What Is Sea Fastening And How Is It Important For Cargo Ships?

A ship’s deck is used to transport many different types of cargo. It is installed from containers to large structures such as cranes or heavy modules of an offshore production plant. During transport, the ship confronts forces from the environment (wind, wave, current). Being on the ship’s deck, the cargo also encounters these forces. Cargoes must be stable while being subjected to these forces. They must be secured to the deck of the vessel using means such as lashing ropes, stoppers, beams, etc. This is called the “Sea-fastening” of cargo.

Sea fastening is the fastening of cargo while transportation at sea. When moving cargo by sea, it must be secured such that any movement which can damage cargo or ship must be avoided. Any major movement of cargo might result in instability problems. This might jeopardize vessels, cargo, and crew onboard.

Sea fastening of containers is done by stacking the containers in vertical guide rails. Another way is by stowing them in stacks or blocks, the containers being connected and fixed to parts of the vessel. The containers themselves are in a stack secured directly to the deck by bottom stackers or bottom twist locks.

How does ship travel on water affect cargo ship design?

There are various guidelines and standards which depend on the model and type of transport, yet 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.

2. Surge

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

3. Sway

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

4. Roll

The roll of a vessel is the rotation of an imaginary axis running horizontally along the ship’s length.

5. Pitch

The pitch of a vessel is the rotation of 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 center of gravity. Another way of thinking about yaw motion is the side-to-side movement of the bow of the ship.

What type of sea fastenings are available for cargo ships?

The heavier a cargo is, the stronger the acceleration forces will be. The position of the cargo on the vessel also affects the acceleration forces. It would be better to put the cargo on hold instead of on the deck or move it to a mid-ship position.

What happens if you plan for 2-meter-high waves, but then encounter 4-meter-high waves? Encountering a worse condition than what was expected is unlikely but is always a possibility. At the event, there is a bit of extra capacity for your lashing materials. Most surveyors look at the breaking point of the lashing material and divide that figure by 2.25 to get the Safe Working Load. This safety factor also accounts for any inconsistencies or impurities in the lashing material.

Lashing Materials such as chains, wire rope, or nylons are used to tighten the cargoes. The strongest material chains, which can last a long time. However, they come in fixed length, which provides fewer lashing options.

Wire rope is cheaper than chains and comes in a variety of sizes, making it more versatile than chains. You can cut the length you need from a spool of wire rope. However, wire rope is for one-time use and typically requires multiple personnel to make up the length and clamp down on the clips.