side of Center Girder") 



Fig. 29 Example of experimental results of ships drifting in waves showing efifect of wave height; wave length constant (from Sato, 



1951) 



Table 7 Summary of Results Obtained on a Model 1723 (Destroyer) in High Irregular Seas (From Lewis and Dalzell, 1958) 

 Average Wave Height 2.19 in. All bending moments in inch-pounds 



Model speed, fps 1.87 2.53 2.92 3.72 4.12 5.05 



Ship speed, knots 9.1 12.2 14.1 18.0 20.0 24.5 



Average sagging moment 22.6 23.7 23.7 25.7 26.4 28.7 38.7 



Average hogging moment 22.3 23.5 22.6 23.7 21.9 21.8 18.8 



Average range 44.9 47.2 46.3 49.4 48.3 50.5 57.5 



Average of 10 pet highest .sagging moments. ,. . 46.4 46.4 44.0 50.0 52.8 58.7 69.4 



Average of 10 pet highest hogging moments.... 42.9 44.6 42.0 42.2 39.0 40.4 39.1 



Average 10 pet highest ranges 87.7 87.3 83.3 83.1 83.5 89.6 98.9 



Largest single sagging moment measured 59.6 55.4 52.3 59.3 -64.3 78.2 79.9 



Largest single hogging moment measured 54.6 53.8 48.4 50.4 44.3 49.2 49.4 



Largest single range measured 108.5 103.9 99.5 95.6 99.7 104.0 115.5 



Number of waves encountered 102 156 150 154 153 159 179 



Number of times model shipped water 13 46 52 61 66 77 99 



Number of times model slammed" 3 8 11 18 21 37 



Number of times model pounded" 1 20 18 30 33 36 37 



» See text for definition. 



4.5 Severity of Experimental Waves. It is one of the 



recognized advantages of the laboratory technique that 

 ambient conditions can be pu.shed to a much greater 



severity than is possible on an actual ship. By doing so, 

 certain important features of a ship's behavior may be 

 discovered. On the other hand, it is important to 



