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Set

The direction which a current flows in a body of water.

In marine navigation, understanding the set of a current is crucial for plotting an accurate course. The set is always described in terms of the direction in which the water moves rather than the direction from which it originates. For example, if the current is flowing toward the east, the set would be described as eastward. This is important because the movement of water can significantly affect the course and speed of a vessel. 

Currents are caused by various factors, including tidal forces, wind patterns, and the Earth’s rotation. In coastal areas, tidal currents are often the most significant, changing direction and strength with the ebb and flow of the tide. Ocean currents like the Gulf Stream or the Kuroshio Current can have a more constant set in open waters, driven by large-scale wind patterns and the Coriolis effect.

Mariners must account for the current’s set (direction) and rate (speed) when navigating. Failure to do so can push the vessel off course, especially over long distances. For instance, if a vessel is travelling on a heading of 090° (due east), but there is a current with a set of 180° (due south), the vessel will be pushed to the south unless corrective action is taken.

Mariners may use tools, including Almanacs, GPS, radar, and visual observations of fixed landmarks or buoys, to determine the current’s set. In some cases, the set can be estimated by observing the angle of the vessel’s wake or the movement of floating objects in the water. However, modern electronic navigation systems often provide real-time information about the set and drift of currents, allowing for more precise navigation.

Alternative Meanings:
  • Set

    The process of securing a boat in a stationary position by deploying and embedding an anchor into the seabed.

    When a mariner 'sets anchor', they are ensuring that the anchor is deployed correctly and securely lodged in the seabed to prevent the vessel from drifting due to wind, currents, or tides. The process begins by selecting an appropriate anchoring location, typically in an area with good holding ground (such as sand, mud, or gravel) and sufficient depth. They will then lower the anchor overboard, allowing it to sink to the bottom. Once the anchor reaches the seabed, the boat is slowly reversed to allow the anchor to dig in and "set" firmly into the substrate. This reverse motion helps ensure the anchor's flukes penetrate the seabed, providing a firm grip.

    The amount of rode that is let out is critical to the success of setting the anchor. A general rule of thumb is to let out a scope of 5:1 to 7:1, meaning that for every meter of water depth, five to seven meters of rode should be released. This allows the anchor to lie at an angle that maximises its holding power.

    Once the anchor is set, the boater typically applies reverse thrust to the engine to test its hold. If the boat remains stationary and the anchor does not drag along the seabed, it is considered properly set. If it does drag, the process may need to be repeated, or a different anchoring location may need to be chosen.

    Factors such as the anchor type, the seabed's nature, and the weather conditions affect how effectively an anchor can be set. Common anchors include the plough anchor, the Danforth anchor, and the mushroom anchor, each designed for different seabed conditions. For example, a Danforth anchor is particularly effective in sandy or muddy bottoms, while a plough anchor is better suited for rocky or weedy areas.