McClure and Hove 



SPEED — KNOTS 



Fig. 4 - Yaw moment vs sp.eed for 

 various drift angles (deep draft) 



Extrapolation of the data to full scale has been done by the simple lambda- 

 cubed relationship. Extrapolation by the customary ATTC friction line resulted 

 in negligible differences, indicating that friction is a minor part of the total, as 

 one would expect. 



Resistance and Moments in Curved Maneuvers 



During positioning maneuvers within the 400-ft-radius circle the platform 

 will be obliged to turn with very short radii. When the turning radius is in the 

 same order as, or smaller than, the dimensions of the platform, resistance and 

 moment cannot be accurately determined by applying straight-line resistance 

 data to the instantaneous direction of motion of the center of gravity. In such 

 maneuvers the two hulls see quite different relative flow angles. Rotating arm 

 tests were conducted in an effort to shed some light on this problem. Unfortu- 

 nately the facilities were limited to a minimum radius several times the model 

 dimension. Therefore, data in the critical range of very small radii could not 

 be obtained. Instead of mapping the moment and forces as functions of heading 

 angle and radius of turn, it was found expedient to consider the six columns and 

 two hulls separately, computing the forces on each part according to local rela- 

 tive velocities, then adding up the contributions to obtain total forces and mo- 

 ments. The manner in which this was done is explained in detail in Appendix C. 



420 



