# Understanding the 50/90 Rule of Tides for Boating

A practical guide for navigating tidal currents effectively.

- **Source:** [SlashGear](https://www.slashgear.com)
- **Published:** 2026-09-27
- **Topic:** [Operations](https://brifing.si/c/operations)
- **Original article:** <https://www.slashgear.com/2264632/50-90-rule-of-tides-for-boating-explained/>
- **On Brifing:** https://brifing.si/s/0cc7a159-a17b-4455-9636-95b67fdac42b

## Introduction 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.

## How 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.

## Practical 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.

## Historical 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.

## Comparison 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.

## Limitations 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.

## Importance 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.

## Conclusion

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.

## Sources covering this story

- https://www.slashgear.com/2264632/50-90-rule-of-tides-for-boating-explained/ — 

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_Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._