Do Nautical Charts Show low Tide?

Depths and Dangers: Do Nautical Charts Show Low Tide?

As an experienced sailor, I am often asked if nautical charts show low tide depths, and the answer is yes, but with some caveats that I will explain in this article.

What Is a Nautical Chart?

A nautical chart is a visual representation of the seafloor, showing depths, hazards, and navigational aids such as buoys and lighthouses in the area being charted.

It also shows land features such as coastal towns, rivers, and mountains that can be used for navigation or as landmarks to help boaters find their way around unfamiliar areas.

What Does the Chart Show?

The chart shows depths in feet or fathoms (6 ft) with contour lines indicating where the water depth changes from one depth to another depth along the charted area’s coastline and seafloor topography.

On paper charts, shoals are shown as stippled areas with depths indicated in red numbers, on electronic charts they are shown as hatched areas with yellow numbers indicating depths at low tide or below low tide levels.

How Does a Nautical Chart Help Boaters?

Nautical charts provide boaters with information to help them navigate safely around unfamiliar waters by showing them potential dangers such as shallow water and rocks or reefs that could damage their boat if they inadvertently hit them while underway.

Charts also show navigational aids like buoys and lighthouses that can help boaters find their way around without running aground or losing their orientation in fog or darkness.

What Is Mean Lower Low Water (MLLW)?

Mean lower low water (MLLW) is an average depth at the lower of each day’s two low tides over a 19-year cycle calculated by NOAA (National Oceanic and Atmospheric Administration).

This measurement helps boaters determine the closest underwater clearance possible for their boat when navigating shallow waters or when checking for potential hazards when entering new ports or harbors along the coastlines of our great nation’s many waterways .

How Is MLLW Calculated?

MLLW is calculated by taking measurements from coastal tide stations over 19 years and then averaging those measurements to determine an average low tide level for each station over a given period of time which then becomes the standard measurement used by NOAA for determining depths on nautical charts nationwide .

What Does MLLW Measure?

MLLW measures not only average depths at lower low tides but also how far above sea level certain points along the coastline are during high tides which helps boaters know what to expect when navigating shallow waters near shorelines or entering new ports or harbors while underway

Do Nautical Charts Show Low Tide?

Yes, nautical charts show low tide depths at MLLW levels which can give boaters an idea of how much clearance they have between their boat and any potential hazards beneath them while underway .

Advantages of Knowing Low Tide Depths on a Chart

Knowing low tide depths on a nautical chart can help boaters plan their voyage accordingly by allowing them to avoid shallow water areas during high tides when there might be less clearance between them and potential hazards lurking beneath the surface .

Knowing these depths can also help captains gauge how far they can venture into shallow waters without risk of running aground during certain times of day when tides are lower than usual .

Disadvantages of Knowing Low Tide Depths on a Chart

The main disadvantage of knowing low tide depths on a nautical chart is that it does not take into account any other factors such as wind speed, wave height, currents, etc., that might affect the safety of navigation in those same shallow waters .

Another disadvantage is that these measurements are only averages taken over nineteen years so they do not always accurately reflect today’s actual water depth in real life situations .

Conclusion

In conclusion, yes nautical charts do show low tide depths at MLLW levels which can be helpful for planning voyages through shallow waters but it should be noted that other factors need to be taken into account before venturing into areas with potentially hazardous conditions beneath them .

With proper knowledge and precautionary measures, sailors should have no problem navigating safely around our great nation’s many waterways!