A tidal stream atlas is a specialized nautical publication used to predict the direction and speed of tidal currents. These atlases are essential tools for mariners and anyone navigating coastal waters where tidal currents significantly influence passage planning and vessel safety.
Understanding a Tidal Stream Atlas
Based on the provided reference:
- Purpose: Its primary function is to help predict how tidal currents will flow over time in a specific area. This includes knowing where the current is heading and how fast it is moving.
- Structure: A typical tidal stream atlas consists of a series of diagrams, usually 12 or 13 in total. Each diagram represents a specific hour within the tidal cycle.
- Content: For a particular coastal region, each diagram uses arrows to visually represent the flow of the current at that hour.
- The direction of the arrows indicates the direction of the tidal current.
- Often, numbers or symbols near the arrows indicate the speed of the current at various locations within the depicted region.
How Tidal Stream Atlases are Used
Navigators use tidal stream atlases by first determining the state of the tide for their location and time (often related to High Water or Low Water at a standard port). They then consult the corresponding diagram in the atlas to see the predicted current direction and speed for their area during that specific tidal hour.
This information is critical for:
- Calculating the vessel's actual track and speed over the ground.
- Planning the best time to depart or arrive to take advantage of (or avoid) strong currents.
- Ensuring safe navigation, especially in narrow channels or areas with complex current patterns.
In essence, a tidal stream atlas provides a graphical snapshot of the tidal current environment hour by hour throughout a complete tidal cycle, allowing for informed decision-making while navigating.
