Huang and von Kerezek 
block-coefficient hulls at small Froude numbers. Crossflow effects are 
very small throughout. The main discrepancy is near the stern and in 
the region of maximum wave slope. The discrepancy near the stern 
is due to a combination of inadequate boundary layer theory, poor 
pressure distribution prediction, and poor body-geometry fitting by 
the surface equations there. Improvement of prediction techniques 
for this region requires special attention. In the region of maximum 
wave slope, we find that the calculated shear stress magnitude and 
the measured shear-stress magnitude agree fairly well, so that the 
differences between C;, measured and Cy, calculated shown in 
Figure 11 is mainly due to differences in streamline direction at 
zero and finite Froude number. 
In the last graph of Figure 11 we have included the calcu- 
lation of Ce, along waterline E of Webster and Huang!> . Here 
the pressure gradient effects on the boundary layer due to body geo- 
metry and the waves are very small, and thus there is little diffe- 
rence from flat plate values except very near the stern and near the 
maximum wave slope. An interesting observation is that the Webster- 
Huang!> calculation seems to have not predicted the effect of the 
wave satisfactorily. This effect is mainly due to change in the shear 
stress direction in accordance with the streamline direction. Webster 
and Huang!> used Guilloton's'’ potential flow method to calculate 
the inviscid velocity on the ship surface. Due to the rather crude 
approximation of the body and the potential flow, accurate stream- 
lines and consequently accurate values for streamline convergence 
and divergence are not obtained. The present calculation is also not 
expected to predict the shear stress near the free surface since the 
effect of the free surface is neglected in the potential flow computa- 
tion. From these considerations it seems that it is very important 
to obtain an accurate discription of the potential flow streamline and 
pressure distribution in order to adequately calculate the proper 
magnitudes of the shear stress components (Cy. 4 Cry . Cr, }. 
It also should be noted that both the present computation 
and the computation of Webster and Huang!5 overpredict C,, near 
the stern, It is not possible to predict thick boundary layer charac- 
teristics near the stern by these methods, 
CONCLUSION 
Comparison of the measured pressure and shear stress 
distributions, trim and sinkage, and wave profiles along the hull of 
BRIAN BORU at various Froude numbers with various theories and 
boundary layer calculations allows the following conclusions to be 
1974 
