Propeller Excitation and Response of 230000 TDW Tankers 



add these data to the paper. 



Finally, by testing the ship model at ballast condition in the 

 cavitation tunnel the afterbody fins more or less coincide with the 

 upper wall of the cavitation tunnel. Due to this fact, no differences in 

 the wake pattern with and without fins will be found. Is this accordance 

 with the measurement results found in the model basin ? 



REPLY TO DISCUSSION 



Carl -Anders Johns son 



Statens Skeppsprovningsanstalt 

 Goteborg, Sweden 



Calculations of different kinds of shaft resonances including 

 magnification effects were carried out for the two ships at the design 

 stage and were decisive when determining the number of blades of the 

 propeller. 



Comparative curves of the wake distributions with and without 

 fins were given in the first report on this investigation [4] and it was 

 not considered necessary to include them again. These curves show 

 that there was a considerable difference between the wake values ob- 

 tained with and without fins in the 12 o'clock position, in particular in 

 fully loaded condition where the measurements in the towing tank in- 

 dicated highly separated flow without fins. This difference was very 

 well reproduced in the tunnel, also in ballast condition, although the 

 agreement between tunnel and towing tank was slightly better in fully 

 loaded condition. This applies to the measurements carried out with- 

 out propeller as well as those performed with rotating propeller. So 

 we think the differences with full-scale what we call cavitation pat- 

 terns cannot be entirely linked together with the wake distribution. 

 There must be some other factors. We have discussed the question of 

 the definition of loading cases. We all know that the definition of load- 

 ing cases is a much more tricky business for ballast conditions. It is 

 not entirely logical compared to what we use in fully loaded condition. 

 May be we can get some useful information from the new vacuum tank 

 regarding what happens to the efficiency and interaction factors under 

 cavitating conditions. 



659 



