42 J. D. van Manen 
Next, a point about the economic comparison between a conventional and a submarine 
tanker. It is stated in the paper that for 20,000 tons deadweight and a speed of 20 to 25 
knots the submarine tanker would have a distinct advantage. One has to be careful here of 
the basis of comparison—I think this is intended to be a surface tanker of 20,000 tons and 
20 to 25 knots speed. This of course is not conventional as regards speed and would cer- 
tainly be less economical than a commercial tanker of this deadweight which would have a 
speed round about 15 to 16 knots. I am speaking here, by the way, of economy on the basis 
of cost per ton-mile of cargo carried. On the other hand, from the military point of view, 
there may of course be some advantage in carrying the cargo at the faster speed. 
J. D. van Manen 
In reply to Mr. Lackenby, the 10,000 hp before 1940 refers to a single screw ship. 
D. Savitsky (Davidson Laboratory, Stevens Institute of Technology) 
The presentations by Mr. Oakley and Dr. van Manen on the subject of high performance 
ships of the future were indeed stimulating and exciting. The variety of hydrodynamic forms 
being considered by the authors is expressive of an open mind toward the consideration of 
solutions to the problem of high speed transport across the ocean. 
Common to each of the vehicle forms considered by the authors is the serious problem 
of negotiating the rough surface of the ocean at high speed—a problem where severity 
appears to increase exponentially with speed. Partial solutions to the rough water problem 
are proposed by the use of submerged hull form, hull forms lifted clear of the water by hydro- 
foils and by ground effect machines flying just above the waves. In each case the roughness 
of the sea is still a serious disturbance, although to a lesser extent than for a displacement 
vessel. Clearly, the solutions proposed by each of the authors consist in a vertical dis- 
placement from the water surface. 
I would like to carry this suggested solution to its logical conclusion and suggest that, 
for high speed transport over waves, let’s leave the water surface entirely. If our mission 
is to transport material or people from one port to another at high speed, there is obviously 
no necessity for exposing the high speed vehicle to the serious disturbances of the sea for 
the entire length of the voyage. Obviously this suggestion leads to the rediscovery of the 
water based aircraft—especially designed for short range, low altitude, and relatively low 
speed operation (for an aircraft)—perhaps 200 to 300 miles/hr. Ordinarily I would not pro- 
pose such a concept at a meeting on Naval Hydrodynamics. However, since the authors 
have discussed ground effect machines operating just over the waves at speeds of 100 
mils/hr or more, I feel they have strayed sufficiently from the area of conventional hydro- 
dynamic forms to allow me the freedom to do likewise. I feel that as the GEM concept is 
developed further and further, its appearance will be more like that of an aircraft. If this 
is to be the case, let us immediately consider the role of the water based aircraft for the 
short range transport vehicle. A well designed seaplane can easily develop a lift-drag ratio 
of 20 at altitude. Perhaps this can be increased by flying at low altitude (in moderate 
ground effect) yet out of the range of the severe wave disturbances of a sea state. To 
obtain equivalent lift-drag ratios, the GEM would probably need a static thrust augmentation 
factor of nearly 40, which would necessitate its operation at very low height-diameter ratios. 
For operation in a sea state of moderate severity, then, the length of the GEM would prob- 
ably be upwards of 500 or 600 feet in order to achieve the required height diameter ratios 
