bannerny
Frequently false beliefs in lashing system of shipping container
  • 14 Jun 2017


Once containers have been loaded and secured, the stow remains in a tight block and does not move – False

Twist lock and sliding socket clearances will allow containers to move before the twist locks engage. The clearance will permit movement of the stow. Wear inside the corner fitting can cause additional movement.


Containers can be stowed in any order and/or combination/mix of weights – False

The most common mistake made when stowing and lashing containers is to load heavy containers over light or to load so that the maximum permissible stack weights are exceeded. Heavy on light can only be accepted when specifically permitted in the Cargo Securing Manual.


Lashings applied from a lashing bridge behave in the same manner as those applied at the base of a stow – False

A lashing bridge is a fixed structure while a hatch cover will move when a ship rolls and pitches. The resulting effect could be that a lashing from a lashing bridge becomes slack or takes excessive load.


Containers loaded on a pedestal and a hatch cover do not suffer additional loading – False

A hatch cover is designed to move as the ship bends and flexes. A container stowed on a pedestal, a fixed point, will attempt to resist hatch cover movement if also secured to a hatch cover.


Lashing rods should be tightened as tight as possible – False

In theory, excessive tightening of lashing rods will result in the rods taking additional strain, which can cause rod failure when under load.


Extra lashings will always make the stow safer – False

Application of extra lashings can, at times, make the stow very rigid, causing large forces to pass to container-securing points and causing them to fracture.


It is not necessary to adjust the tension in lashings while at sea – False

Movement of containers will result in some lashing rods becoming slack. Air temperature differences will cause the tension in the lashings to change. Lashings should be checked and tightened within 24 hours after leaving port and regularly thereafter. This is especially true before the onset of bad weather.


Container strength is equal throughout the container – False

Although strength standards are met, a container is more flexible at the door end and may be more vulnerable in this area.


All twistlocks can be used to lift containers – False

Twistlocks can be used for lifting containers only when they have been approved and certified for that purpose.


Twistlocks are all rated to the same strength – False

Twistlocks can be rated for different tensile loads up to 20 or 25 tonnes. It is important not to use a mix of twistlocks that have different strength ratings.


All containers have the same strength – False

Container strength can vary. There are two ISO standards (pre- and post-1990). Some owners have their own standards and containers can be worn or damaged.


Horizontal lashings from lashing bridges are an alternative to vertical cross lashings – False

Crossed horizontal lashings from lashing bridges will hold a container. However, the container will be held rigidly to the fixed lashing bridge. When a ship bends and twists, the base of a container attached to a hatch cover will move, but container ends held firmly to a lashing bridge with horizontal lashings will not move. The effect will be to put strain on the lashings and even break the bars or damage the container corner castings. Horizontal lashings should not be used unless specifically permitted in the approved lashing plans shown in the Cargo Securing Manual.


Parametric rolling will not occur on ships with a high GM – False

Parametric rolling occurs because of the fine hull form of large post-Panamax container ships. The large bow flare and wide transom increase the effect. The phenomenon occurs because of changes in the water plane area, which can cause large changes in GM as waves pass. At times, GM can become negative. A large initial GM will provide large righting levers that can lead to violent rolling.


Provided stack weights have not been exceeded, the distribution of containers in a stack on deck is not important – False

It is essential to avoid loading heavy containers over light, or at the top of a stack in a deck stow, unless specifically permitted in the Cargo Securing Manual. This is because the securing system would normally have been designed on the assumption that light containers are stowed on top. Stowage may allow for ‘heavy-heavy-light’; however, loading ‘heavy-medium-medium’ may result in the same stack weight but would produce different strain on the securing system, especially if the GM is high.


Containers need not be stowed in block stowage – False

Generally, container stacks do not depend on each other for support. However, they do provide protection to each other from wind and waves, so stowage in isolated stacks, especially in outboard locations, should be avoided.

Previous Post Next Post

top