In maritime mobile satellite communications, received satellite signal level varies due to direction and motion of a ship. Then sometimes the communications are interrupted, because the receiving satellite signal level decreases when the ship's body shadows the antenna. Thus it is important to evaluate how qualities of satellite communications vary during ship operations. However, precise temporal level fluctuations during ship movement are not yet studied. In this paper, to evaluate temporal variances of receiving satellite signal level of the ship in motion, modeling and numerical simulations were performed with considering the effect that the ship's body shadows the antennas. Effects of pitching, rolling and yawing were taken into accounting the calculations. In addition, electric field levels around the ship were estimated when transmitting antennas are in proximity to the ship body.