Navigation and Seamanship

6.7.7.1. System diagram of autopilot

                                                                                    

System diagram of autopilot:

Input: Actual course,derived course and ship’s speed

Output: Derived rudder angle.

Disturbances: wind and wave

Autopilot is a relatively simple device which reliesentirely on ship borne sensors to function. The automatic steering device usually works with a gyro compass but can also work with the help of magnetic compass with a repeater system. The autopilot is in fact the main element of the system of continuous automatic control. This consists of a sensingelement-gyrocompass-a computing system with and amplifier and the steering device.

The system possess the feedback loops

1.Internal – wheel –automatic steering device

2. External –wheel –one gyro compass

When the ship deviates from its predetermined course to starboard side. The synchro receiver(SR) of the gyro compass (GC) rotates this sensing element of the course (SEC),which generates our electric voltage proportional to the deviation of the ship from predetermined course.

Simultaneously the receiving synchro rotates the tacho generators (TG) which in turn generate electric voltage proportional to the rate, of change of deviation in the ship’s course from predetermined course.

Both there voltages are fed to a summing system(SS). After amplification in the amplifier (A) the signal is fed to the actuating motor of the steering drive(SD) which will start to move the rudder to port. Simultaneously the steering pick-up (SP) will also rotate, in turn generating an electric voltage (V4) which is proportional to the deviation of the rudder.