Safety Criterion of a Ship considered from the Stability. By Yos ihiro Watanabe, Kogakuhakushi, Member. When a ship, which is rolling among waves around the steady heel due to wind, is attacked by a sudden gust, sometimes accompanied by the rudder action, if the work done by the gust and rudder action be greater than the reserve of her stability, she capsi es. The condition, that the capsize may not occur, can be expressed by the following relations: