In order to confirm similarity of behavior between navigators who are
engaged in actual work and this simulation model, an experiment using the nocturnal ship
handling simulator which is established at Kobe University of Mercantile Marine was
carried out. Fig.6 shows an example of tracks under the same encounter situation with
targets. Similar behavior could be obtained from other encounter situation, and further,
sufficient results according to simulate the maritime traffic flow were obtained too.
4. INDEX TO ASSESS MARITIME TRAFFIC ENVIRONMENT (2) (3)
After the traffic data were gotten by the observation or the
simulation, an optimum index to assess traffic environment are required. Up to now, as an
index, density, frequency of encounter with other vessels, frequency and degree of
maneuver to prevent a collision and others were used. However, with increasing of
experience to apply to fieldwork, it was known that these indexes were only partially
successful because of lacking of subjective evaluation from a navigator's standpoint.
Fig.7 A comparison with typical encounter
situation. A risk of collision is latent in (a)
and a risk of collision is evident in (b).
For examples, Fig.7 shows the typical encounter situation to explain
that an internal decision making process of a navigator should be evaluated. A risk of
collision is evident in a simple encounter situation shown in figure (b) and a physical
load can be externally measured by the magnitude of a maneuver to prevent a collision. On
the other hand, when every vessel takes the same course as shown in figure (a), a risk of
collision is latent. In this case, any action can not be observed and it is difficult to
measure the mental load of a navigator by means of external observations. And further,
since the magnitude of a maneuver to prevent a collision is in conflict with the remains
of risk of collision, an index to evaluate a mental load should be generalized as well as
a physical load in order to assess maritime traffic environment.
4.1 MANEUVERING SPACE CONCEPT
It can be considered as a mental load of a navigator chiefly comes
about in decision making process. A navigator judges the situation by putting together
various information and selects the best way from a large number of maneuvers that are
combinations of altering course and changing speed. This means that a navigator has a
field to adjust all possible items relating to safety, economy and so on. Considering an
accuracy of a judgment of a navigator and roughness of a magnitude of a practical
maneuver, this field
