602 W. J. Marwood and A. Silverleaf 
The planing form probably can be made to slam more unless trim is adjustable by 
transom flap or similar device. Equally the round form can undoubtedly be made to bury her 
forecastle in the waves and wash down her bridge. Directional stability is much better in 
the planing form and there is less liability to yaw and broach in a following sea. In head 
seas the hard chine craft will lose more speed due to the energy lost in generating spray 
which undergoes an acceleration relatively forward and outward from rest. This feature 
tends to keep the decks and bridge dry. 
So far we have only discussed the relative merits of the round form and hard chine 
planing craft and it may be appropriate to point out here that in the light of development 
over the years the difference between the two classes of craft which used to be clearly 
defined are becoming very much less. 
For instance, both types are in fact planing craft in the generally accepted sense. In 
both types it is fully appreciated that the waves must be met from ahead by relatively soft 
V-shaped or rounded sections. Equally, to obtain good resistance qualities the aft sections 
in both types are relatively flat and wide and run to a “chine” at the sides. To control the 
amount of spray on deck both types work a substantial flare in forward sections leading to a 
“knuckle” or chine. 
In fact it is probably fair to say that in theory the optimum would be represented by a 
rather wide form incorporating the forward sections of a round-form craft with the aft sec- 
tions of a planing form. The draw-back here is that the round form leads to wetness on deck 
and width leads to rather excessive slamming. 
Such a compromise form is represented in Figs. D1 and D2 by model 57. 
As the subject of the Symposium covers high speed craft it may not be out of place 
here to state the admittedly personal opinion that no hydrofoil craft of the surface piercing 
type has given any real evidence of being able to deal with substantially rough conditions 
in the open sea more successfully than the round form or hard chine. 
It seems possible the submerged foil arrangement as demonstrated by Dr. Hoerner 
during this Symposium may be superior in this respect but at the moment this awaits prac- 
tical proof at sea, at least in the larger sizes. 
The ground effect machine may seem to be limited at the present state of the art by the 
very severe effect upon lifting efficiency likely to be experienced if cushion heights suit- 
able for passage over the ocean waves are to be generated. 
Finally as a constructive suggestion we should like to suggest to the authors that we 
could submit for trial a hard chine planing form which would prove a much more serious com- 
petitor to the round form proposed than is the form exemplified in model 2117. 
It would also be most valuable to run a hydrofoil configuration of comparable dimen- 
sions and load-carrying capacity in comparison with the above forms. 
D. Savitsky (Davidson Laboratory, Stevens Institute of Technology) 
I would like to comment on the interpretation given by the authors to the relative sea- 
keeping abilities of the so-called hard chine and round-bilge boats. It is the authors’ 
