A Survey of Ship Motion Stabilization 



Figure 10 shows the effect over various angles of encounter with the sea- 

 way, in both the stabilized and unstabilized condition. While these curves again 

 indicate the general effectiveness of the tanks, they also indicate that the chang- 

 ing environment makes it impossible to draw definitive design conclusions. 



18 



16 



a. 14 



Q. 12 



WIO 



A 6 DEC TANK LEVEL = 39 

 O 6 DEC " " = 0" 



D7DEC " " =36 



07 DEC " " = 0' 



HEAD 



BOW BEAM QUARTER FOLLOWING 



SEA DIRECTION 



Fig. 10 - Effect of sea direction on 

 passive anti-roll tank effectiveness 



Bench tank tests and model tests conducted in irregular seas at the David- 

 son Laboratory [41] showed that significant stabilization was possible, as much 

 as 90 percent at resonance. Figure 11 shows the roll amplitude operator indi- 

 cating this result. It is further concluded that once tanks are tuned to damp out 

 the narrow frequency band of roll response, rolling at resonance is limited to 

 amplitudes approximately equal to the maximum surface wave slope. Finally, 

 as might be expected, bilge keels had small effect in further reducing the roll of 

 a ship already stabilized by a passive tank system. 



763 



