ON THE STEERING OP VESSELS. 67 



" Trial Y. — ^That the ship should bo driven full speed ahead with the helm 

 amidships, and notice taken as to the direction in which the ship turns 

 under the action of the screw, 



" Trial VI. — That the ship should be driven full speed ahead, then the 

 screw reversed, with the helm amidships, and notice taken in which direc- 

 tion the ship turns." 



" May 3, 1876." 



After sending the Circular the Committee received a communication from 

 the Secretary to the Admiralty, to the eifect that the Admiralty had ordered 

 the experiments to be made, and that the results should be forwarded. 



As the result of their application to private owners, the Committee obtained 

 the use of three vessels, upon which the following trials were made. 



Experhneiits made with the ' T'aJetta,' belonging to the Earl of Glasgow, 

 Captain E. Hunter, on the 6th June, between Weniys Bay and the Cumbrae. 



The ' Yaletta ' measures 80 tons, and was drawing during the trials 

 5' 6" foi'ward and G' G" aft. Her screw, which is right-handed, is 5' 6" in 

 diameter, and during the trials was immersed about 1' ; it is 3-bladed, and 

 has a pitch of 8' 6". When at full speed the ' Valetta ' makes about 9| 

 knots an hour. 



During the trials the seconds were called out by Mr. James E. Napier. 

 Mr. Bottomley, who was acting for Sir William Thomson, watched the angles 

 thi-ough which the boat turned, by means of a dumb compass, while the 

 signals for turning and stopping the vessel were given by Professor Eeynolds. 



Tiie first trial was of the effect which the screw exerted to turn the ship 

 with the helm amidships. When at full speed she turned to port at the rate 

 of about 7° per minute, or, as it is usually expressed, she carried a port helm. 

 However, as the speed of the engines was reduced the tendency to turn the 

 ship to port was reduced, and when going very slow (about 5 miles an hour) 

 the ship turned slightly in the opposite direction. When going fast the 

 screw churned air into the water, but not when it was going slow. 



The effect of the screw to turn the ship with the helm amidship, although 

 appreciable, was not of sufficient magnitude to be taken into account in the 

 results of the subsequent experiment. And as this effect was almost the 

 same with the wind on cither bow, it was evident that, although the wind 

 was blowing with some little force, its effect to turn the vessel was also 

 unimportant. 



These preliminaries having been settled, the ship was driven fuU speed 

 ahead, then the screw reversed as suddenly as possible, and immediately the 

 engines began to turn astern the rudder was put hard over. At first on 

 reversal the engines turned but slowly, and it was not until the boat had lost 

 some of her way that they turned full speed astern. 



Four observations were taken in this way with the helm to port, two with 

 head to wind, and two before the wind ; and similar observations were taken 

 with the helm to starboard. All four observations with the helm to port 

 gave nearly the same results, and so with the helm to starboard. 



The mean results were as follows : — 



With the helm ported (which, had the engines been going ahead, would 

 have brought the ship's head round to starboard at a rate of nearly 2° a 

 second) the vessel at first, while the screw was turning but slowly, com- 

 menced turning to starboard, and had turned through 5'^ in 9 seconds ; she 

 then commenced turning to port; and in IG seconds more, when she had 

 nearly lost all way, she had returned 13° to port or about 8° to port of her 



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