200760 - Container stack toppled

Container stack toppled	MARS Report 200760

A newly delivered container vessel began her maiden voyage and arrived at her second loading port. As her berth was occupied, the master decided to anchor for some hours. Unknown to him, in this exposed anchorage, during certain tidal conditions, vessels would lie to the current and be exposed to beam sea and swell.

 

At her first port of call, barring a few containers that were on the hatch covers, several hundred filled containers had already been loaded in the lowest tiers in the holds. For reasons of operational expediency, an isolated three-high stack was placed on a hatch cover and secured as per the ship's cargo securing manual.

 

Due to the bottom-heavy cargo distribution, and having substantial quantities of fuel and ballast in the lower side and double bottom tanks, the vessel was exceptionally stiff.

 

The stay at the anchorage was particularly uncomfortable, with continuous rolling, even in slight sea and swell conditions. On one particular heading, the ship rolled very violently with the result that the lashings parted and the deck stack toppled on to the hatch cover, fortunately, without much damage.

 

The ship berthed soon afterwards and the stow was rectified.

Root cause/contributory factors

1. Exceptionally stiff condition;
2. Anchored vessel tending to lie to current with sea and swell abeam;
3. Short rolling period possibly synchronising with short swell period;
4. Isolated three-high stack;
5. Lashing system not specifically designed for countering 'lifting' forces.

Lessons learnt

1. Although unusual weight distribution is to be expected between the first couple of loading ports on a maiden voyage, steps can be taken to reduce the stiffness by more considered ballast water loading, particularly in the high tanks and by keeping lower tanks slack or empty, as stresses permit.
2. An isolated three-high stack must be avoided, even if it involves some rehandling.
3. If a vessel tends to lie uncomfortably at anchor due to conflicting tide, sea and swell conditions, and if an alternative sheltered anchorage cannot be accessed, the option of weighing the anchor and drifting or cruising offshore at economical speed must be considered.
4. Modern container securing systems, coupled with the latest computer loading and lashing programs, can be very efficient and cost-effective in ensuring scientific planning of loading and execution of lashings, allowing sufficient restraint against lifting forces. Operators using outdated equipment and software should consider replacing these with newer versions.