Sea Trial Survey: What I Test Before You Buy a Motorboat
A static survey alongside or ashore can reveal a great deal about a vessel, but some faults only become apparent when the machinery and systems are working under load. A sea trial is therefore an important part of the pre-purchase process for many motorboats.
The purpose is not simply to see whether the boat reaches a particular speed. I am looking at how the vessel, engines, drives, controls and supporting systems behave throughout the operating range.
What I am looking at before leaving the berth
Before departure I inspect accessible engine-room areas, fluid levels where practical, belts, hoses, mounts, visible leaks, battery voltage, control operation and instrumentation. Engines are observed from cold where possible because starting behaviour can reveal issues that may be hidden once machinery is warm.
Steering and gear engagement are checked at low speed, together with warning systems and any abnormal noise or delay.
How I test the boat underway
The vessel is run progressively through the operating range rather than taken immediately to full throttle. I monitor indicated RPM, temperatures, charging voltage, oil pressure where displayed, engine synchronisation, steering response, vibration, smoke, exhaust condition and control response.
Where safe and appropriate, the vessel is operated at normal cruising speed and maximum permitted test RPM for a short period. The achieved RPM is compared with the engine and propeller installation expectations, because an engine that cannot reach its designed operating range may be overloaded, incorrectly propped or suffering a machinery problem.
What the hull and running gear can reveal
A sea trial can expose vibration from propellers, shafts, couplings or drives that may not be apparent during a static inspection. I also assess steering feel, trim response, unusual structural noise, water ingress and the general behaviour of the vessel at different speeds.
On planing craft, reluctance to plane, excessive bow rise, unusual list or poor trim response may warrant further investigation. Performance should always be considered alongside loading, fuel, weather, sea state and hull cleanliness.
Checks after the run
After the higher-load part of the trial I re-inspect machinery spaces for fresh leaks, abnormal heat, coolant loss, belt debris, fuel leakage or other changes. Drive or gearbox oil condition and temperatures may also be relevant depending on the installation and access.
If an alarm appears during the trial, the circumstances, instrument readings and subsequent behaviour should be recorded rather than simply clearing the alarm and continuing.
Recommendation
Any abnormal vibration, overheating, inability to reach expected RPM, persistent alarm, fluid leak or irregular control response should be investigated before purchase by a competent marine engineer or the relevant engine/drive specialist.
Where the survey identifies a defect but the cause cannot be confirmed non-destructively, further diagnostic work should be completed before exchange of contracts. A sea trial should reduce uncertainty for the purchaser, not replace specialist mechanical diagnosis where the evidence indicates it is required.
