Page 343 equipment and instruments 4432 



4432. Photoelectric Pilot 



The photoelectric pilot is a device for automatic steering in conjunction with the 

 magnetic compass. There are three models of slightly different design for vessels of 

 different sizes, although the same principle is embodied in each. The largest model is in 

 use on the new auxiliary vessels of largest size. It is composed of the following five 

 principal units: 



(a) The binnacle unit, or directive element, consists of a high-grade magnetic compass of special construction, a simple light 

 system, and a photoelectric cell, so arranged that the slightest deviation of the vessel from its course is detected and relayed to the 

 steering engine unit. The binnacle unit is entirely automatic in operation. It is the brains of the pilot and performs accurately under 

 all conditions of steering. It is entirely self-contained and requires no attention. Since it is not referred to in setting a course, it may 

 be located in any convenient place in the vessel. 



(6) The steering enoine unit consists principally of the main casting, differential gearing assembly, motorized speed reducer power 

 unit (electric), wheel-locking brake, limit switch assembly, and the drive to the tiller lines. 



There are three gears in the differential assembly; the motorized speed reducer drives the first, the second being driven from the 

 hand steering wheel, the drive to the steering cables being from the third member, or carrier. 



In any differential gearing assembly, whenever one of the three rotating members is locked and either of the two remaining members 

 is rotated, the one remaining free member will also be rotated. 



For hand steering the first member of the differential is locked and the hand steering wheel is mechanically connected to the second 

 member of the differential. Turning the hand steering wheel rotates the second member of the differential unit and this motion is 

 imparted through the differential gears to the third member of the differential, or the carrier, from which the steering cables are driven. 



For either power or automatic steering, the second member of the differential is locked, the electric circuit to the steering motor 

 is closed, and the motor is operated in response to the impulse from either the automatic compass or the power steering control switch. 

 Operation of the steering motor through the differential gearing moves the steering cables. 



For power steering by hand, the steering motor operates at fuU power for rapid rudder movement, sufficient to move the rudder 

 through an angle of 70° in 25 seconds. 



In automatic steering the motor is automatically slowed down, for considerably less speed is required than in power steering. In 

 automatic steering the hand steering wheel is locked and cannot be rotated. This safety feature prevents anyone from being injured by 

 coming in contact with a rapidly revolving power-driven steering wheel as when the steering wheel shaft is driven directly from the 

 steering motor. 



Limit switches are mounted directly on the steering engine to stop the steering motor just before the rudder gets hard over in either 

 direction. They are adjustable for any degree of rudder angle. 



A roller chain sprocket from the third member of the differential moves the steering cables. 



(c) The electric control cabinet unit is composed of the heavy-duty reversing contactors, transfer relay, motor speed resistance, sensi- 

 tive relay and amplifier units, and the voltage divider unit. The contactors control the current to the steering engine motor. The trans- 

 fer relay is an electromagnetic relay which transfers the control circuits from power steering to automatic steering and vice versa. The 

 sensitive relay and amplifier units and the motor speed resistance are used only in conjunction with the automatic compass in automatic 

 steering. 



(d) The pilothouse wheel, gear, and bearing unit comprise the hand steering wheel shaft, the pilot power steering shaft and switch, 

 and the switch control gearing. 



The hand steering shaft is directly connected to the second member of the differential by a continuous roller chain and chain 

 sprockets. 



The photoelectric pilot power steering wheel drives a shaft with a worm and worm gear which operate the power steering switch. 

 The rudder is moved by the steering motor in direct response to each movement of this pilot wheel. Centering this wheel causes the 

 rudder to move amidships. Moving the pilot wheel halfway hard over to the right gives half-right rudder, etc. A rudder angle indicator 

 indicates the actual rudder position at all times. 



To place the pilot in the automatic steering position, the pilot steering wheel is centered and a push button switch is pressed. This 

 energizes the transfer relay in the control cabinet causing the control to be shifted to the automatic compass. 



To transfer control from automatic to power steering, the pilot steering wheel is moved either way off-center to disengage the transfer 

 relay, causing the control to be shifted to the power steering position. 



(e) The automatic differential unit is a small motor-driven differential connected in the drive between the steering engine and the 

 birmacle unit. It is used only in automatic steering. Its function is to keep the automatic compass continuously alined with the mag- 

 netic compass while steering by hand with the pilot steering wheel so that when a change is made to automatic steering, the automatic 

 compass will always be on the proper heading. 



A smaller model is constructed and recommended for vessels between 50 and 100 

 feet in length. It has been installed on the new wire-drag launches Hilgard and Wain- 

 wright. It comprisQg three units: the steering motor with built-in clutch, the compass 

 unit, and the electric control. 



The steering motor unit may be installed in any convenient location where it can 

 be connected by means of a sprocket and roller chain, so that when the clutch is engaged 

 the steering motor actually operates the rudder system. The compass unit should be 

 located where it is as free from magnetic disturbance as practicable. The electric 

 control system is usually installed in the engine room. 



