Ultrasonic Thickness Measurement for Merchant Ships in Plymouth

Inspection services for ships at Plymouth

Each service has its own page with the method, the class requirements and what the report contains.

Where ships can be gauged around Plymouth

At the Cattewater wharves the work follows the cargo. A coaster with salt or fertiliser is gauged hold by hold as the grabs empty it, with the team working behind the discharge and coming back to the hatch covers and ballast tanks at the end. At Corporation Wharf, where cement ships take the ground at low water, the double bottom and bottom plating repay attention, because repeated sitting on the berth adds loads that an always-afloat ship never sees. Tankers at Cattedown are handled under the terminal's permit system, with deck and engine-room piping the usual scope during a discharge.

At Millbay the ferry berth gives time on the Roscoff and Santander ships between crossings, when tanks and voids released by the crew can be gauged and the vehicle decks and ramps are clear. Plymouth has no commercial drydock open to merchant ships, so a coaster or ferry needing a docking goes to Falmouth along the coast or to a yard abroad, and the readings taken here travel with it as a pre-docking estimate. For ships at anchor in the Sound, launches are booked by the agent, and the dockyard port's rules on movements apply to anything crossing the water.

• Victoria Wharf — hold, frame and tank-top gauging on coasters discharging salt, fertiliser or wood chips.
• Corporation Wharf — bottom plating and double-bottom readings on cement carriers that take the ground at low water.
• Cattedown Wharves — deck, cargo and ballast piping on coastal petroleum tankers under the terminal's permit rules.
• Millbay Docks — ballast tank, void and vehicle-deck gauging on the Roscoff and Santander ferries during lay-overs.
• Plymouth Sound anchorage — launch-borne deck and air-pipe readings on ships waiting for a berth or for orders.
• Research and survey ship berths — hull and sea-water piping checks between research cruises.

Port state control, protected waters and the coastal tanker trade

The Maritime and Coastguard Agency carries out port state control in Plymouth, applying Paris MoU procedures under UK law to foreign-flagged ships. The coasters and coastal tankers that use the Cattewater are often older ships, owned by small European operators, and they are the type most likely to be inspected closely for hold, hatch and tank condition. Coastal tankers also face oil-company vetting: inspections under OCIMF's SIRE 2.0 programme look at hull and piping condition, and a manager with recent thickness readings can answer the inspector's questions with figures rather than assurances.

Plymouth Sound and its estuaries are protected as a special area of conservation, and the city has declared the UK's first national marine park there. The harbour authorities expect contractors working on ships to keep debris and paint out of the water. For a gauging team, that means coating is removed only in small, contained spots to reach bare steel, and the dust is collected. The protected status also affects repair planning: hot work or blasting arising from a finding is planned with the harbour authority and the repair contractor, not improvised on the day.

Ships trading to Plymouth are inside a sulphur emission control area, where fuel must not exceed 0.10% sulphur unless an exhaust gas cleaning system (scrubber) is fitted. Scrubber wash-water piping, the overboard discharge and the hull penetration around it are among the fastest-corroding parts of a modern ship, so they belong in the gauging scope at every docking and, on open-loop systems, between dockings.

How a thickness measurement job runs at Plymouth

The sequence for a thickness measurement job at Plymouth is short and written down, so the yard, the surveyor and the superintendent know who arranges what.

Exeter Airport is the nearest with scheduled international flights; Plymouth's own airport closed some years ago. Teams usually arrive at Heathrow or Gatwick and take the train from London Paddington to Plymouth. Millbay, Cattedown and the other wharves are controlled areas, and the ship's agent arranges passes and any terminal induction in advance. Technicians travel from India on UK visas, so we ask for the expected call as early as possible and fix the visit once the agent confirms the berth.

• Send the vessel name or IMO number, ship type, class society, the survey due (annual, intermediate, renewal survey number, CAP or owner's condition survey), the port and dates, and the scope you expect.
• We confirm the scope against the class rules for that survey, prepare the thickness measurement plan with frame and section references, and say whether the measurement will be credited to a class survey.
• Mobilisation is planned around visa lead times and the vessel's schedule; the ship's agent arranges port access, and the yard or ship arranges staging, lighting, ventilation and gas-free certificates.
• Gauging with calibrated ultrasonic thickness gauges: through sound coatings only where the gauge's through-coating mode has been verified on a coated reference, otherwise on cleaned bare steel, with every reading tied to its frame, strake and location on the sketch.
• Readings are compared with original thicknesses as work proceeds; substantial and excessive corrosion and any cracks are reported to the attending surveyor and the superintendent the same day.
• The final report is issued on the class thickness-measurement formats with sketches, a summary of locations exceeding the allowable margins, piping tables where piping was in scope, and the gauge calibration and technician certificates.

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