3i8 RUDDER TRIALS. U. S. S. STERETT. 



APPENDIX I. 



DESCRIPTION OF SPRING DYNAMOMETER. 



A spring dynamometer was designed to measure the tension in the 

 standing part of the port tiller chain. In order to economize on the very 

 restricted deck space, a vertical "shear-legs" type was chosen, with a 

 reducing motion of one to five. The shear-legs B and C (Fig. B, Plate 113) 

 are of i-inch steel plate doubled, connected by tie T, through pins M and N. 

 At the lower end, the legs B and C are secured by pins G and H to the chain 

 grips E and F. The latter consist each of a pair of i-inch steel plates 

 slotted out to take two links of i-inch chain. These plates are drawn 

 together by bolts to grip the chain securely. Before setting up, at least 

 two inches of slack chain is provided between them. This is ample, because 

 the motion of the chain grip, F, is only A-inch maximum. The tension in 

 the chain is transmitted from the chain grips through the shear-legs to the 

 spring 5. The chain grips, as well as the lower ends of the shear-legs, rest 

 on a slushed iron plate. 



The grip E is secured to the inboard, standing end of the chain, the 

 hand steering gear being locked. The leg B of the dynamometer thus 

 becomes the standing leg, and force is measured by the deflection of the 

 leg C as the spring 5 is compressed. 



The two legs of the dynamometer project vertically through a slot cut 

 in the top of the heavy oak table, shown in Figs. B, 5, 6, and 7, Plates 113, 

 115, 116, and 117. The standing leg B is securely blocked to the table. 

 The leg C is free to move in the direction of the slot. 



Springs of such strength were chosen that the motion of P should be 

 less than half an inch. A limit stop is fitted in the slot to bear against C, 

 and protect the recording gear in case the motion of P is as great as f inch. 



The motion of P is transmitted to the recording gear by a fourfold 

 multiplying purchase consisting of a monel metal wire diameter 0.009, led 

 over two double f-inch indicator pulleys to the carriage on the recording 

 gear. The latter is mounted on a corner of the table top. The motion of 

 |-inch compression in spring is transmitted as a motion of 3 inches of the 

 recording carriage. 



