33a RUDDER TRIAIvS, U. S. S. STERETT. 



APPENDIX VII. 



TURNING TRIALS WITH ENGINES BACKING. 



On completion of the "meeting ship" trials and the turning trials at 

 various speeds ahead, tests were made to determine the turning moment 

 developed by putting helm over with engines backing. Two sets of tests 

 were made; first, two turns with engines backing under all available boiler 

 power; and second, two turns with the engines backing under approxi- 

 mately half of the full boiler power. The full-power backing trials are of 

 particular interest because in them the greatest twisting moment observed 

 throughout the trials was developed. The vibration on these tests was so 

 violent that no correction for friction was applied to the force recorded by 

 the dynamometer. 



On the first backing test, the engines were ordered "full speed astern," 

 and, simultaneously, the helm was put 32° port. The twisting moment 

 rose steadily for a period of ^ minute to 75,080 lbs. -feet, then wavered and 

 rose slowly for \ minute to a value of 136,500 lbs. -feet, fell off for a period 

 of I minute to a minimum value of 74,220 lbs. -feet, and then rose slowly 

 for J minute to a maximum value of 145,030 lbs. -feet. Without moving 

 the helm the engines were ordered stopped and immediately ordered to 

 "half speed ahead," the stress falling off abruptly as soon as the engines 

 were stopped. During this turn, which occupied approximately | minute, 

 the revolutions of the port engine (which were fairly uniform throughout 

 the turn) averaged 358.7 revolutions per minute. The revolutions of the 

 starboard engine averaged 408 per minute. 



On the second full-power backing test, the engines were first ordered 

 to "full speed astern," and after the ship had gathered considerable stem- 

 way, the helm was again put over to 32° port. The twisting moment rose 

 during the first j minute to 111,550 lbs. -feet; during the second J minute 

 to 128,190 lbs. -feet; and at the end of | minute from time of first putting 

 helm over, to a maximum value of 149,090 lbs. -feet. The engines were 

 then ordered to "half speed ahead." The helm was put amidships, the 

 moment falling off rapidly. On this turn the vibration throughout the ship 

 was so violent that the boiler brick walls of two boilers were shaken down. 

 At the same time the quarter-deck was flooded with water so that the 

 electrical connections to the special helm-angle indicator were useless. The 



