of the ship, we have a relative measure of what we might expect to be the upper limit 

 of speed in a rough head sea condition. 



On this basis, it is found that a 500-foot ship built to the lines of the parent 

 Series 60, 0.60 block model, might be expected to be in trouble in a particular sea 

 at around 12 knots. Above this speed the motion would be too violent, and the ship 

 would have to slow down. A ship of this same displacement, with the length over 

 breadth increased from IV2 to 81^, and beam over draft increased from 2Vi to 3, 

 which is one of the new series, would be a 580-foot ship, and on the basis I have 

 outlined we might expect it to run into storm difficulties at a speed of HV2 knots, 

 instead of 12, on a comparative basis. This means a 15% increase in sea speed with 

 a 15% increase in length. 



This advantage of increasing length in irregular head seas has been shown by 

 model tests to be more than theory. In a project at Stevens, sponsored by ONR, a 

 wide variety of different models is now being studied. For example, a trawler model 

 was tested in its original form, and then lengthened out and made more slender. When 

 compared at the same displacement, the greater potentiality for speed for this length- 

 ened ship could be clearly seen. 



Unfortunately, length is, as we well know, the most difficult dimension to 

 increase, not only from the point of view of cost, but from practical reasons, such as 

 limitations of harbors and ports. Still, in many cases there may be a possibility of some 

 increase, and whatever can be done will be to our advantage for speed in rough 

 weather. 



Finally, I should like to emphasize again Professor Weinblum's point about 

 the need for ship data on permissible limits of motions and accelerations, both for 

 comfort and for safety. Without more information of this sort new theoretical and 

 experimental developments cannot be effectively applied. For example, even though 

 model techniques, irregular-wave theory and new oceanographical data permit us to 

 predict for a given condition the average or maximum amplitudes of motion, accelera- 

 tions, etc. with some degree of confidence for a new design over a range of speeds, we 

 still are unable to predict what would be the limiting speed for the actual ship. 



This and the other problems outlined by Professor Weinblum will keep us all 

 busy for some time to come. 



V. G. Szebehely 



It is a pleasure to make these few comments on Professor Weinblum's lecture 

 at his request. 



In order to save time, only a systematic listing of projects connected with the 

 topics mentioned in the lecture will be given with a very few remarks. 



1. In connection with Dr. Weinblum's reference to fins, attention is called to 

 an investigation of the effect of anti-pitching bow fins on the motion of aircraft carriers 

 and merchant vessels. Before the feasibility of applying fins was considered, the effects 

 of bulbous bows on the motion were investigated by theoretical and experimental 

 means. No significant motion reduction was found with normal size bulbs. Fixed fins 

 at the bow have two beneficiary effects; firstly they reduce pitching, secondly they 

 reduce speed losses in waves. Various planforms, profiles, area, combinations, speeds 

 and waves were investigated and it was found that 40-60 percent pitch reduction can 

 be obtained in certain practically important conditions with bow fins whose area was 

 approximately 2 percent of the water plane area [ref. 1. 2]. 



2. A study of speed reduction in waves is given in ref. 3. The work evaluates 

 the speed maintaining characteristics of a destroyer, of a fast and of a slow cargo 

 ship. From simple theoretical consideration, formulas (which are very sensitive to 

 phase relations) were derived and at the present time are being compared with the 

 experimental findings. 



3. Motion predictions were performed in connection with model tests. Phenom- 

 ena in which phase relations play significant part, seem to be hard to predict. Con- 



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