Many ships, in particular, passenger boats and container carriers are recently beeing equipped with an anti-rolling tank for reduction of the rolling angles. However, we sometimes hear that these tanks are not so effective as expected by theoretical analyses or model tank tests. A reasonable explanation can be given when considered from the present design basis, that is regular waves, whereas actual sea state is of irregular waves. Therefore, the author attempted to calculate the effect of the anti-rolling tank in oblique irregular waves, with resulting calculations comparatively coinciding with actually observed resutlts.
