18 O. H. Oakley 
0.30L was needed. It is most difficult to relocate weights in a practical ship design to 
accomplish this. 
By enlarging the end nacelles well beyond the size required for items of equipment, 
the entrained water was increased and this had the most pronounced effect in increasing the 
length of the pitching period. 
The changes did result in moving the resonant speed back to about zero and the final 
design exhibited nearly as good pitch characteristics as the original, as the solid line in 
Fig. 17 shows. 
Fig. 18 compares the escort research ship with a destroyer and a destroyer escort. 
This is a spectral presentation and compares the ships in the same seaway, and at the same 
speed. ‘he results appear dramatic and in a sense they are, although it should be remem- 
bered that the ordinate is a function of pitch amplitude squared, which in effect exaggerates 
the difference in performance as regards pitch amplitude. 
DESTROYER 
DESTROYER ESCORT 
| ee 
— 
— 
f (PITCH AMPLITUDE) 2 
RESEARCH 
FREQUENCY OF ENCOUNTER 
Fig. 18. Predicted pitch spectra in a state 5 sea at a ship speed of 20 knots 
The problems and compromises which practical considerations impose on an ideal con- 
cept are well exemplified in our experience in this design. One facet, however, did not 
develop unfavorably. The speed-power relationships provided a pleasant surprise. Fig. 19 
shows a qualitative comparison with a destroyer escort hull of about the same displace- 
ment. As in the case of the submarine vs destroyer comparison given previously (see Fig. 
4) a significant part of the difference in power is the result of the superior propulsive coef- 
ficient of the escort research ship. Nevertheless, considering the fact that roughly a third 
of the displacement of the research ship resides in the nacelles it is remarkable that they 
cost so little in power. 
