EXPERIMENTS ON THE EULTON AND THEIEROUDE. 5 



The success of the season's work is largely due to the experience, ability 

 and devotion of Professor Everett ; to Mr. Keith is due the computation and 

 presentation of the results, for which his previous experience peculiarly fitted 

 him ; Mr. Pulsifer at all times gave loyal and intelligent assistance. 



The possibility of the prosecution of experiments during the present 

 year was due primarily to Mr. Arthur Curtiss James and Mr. Clinton H. 

 Crane, who guaranteed a sum which I estimated as sufficient ; when it was 

 found that this sum would be much exceeded Mr. Wm. Endicott, Jr., and 

 Mr. Henry A. Morss advanced sums which covered the remainder of the 

 expenditures. Mr. Harrison Loring, Jr., of the R. S. Brine Transportation 

 Co., very kindly sent a receipted bill for the transportation and launching of 

 the Fulton and other services. 



INFLUBNCe OF BLADE-AREA. 



A tow-boat, especially of the harbor type, has three various kinds of 

 duty, namely (i) to run free, passing from place to place, and perhaps seeking 

 business in face of competition; (2) towing at a reduced speed, commonly at 

 half speed or somewhat more; and (3) pulling or pushing a ship into her 

 berth at very slow speed, or nearly without speed. 



Running-free tow-boats differ from other classes only in that being 

 high-powered to enable them to tow, they have relatively high speed even 

 though not designed with that in view. 



To have a ready standard of comparison in our discussion of the effect 

 of width of blade and area-ratio, let us consider that the standard admiralty 

 blade proposed by Froude has been found sufficient for all classes of ships 

 (excepting tow-boats), until cavitation has brought about the use of wide 

 blades in certain cases. Now this standard blade has a maximum developed 

 width of 0.2 of the diameter of the propeller which gives a developed area- 

 ratio for four blades of 0.36 ; the projected area-ratio is somewhat less, depend- 

 ing on the pitch. The experiments on model propellers by Naval Constructor 

 Taylor show that such an area-ratio is preferable for the generality of pro- 

 pellers but that the ratio may be increased up to 0.48 without appreciable 

 disadvantage. From a study of Mr. Taylor's experiments and of the tests 

 about to be related I am ready to advise the use of a projected area-ratio of 

 about 0.5 for four-bladed propellers for all tow-boats. The minimum area- 

 ratio of the propellers used on the Froude in 191 1, as stated on page 2, 

 is 0.44. 



In considering the effect of width of blade and projected area-ratio let 

 us take up the results of experiments on the Froude with the several pro- 



