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the waves is the height-to-length ratio [Figure 8-2]. This ratio is an indication of the amount of motion a seaplane experiences on the water and the threat to cap- sizing. For example, a body of water with 20-foot waves and a swell length of 400 feet has a height-to- length ratio of 1:20, which may not put the seaplane at risk of capsizing, depending on the crosswinds. 

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However, 15-foot waves with a length of 150 feet pro- duce a height-to-length ratio of 1:10, which greatly increases the risk of capsizing, especially if the wave is breaking abeam of the seaplane. As the swell length decreases, swell height becomes increasingly critical to capsizing. Thus, when a high swell height-to-length ratio exists, a crosswind takeoff or landing should not be attempted. Downwind takeoff and landing may be made downswell in light and moderate wind; however, a downwind landing should never be attempted when wind velocities are high regardless of swell direction. 

When two swell systems are in phase, the swells act together and result in higher swells. However, when two swell systems are in opposition, the swells tend to cancel each other or “fill in the troughs.” This provides a relatively flat area that appears as a lesser concentra- tion of whitecaps and shadows. This flat area is a good touchdown spot for landing. [Figure 8-3] 

