Numerical navigator

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Normally, the vessel is controlled by the navigator by means of standard control equipment (rudder, engine telegraph etc.) and running in realtime. However, in fast-time mode, a so-called numerical navigator controls the vessel, and the simulator is running as fast as the computer allows which enables a huge number of simulations to be completed within a short period of time. Once the fast-time simulations have been set up it is relatively easy to perform a large number of runs in various environmental conditions and various channel or harbour layouts. Hence the fast-time simulations are especially suited for relative comparisons of various harbour and navigational channel layouts, thus providing a solid basis for selection of final design. 

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Realistic behaviour 

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The numerical navigator controls the ship and has been developed to behave as far as possible as a mariner. It follows a pre-defined plan which might include straight legs, wheel over-line waypoints and curved tracks with a given turn rate. Furthermore, the plan includes a desired speed over ground. Human errors or misjudgements are included as a random function with a given standard deviation to obtain a number of tracks that are different and to obtain a realistic track envelope. 

Observations and corrective actions are made at discrete time intervals which are given as a mean time interval with a corresponding standard deviation. If the ship is not able to keep the planned track, and the maximum rudder angle is used, the handle setting is increased stepwise until the desired heading is reached. Then the handle setting is decreased stepwise again until the target speed is reached. The time series logged during the simulations are afterwards analyzed statistically with FORCE Technology’s own software program ‘Replay’. 

The statistical analysis provides information on e.g. controllability of the vessel, use of rudder and distances to certain structures.