In above section, authors proposed a concept on functional construction of Bridge Team, and examined the adequacy of the concept. On this section, Fault Tree Analysis for marine casualty is carried out to confirm the effectiveness of Bridge Team. Furthermore, incidence of error in Bridge Team at ship handling simulator is investigated to clarify the effect of Team quantitatively.

　

 As the name of "Fault Tree" shows, it indicates how the combination of basic phenomenon can cause accidents. So it is possible to confirm the effect of two functions of communication and cooperation in out breaking of accident eductively and quantitatively. In chapter 5.1, the construction of Fault Tree for collision that based on the concept of Team function, is explained. In chapter 5.2, 5,3 and 5.4, numerical analysis for the Tree is carried out on structural relation between basic and top phenomenon, In chapter 5.5 and 5.6, the rate of incidence for each basic phenomenon is obtained from the records of Bridge Team maneuver in ship handling simulator, and discuss about the effectiveness of Bridge Team and importance of each basic phenomenon.

　

5.1 Fault Tree for Collision

　

 Generally, Fault Tree is composed based on the data of past disasters, but to obtain the rate of incidence is difficult, because of difficulties in reconstructing the condition at the time when the disaster happened. So author composed a Fault Tree for plural number of Bridge Team a situation of avoiding other vessel for to maneuver under same condition. By this way, it is possible to obtain the rate of incidences from a number of maneuvering records and quantitative analysis can be carried out.

　

　

 Figure 5 shows the Fault Tree for collision. In this Tree, Bridge Team is composed of Captain, second officer and third officer, Quartermaster. In this Tree, captain share lookout and decision for avoidance, second officer shares radar watch, third officer share lookout, and quartermaster shares steering. Each phenomenon is connected under the top phenomenon with "AND" or "OR" gate.

 In addition, communication in this tree means the action for information sharing, and cooperation means the action for collaboration, compensation, and supervision each other among members.

　

5.2 Attaining process of task

　

 At this point, author explains about structural function of Fault Tree, which expresses structural relation between basic and top phenomenon in Fault Tree

　

 About a Fault Tree constructed with number n of different basic phenomenon, the state of basic phenomenon ( i ) is defined introducing binary variable (xi).

　

Variable (x) takes 1 or O

In the case of (xi) =1, phenomenon ( i ) occurs

In the case of (xi) =0, phenomenon ( i ) does not occur

　

Also, the state of accident (,,) also takes 1 or O

In the case of (,, ) =1, accident (,, ) occurs

In the case of (,, ) =0, accident (,, ) does not occur

　

 Where the state of accident (,,) is fixed by the states of each phenomenon ( i ), accident (,,) is a function of basic phenomenon ( i ).

　

ø = ,, (x)

　

 This functions ,,(x) is called structural function of Fault Tree, Formula (1) shows the structural function of Fault Tree.

　

　

 Each phenomenon in Fault Tree of figure 5 is numbered as Table 2, and structural function is as formula (2)

　

　

　

 Based on the concept of thus structural function. process of accomplish task and effectiveness of team play are analyzed.

　

5.3 Minimal cut set

　

 Minimal cut set is the least set of basic phenomenon that cause the accident. For example, when the top phenomenon is an accident and basic phenomenons are causes of accidents, it can be clarified the occurrence of accident and its causes by clarifying all minimal cut sets.

　

 Minimal cut sets for the Fault Tree in figure 5 are shown as follows;

　

　

 In these cut sets, basic phenomenon x1 should be eliminated from the discussion, because the phenomenon is not on the team but on target ship. The cut sets of {x1,x4,x5} means that if the captain mistake the way of avoiding and nobody compensate captain's decision, top phenomenon will break out. And {x1,x2,x3 } means that if quarter master mistake to operate steering and nobody compensate quartermaster, top phenomenon will also break out. On the other hand, the last of cut sets are composed of six different phenomenons except x1. According to the contents of these phenomenons, members of Bridge Team coordinate each other to collect information of target ship. Judging from this, error in the process of judging and taking action should be cared more than error in the process of gathering information.