536 Edward V. Lewis and John P. Breslin 
Table 1 
Characteristics of Unusual Ship Forms 
DD-692 Semisubmerged | Large-Bulb 
Destroyer Ship Ship 
Length overall (ft) 
Length on WL (ft) 
Length of each bulb (ft) 
Beam (ft) 
Draft (ft): hull, normal displ. 
bottom of bulb, normal displ. 
hull, deep displ. 
Displacement (long tons): 
hull, normal 
bulbs 
total 
deep 
A/(LWL/100)° 
Waterplane coefficient 
Longitudinal gyradius 
Natural pitching period, T, (sec) 
Period-length ratio, T,//LWL 
Natural heave period (sec) 
*At deep draft. 
pitching, but heaving accelerations were not unusually high in spite of the high average fre- 
quency of wave encounter. In irregular waves, the highest single value of heave accelera- 
tion was 0.45 g at 25 knots and 0.26 g at 40 knots. The reason for these moderate values 
was that the motion occurred primarily in the natural heaving period. 
No following-sea tests were run, but the natural pitching period is such that subcritical 
operation is anticipated at speeds up to 45 knots. However, as previously noted, the power 
requirement at deep draft is exceedingly high, even in calm water, for practical considera- 
tions. Furthermore, wave impact on the superstructure would be a serious structural prob- 
lem, and it might be necessary to raise the deckhouse up on columns to permit the waves to 
pass under it. Hence, though this type of craft looks interesting as a supercritical ship, 
there are serious problems to be solved to make it practicable. 
Another type of supercritical craft is the slender hull with large bulbs mentioned earlier, 
(D) of Fig. 1. Available results of a model investigation of such a ship now under way at the 
Davidson Laboratory will be summarized. The objective here was to increase the natural 
pitching period by increasing the virtual mass moment of inertia of the hull, without incurring 
a resistance penalty in the process. That is, k,, cf Eq. (1) was greatly increased. The 
bulbs appear to be too deeply immersed to provide appreciable benefit in the form of damping 
of motions. 
The hull form selected was the well-known ideal form developed by Wigley [9] for which 
the theoretical wavemaking resistance has been calculated. In this form, the underwater 
sections are parabolic, the waterlines are sinusoids, and the above water form is wall-sided. 
For the shape of the bulbs, a body of revolution was selected with length/depth =.5. The- 
oretical wave resistance of this type of body has also been calculated. The size of each 
