Autopilots have evolved from simple course holding systems to adaptive computer systems that offer reduced fuel costs and increased transit times. These new systems learn the characteristics of the vessel’s handling and minimize rudder movement reducing drag on the vessel. Increased speed and lower fuel consumption can result in tremendous savings offsetting the cost of new systems within a year.
Marine navigation equipment and steering systems are generally comprised of several subsystems. In a follow up system, when the wheel is turned to a specific angle the rudder responds by moving to the requested angle, hence it follows the helm. A follow up system is spring activated to return to zero when released by the helmsman. Non-follow up system uses a three-position actuator where the center position is neutral. Moving the actuator left or right moves the rudder left or right. The rudder remains in that position and does not return to center when the actuator is centered.
Ship steering systems are comprised of two independent electrical and/or hydraulic systems in the event of a major failure. The last line of defense for steering systems is a device called the Trick Wheel. It is a simple mechanical or hydraulic actuator located on the steering flat that bypasses the helm. This is generally never used except in extreme emergencies. One misconception about steering systems is that failure of the autopilot is treated as a steering failure. Autopilots are not required carriage and therefore not mandatory for the sailing of the vessel.
Autopilots do not replace a human operator, but assist them in controlling the ship, allowing them to focus on broader aspects of operation, such as monitoring the trajectory, weather and systems.
The settings of an autopilot system are as follows:
- Permanent helm: To be used only if a constant influence, like cross wind or beam sea is experienced. If there is a very strong beam wind from starboard side then a permanent 5 degrees starboard helm may be set.
- Rudder: This setting determines the rudder to be given for each degree of course drifted. Eg. 2 degrees for every 1 degree off course.
- Counter rudder: Determines the amount of counter rudder to be given once v/l has started swinging towards correct course to stop swing. Both rudder & counter rudder to be set after considering condition of v/l (ballast, loaded, etc.). Eg. Laden condition full ahead, not advisable to go over 10 degrees rudder.
- Weather: The effect of weather & sea conditions effectively counteracted by use of this control. This setting increases the dead band width. Comes in handy if vessel is yawing excessively.
Autopilot on Autonomous Ships
VTT Technical Research Centre of Finland is developing safe steering for the remote-monitored and controlled autonomous ships of the future. The new technology has been developed for navigation systems and ship autopilots, which steer ships automatically.
The ships of the future will largely be controlled by artificial intelligence. However, these autonomous unmanned vessels must be monitored and controlled on demand by land-based professionals. This trend sets new challenges also for autonomous ship navigation systems, which must be able to control ships in various situations.
“VTT has deep knowledge of autonomous ship research concerning especially reliability and safety topics. Such special expertise has now led to the development of navigation systems for autonomous ships,” says Jussi Martio, a Senior Scientist at VTT. This requires an autopilot, which is used to control a moving vessel, including during evasive manoeuvres according to COLREGs (International Regulations for Preventing Collisions at Sea).
The Apilot autopilot under development by VTT has three modes: track, heading and slow joystick control e.g. for docking situations.
In the ‘track mode’, Apilot steers the ship along a previously agreed route.. If the ship detects another vessel, which must be avoided, the autopilot switches to ‘heading mode’. This enables Apilot to avoid the other vessel with a small change in the ship’s heading. Autopilot returns to track mode after the other vessel has been avoided.
In the ‘joystick mode’, control and propulsion equipment are adjusted to low speeds manoeuvrings. Apilot puts the ship into the desired operating mode, for example to manoeuvre sideways into a dock.
In all situations, the autopilot ensures that the ship remains within a set distance from the planned route. If the limits in question are exceeded, the autopilot gives a warning and remote control must be taken of the ship.
Human factors must be taken of account when designing the remote monitoring and control systems of vessels. VTT has studied interaction between humans and technology in maritime transport and has developed new concepts for the bridges and remote shore control centres of the autonomous ships of the future. In such design activities, the aim is to make operations more safe, efficient and comfortable by seeking new solutions that enhance operating methods, as well as the usability and user experience of technologies.
References: Rice Electronics, Marine Gyaan, Science Daily
Sea News Feature, March 13