What Is the Mariner’s 1-2-3 Rule?

One of the easiest ways to keep ships and their crewmembers safe from hurricanes and strong tropical storms is by making sure they don’t have to be in them at all. This is where the Mariner’s 1-2-3 rule comes in.

The Mariner’s 1-2-3 rule helps vessel navigators avoid encountering a dangerous storm because of a weather forecast error. It’s also known as the Danger Zone Rule, and the “1-2-3" part of the name refers to the 100, 200, 300 nautical mile errors that could be made at 24, 48, or 72 hours respectively before a storm. Since forecast errors are more likely the further ahead of a storm they are made, keeping extra distance from systems helps mitigate dangers associated with them.

Essentially, it describes how far to stay from storms as they approach. It’s meant to help vessels avoid winds of 34 knots, a gust strength that is considered the point at which a vessel’s maneuverability starts to be severely limited.

Originally taken from a training film produced by the US Navy, the Mariner’s 1-2-3 Rule has become important for the safe navigation of any vessel. Even with complex weather equipment, following this policy can further mitigate the risks of being stuck in an unexpected and dangerous weather event.

Always Count on Forecast Error, Even While Following the Rules

While the Mariner’s 1-2-3 Rule is a great way to avoid danger zones of a storm, it’s important to remember that cyclones and other types of severe weather are unpredictable. While technology is a great tool for staying safe from storms while offshore, it isn’t perfect.

We can predict how systems move based on observation and history, natural phenomena can trigger unpredictable deviances from these educated guesses. It's important to never assume a cyclone you’re currently tracking will behave the same as another you’ve encountered before. Likewise, mariners should never assume they're safe because the weather around them isn't dangerous at any given moment.

Cyclones can speed up, slow down, and even stall for longer than predicted. When this happens, vessels can suddenly find themselves too close to a storm they anticipated they’d be able to pass or miss. Careful navigation and respecting errors with forecasts are the best ways to keep a vessel and its crew safe near storms.

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