Why ships fail with “correct” calculations — and why people, not physics, are usually the trigger
Contents
Use the links below to jump to any section:
- Introduction – Stability Accidents Rarely Start With Physics
- The Illusion of Correctness
- Assumption Stacking – How Small Errors Combine
- Over-Reliance on Software and Checklists
- Normalisation of Deviation
- Time Pressure, Commercial Pressure, and Silence
- Communication Breakdown Across Departments
- Authority Gradient and the Failure to Challenge
- Fatigue and Cognitive Narrowing
- Accident Patterns Seen Repeatedly
- What Investigations Actually Conclude
- Building Human Resilience Into Stability Management
- Closing Perspective
- Knowledge Check – Human Error & Stability
- Knowledge Check – Model Answers
1. Introduction – Stability Accidents Rarely Start With Physics
Stability failures are often described using technical language: GM too low, cargo shifted, free surface underestimated.
But when investigations dig deeper, the cause is almost never a missing formula.
It is human behaviour layered on top of a technically acceptable condition.
Ships rarely capsize because the laws of physics were misunderstood.
They capsize because risk was allowed to grow without being challenged.
2. The Illusion of Correctness
One of the most dangerous states on a ship is being confident and wrong.
Loading computers produce neat outputs. Stability booklets show compliance. Plans are signed. Nothing appears alarming.
This creates an illusion that safety is guaranteed — and that illusion suppresses questioning.
When something looks correct, humans stop probing it. That moment is where accidents begin.
3. Assumption Stacking – How Small Errors Combine
Most stability accidents do not involve one large mistake.
They involve several small assumptions made at different times by different people:
- cargo weight assumed instead of verified
- density rounded instead of measured
- one slack tank considered insignificant
- ballast lag accepted “just for now”
- weather expected to remain moderate
Each assumption feels reasonable in isolation. Together, they quietly consume margin.
By the time the ship needs that margin, it is already gone.
4. Over-Reliance on Software and Checklists
Software and checklists are essential. They are also dangerous when they replace thinking.
A loading computer cannot sense:
- cargo shift
- poor securing
- unexpected free surface
- real-time ship behaviour
Checklists confirm that actions were taken — not that conditions remain safe.
Many casualty reports contain phrases like:
“The loading computer indicated compliance.”
That statement explains the outcome. It does not excuse it.
5. Normalisation of Deviation
Normalisation of deviation occurs when unsafe conditions become routine because nothing went wrong last time.
Examples include:
- sailing with marginal GM “because we always do”
- accepting slack tanks for convenience
- delaying ballast correction until later
- operating near limits because schedules demand it
Each uneventful voyage reinforces the belief that the risk is acceptable.
Eventually, the ship encounters conditions that expose the reality that the margin was never there.
6. Time Pressure, Commercial Pressure, and Silence
Cargo operations are rarely conducted in calm, generous conditions.
Time pressure encourages shortcuts. Commercial pressure discourages delay. Together, they encourage silence.
Officers often sense that margins are reducing but hesitate to speak because:
- the plan is approved
- the computer says OK
- stopping operations is unpopular
Silence is not neutrality.
It is a decision to let risk continue growing.
7. Communication Breakdown Across Departments
Stability is cross-departmental, but communication often is not.
Common failures include:
- deck not informing engine of rapid cargo loading
- engine not informing deck of ballast delays
- bridge unaware of transient stability states
Each department believes someone else is “watching it”.
In reality, nobody is.
Stability failures thrive in organisational gaps.
8. Authority Gradient and the Failure to Challenge
The authority gradient matters.
Junior officers may notice:
- excessive list
- unusual rolling
- unexpected trim changes
But if the Master or senior officer appears confident, those observations may never be voiced.
Many investigations record that concerns were noticed — but not escalated.
Professional stability culture depends on the ability to challenge conditions, not personalities.
9. Fatigue and Cognitive Narrowing
Cargo operations often involve long hours, night work, and irregular rest.
Fatigue narrows thinking.
Under fatigue:
- people rely more heavily on automation
- assumptions go unchallenged
- warning signs are rationalised away
A fatigued crew is not careless — it is cognitively constrained.
This is why stability incidents frequently occur at the end of long operations, not the beginning.
10. Accident Patterns Seen Repeatedly
Across decades of casualty reports, the same patterns appear:
- acceptable final condition
- unsafe intermediate state
- multiple minor assumptions
- delayed response
- sudden loss of control
The technical trigger differs. The human pattern does not.
Ships do not fail randomly.
They fail predictably — once the margin is gone.
11. What Investigations Actually Conclude
Formal investigations rarely blame “bad math”.
They cite:
- inadequate monitoring
- failure to reassess conditions
- over-reliance on software
- poor communication
- ineffective challenge culture
These are human system failures.
Understanding this is essential for preventing recurrence — because procedures alone will not fix behaviour.
12. Building Human Resilience Into Stability Management
Resilient ships do not rely on perfection.
They:
- encourage questioning
- treat stability as dynamic
- slow down when uncertainty grows
- assign clear responsibility
- value margin over compliance
They design operations so that human weakness does not immediately become catastrophe.
This is seamanship at a systems level.
13. Closing Perspective
Stability failures are not caused by ignorance.
They are caused by confidence without verification.
Every stability accident is a story of lost margin, not lost equations.
The most important stability skill is not calculation.
It is knowing when to stop, speak, and reassess — even when everything appears correct.
14. Knowledge Check – Human Error & Stability
- Why do most stability accidents not start with physics errors?
- What is the illusion of correctness?
- How do small assumptions combine into major risk?
- Why is over-reliance on software dangerous?
- What is normalisation of deviation?
- How do time and commercial pressure affect stability decisions?
- Why does poor inter-department communication increase risk?
- How does authority gradient suppress safety?
- Why does fatigue increase stability risk?
- What human traits do resilient ships actively encourage?
15. Knowledge Check – Model Answers
- Because behaviour and decision-making allow margin to erode.
- Believing compliance guarantees safety.
- By stacking unnoticed reductions in margin.
- Because software cannot detect real-world deviations.
- Accepting unsafe conditions because they did not fail previously.
- They discourage challenge and promote shortcuts.
- Because stability depends on coordinated timing.
- Juniors hesitate to question seniors.
- Fatigue narrows judgement and reliance on automation.
- Questioning, communication, and willingness to stop operations.