Shear Stress and Pressure Dtstrtbutton on a Shtp Model 
Laboratory (Silver Spring, Maryland), The use and calibration of the 
shear probes is given in the Appendix. The electrical output of the 
calibrated transducers was digitized, averaged for 100 seconds, and 
analyzed in various dimensionless forms using an Interdata computer. 
The results were printed out immediately after each experiment. At 
each Froude number the model was first run free to trim. This trim 
condition was then fixed for subsequent runs at the same F, . 
The total resistance was routinely measured by a floating 
girder and a block gage. The trim and sinkage were measured using 
two potentiometers located at FP and AP, and wave profiles were 
traced along the hull using a colored pencil and then measured. 
These provided a complete set of experimental data for BRIAN BORU. 
RESULTS AND DISCUSSION 
The experimentally measured wave profiles along the hull, 
sinkage and trim, total resistance, and pressure and shear stress 
distributions at various Froude numbers will be presented and com- 
pared with relevant theories and numerical results. 
(1) Wave profiles along the hull. Photographs and a dimen- 
sionless plot of wave profiles along the hull at six different Froude 
numbers are shown in Figures 4 and 5, respectively. Figure 6 shows 
the measured profiles at Fn = 0.22 and 0.28 compared with the 
profiles predicted by Guilloton's method. Although the forward quar- 
ter of the predicted wave profiles on the model compare favorably 
with the measured profile, the agreement becomes poorer downstream, 
The prediction not only overestimates the magnitude of the last trough, 
but also misses the location (phase). 
(2) Sinkage and trim. The measured sinkage and trim,com- 
pared with the first-order thin ship theory computed by Yeung”4 re 
shown in Figure 7. The measured values of sinkage are all smaller 
than that predicted. However, the measured sinkage and trim coeffi- 
cients agree rather well with the calculated values using the zero 
Froude number, slender body(4 or Douglas-Neuman 3)theoretical pres- 
sure distribution. It should be noted that the measured trim does not 
vary with Froude number as much as that predicted. Since the sin- 
kage, and trim and the wave profiles predicted by the thin ship theory 
are not in good agreement with the measured values, the thin ship 
theory may not be suitable for this model which has a flat bottom and a 
moderate block coefficient. No further comparison of experimental 
data with thin ship theory is attempted. 
1971 
