10 RESISTANCE OF BILGE KEELS. 



and stern extensions were fitted these fair waters were cut away so that a square 

 butt joint could be made. 



After the bow and stern extensions of the 3-inch keels were tested and cast 

 off, the fair waters were replaced at the ends of the normal 3-inch keels, 

 thus restoring the boat to the original condition. Experiments were now repeated 

 on this normal 3-inch keel and finally, after it was cast off, the experi- 

 ments made for the bare hull. Our previous experience had shown that the sur- 

 face of the hull, once properly painted, would stay in good condition throughout 

 the season in the Charles River Basin, consequently the surface was not changed 

 in any way, not even when the boat was hauled up to apply the bow and stern ex- 

 tensions of the keels. Experiments with the normal 3-inch keels before and 

 after hauling out and comparison of experiments with the bare hull as made this 

 year and last year confirm this conclusion. 



The resistance of bilge keels under normal conditions is but a few per cent 

 of the total ship's resistance and is determined by the differences of resistances 

 with and without keels; consequently the utmost care and refinement of experi- 

 mental methods are necessary. The apparatus on the Fulton is that described 

 by the writer in an article to be found on page 87, Vol. 19, of the Transactions; 

 with care and skill this apparatus can be made to yield the necessary degree of pre- 

 cision for the work in hand, as will be made evident by the diagrams which show 

 the original observations. It is proper to say here that the success of the year's 

 work depends directly on the skill that has been developed by Professor Harold A. 

 Everett, both in choosing suitable weather conditions and in watching and using the 

 apparatus. His experience convinced him that only perfect weather conditions 

 would enable us to get the certainty and precision needed for this work and that 

 perfection of condition was seized when it came, whether by day or by night — very 

 commonly at 4 o'clock in the morning. He was assisted loyally and intelligently 

 by Mr. J. P. Constable. 



The course for the experimental runs was about 200 feet off the north- 

 western sea-wall of the Charles River Basin, abreast the new location of the In- 

 stitute of Technology. It is marked by small can buoys and land marks have been 

 selected to aid in steering a straight course. The ends of the course this year are 

 marked by certain electric light poles on the parkway along the bank of the Basin ; 

 these formed our back-ranges and the fore-ranges were poles set on an iron fence 

 on the sea-wall. At night the fore-ranges were lighted by lanterns hung on them; 

 the back-ranges were regularly lighted by the lamps of the parkway. This course 

 is just short of an eighth of a knot, quite sufficient for our purposes. 



The observations during a run were : 



1. The time on the course. 



2. The thrust of the propeller. 



3. The revolutions of the propeller. 



4. The power input to the electric motor which drives the propeller. 

 Subsidiary observations were taken of the direction of the run, the direction 



and intensity of the wind and time by stop-watch. 



