Giddings and Wermter 



must again be suspected. Foster [40] continues to explain that a considerable 

 directional spectra must have existed in the confused beam sea and as speed in- 

 creased the frequency of encounter with these directional components approached 

 the natural roll period, resulting in increased roll response. 



USNS GILLISS - Passive Tanks. The USNS GILLISS is a 209-foot, 1200-ton 

 oceanographic research ship and is one of a large class of such ships. The de- 

 sign specifications of the ship limited the displacement to the stated value. 

 Maximum length was maintained consistent with the displacement to provide as 

 much work space as possible. The ship was fitted with anti-roll tanks consist- 

 ing of two wing tanks with an open channel crossover and fixed entrance nozzles. 



Full scale sea trials were conducted by the David Taylor Model Basin in 

 December 1963. Figure 9 presents the results of the tank tuning experiments. 

 These tests were conducted on two separate days in both beam and quartering 

 seas. These curves indicate a very well defined trend toward an optimum water 

 depth of 3.5 feet. It should be noted that the tank effectiveness can be decreased 

 by the addition of too much water. Whether this is due to poor tuning or the 

 limiting of tank fluid transfer due to overhead clearance is not clear. 



□ 4 DEC 63 BEAM SEAS SHIP SPEED 2 KTS — 

 16 DEC 63 QUARTERING SEAS SHIP SPEED 4 K^FS- 



10 20 30 40 50 60 



NOMINAL WATER HEIGHT (INCHES) IN TANK 



70 



Fig. 9 - Effect of various water levels 

 on passive anti-roll tank effectiveness 



762 



