Buying a boat and engine surveys
Pre-purchase engine inspections, sea trials, and the findings that should change your offer.
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.
Are low hours a good sign?
Not necessarily. Very low hours on an older boat usually means long idle periods, which cause fuel, corrosion and seal problems of their own.
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.