In this modern world, several tasks that are considered dangerous or dirty are likely performed by autonomous and robotic systems. Autonomous systems exhibit high precision, efficiency and reliability, and perform the task without human intervention.
There has been extensive research on autonomous sailing boats over the past decade. With the increase in performance in addition to reduction in price and size of hardware, a number of scientific studies are focusing on the applications of autonomous boats.
Sailboats function under a highly dynamic environment, and hence autonomous sailboats need to respond promptly to uncertain environmental conditions.
Autonomous sailboats analyze the data from sensors such as an anemometer, compass, global positioning system (GPS) through intelligent control mechanisms. However, designing and programming the autonomous sailing boat include several challenges with respect to hardware and routing algorithms.
Water resistance is a major limitation in equipping the autonomous sailing boat with required hardware. Also, it is extremely hard to plan routes as these sailboats operate in unstable environmental conditions.
Architecture of Autonomous Sailing Boats
The key components of autonomous sailing boats as discussed by Alt C et al (2011) include the following:
Hardware such as boats, sails, microcontroller and sensors are the key factors for costs and applications in the design of an autonomous sailing boat.
- Boats - Boats are of three types namely Microtransat, SailBot and MicroMagic. Based on its length, the Microtransat class can hold several pieces of equipment and withstand maximum speed in harsh sea conditions. SailBot class is self-constructed or remote-controlled. Remote-controlled sailboats are available in various sizes and equipped with servos. The MicroMagic class is relatively cheap, and uses keel, sails, deck and hull.
- Sails – Sails used in autonomous sailing boats are of two types - conventional fabric sails and wingsails. Conventional fabric sails can be easily repaired and are convenient to use. Wing sails, on the other hand, are more efficient and do not require additional rigging.
- Microcontroller and Sensors – The central component of the autonomous sailing boat is the embedded intelligence that can either be x86 computer or a microcontroller based on the space available in the boat. The anemometer is a sensor for measuring wind speed and direction. Actuators are used to control the sails, rudder and bilge pumps.
As autonomous sailing boats perform various tasks, it has to rapidly respond to the changing environmental conditions such as static or weather obstacles. Therefore, a design of suitable software is required to solve this problem. The autonomous boats can be designed with the following software architecture:
- Top-down planner-based model – In this architecture, a control system includes a sensing system, planning system and executing system. A sense-plan-act approach can be developed using the sensor data along with the knowledge about the environment. However, generating a plan using this approach is a time-consuming task.
- Bottom-up reactive system – In this model, the measured sensor data is linked with the robot actuators. The software designed using this approach enables the autonomous sailing boat to quickly respond to the environmental changes.
- Hybrid architecture – It is a combination of the top-down planner based model and the bottom-up reactive system. In this model, the data regarding weather forecasts and sea maps delivered by the sensors are used for long-term routing. The moving obstacles are detected by a RADAR system. Actuators are controlled based on the sensor data. An operator presets the strategic goals and communicates with the strategic long-term routing layer.
For short distance communication, wireless LAN controllers can be used. GSM transmitters can be used for medium distance communication, and satellite communication can be used for long distance communication. GPS systems are used to measure the speed and position of the boat.
Trimming of the sails and monitoring the rudder are the two main tasks performed by the control system. Fundamental sailing rules such as steering the sails and rudder according to wind direction will be stored in a fuzzy inference system. This system, which imitates the behavior of experienced sailors will then control the rudder and sails.
Collision avoidance is a complex task for autonomous sailboats as they cannot suddenly change their route and all routes are not sailable. Autonomous sailboats employ a reactive approach to collision avoidance, which uses the existing short course routing layer to obtain the best possible route.
Simulation and Testing
Testing the autonomous sailboats is very expensive and time-consuming. However, fatal errors that cause the ship to sink are even more costly, and hence a lot of testing procedures are required before launching the boat. Wind conditions can be tested using a simulation process, and the result can be compared with the real world environment.
Applications of Autonomous Sailing Boats
Some of the major applications of autonomous sailboats include the following:
- They can be used for transportation of goods without requiring an operation of a big crew.
- They can be sent to operate in dangerous regions. For instance, they can be used for measuring nuclear radiation in the ocean neighboring Fukushima.
- They can be used for surveillance of immigration routes.
- They can supply necessary things to remote areas and islands.
- They can be cost-effectively used for mappings, ecological studies of lakes and oceans, and surveys.
Researchers at the University of
Cruz, NA and Alves, JC (2008) stated that the autonomous sailboats are robotic vessels that control the sails and rudders using wind energy, without human intervention.
Research on autonomous surface vehicles has focused mainly on short-range crafts that are powered by electric or combustion engines. They have been widely used for ocean observations for many years. Application of flexible computational systems, high performance renewable power sources and reliable communication device has helped reduce technical limitations and operational risks of autonomous sailboats making this an effective tool for a wide range of applications in real time.
- Alt, C et al, Autonomous Sailing Boats, Institute of Computer Science, Salzburg, 2011
- Cruz, NA and Alves, JC, Autonomous sailboats: An emerging technology for ocean sampling and surveillance, IEEE, 2008, 1-6