Propeller Excitation and Response of 230000 TDW Tankers 



carriers performed by Ormondroyd indicated that the vibration level 

 could drop to one quarter of the original level after the installation of 

 fins. 



Another thing that the vortices seem to affect is the course sta- 

 bility of the ship. These large vortices that are building up on one side 

 or the other seem to produce a circulation around the rudder and the 

 entire hull, and this tend to turn the ship which you then have to cor- 

 rect by giving helm. The ship will experience an added resistance due 

 to this. On Great Lakes carriers a gain of a couple of knots has been 

 realized after the installation of fins. I think that also is significant. 

 I wonder if the authors have found anything similar on their ships ? 



REPLY TO DISCUSSION 



Carl-Anders Johnsson 



Statens Skeepsprovningsanstalt 

 Goteborg 3 Sweden 



After having listened to the discussion we are now fully aware 

 of the disadvantage of writing two papers on the same investigation. 

 We are, however, happy to be able to say that the reference which 

 Professor Michelsen asks for is in the first paper [4] so we think that 

 we have given full credit to Baier and Ormondroyd. We also feel sorry 

 for Professor Michelsen that he missed the fine lecture that Profes- 

 sor Telfer gave in London on some earlier English experiences with 

 fins. 



Referring to the last part of Professor Michelsen' s remarks, 

 we can inform him that, during the model tests, we observed vortices 

 springing between the propeller and the stern. In full scale they could, 

 however, not be observed. It can, however, not be excluded that they 

 were present, as the equipment used was more suited for photograph- 

 ing than for making visual observations. 



A detailed discussion of the results of the resistance and pro- 

 pulsion tests with and without fins, as well as a discussion of the full 

 scale tests was given in the first paper. Model tests indicated a gain 

 in power of 6% in ballast and 1% in fully loaded condition when fins 

 were fitted. 



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