304 RUDDER TRIALS, U. S. S. STERETT. 



METHOD OP CONDUCTING TURNING TRIALS. 



On June 8 and 9, turning trials underway were carried out in Massa- 

 chusetts Bay in the vicinity of Boston Light Ship. The trials made on the 

 first day were not satisfactory^ owing to a stiff breeze and a rough sea. But 

 on June 9 the conditions were so favorable that the whole program of tests 

 previously outlined was completed in the one day. 



The sea was smooth with a long ground swell. The mean displacement 

 of the ship was 835 tons, 12.7 per cent greater than the displacement on 

 standardization. The correction to the speed-revolution curve for this 

 difference is discussed in detail in Appendix VI. The depth of water in 

 which the trials were run varied from 12 to 20 fathoms. 



A ship's telephone circuit was rigged from bridge to quarter-deck, and 

 there was also on the bridge a push-button connected by solenoid to a 

 tracing pen on the recording apparatus. 



The procedure for a run was as follows. The ship was put upon a 

 steady course at the desired speed (the corresponding'revolutions per minute 

 being maintained as nearly as possible except during actual turning, when 

 the throttles were not touched). After steadying on course and speed for 

 a reasonable length of time, a "stand by" was given to the engine-room 

 and to the man in charge of the dynamometer and gear aft. The order 

 was given to the helmsman "starboard 25°," etc., and simultaneously a 

 "start turn" signal was given by bell to the engine-room, and a "jog" 

 transmitted to the record roll (Plate 119). As the ship's head swung past 

 10°, 20°, and 30° by steering compass, one, two, and three notches were trans- 

 mitted to the "signal" line on the record roll. Since a practically steady 

 value of stress was in every case reached at 40° to 60° of swing, the turn 

 was considered finished after swinging through eight points. The helm was 

 then put amidships and the ship steadied on her course at the speed desired 

 for the next turn. On each turn the time to put helm over was checked on 

 a stop-watch, and the helmsman was coached to secure a uniform rate. 

 The average rate at which the helm was put over was 3° per second. 



For convenience the tests were begun at the lowest speed. The "meet 

 ship" turns were run in wherever the speed of ship, and capacity of dyna- 

 mometer spring already fitted, made it convenient. The full-power backing 

 trials were made immediately after the turns at maximum speed ahead, and 

 the trials were concluded with the backing turns at reduced power. 



As a rough guide in the size of spring required at various speeds and 

 helm-angles, Joessel's formula was used with a large coefficient of reduction 

 for safety. After inserting the spring, the dynamometer was set up with 



