LAUNCHING OF SHIPS IN RESTRICTED WATERS. 207 



the keel track reaches the after keel wheel ; the latter then supports the weight until 

 the model pivots, when a special releasing device drops it clear of the forefoot as 

 the model leaves the ways. 



Although not shown on the photographs, the tumbling shores, cribs, wedges, 

 cable reels and brakes were later added to the model, in order that launching drills 

 might be held at the model, and the various gangs acquainted with their duties and 

 the sequence of operations. A small brass preventer dog shore and a set of solenoid- 

 operated mechanical triggers represent accurately the dog shores and hydraulic trig- 

 gers on the ship. Two brass trimming masts, with pencils attached, erected at the 

 forward and after perpendiculars, record the traces of the bow and the stern at all 

 points of the launching operation. 



A special recording mechanism was designed and built, to record simultaneously 

 all data and to make the model as nearly as possible automatic in its operation. 

 Reference to the plates will indicate the general arrangement of this machine. 

 Without undue elaboration of details, the construction and operation of this mechaT 

 nism may be described briefly as follows: — 



A small cord (or cable, as it will hereafter be called) is fastened by a wire 

 hook to an eye plate in the bow of the model at the i6-foot water line. This cable 

 is led forward over an aluminum idler pulley carried on a swinging frame and then 

 back and around a small drum about V/t. inches in diameter. Sufficient cable can be 

 wound in a single layer on this drum to permit the model to run to the far end of 

 the channel. The drum, as shown on Plate 87, has two silver contacts on a small 

 commutator and acts therefore as a chronograph, giving two marks per revolution 

 on the recording paper. A standard navy mean time break-circuit chronometer 

 indicates seconds on the recording paper (by means of suitable solenoids and pen- 

 cils) as a reference for the chronograph readings. The recording paper is that 

 supplied for the Burroughs adding machine ; it is drawn at constant speed over the 

 paper table by two rubber rollers geared to a small D. C. motor. A small controller 

 with adjustable segments, also driven from this motor, controls the current to the 

 solenoid triggers and to the tripping coils of the brakes ; this controller switches on 

 and off the motor and other solenoid circuits and renders the mechanism entirely 

 automatic in its operations. As the entire launch consumes only seven or eight 

 seconds, it is not practicable to arrange for manual operation in this connection. 



The launching brake mechanism, also to be very briefly described, does not, 

 of course, operate in exactly the same manner as the brakes on the full-sized vessel. 

 The small drum upon which the cable is wound is constructed with heads of highly 

 polished steel. Cork insert brakes, carried on swinging plates, bear against the 

 heads of the cable drum and serve to retard the angular motion of the latter when 

 the brakes are applied. The assembly of these plates, together with the cords and 

 weights used to clamp them against the drum, is shown on Plates 86 and 88. It will 

 be seen that a small coil spring holds the plates clear of the drum when the brakes 

 are to run free. 



The weight carriers and weights are released by solenoid operated triggers, as 



