Measurement for mental workload of Bridge Team on leaving/entering port

On entering and leaving ports, a captain needs so many operations of a rudder and engine control, that he/she gives orders for bridge teammates. Moreover, a ship's course control is difficult at a low speed as it is easily affected by wind and current. On entering/leaving port, the cooperation among bridge teammates is most important for safe navigation, and its importance is common knowledge in the world. However, its evaluation depends on a seafarer's experience, not a quantitative index. We need an evaluation method of teamwork and relations among teammates with the quantitative index in order to evaluate Bridge Team Management (BTM for short). The purpose of this paper is to evaluate the mental workload of bridge team (BT for short) on entering and leaving ports with heart rate variability. The experiment is carried out at three ports in Japan. The bridge teammates are a Captain, a Deck officer and a Quartermaster. We calculate the SNS value (LF/HF) with frequency components of R-R intervals, and we use Projective Strain Ratio (PSR for short) value to make a base for each teammate. LF is 0.04 to 0.15 Hz and HF is 0.15 to 0.40 Hz. LF is reflected by the sympathetic nervous system and parasympathetic nervous system and H-F is reflected by the parasympathetic nervous system. This index is used to evaluate the mental workload of a car driver on transportation system. As the results, we show three points on BT evaluation. (1) The evaluation of bridge teammates' mental workload is possible with the SNS (PSR) value. (2) The mental workload is shared among BT-mates when the captain makes a decision to change course, and the deck officer and the quartermaster receive his/her orders. (3) The evaluation of mental workload of BT is possible with the SNS (PSR) value.