Noise pollution: Quietness is one of the main reasons people are turning to four-stroke outboards today. Normal conversation will typically measure about 65 decibels; 90 decibels is the measurement at which unsafe levels of noise begin, and thunder averages around 110 decibels. In our 1997 full-throttle test, at least one of the two-stroke engines hit 100 decibels, an unsafe level for prolonged exposure. This year, we compared noise emission at three speeds: at idle, at 5 knots, and on a steady plane. Among the four-strokes, the Honda came in with the quietest average, followed closely by the Suzuki. In many cases, the difference was less than 2 decibels, almost imperceptible to our ears. The loudest four-stroke at planing speed, the Mercury, registered 94 decibels, only slightly louder than the others, which generated 90 to 92 decibels. Conversely, Mercury had the quietest two-stroke. The two-strokes were 3 to 7 decibels louder than the four-stroke engines at planing speeds and 5 to 6 decibels noisier at 5 knots, a noticeable increase in both instances. The loudest of the bunch was the Johnson two-stroke, which hit 99 decibels on a plane.