What is Turning Circle of Ships ?
⚓ Turning Circle of Ship
📘 Definition
The Turning Circle of a ship is the circular path followed by a vessel when the rudder is put over to a fixed angle (usually hard to port or starboard) and the ship turns continuously at a constant speed.
It is one of the most important maneuvering characteristics of a ship and is tested during sea trials.
🔹 How It Works
When the helm is put hard over (e.g., 35° to starboard):
- The rudder creates a lateral force.
- The stern moves sideways.
- The bow swings in the direction of the turn.
- The ship follows a curved path until it completes a full 360° circle.
📊 Important Terms in Turning Circle
1️⃣ Advance
- The distance the ship travels forward (in original direction) from the point of helm order until it has turned 90°.
2️⃣ Transfer
- The sideways distance traveled from the original track when the ship has turned 90°.
3️⃣ Tactical Diameter
- The distance measured perpendicular to the original course when the ship has turned 180°.
- This is the most important value used to judge maneuverability.
4️⃣ Final Diameter
- The diameter of the steady turning circle once the ship settles into uniform turning.
📐 Why Turning Circle is Important?
- ⚓ Safe navigation in narrow channels
- ⚓ Port maneuvering
- ⚓ Collision avoidance
- ⚓ Emergency maneuvers
- ⚓ Compliance with maneuvering standards under International Maritime Organization guidelines
🚢 Typical Values (General Cargo / Tanker Ships)
- Tactical Diameter ≈ 3 to 5 times ship’s length (L)
- Advance ≈ 4 to 5 times ship’s length
- Smaller vessels → Smaller turning circle
- Large tankers → Larger turning circle
🔎 Factors Affecting Turning Circle
- Ship length & beam
- Draft
- Speed
- Rudder angle
- Propeller type (single/twin screw)
- Wind & current
- Hull design
📝 Simple Definition (Exam Ready)
Turning circle is the path described by a ship when the rudder is put hard over and the ship turns through 360° at constant speed.