NK vessel in Japanese waters

A Japanese patrol boat tugs a wooden ship carrying nine North Korean defectors Tuesday (small picture). The engine of the North Korean ship is assumed to be an improvement of a Chinese model. The average speed of the typical 8-meter North Korean wooden ship equipped with such an engine is 9.26 kilometers per hour. Given that North Korea and Japan are 800 to 900 kilometers apart, the North Korean vessel seems to have continuously sailed for four days.