The history of automated closed-loop ship control started with Elmer Sperry (1860-1930), who constructed the first automatic ship steering mechanism in 1911 for course keeping (Allensworth and Bennet). This device is referred to as the “Metal Mike”, and it was capturing much of the behavior of a skilled pilot or a helmsman. ”Metal Mike” did compensate for varying sea states by using feedback control and automatic gain adjustments. Later in 1922, Nicholas Minorsky (1885-1970), presented a detailed analysis of a position feedback control system where he formulated a three-term control law which today is referred to as Proportional-Integral-Derivative (PID) control (Minorsky). These three different behaviors were motivated by observing the way in which a helmsman steered a ship.
This chapter gives an overview of marine control systems exemplified by dynamically positioned (DP) vessels with electrical propulsion systems. Design aspects related to high-level vessel control such as power management and DP are shown. Design requirements and ability for reconfiguration accounting for physical segregation and redundancy of power, propulsion and automation systems will be presented. Rules and regulations including testing and verification of marine control systems based on Hardware-In-the-Loop (HIL) testing will also are introduced. Other marine control systems; propulsion control systems, control of slender ocean structures, motion control systems for high speed crafts and details on DP systems will be presented in separate chapters later in the text. The design steps combining software (SW) and hardware (HW) architecture, modeling, sensor processing, controller design, simulation and testing will more or less follow the same principles. However, requirements to performance and redundancy, and thereby complexity, may differ for the various marine control system applications.
Offshore exploration and exploitation of hydrocarbons have opened up an era of DP vessels. Currently, there are more than 2000 DP vessels of various kind operating worldwide. DP systems are used for a wide range of vessel types and marine operations:
- Offshore oil and gas industry: Typical applications in the offshore market are offshore service vessels, drilling rigs and drilling ships, shuttle tankers, cable and pipe layers, floating production off-loading and storage units (FPSOs), crane and heavy lift vessels, geological survey vessels and multi-purpose v Cable and pipe laying are typical operations which also need tracking functionality.
- Shipping: Currently there is a trend towards more automatic control of marine/merchant vessels, beyond the conventional autopilot. This involves guidance systems coupled to automatic tracking control systems, either at high or low speed. In addition, more sophisticated weather routing and weather planning systems are expected. Automatic docking systems and a need for precise positioning using DP systems when operating in confined waters will become more used.
- Cruise ships and yachts: The cruise and yacht market also make use of more automatic positioning In areas where anchors are not allowed due to vulnerable coral reefs, DP systems are used for station keeping. Precise positioning is also required for operating in harbors and confined waters.
- Fisheries: Application of more sophisticated guidance, navigation and control systems for ships during fishing are motivated by the need for precise positioning, reduced fuel consumption and intelligent selective fishing.
Electric propulsion is not a very new concept. It has been used as early as in the late 19th century. However, only in few vessels until the 1920s where the electric shaft line concept enabled the design of the largest Trans-Atlantic passenger liners. Variable speed propulsion was used in some few applications during the 1950s and 1960s, while, first when the semiconductor technology became available in large scale commercial applications, this technology became acceptable for a wide range of applications. The introduction of AC drives and podded propulsors was another shift in technology that led to a rapid increase in the use of electric propulsion through the last 15-20 years. Typically, ships with electric propulsion tend to have more system functionality implemented in integrated automation systems, partially because such functionalities are regarded to be necessary for safe and optimal operation, but also because the electric propulsion plant enables the use of such functions. In the commercial market the offshore vessels in addition to cruise ships and ice breakers have been technology drivers concerning automation, power and propulsion systems. They are characterized by the required ability to conduct complex marine operations, operational availability, safety focus, cost effectiveness and flexibility in operational profile concerning transit, station keeping, maneuverability and to some extent also a significant vessel or process load system. These rather complex power plants opened up for an increasing use of fully all electric ships and the introduction of fully integrated computer-controlled systems in order to operate safely and cost efficiently. Such concepts are today applied in an increasing number of ship applications.
Consequently, the complexity has also increased with a variety of solutions consisting of stand-alone systems, partly integrated systems to fully physical and functional integrated systems. Up to now integrated automation systems have been proprietary with a limited number of vendors. However, in the automation industry it is a trend towards openness in communication protocols and network. How this will influence on the technology solutions and responsibilities for multi-vendor integration systems is still a subject for discussion. During the late 1990s the introduction of low-cost off-shelf computers not originally designed for automation purposes have also been taken more into use. This development is driven by the need to make more cost efficient solutions. Nevertheless it also creates new issues of concern:
- New procedures for design and specification that considers compatibility and integration aspects.
- Failure analysis and test methods, adequate to ensure fault-tolerance in the overall system.