Entry & progression
The mains get the attention. The auxiliaries stop the ship. A-III/2: operate, monitor and evaluate the performance of auxiliary machinery; manage safe and effective maintenance.
Generators — the ones that matter most
On a yacht the gensets run every hour of every day, at anchor and alongside, while the mains sit cold. They accumulate hours faster than the mains and they get half the attention. Reverse that priority.
- Load sharing — droop and isochronous, and why two sets fight each other when the governors disagree.
- Reverse power and reverse VAr — what trips, why, and what it is protecting.
- Insulation resistance — trend it. A wet alternator on a yacht is not rare.
- Block loading — an air conditioning plant cutting in is a step load. A genset already at 90% will not take it.
- Low-load running — the same glazing and wet-stacking problem as the mains, and far more common because the sets are oversized for hotel load.
TIP — Blackout starts as a load-sharing problem Most engine room blackouts are not a genset failure. They are a paralleling failure, a protection trip, or a step load that one set could not absorb. Know your emergency generator's start sequence and its automatic start time from memory. Know which board it feeds and which it does not. Know how to close the bus tie by hand. You will need all three in the dark.
Purifiers
A centrifugal separator is simple physics and endless trouble. It works by density difference, and it works only if the gravity disc, the throughput and the temperature are matched to the oil. Get any one of them wrong and you either lose oil over the water side or send water into the tank.
Symptoms to know: repeated bowl opening (dirty operating water, or worn seals); water in the clean oil tank (wrong gravity disc, or feed too hot or too fast); high sludge with no dirt (over-frequent discharge); vibration (unbalanced bowl — stop it, do not run through it).
Pumps and compressors
| Symptom | Likely cause |
|---|---|
| Centrifugal pump loses suction | Air ingress on the suction side, blocked strainer, or the pump is above the water and lost its prime |
| Pump runs, no delivery | Impeller detached, wrong rotation, or the discharge is shut |
| Cavitation noise (gravel) | Suction pressure below vapour pressure — restriction or too high a lift |
| Air compressor makes no pressure | Leaking valves, worn rings, or unloader stuck open |
| Compressor discharge temperature high | Fouled cooler, leaking valve recycling hot air, or overload |
Boilers and heat exchangers
Most yachts have no fired boiler; they have exhaust gas economisers, calorifiers and hot water heaters. The principles are the same and so are the hazards. Water level is everything. Low water in any fired or heated pressure vessel is the mechanism that produces catastrophic failure, and it is why gauge glasses are blown through and level alarms are function-tested rather than admired.
WARNING — Never introduce cold water into an overheated boiler If the water level has been lost and the shell may be overheated, do not feed it. Shut off the fuel, secure the air, isolate, and let it cool naturally. Feeding cold water onto hot, unwetted metal is how a pressure vessel fails explosively. This is a classic oral examination question and there is exactly one right answer.