Maine Sea Kayak Practice Test

The rule of twelfths is a quick way to gauge how fast the tide is moving—that is, how strong the current will be over time. It breaks the total rise or fall in water level into six hourly steps: 1/12, 2/12, 3/12, 3/12, 2/12, 1/12 of the total change. By knowing the overall tidal range, you can estimate how much the water will rise or fall in each hour, which directly relates to how fast the flow is in a given area. For example, if the tide changes by 4 feet from low to high, the hourly changes would be about 0.33 feet in the first hour, 0.67 feet in the second, 1.0 foot in each of the middle two hours, then 0.67 feet, and 0.33 feet in the last hour. That varying rate tells you when the current will be strongest, helping you decide when to cross a channel or plan your route. It's a handy rule of thumb for estimating tidal flow rather than predicting exact heights at a moment. Actual conditions can vary by locale and weather, but this approach gives a practical sense of how quickly the water is moving.