600 W. J. Marwood and A. Silverleaf 
anywhere it is incorrect, though it is conceivable that such an acceleration could be 
recorded at say the stem in exceptional conditions of speed and irregular wave formation. 
In the particular case of this reported research in Ref. 4, however, the objective was 
to find extremely adverse conditions which did not prove easy and eventually resulted in a 
slightly hazardous attempt to run across the bow wave train of the “Nieuw Amsterdam” at 
35 knots. 
As this bow wave train was approaching us at a speed estimated to be 14 knots the 
conditions of encounter were equivalent to the launch meeting the waves at (35 + 14) = 49 
knots. 
Under these circumstances it is not surprising that 6 g was experienced in the wheel- 
house. The maximum acceleration at the stem was recorded as 8.28 g but this was in 
exceptionally adverse conditions. 
The relative merits of the round form and the planing form (so called) are discussed at 
some length in Ref. 4 and in the discussion thereto. 
In this connection it is interesting to mention N.P.L. Report S.H.MV. 5 of Feb. 28, 
1955, where a hard chine and round form were tested in waves. It was reported that there 
was little to choose as regards vertical accelerations between the hard chine and the round 
form. If anything the accelerations appeared less in the case of the planing form and cer- 
tainly the spray on decks was reported as less in the case of the planing form. 
This, of course, does not accord with the comment in the paper we are now discussing 
which reads as follows: 
“The chine form is ‘stiff’? in waves and tends to slam violently. The low chine forward 
throws water forward and up, obscuring wheelhouse vision and producing a wet ship. The 
round bilge form pitches more but this reduces slamming. The flare forward, which was 
designed with particular care, is very effective in throwing water away from the hull. The, 
film records clearly show the superior wave performance of the chineless, round-bilge form. 
Although the behaviour of the hard chine form could be improved by raising the chine line 
forward, it was not possible to reduce its resistance to that of the round-bilge form. It is 
hoped that a vessel having this round-bilge form will shortly be built.” 
Among other comparisons between planing and hard chine craft which are available in 
Ref. 4 is a closely reasoned and cautious judgement made in the course of the discussion 
by Dr. Gawn based on his great experience at the Haslar Tank and his collated data from 
sea reports. His contribution is offered verbatim: 
“The author makes no secret of his preference for a hard chine hull and it does appear 
this type can be drier and generally no less satisfactory at sea than the round bilge. There 
is a need for firm fact to replace some of the contentious opinions often expressed on sea 
behaviour, and the author’s tests go some way in this direction. However, the issue is not 
clear cut in a general sense but depends on the size and speed of the craft. If, for example, 
the speed-length coefficient is less than about 3.7 there is much to be said for the round- 
bilge form because of its resistance advantage in calm water. If, on the other hand, as in 
the launch dealt with in the paper the speed is much greater, then the hard chine hull can 
have a clear advantage as regards resistance in calm water and in my judgement is to be 
recommended, provided there is no overriding emphasis on economic cruising at low speed.” 
