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5. RESULTS OF EXPERIMENT
The time scale may have double effect on manoeuvring:
・Involves changes in mentioned in part 2 of the present paper "feeling for a ship" which results mainly from differences in absolute values of linear and angular velocities. Manned model values of linear velocities are much smaller when comparing with real time manoeuvres, but angular velocities have scale 0.5 bigger values. In effect problems with correct estimation of ship's speed and of ship's reaction for a given rudder deflection may occur.
・Involves changes in operator reaction that should be proportionally shorter especially when taking into account much shorter time constants onboard model. Eventual human errors due to this accelerated undertaking of decisions may occur.
That's why during experiment were compared:
- Behaviour of operator determined by number of rudder deflections and engine orders applied. Eventual differences may be assumed to some extend as reaction of operator to time scale effect;
- Travelled path and heading in manned model tests and in simulator study. In this case eventual differences are assumed to be measure of influence of time effect on ship's manoeuvres.
- For completing set of results also ship's average velocity during experiment calculated as ratio of distance covered to time of manoeuvres was calculated and compared.
Results of the above comparison are presented in table 2 and in following figures:
- In figure 5 trajectories of manoeuvres made by participants of experiments onboard model are shown;
- In figure 6 results of simulator study realised by the same group of participants are shown;
- In figures 7 and 8 comparison of trajectories realised by the same operator during manned model tests and simulator study was made. Two cases are shown: where observed differences in trajectory were maximal and where the same differences were minimal.
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Table 2
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Comparison of realisation of manoeuvres on manned models and on desktop simulator
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| Element compared |
Observed values during tests |
Manned model |
Computer simulator |
| Ship's average speed |
Maximum value |
8.0 kn |
7.2 kn |
| Average value |
6.3 kn |
6.2 kn |
| Minimum value |
5.9 kn |
5.7 kn |
| Average deviation of ship's center
of gravity from centerline of waterway |
Maximum value |
0.85 B |
0.82 B |
| Average value |
0.65 B |
0.61 B |
| Minimum value |
0.42 B |
0.35 B |
| Average deviation from leading
line |
Maximum value |
2.3 ° |
2.2 ° |
| Average value |
1.3° |
0.9° |
| Minimum value |
0.5° |
0.5° |
| Number of engine orders |
Maximum value |
25 |
23 |
| Average value |
17 |
18 |
| Minimum value |
5 |
7 |
| Number of rudder deflections executed
by operator during tests |
Maximum value |
96 |
90 |
| Average value |
71 |
69 |
| Minimum value |
52 |
44 |
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Before starting experiment authors expected that there will be not a big difference in trajectory and heading obtained from both methods of training, but they were not quite sure if small difference would be also observed in behaviour of operators (number of use of control forces - rudder deflection and engine setting).
In all cases of manned model test and of simulator study no special difficulties were observed. The final result - path travelled by the model was very similar to trajectory obtained from realisation of simulator manoeuvres, Also practically the same behaviour of operator was noted - for all operators differences in frequency of use of rudder or of main engine were not important. For example person using more frequently rudder or engine was in both cases the same. The biggest difference was observed in engine settings: person using only 5 times engine orders in case of manned model test, was obliged to apply 8 times changes in engine revolution settings when realizing test on electronic simulator.
Fig.5 |
Trajectories realised during tests on manned model |
Fig.6 |
Trajectories realised during test on electronic desktop simulator |
Fig.7 |
Comparison of trajectories realised on manned model and desktop simulator- the best case |
Fig.8 |
Comparison of trajectories realised on manned model and desktop simulator- case with maximal difference in trajectory |
6. CONCLUSION
The experiment carried out has not shown any important influence of time scale effect on results of manoeuvres realised on manned models. Monitored parameters affecting realisation of manoeuvres: engine setting, heading deviation, rudder deflection angles applied and path travelled in case of computer simulator and of manned model had very close value. Small differences noted in course of experiment made on models and on desktop simulator may result also from discrepancy in manoeuvring characteristics of the training model and mathematical description of this model. It must also be noted that some participants of experiment were not familiarised with computer simulators at all. This fact could also affect the behaviour of participants during experiment conducted on desktop simulator.
The final conclusion of the authors is that typical for manned models time scale effect does not change behaviour of trainees during realised manoeuvres in any significant degree having influence on results of training.
Because of high degree of adaptability of operators, the problem of "real time" and "model time", even if affects somebody's behaviour, disappears after first few hours of training. The new reference level results now rather from the difference in manoeuvring qualities of various ship types used for training. In addition, the time scale "enhances" ship reactions and eventual mistakes are quickly apparent - so it can be very useful in understanding problems of ship handling.
To exclude definitely the influence of time scale effect further study including full mission real time simulator with 3-D visualisation of manoeuvring areas will be carried out in the near future.
AUTHORS BIOGRAPHY
Lech Kobyliński is professor emeritus of the Technical University of Gdansk and corresponding member of the Polish Academy of Sciences. Currently he is the President of the Board of the Foundation for Safety of Navigation and Environment Protection. He is fellow of RINA, member of STG, chairman or member of several Scientific Councils. He is member of scientific committees of several international and national conferences. He has published more than 200 books and papers. He has long experience in cooperation with IMO. He is specializing in hydrodynamic problems of ships safety.
Jacek Nowicki (M.Sc. Eng) is director of the Foundation for Safety of Navigation and Environment Protection, Ilawa, Poland . His specialization is manoeuvrability of ships. Author of several papers and books concerning different aspects of ship's safety.
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