simple. For example, to double the speed of a 50,000 ton displacement ship from 30 

 knots to 60 knots would require an increase of power by a factor of about ten. Which 

 in this case would mean increasing the power from 140,000 to 1,400,000. In this ex- 

 ample the displacement was assumed constant. This, of course, could not be so unless 

 the increased power and fuel requirements could be met without increase in weight and 

 space. To some degree this has been the case in surface ships because of the improve- 

 ments, over the years, in the reduction of the machinery fuel rate and weight per shaft 

 horsepower. Much of our increase in the speed of surface ships can be attributed to 

 the improvements in the machinery plant rather than to any recently gained knowledge 

 of ship hydrodynamics. On the other hand, the speeds of submarines have been in- 

 creased because of recent work concerning hydrodynamics of submarine hull forms. 



Frictional or viscous resistance has been under constant study since 1872 [1], [2], 

 [3], [4], and we are still in doubt as to the exact nature of this phenomenon. While the 

 correct understanding of frictional resistance cannot be considered a serious barrier, its 

 importance should be recognized. This kind of resistance [3] accounts for some 50 per 

 cent of the total resistance of many of our surface warships. Ship trials have indicated 

 that the effect of different paints may cause as much as 15 per cent variance in total 

 power, or some 30 per cent in skin friction. When the amount of power being de- 

 veloped in such ships to overcome frictional resistance is considered, the necessity for 

 an understanding of the mechanism of skin friction should be obvious. Not only does 

 the nature of the surface affect the drag but the wake is also changed, which is reflected 

 in differences in the propeller performance. In the case of submarines practically all of 

 the submerged resistance is frictional or viscous drag. To reduce this drag has intrigued 

 many research minds and some thought has been given to the possibility of maintaining 

 laminar flow by boundary layer control. 



It is in the area of wave-making resistance where the surface ship meets some 

 of the most formidable barriers, and it has been one of our great aims in life to avoid 

 or reduce this type of resistance. The determination of the wave-making resistance has 

 been one of our most active fields for theoretical and applied research. We have had 

 to rely entirely on the results of model tests, singly and in groups or series, for the 

 specific values of the effects of wave making on resistance. The basic problem results 

 from the failure of the residual resistance coefficients to follow a simple law for different 

 speeds and hull forms because of the change in the flow pattern with speed. Remark- 

 able results have been obtained from the application of mathematical methods to the 

 investigation of wave-making resistance of well-defined ship hull forms. The results of 

 these investigations have reached a stage in which they have been correlated by experi- 

 ment; but direct application to problems of actual surface ships have not been realized 

 as yet [5], [6], [7]. 



An important property which has been well established is that maximum values 

 of the residual resistance occur in Froude number (speed-length ratios) ranges of prac- 

 tical interest. The criticalK/yL values at which the maxima or humps occur are close 

 to 0.8, 1.0, 1.5. Most of our large ships are limited in speed because of the great in- 

 crease in power required to drive them beyond the speed-length range of 1 to 1.25. At 

 the present time we see little likelihood of breaking down this barrier to high speed in 

 large ships. As a point of interest I would like to mention that the fast ocean liners 

 operate at speeds close to V/y/L of 1.0 in smooth water. 



The two most obvious motions of a ship in a seaway are pitching and rolling. 

 Rolling can be the more violent of the two and in a heavy sea a captain will change 

 course to reduce this violent motion. Such a course change will result in increased 

 pitching but this can be controlled to some extent by speed reduction. In rough water 

 a surface ship may be forced to slow down for several reasons and pitching is probably 

 the principal one. Pitching exaggerates nearly all causes of speed loss. It leads to ship- 

 ping water over the bow, slamming, and increased resistance. The point of greatest 



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