Chartwork is an essential skill for seafarers, especially when it comes to navigating through areas with tidal currents. To counteract the effect of these currents and find the correct course to steer, seafarers rely on various chartwork techniques. Here's a description of how this process typically unfolds:
Obtain the necessary information: Before planning a voyage, seafarers gather important information about tidal currents in the area they will be navigating. This includes tidal stream atlases, tide tables, and tidal stream charts. These resources provide data on the speed, direction, and timing of tidal currents at different locations.
Identify tidal diamonds: Using the tidal stream charts, seafarers locate tidal diamonds, which are marked on the chart. These diamonds represent the direction and rate of tidal streams at specific locations. By analyzing the tidal diamonds, seafarers can determine the strength and direction of the currents in the area.
Calculate the tidal vectors: Seafarers then calculate the tidal vectors, which are vectors representing the direction and magnitude of the tidal currents. They use the tidal diamonds' information to determine these vectors accurately.
Determine the tidal set and rate: Next, seafarers determine the tidal set and rate at their current location. The tidal set refers to the direction in which the tidal current is flowing, while the tidal rate indicates its speed. This is done by comparing the tidal vectors with the vessel's position on the chart.
Calculate the course to steer: With the tidal set and rate established, seafarers can calculate the course to steer to counteract the effect of the tidal currents. This involves adjusting the desired course by an appropriate angle to compensate for the influence of the currents. The angle is determined based on the tidal set and rate, as well as the vessel's intended speed and desired track.
Monitor and adjust: Once underway, seafarers continuously monitor the vessel's progress using navigation instruments such as a GPS or radar. They also track the changes in tidal currents to ensure that the course to steer remains accurate and effective. Adjustments may be necessary if there are changes in tidal conditions or if the vessel's speed deviates from the planned value.
