A borescope shows places the eye cannot reach, through a slim camera head. On a survey it is used mostly behind linings, in closed compartments and in bilge recesses. Inside the engine and inside tanks is a separate job; knowing which is done on the survey and which as a separate service sets the right expectations.
The borescope on a standard survey
It goes in through existing openings; nothing is dismantled. Typical uses:
- Leak marks and wet timber behind headlining and wall linings.
- Corrosion in closed compartments, especially on steel boats.
- Around and under tanks; weeping at welds and connections.
- Bilge recesses, around keel bolts, cable and hose penetrations.
Inside the engine
Seeing inside a cylinder means removing an injector or glow plug. That is outside the survey's non-destructive, no-dismantling scope; it is a separate service coordinated with an independent engine technician, together with compression and blowby readings. Scoring on cylinder walls, carbon on valves and unusual marks on piston crowns are seen this way.
Inside tanks
If a tank has an inspection hatch, the inside can be viewed: water, sediment and microbial sludge at the bottom of a fuel tank; scale and internal corrosion in a water tank. Without a hatch, viewing the inside means opening the tank and is planned as refit work.
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- Fuel system: From deck fill to injectors.
What a borescope shows
A borescope is a thin probe with a camera and light at its tip; it lets you look inside closed or narrow spaces without dismantling. In an engine, the cylinder interior, exhaust elbow and cooling passages can be seen through an injector or glow-plug hole. Around the boat, tank interiors, wiring behind linings, the inside of the mast, unreachable parts of the hull and closed compartments can be examined. The images are recorded and added to the report, so the buyer sees what the surveyor saw.
What is looked for in a cylinder
The state of the honing pattern on the cylinder wall, scoring, rust and discolouration, carbon on the piston crown and water marks are examined. Clear scoring or rust suggests the engine may once have taken in water, or that wear has advanced. A borescope finding is not a verdict on its own; it gains meaning read alongside compression readings and oil analysis.
Its limits
A borescope shows what it sees and nothing else. Corners the probe cannot reach, tight bends or dirty surfaces limit the image. So the report states plainly where the borescope looked and where it could not reach.
When it is recommended
- When a cylinder runs unevenly or smokes on the sea trial.
- When there are signs or suspicion that the engine has taken in water.
- When corrosion or sediment is suspected in a fuel or water tank.
- When leak marks show behind a lining.
Working with the engine technician
Where an injector or glow plug must come out, a technician does it; the borescope inspection is planned in the same visit and the results assessed together.
Recorded images are also kept for comparison at the next survey, so any change inside is easy to see.
Adding the images to the report lets the buyer judge each finding with their own eyes rather than on description alone.