Fig. 18 |
Contour map on maximum lateral deviation (unit: m) |
Fig. 19 |
Contour map on mean lateral deviation (unit: m) |
Fig.20 |
Contour map on maximum rudder angle for checking turn (unit: deg.) |
Fig.21 |
Contour map on proportion of rudder angle for checking turn (unit: %) |
In Fig.21, when the proportion exceeds 10%, the contour line is remarkably dense. In the area like this, a steering rudder angle and the time for checking turn increase sharp with increasing length of a ship or loop width.
It has been verified that the control results for position control becomes worse as the length of a ship and loop width become larger.
The estimated results are compared to IMO standard. For example, 240-meter and 300-meter ships, the loop width of which is 5 degrees, satisfy IMO regulation whereas, as described above and as Figure 20 and Figure 21 show, they reach or exceed the limitation on position control.
It has been proved that the present regulation is not enough for mariners to keep safe navigation in a restricted water area.
6. CONCLUSION
In this study, maneuverability on unstable ships has been discussed from the viewpoint of position control. Various unstable ships have been maneuvered along a fairway and a rudder control law has been developed on the basis of handling results. It has been verified that normal human steering can be estimated by the control law.
Results of human steering and of the numerical simulation lead to following:
as the length of a ship or spiral loop width becomes larger,
(1) lateral deviations from the center of a fairway increase.
(2) rudder angles for checking turn increase and achieve the limitation.
(3) time and large rudder angles are required to check her late of turn.
It has been proved that human control results (on lateral deviation and rudder angles) become worse as the length of a ship or spiral loop width becomes larger. This indicates that one should evaluate the following two matters for unstable ships to keep safe navigation in a restricted water area. One of them is the yaw checking and course keeping abilities which have been suggested in IMO standard, and the other is the limitation, developed in this study, to control a position of a ship.
In this study, it has been proved that ships may exceed the limitation on position control even if IMO standard is satisfied. The present regulation is not enough for mariners to keep safe navigation in a restricted water area. In order to solve these problems, the establishment of a new regulation which takes ship maneuverability for position control into consideration is expected.
REFERENCES
[1] SENDA S., et al. "Human Handling Characteristics on Ship' s Motion in Restricted Condition", Marine Technology 4, pp2-12,WIT Press 2001
[2] NISHIMURA T., KOBAYASHI H. "Human Characteristics on Maneuvering Ship with Course-instability on Passing Fairway", The Journal of Japan Institute of Navigation, Vol.107, pp 69-76, 2002
[3] NISHIMURA. T., KOBAYASHI. H. "Human Factors on Maneuvering Ship in Restricted Water Area", Proceedings of International Navigation Simulator Lectures Conference, California, USA, August, 2002
AUTHOR' S BIOGRAPHY
NISHIMURA Tomohisa is a Japan Coast Guard Officer. He received a Bachelor's degree (Maritime Safety) from Japan Coast Guard Academy in 1997. From 1997 to 1998, he engaged in maritime safety duties such as rescue as a second officer of a patrol vessel "Tsugaru". From 1998 to 2000 he assumed an instructor of a training ship "Miura" in Japan Coast Guard School. From 2000, he has taken on on-shore duty at the Headquarters in Tokyo, taking charge of personal management. He is also a graduated school student (master course) of Tokyo University of Mercantile Marine from 2002. He studies maneuverability of unstable ships and bridge team management under Prof. KOBAYASHI. His previous paper concerning unstable ships was recognized by Japan Institute of Navigation [2].
|
