Semisubmerged Ships 529 
wavemaking resistance and thus compensate for increased frictional resistance. As the 
speed of this ship goes up, the EHP curve almost coincides with the curve for the shallow- 
running submarine with a small strut. This suggests the latter type of craft has no resist- 
ance advantage over a slender destroyer designed specifically to go at very high speed. 
However, the very slender destroyer would run into trouble at high speed in rough water, 
and the near-surface ship with strut may have advantages. 
A submarine with a very large strut (F), as suggested by Boericke [1] and investigated 
by Mandel [2], shows comparatively high resistance, especially at high speeds. An all-strut 
ship — that is, a ship of the same displacement and about the same draft as the others but 
with its entire hull extending through the surface — has a very high EHP. Figure 2 also in- 
dicates that a large planing boat (B) of optimum-breadth would be better only at very high 
speeds (near the limit of this figure). 
The semisubmerged hull form (E), reported by Lewis and Odenbrett [3], and the slender 
hull with large bow and stern bulbs (D) are capable of high-speed supercritical operation in 
rough seas with comparatively small pitching motions. The first of these ships, (E), shows 
rather poor calm-water EHP performance at deep rough-water draft, but the latter, (D), is 
remarkably good up to the limit of the speed range so far tested. 
Therefore, a number of types of craft intermediate between conventional ships and sub- 
marines are feasible that promise remarkably low power requirements. However, the larger 
the proportion of the hull that is submerged, the more difficult the ship design problem be- 
comes; available hull volume is curtailed and problems of transverse stability (static) be- 
come increasingly difficult with greater submergence. The cost of the craft can also be ex- 
pected to increase correspondingly. Hence, it is desirable to consider and compare all types 
of craft thoroughly to determine the most satisfactory compromise for any particular need. 
ROUGH-WATER PERFORMANCE 
Of course, it is not enough for a surface or near-surface craft to show favorable calm- 
water resistance at high speed. If it is to compete with a deeply submerged submarine, the 
ship must be able to maintain good speed in rough-storm seas. This may be, in part, a pow- 
ering problem. However, in high-speed craft, it is usually mainly a matter of avoiding or 
minimizing ship motions and indirect effects — such as wet decks, slamming, propeller rac- 
ing, local high accelerations, etc. The ideal craft, therefore, is one that provides the best 
compromise between low-resistance characteristics and outstandingly good performance in 
rough water — capable of high speed in any sea condition. 
(As background for the discussion of the problems of rough water performance, the bal- 
ance of this section has been adapted from Ref. 4.) 
Ship motions at sea are usually resolved into six components for study: the angular mo- 
tions of roll, yaw, and pitch and the translatory motions of heave, surge, and sway. Some 
are more troublesome than others, but when one or two are reduced the others are apt to be- 
come more noticeable. Rolling has received particular attention ever since steam replaced 
sails and the steadying effect of canvas was lost. Because the forces involved in rolling 
are small, it has proved feasible to reduce these amplitudes drastically by various antiroll- 
ing devices. The simplest device is the bilge keel, which has been generally accepted in 
shipbuilding for many years. Its effectiveness can be explained on the basis of the theory 
that irregular storm seas contain many regular component waves of a wide range of periods 
superimposed on one another. A ship will respond much more violently to one particular 
