Abstract
By questionnaire investigations, we have attempted to examine the above subject from 1,233 navigators of vessels over DW 5,000 tons. We obtained the following results: 1. Mental strain of navigators does not depend upon the human factors (for example their respective position on duty and career) and the vessel's factors (for example the magnitude of vessel), but upon their preoccupation concerning with natural factors of water way. The most important of the last was existed in traffic convergency. 2. The most difficult area to pass through was Kurushima Kaikyo with Kanmon Kaikyo. 3. A large number of captains said that under meeting condition they should have 2, 000 meters water way in width, in passing it through without anxiety or tensity.
