Shear Stress Pressure Dtstrtbutton on a Shtp Model 
drawn : 
1, The sinkage and trim, and the wave profiles along the 
hull predicted by thin ship theory are not in good agreement with the 
measured values. Thin ship theory is not satisfactory for ships 
having a flat bottom and a moderate block coefficient. 
2. The measured pressure distributions on the after half 
of the ship bottom are rather close to those computed on a double- 
hull model and show little effects from waves (Froude number). Thin 
ship theory does not give a good approximation of the flow in this 
region. Near the free surface the pressure distributions behave like 
a linearized wave, which agrees with the thin ship approximation, 
The flows near and on the forward half of the ship bottom are affect- 
ed by the combination of the free surface waves and the details of 
the ship geometry. A new physical model is needed in order to pre- 
dict the flow over the after half of the hull. 
3. The measured shear stress vectors at selected points 
on the model show that the shear stress vectors are oriented in 
nearly the same direction as the local streamlines indicating, as has 
been found previously, that boundary layer crossflow is small on 
moderate block coefficient hull forms. Although the local shear 
stress values depart little from equivalent flat plate values, the 
trend of the departure is fairly well predicted by the Cumpsty-Head- 
Smith boundary-layer calculation method with the small crossflow 
assumption, especially along streamlines where wave effects are 
negligible. This indicates that boundary layer calculations carried 
out along the streamlines, taking into account pressure gradients 
and streamline convergence or divergence, using momentum integral 
methods can be quite useful. It is important, however, to develop an 
accurate potential flow calculation methods and methods for calcu- 
lating thick boundary-layer approaching separation, 
ACKNOW LEDGMENT 
The authors are indebted to J.H. McCarthy of the Naval 
Ship Research and Development Center for his stimulation and in- 
terest during the course of this work. The authors would also like 
to thank Messrs. N. Santelli, G.S. Belt, and L.B. Crook for their 
assistance during the experiment. Mr. C.W. Dawson is also thank- 
ed for performing the exact double hull potential flow computation. 
This work was authorized and funded by the Naval Ship Systems 
Command under its General Hydromechanics Research Program, 
Task SR0090103. 
1975 
