出入港時の要素操船性能について-III : 変針操船とその限界

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In the previous report, the authors have proposed to introduce the concept of elemental manoeuvres in harbors and studied on manual course-keeping manoeuvres from the viewpoint of evaluating the allowable limit of directional instability of ships. In the present report, an attempt is done to analyze manual course-changing manoeuvres of directionally unstable ships with a special emphasis on the allowable limit of ship manoeuvrability. Carrying out manual course-keeping simulations, two kinds of manual course-changing patterns, bang-bang control and bang-bang control with zero are picked up. In these controls, it seems very important for successful course-keeping manoeuvres to choose a good timing of executing a counter rudder. An error in the timing causes a large error in final heading angle in significantly unstable ships. Then the ratio of the error in final heading to the error in counter rudder executing, or the overshoot angle after executing counter rudder to reaching final heading are employed as parameters to indicate the difficulty in manual course-keeping. The difficulties in course-changing were assessed by helmsmen and the results of course-changing simulations were examined. Both seem to correspond well each other. It is pointed out from the simulation results that the rudder angle becomes significantly large with the increase in directional instability of ships. The maximum rudder angle is frequently applied for ships with large instability. This means ships are deprived of some margin in control power and there is a kind of allowable limit in the sense of safety. The difficulties in course-changing increase remarkably in decelerating conditions because of the decreased effectiveness of counter rudder by reduced propeller revolution. It seems difficult to evaluate clearly the allowable limit of directional instability of ships and further comprehensive investigations are required for making it clear. It can be pointed out that the increase in directional instability deprive a ship of the margin in her control power.
社団法人日本航海学会の論文
1990-03-20

出入港時の要素操船性能について-III : 変針操船とその限界

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