Servicing, layup and recommissioning
Service intervals by hours and by calendar, winter layup, recommissioning, and why low hours is not good news.
How often should anodes be replaced?
When roughly half consumed. That interval varies enormously with water temperature, salinity, shore power and how the boat is used.
Full guide: Sacrificial Anode Inspection and Replacement
Does my engine have anodes inside it?
Very likely — a pencil anode in the heat exchanger at minimum, plus possibly the aftercooler and coolers. These are the ones owners most often never check.
Zinc or aluminium?
Aluminium is now widely used in salt and brackish water; zinc remains common in salt. Magnesium is for fresh water only and wastes rapidly in salt.
Why are my anodes disappearing so fast?
Stray current, a bonding fault, galvanic interaction through shore power, or simply warm tropical water. A sudden change in rate is worth investigating.
Can I paint over anodes when antifouling?
No. A painted anode provides no protection at all.
Why is my engine corroding when it never touches seawater directly?
Salt-laden air in the engine bay is enough. Electrical connections and alloy housings corrode from the atmosphere alone.
Full guide: Marine Engine Corrosion Repair
What is stray current corrosion?
An electrical fault putting current through the water, dramatically accelerating metal loss. It can destroy a propeller or drive leg in months and needs electrical diagnosis, not more anodes.
Can a corroded engine block be repaired?
Sometimes locally, but corrosion into a water jacket usually ends the block. Get an honest assessment before spending on piecemeal repairs.
Does tropical water corrode faster?
Yes. Warm, saline water accelerates galvanic activity considerably, which is why northern Australian boats need shorter anode intervals.
Is oil analysis worth it for a private boat?
For a high-value engine, remote cruising, or a boat you intend to keep, yes. It is inexpensive and it gives warning that nothing else provides.
Full guide: Marine Engine Oil Analysis
How many samples before it means anything?
Three or four to establish a baseline. Single results have limited value without a trend to compare against.
Can oil analysis detect seawater ingress?
Yes — sodium and chloride confirm it, often before the oil looks visibly milky. On a marine engine that early warning is worth a great deal.
Should I sample the gearbox too?
Yes. Water and metal in gearbox oil are early indicators of seal and clutch problems.
When should I take the sample?
Warm, after running, from mid-stream — and the same way every time so the trend is comparable.
How often should a marine diesel be serviced?
By hours or annually, whichever comes first. For most recreational boats the annual interval arrives well before the hours.
Full guide: Marine Engine Servicing
My boat did 20 hours this year — can I skip a service?
No. The damage in a lightly used marine engine is time-based: fuel degradation, impeller set, coolant inhibitor depletion, anode consumption and perishing rubber.
Is marine oil different from automotive oil?
Marine engines run at sustained high load, and the correct specification matters. Use what the engine maker specifies rather than the nearest automotive equivalent.
Does the gearbox get serviced at the same time?
It should, but it has its own oil and its own interval and is frequently overlooked. Ask explicitly.
What is the most commonly skipped service item?
The engine's internal anodes and the exhaust elbow inspection. Both are cheap and both prevent expensive failures.
Why do so many failures happen on the first trip of the season?
Because layup damage only reveals itself under load. The engine that idles perfectly at the dock is a different proposition twenty minutes into a passage.
Full guide: Recommissioning After Layup
Isn't starting the engine enough of a test?
No. Fuel starvation, overheating, gearbox slip and charging faults appear under sustained load and nowhere else.
What should I check first after a layup?
That every bung, seal and closure fitted during layup has been removed — especially the exhaust — and that water flows at the exhaust within seconds of starting.
My boat sat all winter with an untreated tank — what now?
Assume filter problems. Sample the tank, carry spares, and consider polishing before the season rather than mid-passage.
Why winterise in Australia when nothing freezes?
Because the damage is from idle time, not frost — fuel degradation, microbial growth, impeller set, acidic oil, depleted coolant and flat batteries.
Full guide: Winterisation and Seasonal Layup
Should I change the oil before or after layup?
Before. Used oil is acidic and attacks bearings the entire time the engine sits.
Full or empty fuel tank over winter?
Full. Air space condenses moisture, and water is what feeds diesel bug.
Do I need to do this if the boat only sits for two months?
The full routine, no. Fuel treatment, a battery maintainer and clean oil, yes — they cost little and prevent most of it.
What is the most commonly skipped item?
Relieving the impeller and treating the fuel. Both cause first-trip failures in spring.