Tidal Stream Atlas

A collection of charts that depict the set (direction) and rate (speed) of tidal currents at various stages of the tidal cycle.

A Tidal Stream Atlas is an essential navigational tool used by mariners to understand the movement of water caused by tides in a specific area. These atlases provide detailed information about the direction and velocity of tidal streams at various times relative to high water at a reference port, typically in hourly intervals. Each page or chart within the atlas represents a snapshot of the tidal stream at a particular point in the tidal cycle, often over a six-hour period before and after high water. The charts are usually overlaid with arrows indicating the direction of the tidal flow, with numbers or symbols to represent the speed of the current, often in knots. 

Tidal streams can have a significant impact on a vessel’s course and speed, so understanding them is crucial for safe and efficient navigation. For example, a strong tidal stream flowing in the same direction as a vessel can increase its speed over the ground, while a stream flowing against the vessel can slow it down or even make progress difficult. In narrow channels or around headlands, tidal streams can also cause dangerous conditions, such as overfalls or eddies, which can affect the handling of the vessel. By consulting a Tidal Stream Atlas, mariners can plan their routes to take advantage of favourable tidal conditions or avoid areas where the tidal streams may pose a hazard.