Str^m-Tejsen and Chislett 



Reynolds' number has no systematic effect on the lift-curve slope, whereas the 

 variation of maximum lift might be appreciable because separation or flow break- 

 down occurs earlier for the relatively thicker boundary layer around a model 

 body. As most of the hydrodynamic coefficients are due to related circulation 

 and viscous drag effects, scale effects should not be expected for any of the 

 first-order coefficients, Y^, Y,., Y^, N^, N^, N5 , etc. In the case of the non- 

 linear coefficients, however, scale effects could be more serious, as these 

 coefficients are more likely to be influenced by separation or flow breakdown. 

 Normally, nonlinear coefficients of the motion parameters v and r, for instance 

 Y^^^ and Y^j.^, are determined for relatively small values of v and r corre- 

 sponding to angles of attack below that at which separation takes place. For this 

 reason, scale effects are probably also negligible for these coefficients. This 

 is not true for the rudder, as rudder deflection for which rudder characteris- 

 tics are measured will generally cover the range of rudder-lift breakdown. For 

 the coefficients Yggj and Ng^j in particular, it has sometimes been found desir- 

 able to make corrections for this scale effect. 



Re'sume'of Experimental Program 



A summary of a typical experimental program is given in Table 6. This 

 program is used as a standard when testing cargo ships for which complete 

 predictions of extreme manoeuvres are required. 



The table refers to the series of planar-motion mechanism experiments 

 which are necessary for the prediction of manoeuvres made for one given ini- 

 tial, or approach, speed. If other approach speeds are wanted, additional tests 

 are necessary. 



Short descriptions of each test are given in the table, together with suggested 

 settings of the planar-motion mechanism, and the hydrodynamic coefficients ob- 

 tained from each of the tests are also indicated. 



Typical values for the different coefficients and examples of predicted full- 

 scale turning circles, zigzag, and spiral manoeuvres are to be found in Refs. 

 4 and 5. 



INFLUENCE OF SPEED ON DIMENSIONLESS FORCE 

 AND MOMENT COEFFICIENTS 



The mathematical model (Eqs. (5)) is composed of coefficients expressing 

 relationships between orientations, velocities, and accelerations and the result- 

 ing inertial and hydrodynamic forces and moments which act on a given hull- 

 rudder -propeller combination. These coefficients are nondimensionalized, ac- 

 cording to the consistent system described in Ref. 2, by dividing mass by pL^p/2, 

 length by Lpp and time by L /u, where u is the instantaneous velocity of the 

 origin of the body-axes relative to the fluid. The resulting nondimensionalizing 

 factors used are given in Table 7. 



Forces and moments resulting from surge, sway, and yaw accelerations u, 

 V, and r have been found, in general, to be independent of the velocity of the 



364 



