Why can ships far from shore barely notice a passing tsunami?

Ships far from shore barely notice a passing tsunami because of the wave's unique physical characteristics in the open ocean. While these waves travel at high speeds—up to 800 km (500 miles) per hour—their amplitudes (heights) are very small, typically measuring only 30 to 60 cm (1 to 2 feet).12

Furthermore, tsunamis have enormous wavelengths that can exceed 500 km (310 miles) and very long periods, with the time between successive crests or troughs lasting from five minutes to over an hour. Because of this low steepness and height, the passage of a tsunami is often completely obscured in deep water by normal wind waves and swell. Consequently, a vessel on the high seas experiences the event only as an insignificant, gradual rise and fall of the water surface.12