This paper proposes "Vertical Weight Stabilizer (VWS)" which is a new type of stabilizer. VWS is composed of a weight which can be shifted vertically by a servo motor. The weight gives to the ship two kinds of effects. The first one is an anti rolling moment given by the Corioli's force. The moment reduces the roll motion given by the wind and wave etc. Another one is change the moment of inertia of the ship. Roll of the ship is reduced when the difference between natural roll period and wave period is increased. Actual ship experiment was done at Lake Biwa by the VWS research group. The study intended to do experiments on still water and irregular waves. However, only still water condition was able to be done because of the weather.The experimental results show a reduction of the roll movement caused mainly by the dissipation of motion energy by Corioli's effect. It was observed that VWS reduce significant value of about 50% in free roll trial
