High Speed Displacement-Type Hulls 6l1l 
Professor Telfer rightly draws attention to our statement that “again there is no clear 
evidence of any predominant form parameter.” We agree that, for clarity, this would have 
been better if qualified by the important reservation “apart from displacement/length ratio 
or its equivalent @ .” We also agree that a presentation based on @ would be better 
than one with displacement alone as basis. Professor Telfer’s advocacy of © @ as the 
best criterion for power comparisons at different displacements also has much to commend 
it. However, we were primarily concerned with presenting the basic information as simply 
as possible, and presumed that those who used it would know how to do so correctly. 
Mr. Barnaby also advocates an alternative basis of comparison. However, his factor 
K = V\V/A/P also has disadvantages. It has the dimensions of a velocity, and it seems 
that a nondimensional factor K/\/V would serve Mr. Barnaby’s purpose better. This is 
closely related to what is sometimes called transport efficiency, and when the values 
quoted by Mr. Barnaby are converted into this form the very valid practical advantages 
which he claims for this type of comparison factor are demonstrated more clearly. It is also 
worth pointing out that much of the data given in the paper are for speeds at which hydro- 
dynamic lift is relatively unimportant, and to that extent © is still a reasonable drag 
criterion. 
The comments of Mr. Hadler and Mr. Clement also form a valuable addition to the paper. 
We hope that further work will be undertaken at DTMB and other establishments to examine 
the potentialities of hybrid craft with partial hydrofoil support. The additional information 
requested on details of propulsion arrangements will be included in a subsequent paper 
intended to give results of systematic propulsion experiments with models of high speed 
displacement-type hulls. 
