The speed of an ocean wave depends on the distance between two successive crests, its wavelength. The longer the wavelength, the faster the wave travels. A small surface wave, such as a ripple created by the wind, travels quite slowly because it has such a short wavelength. A swell, the larger, longer wavelength waves created by constant winds, have longer wavelengths and travel at higher velocities. The energy that the wave carries depends on the square of the height of the wave, which explains why high waves can cause so much damage to shorelines.
Waves break as they approach a shoreline because the lower part of the wave moves more slowly than the top part of the wave due to increasing friction with the shallower ocean bottom.