Seafastening Design and Knowing the Vessel Motions to Consider

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For those doing seafastening design for the first time, it is worth knowing the type of loads the secured cargo will be subjected to.

There are various guidelines and standards which depend on the mode and type of transport, however most codes share the same tips when it comes to ensuring that the cargo is transported safely.

1. Heave
Heave is simply the vertical motion of the vessel moving up and down. Translation in this direction causes the cargo to weigh more when the vessel heaves up, and weigh less, when the vessel heaves down.

2. Surge
Surge is the linear longitudinal (front/back) motion. This causes the cargo to want to move laterally to the front of the vessel and and the rear of the vessel.

3. Sway
Sway, much like Heave is the linear lateral (side-to-side) motion. This ignores any rotations of the vessel which we will cover later. This causes the cargo to want to move laterally across the deck in a port / starboard direction.

4. Roll
The roll of a vessel is the rotation about an imaginary axis running horizontally along the ships length.

5. Pitch
The pitch of a vessel is the rotation about the axis running across the width. Pitch motion can be thought of as an up-or-down movement of the bow of the ship.

6. Yaw
Yaw rotation of the vessel on its vertical axis. This is the axis running vertically through the ship and through its centre of gravity. Another way of thinking about yaw motion is side-to side movement of the bow of the ship.

 

Heave Vessel motion

Heave vessel motion

Surge Vessel Motion

Surge Vessel Motion

Sway Vessel Motion

Sway Vessel Motion

Yaw Vessel Motion

Yaw Vessel Motion

Roll Vessel Motion

Roll Vessel Motion

Pitch Vessel Motion

Pitch Vessel Motion