Abstract: It is said that more than 80 % of the cause for marine accidents is human error. And for prevention of marine accidents, all sorts of measures toward human error have been executed in all over the world. However, the number of marine accidents is not tending downward. Therefore, authors paid attention to human insufficient behavior treated as human error. Human insufficient behavior often cause the error that lead to an accident. If we can find the condition for an occurrence of human insufficient behavior and its characteristics, it is possible to estimate safety degree on ship's operations. In this paper, the condition for an occurrence of human insufficient behavior was analyzed by determination of a quantity of human competency. Furthermore, safety degree on ship's operations was estimated quantitatively using extracted characteristic of human insufficient behavior.

　

 It is necessary to maintain the balance between required competency by navigational environment and attainable competency by mariner for safer ship 's operations. And it has been found that mariner's insufficient action was apt to occur when this balance was broken. In this study, this action has been called human insufficient behavior. Human insufficient behavior has been defined as human action that dose not appropriate to the objective. On the other hand, it is necessary to determine the quantity of required competency by navigational environment and attainable competency by mariner for verification of proposal concept. In this paper, determinations of the quantity of required and attainable competency were executed, and the condition for an occurrence of human insufficient behavior was discussed. Moreover, safety degree on ship's operations was estimated quantitatively.

　

2.1 Relation between a Quantity of the Task and Elemental Task

　

 In this study, required competency means a quantity of the task that was required by navigational environment. And the task means ship-handling technique. It was already clarified that ship-handling technique could be systematized by combination of 9 elemental techniques. And each elemental technique is subdivided into the contents corresponding to elemental task. Therefore, the relation between a quantity of the task and a quantity of elemental task was formulated.

　

 Formula (1) indicates the relation between a quantity of the task and elemental tasks

　

　

 In formula (1), Q means a quantity of the task, J means a quantity of elemental tasks, and N means the number of elemental task. The quantity of the task can be calculated by the sum of each quantity of elemental task.

　

2.2 Conversion of the Task into Time

　

 In previous section, it was indicated that a quantity of the task could be calculated by formula (1). However how to determine a quantity of the elemental task must be indicated. In general, it is said that it takes a short time to accomplish an easy elemental task, while it takes a long time to accomplish a difficult elemental task for inexperienced mates. However, it has known that Captain or experienced mates can accomplish a difficult elemental task within a given time in most of cases. Therefore, we made a proposal to convert the consumption of the mean time to accomplish an elemental task on 1^st grade navigation officers into a quantity of an elemental task. And the consumption of the mean time to accomplish each elemental task was measured on 1^st grade navigation officers. Elemental techniques corresponding to elemental task are selected as follows; (1) Positioning, (2) Planning, (3) Maneuvering and (4) Communication. These techniques are placed in important tasks on practical ship's operations. Meanwhile, each elemental technique is subdivided into 5 ranks as the difficulty of each elemental technique to be done. Details of each elemental task are indicated in Table 1. In Table 1, the large number of rank is expressed as high difficulty. And measurement conditions for each task are indicated in Table 2. Experiments for measurement of a time consumption to accomplish elemental task were carried out at simulator center in Tokyo University of Mercantile Marine. And subjects of experiments are 5 experienced mates who have 1^st grade license. Before carrying out of experiments, an experimental condition was shown to all subjects. It is that all subjects have to give full play to own perfect competency without spare time. On the other hand, objects for measuring of compass bearing are appointed in an elemental technique "Positioning". And autopilot system was adopted in elemental technique "Maneuvering", and the contents of conversation by VHF radio were also appointed in elemental technique "Communication". Moreover, container vessel of 280m in length was used as own vessel in each simulation, and bulk carrier of 330m in length was also used as own vessel in elemental technique "Maneuvering" of rank 2, 3, and 4.

　

2.3 Results of experiments and analysis

　

 The time consumption for accomplishment on each elemental task is indicated in Fig.1 (a)-(d). Vertical axis in each figure shows the time consumption, namely, a quantity of elemental task, and horizontal axis show the rank of elemental task. All values are given by the second. And vertical lines drawn on each symbols show the deviation value. The circles in Fig.1 (a) indicate mean time on all experimental results of "Positioning", the triangles in Fig.1 (b) indicate mean time on all experimental results of "Planning", and the squares in Fig.1 (c) indicate mean time on all experimental results of "Maneuvering" except rank 5. The measurement of rank 5 in "Maneuvering" was canceled because the defectiveness was found in measurement condition. And the diamonds in Fig.l (d) also indicate mean time on all experimental results of "Communication". As the results of experiments, it was confirmed that elemental task could be quantified by time conversion, and measured competency on experienced mates was not dispersing. Moreover, the normalization of the difficulty on each elemental task was executed. The rank-1 in "Communication" was chosen as a base because it was found that the dispersion of competency was very little. Fig.2 indicates the normalization of a quantity of elemental task. In Fig, 2, vertical axis shows the unit of unified elemental task. And horizontal axis shows each rank of unified elemental task. From the value in Fig.2, the weight of each elemental task can be obtained.

　

　

　

　

　

　

　

　

　

3.1 Relation between Human Competency to Accomplish the Task and Elemental Task

　

 In previous section, it was found that the weight of each elemental task could be obtained by normalization of the quantity of elemental task. The relation between human competency to accomplish the task and human competency to accomplish elemental tasks indicates in Formula (2).

　

　

Where

　

 In formula (2), C means human competency to accomplish the task, K means human competency to accomplish elemental tasks, and N means the number of composing task. Human competency to accomplish the task can be calculated by the sum of competency to accomplish each elemental task.

　

3.2 Conversion of Competency into Time

　

 It was already confirmed that a quantity of the task could be quantified by time consumption without spare time for accomplishment of the task in section 2.2. In this section, we made a proposal to convert the consumption of the mean time to accomplish the task on normal performance into human competency. Then, attainable competency on 5 subjects, who have 3^rd grade license, was measured on each elemental task which was indicated in Table 1. At that time, the conditions for measurement and experiments were the same that was explained in section 2.2. And competency measured by experiments indicates in Fig.3 (a)-(d). Vertical axis in each figure shows the time consumption to accomplish the task designate, namely, a quantity of human competency. Horizontal axis shows the rank of elemental task. And all values are given by the second. The black circles in Fig.3 (a) indicate mean time of all experimental results of "Positioning", the black triangles in Fig.3 (b) indicate mean time of all experimental results of "Planning", and the black squares in Fig.3 (c) indicate mean time of all experimental results of "Maneuvering". And the black diamonds in Fig 3 (d) also indicate mean time of all experimental results of "Communication".