610 W. J. Marwood and A. Silverleaf 
can be designed to differ much less, and the differences between them in performance will 
then also be much less. Indeed, the round-bilge form as quoted by Cdr. du Cane retains a 
chine line forward and aft intended to influence the flow pattern. 
There seems to be some doubt as to the correct interpretation of some of the results 
given by Cdr. du Cane in Ref. 4. Table IV of that paper gives for Run 35 the maximum 
acceleration in the fore peak (position Al) as 8.36 g in waves 2 to 3 feet high. On the 
other hand, Table III gives a value of 2.86 g for the same run; this may be an average value 
of the measured acceleration, and agrees well with model values measured at N.P.L. 
The experiments quoted by Dr. Graff, carried out in Duisburg with high power round- 
bilge forms in deep and shallow water, are of considerable interest. A full account of these 
experiments has been given,* and the results show the same characteristics as those given 
here for similar experiments. However, detailed comparison shows some differences in the 
absolute values of resistance coefficients, and these discrepancies emphasise the need for 
further investigations of shallow water effects. 
Mr. Newton’s contribution is a most valuable addition to the paper, for which we are 
very grateful. In drawing on the extensive store of information available at Haslar he has 
raised many points which we are not qualified to discuss, and we shall restrict our com- 
ments to four of the topics he mentions. First, we agree that a narrow transom does give 
increased running trim, but only for speed/length ratios V/\/L greater than 1.8, and it then 
also increases the resistance. However, at lower speeds, particularly below the resistance 
hump around V/VZ, = 1.5, when there is little or no hydrodynamic lift, a narrow transom is 
found to decrease resistance. Indeed, at lower speeds still it becomes advantageous to fit 
a cruiser stern. Second, we are slightly surprised at Mr. Newton’s statement that propellers 
increase running trim significantly. Provided the model is towed along the shaft axis when 
the resistance and trim are measured, we should not expect the trim to alter appreciably 
when it is self-propelled, unless the propellers have a marked influence on the average sur- 
face pressures over the after body. Third, we agree that at planing speeds the pitching 
centre is well aft; indeed, it can be aft of the transom. Fourth, experiments made at N.P.L. 
support Mr. Newton’s views about transom flaps. Attempts to turn or “hook” the extreme 
afterbuttock lines have also succeeded in reducing calm water resistance. However, we 
believe that, in a vessel designed to operate mostly at one speed, transom flaps are only 
needed when the basic hull design is faulty. For a vessel intended to operate at several 
different speeds, the fitting of flaps is more easily justified. Some interesting effects of 
flaps on heave and pitch have been observed in experiments at N.P.L., and these agree well 
with the comments made by Mr. Newton. 
Mr. Savitsky points out that the terms round bilge and hard chine are not satisfactory 
descriptions for comparing ship performance in waves. We agree with this criticism, and 
agree also that the deadrise angle forward is a more realistic criterion to adopt. The 
principal justification for the descriptive terms used in this paper is that they are commonly 
employed by naval architects, and it was hoped that they would be sufficiently precise for 
the purposes of this preliminary report. We must also apologise for not referring explicitly 
to the Davidson Laboratory reports on planing craft. 
*W. Sturtzel and W. Graff, “Systematische Untersuchungen von Kleinschiffsformen auf Flachem 
Wasser im Unter- und Uberkritischen Geschwindigkeitsbereich,” Report 617, Versuchsanstalt 
fir Binnenschiffbau, Duisburg, 1958. 
