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Buying a boat and engine surveys marine diesel questions
Pre-purchase engine inspections, sea trials, and the findings that should change your offer.
Do I need survey for a charter boat in Australia?
A vessel used for hire or reward is generally a domestic commercial vessel and subject to the national system. Check your specific operation with AMSA or an accredited surveyor.
Full guide: Engine Requirements For Commercial Vessel Survey
Who regulates commercial vessels in Australia?
AMSA administers the national system for domestic commercial vessels, with survey performed by accredited marine surveyors.
Can I use a recreational engine in a commercial vessel?
Engines are usually rated by the manufacturer for a duty cycle — recreational, light commercial, continuous. Using an engine outside its rating affects both compliance and warranty.
What engine records does survey want?
A maintenance system with dated records of servicing and repairs to the propulsion machinery and its associated systems.
Does a repower need to be approved?
Changing the propulsion machinery changes the surveyed installation. Speak to your surveyor before committing to the work.
Isn't the engine covered by the general marine survey?
Usually only superficially. If the boat's value is substantially in its engines, commission an engine survey as well.
Full guide: Marine Engine Survey and Pre-Purchase Inspection
Do I need a sea trial?
Yes. Many faults — overheating, fuel starvation, gearbox slip, failure to reach rated RPM — appear only under sustained load.
The seller has warmed the engine up for me — is that a problem?
Yes, and it is worth insisting on a genuine cold start. Cold starting behaviour and start-up smoke are among the most informative things you can observe.
What if the survey finds problems?
That is what it is for. Findings are either a reason to renegotiate, a repair list, or a reason to walk away — all three are better outcomes than discovering them afterwards.
What is the most important thing to measure on a sea trial?
Whether the engine reaches its rated wide open throttle RPM. It tells you whether engine, propeller and hull are correctly matched.
Full guide: Sea Trial and Engine Performance Testing
My boat won't reach rated RPM — what does that mean?
The engine is overloaded. Check the bottom first, then the propeller pitch, then the engine. Running a diesel chronically overloaded shortens its life substantially.
How long should a sea trial run?
Long enough to reach thermal equilibrium under sustained cruise — commonly twenty to thirty minutes, not ten.
Do I need a sea trial after antifouling?
It is worth checking RPM afterwards. A clean bottom can change the picture significantly, and it is the correct baseline for propeller decisions.