Hydrodynamics of High-Speed Hydrofoils 129 
INTOLERABLE 
gs 
RMS Heaving Accelerations in 
PERCEPTIBLE 
Ol 1.0 10 
Frequency of Heaving in cycles/sec 
Fig. 6. Human sensitivity to heaving oscillations 
such a sea cannot, for reasons of comfort alone, be followed to any extent, but must be 
plowed. Such an effort, of course, requires a boat with sufficient hull clearance and foil 
submergence for the hull to pass over crests and the foil system to extend under wave 
troughs. Variable incidence foil systems particularly recommend themselves for plowing, 
since a typical surface-piercing foil would during such motions experience fluctuations in 
load due not only to the orbital subsurface velocities associated with waves, but also to 
changes in wetted area. 
It is of interest to calculate the fluctuating loads acting on a plowing fully submerged 
foil system, without trim changes, flap or spoiler actuation (in other words, a passive foil 
system), in order that the problem of controlling these loads by one or another of the means 
just mentioned can be properly assessed. These loads will actually depend on the rigid body 
motions of the vehicle and the structural flexing. Aircraft experience [10, 11] would lead 
us to believe that such dynamic effects tend to increase the loads calculated on the basis 
of a rigid structure and quasi-static analysis such as we make here. Thus, alarming as our 
results may be, they are probably not to be relieved by more rigorous calculations, but only 
through a relaxing of the sea conditions that we have referred to. The dynamic g loadings 
(in addition to static loadings) induced by the seaway on a fully submerged wing are, accord- 
ing to quasi-static and rigid-body theory, approximately equal to 
(CL,/CLU0)7 
