Why lifts fail when nothing breaks — and why numbers don’t protect people
Category: ON DECK → Lifting Operations
Estimated read time: 65–80 minutes
Audience: Zero knowledge → competent AB → junior officer → senior deck officer
Introduction – The danger of believing the plate
Every crane, davit, and lifting appliance on board carries a plate. On that plate is a number — Safe Working Load. For someone new to deck operations, that number feels authoritative. It looks like a boundary between “safe” and “unsafe”, a line that, if respected, guarantees control.
That belief is comforting.
It is also wrong.
SWL does not describe what a crane will do. It describes what it should be able to do under specific assumptions. Deck accidents happen when those assumptions quietly stop being true — long before anyone realises it.
What SWL actually means (and what it doesn’t)
Safe Working Load is derived from structural limits, material strength, and design margins under controlled conditions. It assumes correct radius, steady lift, no shock loading, proper rigging, and a stable platform. On a moving ship, exposed to wind and human correction, those conditions exist only briefly, if at all.
The most important concept to learn from zero knowledge is this: SWL is a static value applied to a dynamic system. The moment motion, wind, or correction enters the picture, forces increase beyond what the number alone suggests.
This is how cranes are overloaded without ever lifting “too much”.
Radius, not weight, is what kills cranes
Deck cranes fail far more often due to radius error than excess mass. As the boom extends, leverage increases dramatically. A load that is well within SWL at short radius can exceed structural limits at longer reach — even if the weight has not changed.
On deck, radius changes constantly. The crane slews. The ship lists. The load swings. Each movement alters the effective lever arm. Operators who think only in tonnes miss the real hazard developing in metres.
Experienced deck officers watch the geometry, not the hook.
Dynamic loading: when motion multiplies force
A static lift is rare at sea. As a load clears the deck, friction is removed and the true centre of gravity asserts itself. The load may rotate, swing, or drop slightly into the slings. Each of these movements introduces shock loading — a brief but powerful spike in force.
These spikes are invisible on paper but devastating in reality. They are why cranes fail during “routine” lifts and why davits part during what appear to be controlled launches.
🔻 Real-World Failure: Heavy Lift Vessel Orion — Crane Load Test Collapse (Rostock)
During load testing alongside in Rostock, the offshore wind installation vessel Orion suffered catastrophic failure of its newly installed Liebherr HLC 295000 heavy-lift crane. The vessel was stationary, moored, and conducting a controlled test — not an offshore operation.
At the time of failure, the crane was lifting approximately 2,600 tonnes, less than half of its ultimate test load. Despite this, the crane’s main lattice boom flipped backwards and the hoist hook failed. Two personnel were hospitalised and ten others treated for minor injuries.
Investigators concluded that the failure originated in the hook itself, which had been supplied by a third party. The crane structure and vessel were not at fault. What failed was a single component in the load path — and when it failed, the system offered no second chance.
For deck crews, the Orion incident demonstrates a critical truth:
Lifting systems do not fail gradually. They fail when hidden margins vanish.
Everything was certified. Everything was new. Everything was “within limits”.
None of that mattered once the weakest component behaved differently than assumed.
Davits: small cranes with the same physics
Davits are often treated as simpler, safer machines because they lift smaller loads. In reality, they are often less forgiving. They operate close to personnel, involve suspended boats with people inside, and are exposed to vessel motion at the ship’s side.
Davits experience dynamic loads during launching and recovery, particularly when boats enter or leave the water. Wave interaction, pendulum motion, and brake behaviour all combine to create load spikes that exceed static ratings.
Many davit failures occur not because the davit is weak, but because timing and motion were misjudged.
Why “nothing broke” until everything failed
A recurring theme in crane and davit incidents is the absence of visible warning. There is no gradual deformation, no audible crack, no slow decline. The system behaves normally — until it doesn’t.
This is because lifting appliances operate with narrow margins once dynamic effects are included. The transition from safe to catastrophic is measured in seconds.
Knowledge to Carry Forward
Safe Working Load is not a guarantee. It is a conditional value that assumes perfect geometry, steady motion, and correct human behaviour. Cranes and davits fail when those assumptions quietly break down. Competent deck officers manage radius, motion, and timing, not just weight. They assume margins are smaller than advertised — and act accordingly.
Tags
On Deck, Lifting Operations, Deck Cranes, Davits, Safe Working Load, Dynamic Load, Radius Effect, Heavy Lift, Human Factors, Failure Modes