EXPERIMENTS ON THE FULTON AND THE FROUDE. ii 



TOWING ABREAST. 



In a seaway ships and barges are always towed with considerable length 

 of line for obvious reasons ; in smooth, restricted waters the tow-boat is com- 

 monly brought alongside. On Plate 15 curves are shown with the Fulton 

 towing -ndth an 80-foot line (less than three times its length), and towing 

 abreast. There is an advantage of ten or twelve per cent when towing 

 abreast, which is about the advantage of using a long tow-line (six or seven 

 lengths) . The common practice of either using a long line or towing abreast 

 appears to be well founded. 



DESIGNING. 



The most practical use that can be made of the results of these tests on 

 towing is for the design of new boats. Fortunately both the Manning and 

 the Sotoyomo are well designed, having good forms and fair lines. Perhaps 

 the Manning is a little too fine for an ocean tow-boat, Vv^hich is likely to be 

 rather shorter and more beamy; the form of the Sotoyomo appears to be 

 exceptionally good for speed and might well be taken as a type for design 

 except where speed is of minor importance, in which case a fuller body might 

 enable a boat to carry more power. 



It may therefore be suggested that designs for tow-boats shall be based 

 directly on the tests of the Froude and the Fulton by the theory of mechani- 

 cal similitude, bearing in mind that the experiments were all made in fresh 

 water. The usual method of assuming resistance and power to be propor- 

 tional to the density can be used in applying our results to boats operating 

 on salt water. 



Our results are given in brake horse-power, while engines are habitually 

 designed for indicated power. My own opinion is that a mechanical eflS- 

 ciency of 0.90 may be obtained for a well-built engine when in good condition ; 

 0.85 may be used by those who wish to be conservative. 



Plate 10 shows that tow-boats are likely to be driven well up to the 

 critical speed at which the power increases more rapidly than the cube of 

 the speed; consequently the common method of using an admiralty coefii- 

 cient for estimating power is, in my opinion, entirely inapplicable. 



The speed for towing (about 0.6 full speed) is well under the critical 

 speeds and our experiments show that power varies nearly as the cube of the 

 speed and consequently the method of the admiralty coefficient may properly 

 be used. 



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