A Survey of Ship Motion Stabilization 



Many other investigators have also made the point that the time differential 

 of port and starboard collapse also add to the severity of the vibration. Ochi 

 goes further and states that if this time differential is the same as the loading 

 time, the vibration will be magnified. It is further stated that if the fins remain 

 below the water surface within some limit (8 feet for the MARINER), the cavity 

 will not form and thus vibration will not occur. 



Some other general conclusions are as follows: 



1. Maximum pitch reduction is achieved by fins located in the forward 10 

 percent of the ship. 



2. More severe vibration is induced by fins in these forward locations. 



3. Planform area and pitch reduction are linearly proportional for the 

 MARINER hull. 



4. Vibration increases with fin area and with violence of pitching. 



5. Fins with properly designed holes can be as effective as solid fins in re- 

 ducing pitch and are superior in reducii^ vibration. 



In selecting an optimum fin location, Ochi presents an interesting compari- 

 son of parameters which is reproduced here as Table 4. The values underlined 

 with the double line are considered to be acceptable design values and of course 

 only the location with all parameters underlined will be optimum. 



Table 4 

 Optimum Fin Location for Various Parameters at a 15-Knot Ship Speed 



221-249 O - 66 - 51 



785 



