Ultrasonic Thickness Measurement

Ultrasonic thickness measurement establishes the remaining plate thickness of steel and aluminium hulls without damage. Corrosion loss, past repairs and plate renewals become numbers.

Thickness is the hull’s memory

A hull’s plate thickness tells two stories: what corrosion has consumed so far, and where past repairs were made. Neither is visible from outside — paint covers everything. Ultrasonic measurement reads thickness to sub-millimetre precision from the echo of a sound wave, and turns both stories into a table of numbers.

What it establishes

On steel and aluminium hulls, corrosion-prone areas — below the waterline, bilges, tank surrounds, stern gear — are measured on a grid and compared against original plate thickness and allowable limits, with marginal areas flagged on a map. Repaired zones read differently from their surroundings: a thickness pattern appearing in an apparently flawless hull is the most dependable evidence of an undisclosed accident history, and indicates whether the repair was done to the original standard or hurried. Around welds, thinning and irregularities are measured, with suspect seams cross-checked for surface cracking by dye penetrant testing.

Why a map, not a point?

A thickness reading from a single point tells you nothing; what tells you something is the distribution. Plate does not thin evenly — corrosion concentrates along the bilge line, under tanks and at weld seams.

The measurement therefore runs over a grid and every point is numbered onto a map. This means:

• Whether the loss is widespread or local becomes visible.
• The same points can be measured again in a few years; the rate of loss follows.
• Areas below the limit take priority in the repair plan.

The report

Every point is tabled with location, reading and deviation from reference. Areas at risk of progressive thinning get a monitoring interval or repair recommendation. On steel-boat purchases, this table is the backbone of the survey.

Duration and fee

This inspection is a chapter within a survey: it is carried out within a hull survey and a pre-purchase survey and is not billed separately. We do not sell it as a standalone item, because coming to the boat once to look at this heading alone serves neither you nor us.

If you do need this heading on its own — in a dispute, or for a second opinion — the door is not closed. Call us and we will talk about the boat.

Fees vary with the length of the boat, where she lies and the season. For a firm price call us — tell us about the boat and we will give you the number on the phone.

Estimate your survey fee