Giddings and Wermter 



Table 6 

 Effect of Fins in Irregular Waves 



Gersten and Cox performed additional work with activated stern fins at the 

 David Taylor Model Basin. The results of these experiments are as yet unpub- 

 lished. The tests were conducted on a model of the DE 1040 fitted witii a pump- 

 jet. The aft end of the pumpjet was further fitted with an oscillating flap in ad- 

 dition to an upper and lower flap in the shroud. An automatic control loop usii^ 

 pitch and pitch rate as control parameters was incorporated in these tests. 



Experiments were conducted in calm water to determine which of several 

 flap configurations could produce the largest pitching moment. Comparative 

 tests with and without a flap fitted to the pumpjet were further conducted in ir- 

 regular seas. As might be expected the flap arrangement with the largest total 

 area produced the greatest calm water pitching (41.2 sq ft of flaps in pumpjet 

 shroud plus 95.6 sq ft of flap C fitted to stern of pumpjet). Table 7 shows the 

 preliminary results of the tests conducted in irregular waves. The table indi- 

 cates that some pitch reduction was achieved in each case. These test data are 

 undergoing complete analysis and a report should be issued soon. The decrease 

 in fin effectiveness for increased wave height is an unexpected result. 



Miscellaneous 



One other area appears worthy of mention although it does not fall within 

 any of the above categories. This is a technique of effectively reducing water- 

 plane area by the use of open tanks. Linearized equations of motion for such a 

 system are given in the Appendix. Results of such tests will be reported by 

 Gersten in a forthcoming Taylor Model Basin Report. The work was performed 

 on an oddly formed special purpose type naval vessel. A stern tank with sides 

 open to the sea was fitted to this ship which had unusually bad pitching charac- 

 teristics. Results of these tests indicated that while maximum motions were 

 not reduced through the use of the tank, these maximums were transferred to 

 much lower speeds. This would permit the ship to operate effectively in the 

 design speed range. 



790 



