CHAPTER - 14

SAILING

Learning Outcomes

1. Understand Basic Sailing Concepts

Define key sailing terms such as heading, course, speed, drift, and leeway.
Explain the difference between true course, magnetic course, and compass course.
Understand the effects of wind, current, and tide on sailing.

2. Types of Sailing Methods

Explain and differentiate between plane sailing, parallel sailing, mid-latitude sailing, and Mercator sailing.
Understand the concept of great circle sailing for long-distance routes.
Describe rhumb line sailing for maintaining constant compass bearings.

3. Calculate Course and Distance

Calculate distance, speed, and time using simple sailing formulas.
Determine the course to steer (CTS) considering wind, current, and leeway.
Calculate the difference in latitude and longitude during a voyage.

4. Apply Sailing Techniques in Navigation

Plot sailing routes on nautical charts using different methods (e.g., plane and Mercator sailing).
Use dead reckoning (DR) and estimated position (EP) techniques to track the vessel's progress.
Apply great circle sailing for efficient and safe passage over long distances.

5. Solve Practical Sailing Problems

Solve problems involving current, wind drift, and leeway affecting the ship's course and speed.
Use calculations to correct the vessel’s course for external factors.

6. Use Navigation Tools and Technology

Use navigational tools such as compasses, charts, GPS, and ECDIS for accurate route planning.
Interpret data from navigational instruments to make informed decisions during sailing.

7. Communicate and Record Sailing Information

Accurately record sailing data in the ship's logbook.
Communicate navigational plans and decisions clearly using standard maritime terminology.

Differentiate between plane sailing, parallel sailing, mid-latitude sailing, and Mercator sailing.

1. Plane Sailing

Definition: A simple method used for short distances, assuming the Earth is flat.
Purpose: To calculate distance, course, and position using basic trigonometry.
Key Calculations:
- Difference in latitude (D'Lat) and departure (east-west distance).
- Simple right-angled triangle formulas are used.
When to Use: For short coastal voyages where curvature of the Earth can be ignored.
Limitation: Not accurate for long distances because it doesn't account for Earth's curvature.

2. Parallel Sailing

Definition: A method for calculating distances along the same latitude (parallel).
Purpose: To find the departure (east-west distance) when sailing on a constant latitude.
Key Calculations:
- Departure = Difference in Longitude (D'Lo) × Cosine of Latitude.
When to Use: When sailing along the equator or any parallel of latitude.
Limitation: Not suitable when there is a change in latitude.

3. Mid-Latitude Sailing

Definition: A method for calculating distance and course when traveling between two points with different latitudes.
Purpose: To simplify calculations by using the average (mid) latitude.
Key Calculations:
- Departure = D'Lo × Cosine of the mid-latitude.
When to Use: For moderate distances where a change in latitude occurs, but curvature isn't significant.
Limitation: Less accurate for long distances or when there's a large difference in latitude.

4. Mercator Sailing

Definition: A method based on the Mercator chart, which represents the Earth’s surface for accurate plotting.
Purpose: To solve sailing problems involving changes in both latitude and longitude over longer distances.
Key Calculations:
- Uses meridional parts (a calculated value) to account for Earth's curvature.
- More complex mathematical formulas are used for accuracy.
When to Use: For long-distance navigation over significant changes in latitude and longitude.
Limitation: Requires understanding of meridional parts and more complex calculations.

Understand the effects of wind, current, and tide on sailing

🌬️ 1. Effects of Wind

Leeway: Wind blowing across the ship's side causes it to drift sideways, away from the intended course. This sideways movement is called leeway.
Course to Steer (CTS): To counter leeway, the vessel must adjust its heading slightly into the wind to stay on course.
Speed Impact: Strong headwinds can reduce speed, while tailwinds can increase speed.
Maneuvering: Wind strength and direction affect how easily a ship can turn and maneuver, especially in tight areas like ports.

✅ How to Manage Wind Effects:

Calculate and apply a leeway correction to maintain the correct course.
Reduce sail or adjust engine power in strong winds.
Monitor weather forecasts to anticipate wind changes.

🌊 2. Effects of Current

Set: The direction in which the current is flowing.
Drift: The speed at which the current is moving.
Resultant Path: A current can cause the ship to drift off course or affect its speed over ground (SOG).
Cross Current: When a current hits the ship from the side, it can push the vessel off its intended track.

✅ How to Manage Current Effects:

Calculate the Course to Steer (CTS) to offset the current’s influence.
Use vector diagrams to determine the actual direction and speed of travel.
Check current forecasts and nautical charts to plan for strong currents.

🌊 3. Effects of Tide

Tidal Streams: Horizontal movement of water due to the rise and fall of tides, which can push the ship off course.
High and Low Tide: These affect the depth of water—important for ensuring enough clearance under the vessel.
Tidal Set and Drift: Similar to current, but caused by the movement of tides, impacting course and speed.

✅ How to Manage Tidal Effects:

Plan sailing times according to tidal charts to avoid shallow areas during low tide.
Account for the set and drift of tidal streams in navigation planning.
Use port tide tables to understand local tide conditions.

⚓ Combined Effect and Corrections

In reality, wind, current, and tide can act together to affect a vessel’s navigation.
To maintain the correct course:
1. Determine the set and drift of both current and tide.
2. Calculate leeway correction for wind.
3. Adjust the ship’s heading to maintain the desired course over ground (COG).
4. Regularly check the ship’s position using GPS or visual bearings.

✅ 1. Calculating Course to Steer (CTS) to Counter Wind and Current

When a vessel is affected by wind and current, we need to adjust the Course to Steer (CTS) to stay on the desired course.

Given Data

Desired Course (DC) = 090° (East)
Ship’s Speed (Speed Through Water - STW) = 12 knots
Current Direction (Set) = 180° (from South)
Current Speed (Drift) = 2 knots
Wind causes Leeway = 5° to the south

1. Parallel Sailing

DEP = DIST = D. Long × Cos Lat Course = 090° ( T ) or 270° ( T )

2. Meridian Sailing

DIST = D. Lat Course = 000° ( T ) or 180° ( T )

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