Understanding the 50/90 Rule of Tides for Boating
A practical guide for navigating tidal currents effectively.
1Introduction to the 50/90 Rule
The 50/90 rule is a practical method for boaters to estimate the speed of tidal currents between slack water and peak flow. It divides the tidal cycle into three intervals, each representing different stages of current speed. This rule helps boaters understand how tidal currents change over time, providing a useful approximation for navigation.
2How the Rule Works
The rule breaks the tidal cycle into three intervals. In the first interval, the current reaches about 50% of its maximum speed. During the second interval, it increases to around 90%, and in the third interval, it reaches full speed. As the current slows, the pattern reverses, dropping to 90% and then 50% before returning to slack water.
3Practical Application
The 50/90 rule is particularly useful for kayakers and small-craft boaters navigating areas with strong tidal currents. It helps in planning routes and determining the most favorable conditions for travel. Even when only the maximum current speed is known, the rule allows boaters to estimate speeds at other points in the cycle.
4Historical Context
The 50/90 rule was developed by Starpath in 1987 and first published in 'Fundamentals of Kayak Navigation.' It has since been adopted by organizations like the American Canoe Association and the British Canoeing Awarding Body. Despite being a relatively recent concept, it has become a valuable tool in coastal navigation training.
5Comparison with Rule of Twelfths
The 50/90 rule shares similarities with the Rule of Twelfths, another method used to estimate tidal changes. While the 50/90 rule focuses on current speed, the Rule of Twelfths estimates tidal height changes. Both methods divide the tidal cycle into intervals but serve different purposes in navigation.
6Limitations of the Rule
While the 50/90 rule provides a good approximation of tidal current speed, it is not always precise. Local tidal conditions can vary, and the rule serves as a general guide rather than an exact prediction. Boaters should use it in conjunction with other navigational tools for safer travel.
7Importance for Small Craft
For kayakers and small-craft boaters, understanding the 50/90 rule is crucial. Strong tidal currents can pose significant challenges, and this rule helps in planning safer and more efficient routes. It is especially useful in areas where tidal information is limited or only provides maximum current speeds.
8Conclusion
The 50/90 rule is a valuable tool for boaters navigating tidal currents. It offers a practical method to estimate current speeds and plan routes effectively. While it has limitations, its adoption by major organizations underscores its importance in coastal navigation training.
Original article: SlashGear — Understanding the 50/90 Rule of Tides for Boating