Navigation and Seamanship

6.7.1. Automatic Steering System or Auto Pilot

                                                                                  

The automatic steering device or the autopilot is an instrument controlling the steering system that automatically maintains the ship on a predetermined course. The autopilot must fulfill all the functions of the steering system under different conditions of steering in any type of ship.The use of thus instrument leads to a reduction in the running costs of a ship. This is used for steering the vessel without constant handling of steering wheel manually.

The basic functions of autopilot are

The desired course is set into the autopilot by the user and this course is compared in the autopilot with this actual course achieved. The difference between the two, this course error, is their acted on by the autopilot and an output signal is sent to this rudder control mechanism.This demanded rudder command corresponds to the helm or wheel order with the rudder control system in hand control.

The degree of success with which the autopilot will be able to control the ship is course depends on a number of factors. They are

1. The speed of the ship:

At zero ship speed, clearly any movement of the rudder will have no effect on the ship’s course at all. As this speed increase the amount of rudder to be used for a given ship response will be less until, at maximum speed, a very small alteration will suffice. For this reason, the ship is speed is usually fed into the autopilot.

2. The Environmental condition:

The presence of wind and waves will affect the ship’s response. In heavy quantering seas it is highly unlikely that the autopilot will be able to control the ship satisfactorily at all.

3. The condition of the autopilot:

4. The number of pumps running in the steering gear:

With two pumps running the rudder will move at approximately twice the speed at which it will operate with only one. In smaller ships this will have a marked effect on the turning ability.