measure *the* force of a wave? "In general, large waves are more powerful. Specifically, wave power is determined by wave height, wave speed, wavelength, and water density. Wave size is determined by wind speed and fetch (the distance over which the wind excites the waves) and by the depth and topography of the seafloor (which can focus or disperse the energy of the waves). A given wind speed has a matching practical limit over which time or distance will not produce larger waves. This limit is called a "fully developed sea." Oscillatory motion is highest at the surface and diminishes exponentially with depth. However, for standing waves (clapotis) near a reflecting coast, wave energy is also present as pressure oscillations at great depth, producing microseisms.[4] These pressure fluctuations at greater depth are too small to be interesting from the point of view of wave power. The waves propagate on the ocean surface, and the wave energy is also transported horizontally with the group velocity. The mean transport rate of the wave energy through a vertical plane of unit width, parallel to a wave crest, is called the wave energy flux (or wave power, which must not be confused with the actual power generated by a wave power device)." "In deep water, if the water depth is larger than half the wavelength, the wave energy flux is P = (ρ * g^2/24*π)*Hm0^2 * T where - P the wave energy flux per unit wave crest length (kW/m); - Hm0 is the significant wave height (meter), as measured by wave buoys and predicted by wave forecast models. By definition, Hm0 is four times the standard deviation of the water surface elevation; - T is the wave period (second); - ρ is the mass density of the water (kg/m3), and - g is the acceleration by gravity (m/s2). The above formula states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meters, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter wavefront length." Source and further information: http://en.wikipedia.org/wiki/Wave_power