Construction, Ratings, and Why “Available Power” Is a Lie
Introduction — generators don’t fail suddenly, systems do
Marine generators are often treated as rugged, forgiving machines: big diesel engines, heavy alternators, plenty of margin. When a ship blacks out, crews frequently say:
“The generator failed.”
In reality, generators rarely fail in isolation. What fails is the interaction between load, protection, control, and excitation.
A generator that trips is usually obeying rules set long before the incident — often without anyone realising what those rules imply at sea.
What a marine generator actually is (beyond the nameplate)
A ship’s generator is not just an engine turning a rotor. It is a tightly coupled system consisting of:
- prime mover (diesel engine)
- alternator (stator + rotor)
- excitation system
- AVR
- protection relays
- governor and fuel system
- PMS logic
- cooling and lubrication systems
Failure in any one can remove electrical power — even if the engine itself is mechanically sound.
Generator ratings — misunderstood and routinely abused
Key ratings that matter onboard:
- Rated power (kW / kVA) — continuous capability
- Power factor (usually 0.8) — defines real vs reactive capacity
- Short-circuit capability — ability to feed fault current
- Step-load acceptance — how much load can be applied instantly
- Overload limits — thermal, electrical, mechanical
ETO trap:
Operating generators “below nameplate” does not mean safe margin if:
- reactive power is high
- harmonics distort current
- excitation is near limit
- cooling conditions are degraded
🔧 Regulatory anchors (non-negotiable)
SOLAS Chapter II-1, Regulation 42
Requires:
- sufficient generating capacity for normal operation
- redundancy appropriate to ship type
- ability to supply essential services simultaneously
SOLAS Chapter II-1, Regulation 43
Requires:
- emergency power independent of main generation
- automatic availability after failure
IEC 60092-301 / 302
Define:
- generator construction requirements
- performance under abnormal conditions
- protection coordination expectations
IACS E11
Class expects:
- generators capable of withstanding defined disturbances
- protection that prevents catastrophic damage
- documentation matching real configuration
🔻 Real-World Case: MV Viking Sky — Generator Loss and Near Catastrophe (2019)
On 23 March 2019, the cruise vessel MV Viking Sky suffered a near-total loss of propulsion off the coast of Norway during severe weather.
Facts established by investigation:
- multiple diesel generators tripped
- lubricating oil pressure fell due to excessive rolling
- generators shut down on protection
- the vessel drifted toward a rocky shoreline
- evacuation by helicopter was required
- only last-minute generator recovery prevented grounding
This was not a single generator failure.
It was a systemic interaction between machinery design, operating limits, and protection philosophy.
Why this is a generator-protection lesson
The generators shut down correctly:
- low oil pressure protection operated
- engines were protected from damage
But the ship nearly became a total loss.
This raises the uncomfortable maritime question:
Is it acceptable for generator protection to sacrifice the ship to save the engine?
On land, yes.
At sea, often no.
Common generator-related failure chains onboard ships
- reactive overload → AVR saturation → voltage collapse
- poor load sharing → one generator overloaded → trip
- protection settings copied from shore plants
- degraded cooling reducing true capacity
- PMS logic shedding loads too late
In many blackouts, the generator is the last component to act, not the first to fail.
How professional ETOs think about generators
They don’t ask:
- “Is the generator healthy?”
They ask:
- How close are we to excitation limits?
- What happens if one unit trips right now?
- Can the remaining units carry propulsion load?
- How fast does recovery need to be at this speed and position?
A generator’s job is not just to produce power — it is to buy time.
Knowledge to Carry Forward
Marine generators are not protected assets — they are risk buffers.
A generator that trips at the wrong time can turn a manageable fault into a casualty. Protection must balance engine survival against ship survivability, especially during manoeuvring and heavy weather.
If protection philosophy answers the wrong question, the generator will “do the right thing” — and the ship will still be lost.
Tags
ETO, Marine Generators, Blackout, Viking Sky, Generator Protection, SOLAS II-1, IEC 60092, Ship Power Failure, Accident Case Study