26/11/2025
🌊 MOTION OF THE OCEAN — Six Degrees of Freedom of a Ship.
Every vessel at sea moves in six different ways. These motions affect stability, comfort, cargo safety, navigation, and ship handling.
✅1. TRANSLATIONAL MOTIONS (Straight-line movements)
1️⃣ Heave (Vertical Up & Down Motion)
• The ship moves straight up and down, lifted by waves.
• Caused by long swell or steep waves.
• Excessive heaving affects comfort and can cause damage in heavy seas.
Example: Ship rising and falling as a wave passes underneath.
2️⃣ Surge (Forward & Backward Motion)
• Movement along the ship’s longitudinal axis.
• The vessel is pushed forward or backward by waves.
• Common in following seas or during berthing when waves push the ship.
Example: Ship surging ahead unexpectedly toward the pier.
3️⃣ Sway (Side-to-Side Motion)
• Sideways motion of the vessel.
• Caused by beam seas, strong winds, or currents.
• Mainly affects maneuvering and mooring operations.
Example: Ship drifting sideways toward another vessel.
✅2. ROTATIONAL MOTIONS (Turning motions)
4️⃣ Yaw (Turning Left & Right — Heading Change)
• Rotation around the vertical axis.
• The ship’s bow swings left or right.
• Excessive yaw makes steering difficult.
Example: Ship cannot maintain a straight course in rough seas.
5️⃣ Pitch (Tilting Forward & Backward)
• Rotation around the transverse (side-to-side) axis.
• The bow goes up while the stern goes down, and vice versa.
• Common when heading into waves or swell.
Example: Ship plunges into waves, causing water on deck.
6️⃣ Roll (Sideways Tilting to Port & Starboard)
• Rotation around the longitudinal axis.
• The ship leans side to side.
• Most dangerous motion because excessive roll can lead to capsizing.
Example: Ship rolls heavily in beam seas.
✅Why These Motions Matter ✅
✔ Stability and safety
Understanding motions helps prevent:
• Capsizing
• Cargo shifting
• Structural stress
✔ Navigation and steering
🫸Certain sea states affect steering and heading control.
✔ Passenger and crew comfort
🫸Heavy roll or pitch causes seasickness.
✔ Equipment operation
🫸Crane, winch, and deck operations depend on motion limits.