The course to steer (CTS) is a crucial concept in navigation, helping sailors and pilots maintain a proper course when wind or current influences the path. This guide covers how to calculate CTS, its importance, the formula, tools to use, and common real-world scenarios for better understanding.
Navigating through open waters or the air involves much more than simply following a straight path from point A to point B. Factors like wind, current, and other environmental forces can significantly affect the direction a vessel or aircraft needs to follow to reach its destination. This is where the concept of Course to Steer (CTS) comes into play.
What Is Course to Steer (CTS)?
Course to Steer (CTS) is the angle or direction a pilot or mariner must set in order to compensate for the effects of wind or current while traveling from one point to another. It’s the adjusted course that allows the vehicle to reach its destination, taking into account the natural forces that may push or pull it off its intended path.
In maritime navigation, CTS is often calculated to ensure the vessel doesn’t drift off course due to ocean currents or wind. In aviation, pilots must consider wind correction angles to maintain the desired flight path.
Why Is CTS Important?
Understanding and calculating CTS is essential for several reasons:
- Accurate Navigation: Without considering external forces like wind and currents, your vessel or aircraft will drift, leading to a significant delay or failure in reaching the intended destination.
- Safety: An accurate course reduces the risk of collisions, getting lost, or running into hazardous zones (e.g., bad weather, no-fly zones).
- Efficiency: With the correct CTS, you can optimize travel time and fuel consumption by choosing the best route that compensates for natural forces.
Tools You Need to Calculate Course to Steer
Before we dive into the formulas, it’s important to know the tools used in calculating CTS. Common tools include:
- A Plotter: A navigation chart tool used to plot courses on a map.
- Compass or GPS: To help determine the vessel’s heading or current position.
- Protractor/Graph Paper: For precise measurements of angles.
- Current and Wind Data: For understanding the forces at play (e.g., direction and speed).
- A Nautical Almanac or Wind/Wave Tables: To look up current and wind directions and their strengths.
How to Calculate Course to Steer (CTS): Step-by-Step
1. Understand the Initial Parameters
- True Course (TC): The intended course from the starting point to the destination, typically measured in degrees.
- Current/Drift (Set and Drift): The direction and speed at which the current or wind is pushing the vessel off course.
- Wind Correction Angle (WCA): The angle you must adjust to counter the drift from the wind.
2. Measure the Current or Wind Drift
First, you need to know the current or wind’s direction and speed. For example, if the wind is coming from the northwest, the drift will push your vessel to the southeast. Use charts or tables to measure this information.
3. Apply the Drift to the True Course
Once you know the direction and speed of the wind or current, you can adjust your true course to steer the vessel in the opposite direction of the drift.
- For example:
- True Course (TC): 90° (East)
- Wind from the Northwest (toward the southeast)
- Wind Correction Angle (WCA): 5° to the north
- Course to Steer (CTS) = TC – WCA = 90° – 5° = 85°.
This adjustment ensures that your vessel will maintain a straight course toward the destination.
4. Use the Dead Reckoning Formula (If Applicable)
If you’re using dead reckoning, a method based on current speed and direction, calculate the drift distance (the distance the current or wind pushes you off course over a set time). You then add or subtract this drift from the true course, depending on whether the drift is pushing you left or right.
- Example Formula:
CTS = True Course ± Drift Angle.
5. Adjust for Errors or Variations
Remember, instruments like compasses can have errors (e.g., magnetic deviation), and there may be factors like tides or shifting winds that alter your calculation. Always adjust for these variances when calculating CTS.
Let’s say you’re sailing from Port A to Port B, with a true course of 180° (south). However, there’s a current pushing you from the west at 3 knots. You calculate the Course to Steer (CTS) using the following steps:
- Step 1: True Course (TC) = 180° (South).
- Step 2: Current pushing from the west at 3 knots.
- Step 3: Apply the drift angle (say, 5° to the east).
- Step 4: Course to Steer (CTS) = TC + Drift Angle = 180° + 5° = 185°.
Now, you can adjust the rudder or steering to follow a 185° course to reach Port B, compensating for the current.
For aviation, you may need to calculate CTS by taking into account wind direction and speed. Let’s say a pilot wants to travel on a true course of 90° (east), but a crosswind from the north at 20 knots is pushing the aircraft southward.
- Step 1: True Course (TC) = 90°.
- Step 2: Wind correction angle (WCA) = 5° (to the north).
- Step 3: Course to Steer (CTS) = 90° + 5° = 95°.
By adjusting the aircraft’s heading to 95°, the pilot ensures the aircraft stays on the intended course, compensating for the wind’s effect.
Common Mistakes to Avoid
- Not Account for All Forces: Always remember to factor in all forces like wind, current, and magnetic variation. One missing element can cause a significant error in navigation.
- Ignoring Wind or Current Changes: Forces like wind and currents change over time, so recalculating CTS regularly is essential.
- Failure to Account for Compass Deviation: A compass might not always point true north due to nearby magnetic fields, so you must correct for this deviation.
Final Thoughts
Calculating Course to Steer (CTS) is a fundamental skill for navigators to ensure they reach their destination efficiently and safely. By understanding the underlying principles and applying the right techniques and tools, anyone can adjust their course to counteract the effects of wind and current. Whether you’re a sailor, pilot, or just an enthusiast, mastering CTS will enhance your navigation accuracy and confidence in challenging environments.
Happy Boating!
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Read How To Calculate Course Over Ground until we meet in the next article.