3.3 Practical approach to inclusion of the human element
3.3.1 A human element model for simulations
A simple human operator model can be used to represent a part of the function of the human element for navigation/maneuvering. The condensed schematic of Figure 1.3.1 include the three basic functions of the human element; plans, observation and execution. An operator focused decomposition of the human element is seen in Figure 3.3.2 where these functions are separated. The separation is a practical measure with the intent on reducing the complexity of the human operator representation by introducing assump- tions and static representations of the functions. The structure is consistent with the three stage structure presented by (Chen and Stanney, 1999) to describe way-finding and is a combination of the following functions
Plan: A prepared strategy to take the vessel from A to B which includes detailed plans for confined waters.
Observation: Observation of the environment and monitoring the vessels progress and position is according to the plan.
Execution: Executing a particular short term planned maneuver such as maintaining course by manipulating the rudder or ensuring that a navigational marker maintains its bearing.
The separation is dependent on the assumption that there is a well prepared plan which can be treated as a static entity and that the operator is competent in executing the intended actions. Competence of the operator is represented by an automatic control formulation of basic maneuver types and the deterministic function of an control algorithm. A static plan can be estimated by the method of Chapter 2 and this leaves observation, and implicit decisions, as the area of the human operator which must be addressed in order to represent this view of the human element in a simulation.
Plan Piloting a ship is a complex task where passage plans are constructed by the master before any significant voyage. The plan outlines the ships preferred path, and in confined
3.3. PRACTICAL APPROACH TO INCLUSION OF THE HUMAN ELEMENT 47 waters, prescribe the geometric properties of the planned path. (Lützhöft and Nyce, 2006) described the training of certified pilots for the Stockholm archipelago which included creation of a personal preferred passage plan of the area and a similar concept of standard practices and a-priori planning is found in (Gould et al., 2009). The passage plan was described in detail by (Lützhöft and Nyce, 2006) as an interconnected sequence of straight course lines and circular turns with the following properties
Straight course line: Course lines with notes for both in-bound and out-bound course angles
Circular connecting sections: The radius of the turn was noted together with land marks or navigational markings and their bearing to determine when to initiate a course change.
The planning process as described by (Lützhöft and Nyce, 2006) includes reference to both the environment in the form of landmarks, navigational markings and references to a set of basic maneuvers used to traverse the plan. This description motivated the for- mulation of the previously mentioned “simple traffic model” and the output of the traffic analysis can be used as input for the plan representation during simulations. This formu- lation is extendible as it allows new maneuver types to be available during maneuvering by implementing a suitable autopilot and referencing them in the plan.
Observation Observation of the vessels position and relative orientation to landmarks on a modern bridge is a dual-process which involves both electronic navigation systems and visual observation. Bridge systems have undergone a dramatic development form ob- servation decks with communications to the engine room and wheelhouse to a integrated command and control center (Lazet and Walraven, 1971). Electronic navigation systems such as GPS and the former Loran C has long been used to obtain a position fix for the vessel, but the orientation of the vessel relative to the environment is still verified visu- ally by means of landmarks and navigational markers. While electronic chart display and voyage planning systems are installed on most bridges, observation of the environment by radar, and visually (when possible) is still an integral part of bridge procedures. Over reliance and misplaced confidence in the electronic positioning systems has lead to acci- dents as by (Lützhöft and Dekker, 2002) in a case study of the ROYALMAJESTYwhere a malfunctioning electronic navigation system combined with incorrect visual confirmation of navigation markers led to the grounding of the vessel. The reliance on visual observa- tion is emphasized by the prominent presentation of navigational aids on electronic chart systems, and ensures an continuous involvement of the bridge personal while navigating confined and congested waters.
Execution The execution of individual maneuvers is performed in a tight loop with continuous observation of the properties of the ship and the environment. The continu- ous manipulation of the vessel is reminiscent of an automatic control algorithm, and did inspire the first course autopilot for ships (Fossen, 2002). Manual control and autopilots
has a symbiotic relationship where the autopilot will translate the operators intentions into actuator actions as in thrust allocation by DP-control systems, and the manipula- tion of course autopilot settings (Accident Investigation Board Norway and The Bahamas Maritime Authority, 2010) instead of the rudder. The human operator and the high level control system becomes indistinguishable from the view of the vessels low-level actuator systems.