538 Edward V. Lewis and John P. Breslin 
bulb was fixed at 20 percent of the volume of the hull alone. Thus, both bulbs represent 
28.6 percent of the total displacement. The bulbs were attached to the hull in a manner that 
permitted their fore and aft location to be varied. 
Figure 7 shows the model with 40 percent of the length of the forward bulb extending 
forward of the FP and 60 percent of the aft bulb extending aft of the AP. Full-scale char- 
acteristics of the large-bulb ship are given in Table 1, and compared with those of the typi- 
cal destroyer and semisubmerged hull. 
Fig. 7. Slender ship with large bow and stern bulbs 
At present, neither the testing nor the analysis in this project has been completed. Re- 
sults presented here are preliminary and subject to further evaluation when the testing pro- 
gram is completed. Because the forward position of the bow bulb showed the least resistance 
of the positions tested, it was selected for the regular 2.0L wave tests. Figure 8 com- 
pares the pitching motions of three types of ships. The worst pitching motions for the 
large-bulb model occur at about the speed for synchronous motions, 2.4 fps or 9.8 knots. At 
intermediate speeds, the motion of the large-bulb model was somewhat greater than the semi- 
submerged model, but at high speeds it was somewhat less. 
Figure 9 shows one real shortcoming of the model. Worst heaving motions occur in the 
vicinity of 34 knots ship speed, where the amplitude approaches 2-1/2 times the amplitude 
of the wave. Synchronism for heave occurs at 6.8 fps or 28 knots ship speed. While the 
heaving was severe, maximum acceleration amidships accompanying the motion was 0.45 g 
in an LWL/41 wave, no worse than the semisubmerged model. However, the large heave am- 
plitudes may actually cause the middle body of the ship to emerge from the water at speeds 
where maximum heaving motions occur. Nevertheless, this type of craft appears to offer 
real potentialities of high speed in rough water, and research is continuing on possible 
means of improving performance further. It has the advantage over the semisubmerged de- 
sign in having less hull-volume limitations, and sufficient freeboard and flare can be pro- 
vided forward to keep water off the foredeck. 
SEMISUBMARINE 
Characteristics 
Finally, we may consider the possibility of larger proportions of submerged hull. Mandel 
has considered a hull with a surface-piercing fin almost as long as the hull ((F) of Fig. 1) 
with some success [2].. However, it is believed that the power requirements are excessive 
and that the only hope for success with this type of craft is to reduce the fin to the absolute 
minimum. Mr. E. Frankel stated at the Seminar on Ship Behavior at Sea, Stevens Institute of 
Technology, June 1960, that a model is now being investigated at M.I.T. in which the fin has 
been reduced to about 1/6 the length. Resistance and control problems for such a craft ((G) 
of Fig. 1) are now being investigated at Stevens. 
