Why cargo shifts long before it looks dangerous
Estimated read time: 75–90 minutes
Audience: Cadet → AB → Junior Officer → Chief Mate
Introduction – The quiet phase before things go wrong
Cargo failures at sea are rarely dramatic at the start. There is no bang, no immediate alarm, no visible catastrophe. What happens instead is subtle: a lashing takes a little more load than intended, a twistlock works slightly loose, a vehicle on a Ro-Ro deck creeps against its restraint. For hours, sometimes days, nothing appears wrong.
By the time the problem is visible, the system has already failed.
Cargo securing is not about preventing movement entirely. It is about controlling movement within tolerances. When those tolerances are exceeded — often incrementally — failure accelerates beyond recovery.
What cargo securing actually does
Lashings do not “hold cargo still”. They manage forces generated by ship motion. Rolling, pitching, and heaving continuously apply cyclic loads to cargo units. Every cycle adds fatigue to lashings, fittings, and cargo interfaces.
A critical concept for zero knowledge readers is this:
Cargo securing systems are designed to survive movement, not eliminate it.
Once movement becomes uncontrolled or asymmetric, forces redistribute rapidly, and components that were never meant to be primary load-bearers suddenly become so.
Containers: strength hides vulnerability
Containers appear rigid and uniform, which leads crews to overestimate the robustness of the securing system. In reality, the system depends on small components — twistlocks, lashing rods, turnbuckles, and foundations — all working together.
If one element loses effectiveness, the load it was carrying does not disappear. It transfers to neighbouring components. Those components may already be near their working limit. This is why container stack failures often cascade: the first failure overloads the next, and so on, until an entire bay is compromised.
Lashing tension and the danger of “tight enough”
Lashings that are too loose allow movement. Lashings that are too tight introduce high pre-loads that reduce fatigue life and leave no margin for dynamic forces. Achieving the correct balance requires judgement, not brute force.
Over-tightening is a common error among less experienced crew, driven by the belief that tighter is safer. In reality, excessively tight lashings are more likely to fail under cyclic loading because they operate closer to their material limits from the outset.
Ro-Ro cargo: movement you can’t see
On Ro-Ro decks, cargo failures are often hidden. Vehicles may appear secure while restraints gradually loosen under vibration and motion. Unlike containers, Ro-Ro cargo does not share load symmetrically. A single vehicle shifting can change load paths across an entire lane.
This is why Ro-Ro cargo incidents escalate rapidly. Once one unit moves, others follow, and access to the affected area may already be compromised.
🔻 Real-World Failure: Container Loss and Stack Collapse on MSC Zoe (2019)
In January 2019, the container vessel MSC Zoe lost over 340 containers in the North Sea during heavy weather. Subsequent investigations found that cargo securing arrangements had been insufficient for the encountered conditions, despite being considered acceptable under normal operations.
Lashings failed progressively as the vessel rolled. Once initial failures occurred, load redistribution overwhelmed remaining components. Containers collapsed and were lost overboard, causing environmental damage and widespread disruption.
What is instructive for deck crews is that the failure did not occur at the peak of the storm. It occurred after hours of cyclic loading had already degraded the securing system. By the time visible loss began, intervention was impossible.
The lesson is stark:
Cargo securing failures begin long before cargo moves.
Inspections at sea: too late or just in time?
Cargo inspections during passage are often treated as formalities. In reality, they are one of the last opportunities to identify early failure indicators: slack lashings, bent rods, deformed fittings, or unusual noises.
Experienced deck officers do not expect to “fix” cargo at sea. They expect to recognise when margins are disappearing and take preventive action early — speed reduction, course alteration, or increased monitoring — before the system crosses the point of no return.
Knowledge to Carry Forward
Cargo securing is a fatigue problem disguised as a strength problem. Failures are incremental, cumulative, and unforgiving once they accelerate. Safe cargo operations depend on understanding load redistribution, avoiding over-tensioning, and recognising early warning signs before movement becomes visible.
Competent deck officers assume that if cargo can move, it eventually will — unless margins are actively protected.
Tags
On Deck, Cargo Securing, Lashing, Containers, Ro-Ro Cargo, CSS Code, Fatigue, Load Redistribution, Deck Safety, Failure Modes