LO1.
5 EXPLAIN THE EFFECTS OF SET AND DRIFT ON VESSEL’S
MOVEMENT AND
HOW IT AFFECTS THE SHIP’S POSITION.
Set and drift are navigational terms used to describe the impact of currents and winds on a vessel’s
movement, which can significantly affect its position and intended course.
Set
● Definition: The set is the direction in which a current or wind is pushing the vessel.
Set refers to the direction in which a current or wind is pushing the vessel. This direction can cause
the vessel to deviate from its intended course if not accounted for (1).
● Effect on Movement: The set can cause a vessel to deviate from its intended course. If not
accounted for, the vessel will be off its planned track, leading to potential navigational hazards
or delays.
● Example: If a vessel is heading north but the set is coming from the east, the vessel will be
pushed westward.
Drift
● Definition: Drift is the speed at which the current or wind is moving the vessel, typically
measured in knots.
Drift measures the speed at which the current or wind is moving the vessel off its intended path,
typically measured in knots (2).
● Effect on Movement: Drift determines how fast the vessel is being pushed off course. The
stronger the drift, the more significant the deviation over time.
● Example: If a current is moving at 3 knots to the north while the vessel is trying to head east,
the vessel will be pushed north at 3 knots.
Combined Effect on Ship’s Position
1. Course and Speed Adjustments: Navigators must adjust the vessel’s course and speed to
counteract the effects of set and drift. This often involves calculating a new course
(compensated course) that takes into account the current and wind to ensure the vessel
stays on its intended path.
2. Navigational Planning: Accurate charts, current data, and weather forecasts are crucial.
Modern navigation systems often include tools to predict and compensate for set and
drift.
3. Safety Considerations: Failure to account for set and drift can lead to navigational errors,
grounding, collisions, or entering restricted or dangerous waters.
If set and drift are not accounted for, the vessel will be pushed off its intended course, leading
to potential navigational errors, such as grounding, collisions, or entering restricted
waters (3).
A navigator needs to adjust the vessel’s course to compensate for set and drift when the
vessel is affected by currents or winds pushing it off its intended course. This ensures the
vessel reaches its intended destination (4).
The primary purpose of compensating for set and drift during navigational planning is to
accurately reach the intended destination by adjusting for the effects of currents and
winds, ensuring safe and efficient navigation (5)
Practical Example
● Intended Course: A ship plans to travel directly from Point A to Point B, a distance of 100
nautical miles to the north.
● Set and Drift: A current flows from the east at 2 knots.
● Uncorrected Path: If the ship travels at 10 knots directly north without correcting for the
eastward set, after 10 hours (when it should be at Point B), it will have been pushed 20 nautical
miles west of its intended position.
● Corrected Path: The navigator adjusts the course to head slightly eastward, compensating for
the current, ensuring that the actual path taken leads directly to Point B despite the set and
drift.
By understanding and compensating for set and drift, navigators can maintain their intended
course and ensure the vessel arrives safely and efficiently at its destination.
