Compared with other kind of ships ， small fishing boats tend to roll by relatively small wave ． Especially ， rolling motion with sudden change is very dangerous for crew working on the deck ． Therefore estimation for rolling motion is very i皿 portant ． However ， it is dangerous to predict rolling motlon recklessly without consideration for limitation of prediction models ． In many cases ， the prediction model for ship motiens in irregular seas is based upon probabilis −